Alphabetic list of terms

Figure 6 shows an ATMP tunnel between two MAX TNT units. A mobile client, such as a traveling salesperson, initiates the connection. The unit that authenticates the mobile client is the ATMP foreign agent. The unit that accesses the home network is the ATMP home agent. The home network is the destination network for mobile clients.

In Figure 6, the mobile client is a salesperson who logs into an ISP (the foreign agent) to access his or her home network.

Figure 6. ATMP tunnel across the Internet

As described in RFC 1701, GRE hides packet contents and enables transmission of packets that the Internet would otherwise not accept. When you use ATMP with the MAX TNT, you can transmit IP packets that use unregistered addresses. See also foreign agent, Frame Relay, GRE, home agent, home network, IP, IPX, ISP, mobile client, UDP, VPN.

Attached Resource Computer Network

See ARCnet.

attribute

A series of values in a RADIUS user profile or pseudo-user profile. The attributes indicate a user name and password, and enable you to configure routing, call management, and usage restrictions. See also pseudo-user profile, RADIUS, RADIUS server, user profile.

AUI

Auxiliary Unit Interface. An AUI is a 15-pin D-type connector for Ethernet connections. It typically links a cable to a Network Interface Card (NIC). An AUI is also known as a Digital, Intel, Xerox (DIX) connector. See also Ethernet, NIC.

authentication

A method of identifying users permitted to access network resources. Authentication is the first line of defense against unauthorized access to your network. The MAX TNT supports a variety of authentication methods. You can use:

Calling-Line ID (CLID) to verify that the call is being placed from a trusted telephone number.
Called-number authentication to verify the number called.
Callback security. After authentication is complete, the MAX TNT can hang up and call back, ensuring that the connection is made only with a trusted number.
Expect-send scripts to authenticate logins to the terminal server.
Name and password authentication of Point-To-Point Protocol (PPP) calls. The MAX TNT supports Password Authentication Protocol (PAP), PAP with encryption (PAP-DES), Challenge Handshake Authentication Protocol (CHAP), and Microsoft's extension of CHAP (MS-CHAP).
Token cards. Using a token-card server, you can accept or reject calls by means of PAP-Token, PAP-Token-CHAP, or Cache-Token authentication.

When the MAX TNT is shipped from the factory, it is set to not require any authentication.

authentication request

A request that the MAX TNT sends an authentication server on behalf of a client requesting access. See also authentication response, authentication server,

authentication response

A response from an authentication server, notifying the MAX TNT that a user's request for access has been either granted or denied. See also authentication request, authentication server.

authentication server

An external server, such as a RADIUS, TACACS, TACACS+, or token-card server, that verifies whether a user requesting access to the network has permission to use network resources. See also RADIUS, RADIUS server, TACACS, TACACS+, token-card server.

authorization

Permission for a user to carry out a certain set of tasks after he or she has access to your LAN. Authorization occurs after authentication is complete. On the MAX TNT, you configure authorization in the following profiles:

The Terminal-Server profile, to restrict access to the terminal-server software.
The SNMP profile, to restrict access to the system by means of Simple Network Management Protocol (SNMP) manager utilities.
IP-Global and Connection profiles, to restrict access to certain Domain Name System (DNS) servers.

B

backbone

The part of the communications network designed to carry the bulk of the traffic. The backbone provides connectivity between subnets in an enterprise-wide network. See also enterprise-wide network, IP subnet.

backbone area

An Open Shortest Path First (OSPF) area that connects routers for the purpose of hierarchical routing. The backbone area is special and always has the area number 0.0.0.0. To tie areas together, some routers belong to the backbone area and one other area. These routers are called Area Border Routers (ABRs). See also ABR, area, OSPF, router.

backbone network

A network with a central cabling scheme linking it to other networks. Hosts on networks linked to the backbone can communicate with one another.

backbone router

A router attached to a backbone network by nailed-up lines. Usually, a backbone router does not have any built-in digital dial-up WAN interfaces. Manufacturers of backbone routers include Cisco, Wellfleet, 3Com, and CrossCom. See also backbone network, router.

backoff queue

A file in which the RADIUS accounting server stores unacknowledged records. See also accounting server, RADIUS.

Backup Designated Router

See BDR.

Backward Explicit Congestion Notification

See BECN.

bandwidth

The amount of data a link can carry, measured bits per second (bps) for digital signals, and in hertz (Hz) for analog signals. See also analog signal, digital signal.

base channel count

The number of channels to use for a Multilink Protocol (MP) connection. Because MP does not support Dynamic Bandwidth Allocation (DBA), the number of channels is fixed for the duration of the session. See also DBA, MP.

Basic Rate Interface line

See ISDN BRI line.

B channel

A 64-Kbps channel that carries user data. A B channel is a bearer channel, one of the fundamental components of the ISDN interface. See also E1 PRI line, ISDN, ISDN BRI line, T1 PRI line.

B-channel bundling

A technique for putting multiple voice conversations on a single line. Speech is divided so that bits are transmitted only when someone is speaking. In T1 multiplexing, bundles consist of four bits, represent 11 channels of 32-Kbps compressed data, and have an associated signaling Delta channel. See also B channel.

BDR

Backup Designated Router. A BDR is the router that the Open Shortest Path First (OSPF) area uses in the event that the Designated Router (DR) goes out of service. To prevent the DR from becoming a serious liability to the network if it fails, OSPF elects a Backup Designated Router (BDR). Other routers maintain adjacencies with both the DR and BDR, but the backup router leaves as many processing tasks as possible to the DR. If the DR fails, the backup immediately becomes the DR and a new backup is elected.

The MAX TNT can function as either a DR or a BDR. However, many sites choose to assign LAN-based routers to these functions in order to dedicate the MAX TNT to WAN processing. See also adjacency, area, DR, OSPF, router.

bearer channel

See B channel.

bearer service

An ISDN service for transmitting information from one device to another. Common bearer services are circuit-switched and Frame Relay services. See also circuit switching, Frame Relay.

BECN

Backward Explicit Congestion Notification. BECN is a bit set in a Frame Relay header to notify a source node that there is traffic congestion on the network. See also FECN, Frame Relay.

BGP

Border Gateway Protocol version 4. BGP routes packets between networks that use different types of protocols. It is known as an Exterior Gateway Protocol (EGP), and replaces an older protocol called EGP. See also EGP.

B-ISDN

Broadband-Integrated Services Digital Network. B-ISDN is a very high-speed data service, providing data transmission at rates higher than T1 or E1. See also broadband, E1 line, ISDN, T1 line.

Bit

Binary digit, the smallest unit of information a computer can process, representing one of two states (indicated by 1 and 0).

bits per second

See bps.

blackhole interface

An interface that enables the router to handle packets whose IP address matches an unused IP address in a summarized address pool. The blackhole interface has an IP address of 127.0.0.3. When you specify this address as the router to the destination pool network, the MAX TNT silently discards packets to an invalid host on that network. See also pool summary.

BOOTP

Boot Protocol. BOOTP starts up a network device by using information from a server. The MAX TNT can use BOOTP to get settings and check for a new software load. In addition, you can enable the terminal server to respond to BOOTP within a Serial Line Internet Protocol (SLIP) session. An interactive user who initiates a SLIP session can get an IP address from a designated IP address pool by means of BOOTP. See also IP address, IP address pool, SLIP, terminal server.

Boot Protocol

See BOOTP.

Border Gateway Protocol version 4

See BGP.

bps

A nested acronym, meaning binary digits per second, and a measure of the capacity of a line.

BRI line

See ISDN BRI line.

broadband

A data communications technology that transmits data in channels and uses those channels simultaneously.

Broadband Integrated Services Digital Network

See B-ISDN.

Broadband ISDN

See B-ISDN.

broadcast network

A network in which the router sends packets to all users, whether they appear on subscription lists or not. In an Open Shortest Path First (OSPF) topology, a broadcast network is any network that has more than two OSPF routers attached and can address a single physical message to all of them. See also OSPF, multicast network, router, unicast network.

builddbm file

A file that enables you to create a UNIX DBM database for use with the Ascend RADIUS daemon. See also DBM database, RADIUS daemon.

bus

A path for signals transmitted between a computer's CPU and other hardware devices.

byte

8 bits of data, also called an octet.

C

cached token

A password dynamically generated on a token card, transmitted by Challenge Handshake Authentication Protocol (CHAP), and then cached for reuse. When the MAX TNT needs to add channels or make a new call, the MAX TNT uses the cached token to authenticate the additional bandwidth. You can specify a timeout value for the cached token, or configure the system to maintain the token throughout the session. See also Cache-Token authentication, CHAP, token, token card, token-card authentication, token-card server.

Cache-Token authentication

An authentication method that uses Challenge Handshake Authentication Protocol (CHAP) to transmit the initial token, and then caches the token for reuse. The system later uses the cached token when the MAX TNT adds new channels or makes a new call. See also ACE authentication, cached token, SafeWord authentication, token, token card, token-card authentication, token-card server.

call

A single session in which a calling device and an answering device connect over the WAN.

callback

A type of security in which you instruct the MAX TNT to hang up and call back when it receives an incoming call. You can require callback to ensure that the MAX TNT makes a connection with a known device. Hanging up and calling back adds a level of certainty that the connection is with a trusted user, especially because the MAX TNT calls back immediately after verifying the user's name and password. For the MAX TNT to use callback, it must be able to both receive and initiate calls. Callback security applies only to switched lines. See also authentication, switched line.

called-number authentication

A form of authentication in which the MAX TNT uses the called-party number to authenticate the connection. The remote end uses this form of authentication to make sure that the call goes to a known destination. When the profile requires called-number authentication, the number called must match a phone number in a Connection profile or RADIUS user profile. The MAX TNT also uses the called number to direct incoming calls to a particular device. See also called-party number, Connection profile, user profile.

called-party number

An information element of the Q.931 ISDN signaling protocol. The called-party number is the phone number the remote device calls to connect to the MAX TNT, but without a trunk group or dialing prefix specification. This number is always available if specified in a profile. See also called-number authentication.

caller ID

See CLID.

call filter

A packet filter that defines which packets can bring up a connection or reset the idle timer for an established link (Figure 7). A call filter prevents unnecessary connections and helps the MAX TNT distinguish active traffic from "noise."

Figure 7. Call filters can prevent certain packets from resetting the timer

By default, any traffic to a remote site triggers a call, and any traffic across an active connection resets the connection's idle timer. When a session's idle timer expires, the MAX TNT terminates the session. The idle timer is set to 120 seconds by default, so if a connection is inactive for two minutes, the MAX TNT terminates the connection.

When you apply a call filter, its forwarding action does not affect which packets are sent across an active connection. For a call filter to prevent an interface from remaining active unnecessarily, you must define rules for both incoming and outgoing packets. Otherwise, if only input rules are defined, outgoing packets keep a connection active. If only output rules are defined, incoming packets keep a connection active.

Compare with data filter. See also input filter, output filter, packet filter.

Calling-Line ID

See CLID.

Calling-Line ID authentication

See CLID authentication.

call logging

A method of logging call information from the MAX TNT. Based on RADIUS accounting, call logging enables you to keep records for resource management or troubleshooting. When you set up call logging, you can create duplicate accounting information for sites that wish to keep accounting records separate from call logging records.

The MAX TNT sends Start session, Stop session, and Failure-to-start session packets to a call-log host. The call-log information is sent independently of RADIUS accounting records. If both call logging and RADIUS accounting are in use, the information is sent in parallel.

call-log host

A local host that supports the RADIUS accounting protocol and is configured to communicate with the MAX TNT. See also accounting, call logging.

Call-Route profile

A profile that determines how to route calls with the MAX TNT. The MAX TNT creates a default Call-Route profile for the system itself and for each card.

The system default is the most general default Call-Route profile. It simply stops the MAX TNT from dropping calls for which it has no specified route. The system default simply says "Take any call and route it to any device in the system." It is not a very useful route, and the system expects to find more specific ones in its call-routing database.

The default Call-Route profile for the T1 card says "Take any trunk call and route it to the address of the T1 card." The default Call-Route profile for the Digital Modem card says "Route any voice call to the address of the Digital Modem card." The default Call-Route profile for the HDLC card says "Route any digital call to the address of the HDLC card."

When using a configured Call-Route profile to route a call, the MAX TNT starts with a list of all possible destinations in the system and removes certain destinations from consideration by using the following algorithm:

Remove ports that are currently in use. If a port is currently in use, the MAX TNT does not consider it a possible destination for the call.
Sort the remaining ports. The MAX TNT sorts the remaining list of call-routing entries in the following order:
- Trunk-group number (in descending order)
- Phone-number (with empty phone numbers last)
- Destination address (with zero components sorted after non-zero components)
- Source address (with zero components sorted after non-zero components)
- Routing type
Sort by use count, placing devices that have been used less frequently ahead of those that have been used more frequently.
Compare parameter values in the Call-Route profile to the call's information. Use the sort order specified in step 2.

After each comparison pass, the MAX TNT may find a non-matching profile, which it stops considering as a possible destination for the call. Each comparison pass narrows the list of possible destinations. Ultimately, the MAX TNT routes the call to the best match-that is, to the port that matches the greatest number of parameter values without the use of zero addresses. If more than one device matches the call's parameters equally, the MAX TNT routes the call to the first entry in the database that matches the call's parameters.

If the list becomes empty at any point, the MAX TNT drops the call. Depending on the type of call, the signaling being used, and the configuration of the Central Office (CO) switch, dropping the call may result in the switch returning a busy indication to the caller. If the caller receives a busy indication on a voice line, it originates from the CO switch equipment, not from the MAX TNT.

call routing

The process of directing a call to the appropriate host port (digital modem or HDLC channel) for processing. In some cases, the MAX TNT might forward a call to a Frame Relay switch or to a network host without processing the call or handling its encapsulation. In all other cases, when the MAX TNT receives a call, it routes the call to a host port for encapsulation processing before forwarding the call to the router or terminal-server software.

When the MAX TNT receives a call, it gathers the following information about it:

The trunk group on which the call came in (if trunk groups are in use)
The phone number on which the call came in
The line or channel on which the call came in
The bearer-capability of the call (whether the line uses ISDN signaling)

All this information is specified in a Call-Route profile. If the call's information matches the information in the profile, the MAX TNT routes the call to the address specified by the profile's Index parameter.

If the network port supports ISDN signaling, the MAX TNT is able to ascertain the bearer-capability of the call-voice or data. It can then use that information to route the call to a modem (if it is a voice-service call) or to an HDLC channel (if it is a data call). If the line is configured for inband signaling, all calls are assumed to be digital unless the T1 profile sets the default call type to voice.

call-routing database

A database containing a sorted list of all installed MAX TNT devices. Using the call-routing database in conjunction with Call-Route profiles, the MAX TNT determines how to route each call it receives. The MAX TNT creates the call-routing database whenever it is reset. During active use, the sort order depends on system activity, but the initial sort order determines the order in which the MAX TNT first uses modems and HDLC channels:

For analog calls, the initial sort order is by item number, shelf, and slot. This sort order provides load balancing across multiple host cards.
For digital calls, the initial sort order is by shelf and slot, and then by item number. By concentrating the channels of a call on one HDLC card, this sort order improves system performance for Multilink Protocol (MP) and Multilink Protocol Plus (MP+) calls.

Carrier Detect

See CD.

C-bit Parity Errors

See CPERR.

CCITT

Consultative Committee on International Telegraphy and Telephony. The CCITT is a disbanded organization whose standards were moved to the UN-sanctioned ITU-T on March 1, 1993.

CCP

Compression Control Protocol. CCP enables both ends of a Point-To-Point Protocol (PPP) connection to negotiate whether to use data compression, and if so, which algorithm to use.

CD

Carrier Detect. CD is a signal sent from a modem to a host, indicating that the modem is online.

cell relay

See ATM.

Central Office

See CO.

Central Processing Unit

See CPU.

Challenge Handshake Authentication Protocol

See CHAP.

Change-Filter-Request packet

A request to change the packet filters for a routing session. See also Change-Filter-Request-ACKed packet, Change-Filter-Request-NAKed packet.

Change-Filter-Request-ACKed packet

A message the MAX TNT sends if it found at least one routing session for which it could change packet filters. Compare with Change-Filter-Request-NAKed packet. See also Change-Filter-Request packet.

Change-Filter-Request-NAKed packet

A message the MAX TNT sends if it could not find a routing session for which it could change packet filters. Compare with Change-Filter-Request-ACKed packet. See also Change-Filter-Request packet.

channel

A portion of a line's bandwidth. A line contains a fixed number of channels. Each line can contain switched channels only, nailed-up channels only, or a combination of switched and nailed-up channels. See also bandwidth, line, nailed-up channel, switched channel.

channelized T1 PRI/E1 PRI

A T1 PRI or E1 PRI line divided into individual 64-Kbps channels, or into channels whose data rate is a multiple of 64 Kbps (such as a 256-Kbps channel made from four 64-Kbps channels). Channelized T1 PRI or E1 PRI lines can consist of switched lines with inband signaling, or nailed-up lines. For example, a nailed-up line can run from the Central Office (CO) to the corporate headquarters as a single, unchannelized T1 PRI or E1 PRI line, and can then be divided into channels when it runs to remote sites from the corporate headquarters. See also E1 line, E1 PRI line, inband signaling, nailed-up line, switched line, T1 line, T1 PRI line, unchannelized service.

Channel Service Unit

See CSU.

CHAP

Challenge Handshake Authentication Protocol. CHAP authentication verifies the caller's identity by using a three-way handshake upon initial link establishment, and then by repeating the handshake any number of times. In CHAP authentication, the authentication server sends a challenge to the caller. The caller responds with an MD5 digest calculated from the password. The authentication server then checks the digest against its own calculation of the expected hash value to authenticate the call. The server can send a new challenge at random intervals.

CHAP is a stronger authentication method than Password Authentication Protocol (PAP), because the password does not travel across the line as plain text. In addition, the use of repeated challenges limits the time of exposure to any single attempt to break the encryption code, and the server is in control of how often it sends challenges. See also encryption, PAP.

circuit

A connection between endpoints over a physical medium.

circuit connection

A connection that follows a specified path through the Frame Relay switch. By linking two Data Link Connection Indicator (DLCI) endpoints, the MAX TNT creates a Permanent Virtual Circuit (PVC). The two DLCI endpoints act as a tunnel. A circuit connection is illustrated in Figure 8.

Figure 8. Circuit connection

Data that the MAX TNT receives on one DLCI bypasses the Ascend router and goes out on the other DLCI. If any one of the DLCIs in a PVC becomes inactive because of a disconnect or failure, the PVC using that DLCI becomes inactive. A physical line can carry multiple DLCIs, and the failure of the line causes the failure of all the DLCIs it carries. Compare with direct connection, gateway connection. See also DLCI, Frame Relay switch, PVC, router.

circuit switching

A mode of data transfer in which a dedicated connection is busy for the duration of the call. Compare with packet switching.

Clear To Send

See CTS.

CLI

Command-Line Interface. The CLI enables you to configure the MAX TNT by means of commands that you enter at a prompt.

CLID

Calling-Line ID. The CLID is the telco-provided phone number of the calling device that wants to connect to the MAX TNT. A CLID is also known as a caller ID. See also CLID authentication.

CLID authentication

Calling-Line ID authentication. CLID authentication is a method the MAX TNT uses to authenticate incoming calls by checking the calling party's phone number as received from the telco. The CLID is the phone number of the calling device. The MAX TNT performs CLID authentication before enabling the MAX TNT to answer an incoming call. When the profile requires CLID authentication, the caller's phone number must match a phone number specified in a local Connection profile or RADIUS user profile. You can thereby ensure that the call comes from a known source.

You can use CLID authentication only where the call information is available end-to-end and Automatic Number Identification (ANI) applies to the call. In some areas, the WAN provider might not be able to deliver CLIDs, or a caller might keep a CLID private. Typically, a site uses CLID authentication to protect against a situation in which an unauthorized user obtains the name, password, and IP address of an authorized user, and then calls the MAX TNT from another location.

client

A user or device that requires services from another unit or program. For example, a user requesting access is a client of the MAX TNT, and a MAX TNT making a RADIUS authentication request is a client of the RADIUS server. See also RADIUS server.

client DNS

A configuration that enables the MAX TNT to direct incoming connections to a Domain Name System (DNS) server belonging to a particular client or location, thereby preventing WAN users from accessing a local DNS server. Client DNS has two levels: a global configuration that applies to all PPP connections, and a connection-specific configuration. The MAX TNT uses the global client addresses only if none are specified in the Connection profile. The addresses configured for client DNS servers are presented to WAN connections during IPCP negotiation. You can also choose to present your local DNS servers if no client servers are defined or available. See also Domain Name System, IPCP.

clients file

A file that defines the client machines permitted to make requests to the RADIUS server. For the RADIUS daemon to respond to client requests from the MAX TNT, you must enter a line specifying the MAX TNT unit's name and password in the clients file. See also RADIUS daemon, RADIUS server.

clock

A timing mechanism for synchronizing data communication and processing tasks. A clock divides time into very short intervals. The clock speed is the number of intervals per second. See also clock source.

clock source

The master source for clocking of synchronous connections. The entire multishelf MAX TNT system uses a single synchronous clock source. The MAX TNT chooses the clock source from the T1 or E1 lines you specify as possible external sources. If there are no eligible external sources, the system uses an internal clock generated by the master shelf controller.

You can use the Clock-Source diagnostic command to determine the current master clock source. If you execute the command on the shelf controller, the output tells which slot (if any) is the clock source. If you execute the command on a T1 or E1 card, the output tells which line is the clock source.

CO

Central Office. The CO is the telephone switching office to which a customer directly connects. It connects the customer to other portions of the telephone network.

codec

COder/DECoder. A codec is a device that encodes analog data into a digital signal for transmission over a digital medium. Codecs are often used for videoconferencing. See also analog data, digital signal.

command-history buffer

A file containing the last 20 commands entered at the MAX TNT unit's Command-Line Interface (CLI). When the buffer is full and you enter a new command, the oldest command line is deleted. See also CLI.

Command-Line Interface

See CLI.

command mode

A terminal-server mode in which you can enter commands at the terminal-server prompt. Compare with immediate mode, menu mode.

comment line

A line in a RADIUS user profile or pseudo-user profile that describes the purpose of one or more lines of the profile. Beginning with the # character at column one, the comment line consists of text that extends to the end of the line. You can embed a comment line anywhere in a profile. See also pseudo-user profile, user profile.

community name

A password that the MAX TNT sends to the Simple Network Management Protocol (SNMP) manager when an SNMP trap event occurs, and that the manager sends to the MAX TNT with each polling request. The password authenticates the sender. The default is public. See also agent, manager, SNMP.

Compressed Serial Line Internet Protocol

See CSLIP.

compression

A process that reduces the quantity of bandwidth or storage space required to encode a block of information. See also VJ compression.

Connection profile

A local profile containing authentication and configuration information about a remote device or user.

Consultative Committee on International Telegraphy and Telephony

See CCITT.

context

A subprofile that resides directly below a profile, or that is nested within another subprofile. See also profile, subprofile.

convergence

The time it takes all routers to receive information about a change to the network topology. A slow convergence can result in routing loops and errors. A Routing Information Protocol (RIP) router broadcasts its entire routing table every 30 seconds. On a 15-hop network, convergence can be as high as 7.5 minutes. In contrast, Open Shortest Path First (OSPF) uses a link-state database of the network, and propagates only changes to the database, resulting in faster convergence. See also link-state database, OSPF, RIP.

Coordinated Universal Time

See UTC.

cost

An Open Shortest Path First (OSPF) value you assign to the output side of each router interface. The cost indicates the likelihood that the MAX TNT will use the interface to transmit data. The lower the cost, the more likely that the MAX TNT will use the interface.

Figure 9 shows how costs are used to direct traffic over high-speed links. For example, if Router-2 in Figure 9 receives packets destined for Host B, it will route them through Router-1 across two T1 links (Cost=20) rather than across one 56kbps B-channel to Router-3 (Cost=240).

Figure 9. OSPF costs for different types of links

You can use the cost to perform preferred path selection. If two paths to a destination have equal costs, you can assign a higher cost to one of the paths, making it a backup when the primary path is not available. In addition, you may want to reflect the bandwidth of a connection when assigning costs. As in Figure 9, the cost of a single B-channel connection could be 24 times greater than the cost of a T1 link.

The MAX TNT has a default cost of 1 for a connected route (Ethernet) and 10 for a WAN link. Be careful when assigning costs. Incorrect cost metrics can cause delays and congestion on the network.

D

D4-framed T1 line

A T1 line that uses the D4 format, also known as the Superframe format, to frame data at the physical layer. The D4 format consists of 12 consecutive frames, each one separated by framing bits. T1 lines that do not use ISDN D-channel signaling use the D4 format. See also T1 line.

Database-Description packet

A Type-2 Open Shortest Path First (OSPF) packet. OSPF routers exchange Database-Description packets when an adjacency is being initialized. Each packet describes the contents of the link-state database. The routers use a poll-response procedure. One of the routers is the master, and the other a slave. The master sends Database-Description poll packets, and the slave sends Database-Description response packets. OSPF links the responses to the polls by means of a sequence number in each packet. See also adjacency, link-state database, OSPF.

Data Circuit-terminating Equipment

See DCE.

Data Communications Equipment

See DCE.

data compression

See compression.

Data Encryption Standard

See DES.

data filter

A packet filter that defines which packets the MAX TNT can transmit on a connection. When you apply a data filter, its forward or drop action affects the actual data stream by preventing certain packets from reaching the Ethernet from the WAN, or vice versa (Figure 10).

Figure 10. Data filters can drop or forward certain packets

Many sites use data filters for security purposes, but you can apply data filters to any purpose that requires the MAX TNT to drop or forward only specific packets. For example, you can use data filters to drop packets addressed to particular hosts or to prevent broadcasts from going across the WAN. You can also use data filters to allow users to access only specific devices across the WAN. Compare with call filter. See also packet filter.

Datagram Delivery Protocol

See DDP.

Data Link Connection Indicator

See DLCI.

Data Link layer

The second layer of the OSI Reference Model. The Data Link layer creates, sends, and receives data packets appropriate for the type of network in use. Data-Link-layer protocols include High-Level Data Link Control (HDLC), Link Access Procedure, Balanced (LAPB), Link Access Procedure, D channel (LAPD), Point-To-Point Protocol (PPP), and Serial Line Internet Protocol (SLIP). See also HDLC, LAPD, OSI Reference Model, PPP, SLIP.

data service

A service provided over a WAN line and characterized by the unit measure of its bandwidth. A data service can transmit either data or digitized voice. The following types of data services are available: Switched-56, Switched-64, Switched-384 (also known as H0), Switched-1536 (also known as H11), MultiRate, and GloBanD. See also GloBanD, MultiRate, Switched-56, Switched-64, Switched-384, Switched-1536.

Data Service Unit

See DSU.

Data Set Ready

See DSR.

Data Terminal Equipment

See DTE.

Data Transmit Ready

See DTR.

DBA

Dynamic Bandwidth Allocation. DBA denotes the process of adding or subtracting bandwidth from a switched connection in real time without terminating the link. Multilink Protocol Plus (MP+) supports DBA based upon a set of parameters you specify. To add bandwidth, the MAX TNT dials additional connections.

The MAX TNT can reject a request to add bandwidth if no more channels are available, or if the network is congested. Under either of these conditions, the two ends enter bandwidth-addition-lockout mode, in which neither side can request bandwidth. The lockout prevents both ends from continually trying to add new channels unsuccessfully. The MAX TNT and the Ascend unit at the other end of the link automatically remove the lockout restriction when the conditions that caused the lockout change. Changes typically result from plugging in a new switched-service line, reconfiguring a Line profile, or experiencing a switched-service congestion timeout. When the lockout ends, each end is free to add bandwidth.

If you use a circuit between two locations to capacity 24 hours per day, using a nailed-up line is more cost effective than using a switched line. However, if you need the circuit only sporadically, or if the circuit is sometimes underutilized, it often makes more sense to lease a smaller amount of nailed-up bandwidth and then supplement it with additional switched bandwidth as traffic requirements dictate.

For example, you might establish some connections only when you need to transfer data, and a single circuit can accommodate low traffic levels. However, if traffic levels grow beyond the capacity of the circuit (such as during a large file transfer), DBA automatically adds additional switched channels. When traffic levels subside, DBA automatically removes the channels from the connection. The bandwidth and connection costs are thereby reduced. You pay only for bandwidth when you need it.

DBM database

A RADIUS users file in UNIX database format. Compare with flat ASCII users file. See also users file.

DCE

Data Circuit-terminating Equipment (also Data Communications Equipment). A DCE is a device that connects Data Terminal Equipment (DTE) to a communications channel, such as a telephone line. A DTE refers to a device that an operator uses, such as a computer or a terminal. A DCE converts the format of the data coming from the DTE into a signal suitable to the communications channel. An example of a DCE is a modem, which converts digital data from a computer to analog signals suitable for sending over a telephone line. See also analog signal, digital data, DTE, modem.

D channel

A channel that carries WAN synchronization and signaling information on a T1 PRI or E1 PRI line. See also E1 PRI line, T1 PRI line.

DDP

Datagram Delivery Protocol. DDP is an AppleTalk Network-layer protocol. It provides connectionless service between sockets, and handles both addressing and routing. See also routing, socket.

DDP-IP gateway

A gateway that adds Datagram Delivery Protocol (DDP) encapsulation to Internet Protocol (IP) packets it transmits, and removes DDP from IP packets it receives. This type of gateway enables the use of AppleTalk Remote Access (ARA) client software for an IP connection.

In Figure 11, the dial-in client is running ARA 3.0 (which includes DDP-IP tunneling capabilities) and Telnet to communicate with an IP host on the MAX TNT local interface. The client has its own host route.

Figure 11. DDP-IP connection using ARA 3.0

The MAX TNT is configured as an IP router and an AppleTalk router. See also ARA, AppleTalk routing, DDP, IP, IP router.

DE

Discard Eligibility. DE is a bit in a Frame Relay packet header. You set the DE bit to indicate that the network can discard the packet when traffic reaches a high level. See also Frame Relay.

default gateway

The default router the Ascend unit uses for traffic from a specific connection if it finds no explicit route in the IP routing table. See also IP router, IP routing table.

default route

The route the Ascend unit uses if it does not find a match for a packet's destination address. The default route has the destination address 0.0.0.0. If the Ascend unit finds a default route, it brings up the required connection (if necessary) and forwards the packet.

Figure 12 shows a router on a local subnet configured as the default route in a MAX TNT. This type of configuration enables the MAX TNT to turn off RIP on its local interfaces, and forward all local packets to the default route.

Figure 12. Default route to a local IP router

If the routing table has no default route and no route that matches a packet's destination address, the MAX TNT drops the packet. See also IP route, IP router, IP routing table.

Default user name

A name the RADIUS server uses to grant access to clients who do not appear in the users file. You can configure only one Default profile. It must specify the user name Default, and it must be the last profile in the users file. See also user profile, users file.

default zone

The zone assigned to an AppleTalk service on an interface if the service does not select a zone in which to reside. See also zone, zone list.

Denial of Service attack

See DoS attack.

DES

Data Encryption Standard. DES is the U.S. encryption standard for nonclassified documents. This standard uses a 64-bit key and private-key encryption. In private-key encryption, only the sender and receiver know the key for encrypting the data. DES cannot ensure that the sender and receiver are legitimate. A sender who has learned the key can fraudulently use it. See also encryption, private-key encryption.

Designated Router

See DR.

Destination Service Access Point

See DSAP.

detail file

A file containing RADIUS accounting records. See also accounting, RADIUS.

device address

The address of a device in the MAX TNT. The device address is expressed in the format {shelf slot item}. The following table lists each element of the syntax:

Syntax element

Indicates

shelf

Shelf in which the item resides. If you are using a single-shelf system, the shelf number is always 1. For call-routing purposes, a value of 0 (zero) or any-shelf specifies any shelf.

slot

Number of the item's slot. Physical slots are numbered from 1 to 16, starting with 1 for the slot just below the shelf controller. The slot value 17, controller, or c specifies the shelf-controller card. For call-routing purposes, a value of 0 (zero) or any-slot specifies any slot. For example, to address the first slot on shelf 1:

{ 1 1 0 }

item

Item on the slot card, such as a digital modem or T1 line. Items are numbered starting with #1 for the leftmost item on the card. An item number of 0 denotes the entire slot. For example, to address modem #48 on a modem card in slot #2 on shelf 1:

{ 1 2 48 }

Syntax element	Indicates
shelf	Shelf in which the item resides. If you are using a single-shelf system, the shelf number is always 1. For call-routing purposes, a value of 0 (zero) or `any-shelf` specifies any shelf.
slot	Number of the item's slot. Physical slots are numbered from 1 to 16, starting with 1 for the slot just below the shelf controller. The slot value 17, `controller`, or `c` specifies the shelf-controller card. For call-routing purposes, a value of 0 (zero) or `any-slot` specifies any slot. For example, to address the first slot on shelf 1: { 1 1 0 }
item	Item on the slot card, such as a digital modem or T1 line. Items are numbered starting with #1 for the leftmost item on the card. An item number of 0 denotes the entire slot. For example, to address modem #48 on a modem card in slot #2 on shelf 1: { 1 2 48 }

Domain identifier	Description
.arpa	ARPANET
.com	Commercial enterprise
.edu	Educational institution
.gov	Governmental organization
.mil	Military organization
.org	An organization not covered by the other categories

E

E1 card

A MAX TNT card that provides eight ports, each of which can be connected to an E1 PRI line or an unchannelized E1 line. When the MAX TNT detects an E1 card, it creates a default E1 line profile for each of the eight lines on the card. See also E1 line, E1 PRI line.

E1 line

A 2.048-Mbps line that supports 32 64-kbps channels, each of which can transmit and receive data or digitized voice. The line uses framing and signaling to achieve synchronous and reliable transmission. The most common configurations for E1 lines are E1 PRI and unchannelized E1. See also E1 card, E1 PRI line, unchannelized service.

E1 PRI line

E1 Primary Rate Interface line. An E1 PRI line consists of 32 64-Kbps channels. It uses 30 B channels for user data, 1 64-Kbps D channel for ISDN D-channel signaling, and one framing channel. The B channels can be all switched, all nailed up, or a combination of switched and nailed up. The E1 PRI line is a standard in Europe and Asia called CEPT G.703. Compare with ISDN BRI line, T1 PRI line, unchannelized service. See also B channel, D channel, E1 line, ISDN D-channel signaling, nailed-up channel, switched channel.

E1 Primary Rate Interface line

See E1 PRI line.

E2 line

An 8.45-Mbps line that supports four 2.048-Mbps E1 channels.

E3 line

A 34-Mbps line that supports 16 2.048-Mbps E1 channels.

EAS

External Authentication Server. See authentication server.

Echo

A signal that determines whether a node can receive and acknowledge data transmissions. A host sends an Echo Request packet. If the destination is properly connected and receives the Echo Request packet, it sends back an Echo Reply packet.

echo cancellation

A method that the telephone company uses to remove echoes from an analog line. See also analog line.

ECN

Explicit Congestion Notification. ECN is a method of informing Frame Relay nodes that there is traffic congestion on the network. The Frame Relay header can use a Backward Explicit Congestion Notification (BECN) bit or a Forward Explicit Congestion Notification (FECN) bit to notify nodes of traffic congestion. BECN, FECN, Frame Relay.

EEPROM

Electronically Erasable Programmable Read-Only Memory. EEPROM is a type of Programmable Read-Only Memory (PROM) that can be erased by exposing it to an electrical charge. It retains its contents across resets and power cycles, and is similar to NVRAM. With EEPROM, data is written or erased one byte at a time; with NVRAM, data is written or erased in blocks. See also NVRAM, PROM.

EGP

Exterior Gateway Protocol. EGP is a type of protocol used to exchange routing information between one Open Shortest Path First (OSPF) Autonomous System (AS) and another. The AS number may be used by Area Border Routers (ABRs) to filter out certain EGP routing information. OSPF can make use of EGP data generated by other border routers and added to the OSPF system as Autonomous System Externals (ASEs). See also ABR, AS, ASE, OSPF.

EIA

Electronic Industries Association. The EIA is a group that determines standards for electrical transmission.

EIA/TIA-232

A Physical-layer standard nearly identical to V.24. EIA/TIA-232 is also known as RS-232. See also RS-232.

EIA-449

A Physical-layer standard also known as RS-449. See also RS-449.

EIA-530

A way of referring to RS-422 and RS-423. See also RS-422, RS-423.

Electronically Erasable Programmable Read-Only Memory

See EEPROM.

Electronic Industries Association

See EIA.

Embedded Operations Channel

See EOC.

encapsulation

A technique used by layered protocols in which a low-level protocol accepts a message from a higher-level protocol, and then places the message in the data portion of the lower-level frame. The logistics of encapsulation require that packets traveling over a physical network contain a sequence of headers. Encapsulation enables the transmission of data over networks that use differing protocols.

encryption

A process that takes ordinary data and converts it into a format unreadable to anyone without a decryption key. Authorized personnel with access to this key can unscramble the information. Data encryption is a useful tool against network snoopers. See also private-key encryption, public-key encryption.

Enigma

An important provider of network security applications. Enigma's SafeWord AS (also known as the Enigma Logic SafeWord server) is a UNIX-based software authentication server that identifies users by means of dynamic passwords (called tokens). The server identifies users at the point of connection to a TCP/IP network, and uses standard network authentication protocols and token cards. See also SafeWord authentication, SafeWord token, token card.

Enigma Logic SafeWord server

A token-card authentication server from Enigma. See also Enigma, SafeWord authentication, SafeWord token, token card, token-card authentication, token-card server.

enterprise-wide network

A network that contains all or most of a company's hardware and software resources. Typically, an enterprise-wide network includes computers that run different operating systems and reside on different types of networks. Therefore, achieving interoperability is the biggest challenge facing the administrator of an enterprise-wide network.

entry number

An identifier that distinguishes Call-Route profiles for the same device. See also Call-Route profile.

EOC

Embedded Operations Channel. In the BRI-U interface, EOC is the out-of-band mechanism for implementing maintenance functions. Instead of using the D or B channels, EOC uses the maintenance bits of the U-interface superframe. Maintenance functions include test loopback, statistics gathering, and requests to generate errors (to check that the block-error counters work). You can perform EOC loopback on a B channel during a session with an IDSL card. See also B channel, D channel, IDSL card.

ESF

Extended SuperFrame. ESF is a framing format that consists of 24 consecutive frames, separated by framing bits. The ISDN specification advises that you use ESF with ISDN D-channel signaling. See also ISDN D-channel signaling.

Ethernet

The most commonly used architecture for Local Area Networks (LANs), connecting devices such as computers, printers, and terminals. An Ethernet network uses the Physical and Data Link layers for data transmission. Ethernet incorporates a bus topology, and can operate at a rate of up to 10 Mbps. See also Data Link layer, Physical layer.

Ethernet II

A protocol specification for the Media Access Control (MAC) header of an IPX frame. Compare with 802.2, 802.3, SNAP. See also IPX frame, MAC.

Ethernet card

A card that provides the MAX TNT with access to Ethernet networks. Two types of Ethernet cards are available: a 10-Mbps Ethernet card and a 10/100-Mbps Ethernet card. See also 10-Mbps Ethernet card, 10/100-Mbps Ethernet card.

Ethernet transceiver

A device that connects workstations to standard thick or thin Ethernet-style cable. An Ethernet transceiver sends and receives information, and offers data-packet collision detection. See also Thick Ethernet, Thin Ethernet.

even parity

See parity.

expect-send script

A script whose lines begin with either the send or the expect command. A line that begins with send causes all the other characters on the line to go through the WAN port running the script. A line that begins with expect causes the router to wait for matching characters from the WAN port. You can use an expect-send script to authenticate logins to the terminal server, or to start a Point-To-Point Protocol (PPP) or Serial Line Internet Protocol (SLIP) session from within a terminal-server connection. See also authentication, PPP, SLIP, terminal mode.

Explicit Congestion Notification

See ECN.

Extended SuperFrame

See ESF.

Exterior Gateway Protocol

See EGP.

external authentication

A remote method of identifying the users permitted to access network resources. The remote server can be a RADIUS, TACACS, TACACS+, or token-card server. See also RADIUS, RADIUS server, TACACS, TACACS+, token-card server.

External Authentication Server

See authentication server.

external route

A route imported into the Open Shortest Path First (OSPF) database from outside the router's Autonomous System (AS). Compare with intra-area route. See also AS, OSPF, route.

F

Facilities Data Link

See FDL.

Failure-to-start record

A RADIUS-accounting or call-logging record that contains information about a failed login attempt. See also Failure-to-start session.

Failure-to-start session

An event denoting that a login attempt has failed. Information about this event appears in a RADIUS-accounting or call-logging Failure-to-start record.

Far-End Block Error

See FEBE.

FDDI

Fiber Distributed Data Interface. FDDI is a proposed ANSI standard for a network architecture that uses high-speed fiber-optic lines and supports transmission rates of up to 100 Mbps.

FDL

Facilities Data Link. An FDL is a 4-Kbps digital link between a sender and the telephone company's monitors. The link uses Extended Superframe (ESF) framing. The telephone company uses an FDL to check on the quality and performance of T1 lines. You cannot use FDL reporting on a line configured for D4 framing. However, you can obtain D4 and ESF performance statistics in the FDL Stats windows of the MAX TNT or in the DSX MIB. See also ESF, T1 line.

FEBE

Far-End Block Error. FEBE is a signal the remote end sends to indicate that it has received DS3 or E1 frames with either Framing Errors (FERR) or C-bit Parity Errors (CPERR). A block error is detected each time the calculated checksum of the received data does not correspond to the control checksum transmitted in the successive superframe. One block error indicates that one superframe has not been transmitted correctly. No conclusion with respect to the number of bit errors can be drawn from the block-error counter. Compare with NEBE. See also CPERR, DS3 line, FERR.

FECN

Forward Explicit Congestion Notification. FECN is a bit set in a Frame Relay header to notify a destination node that there is traffic congestion on the network. Compare with BECN. See also Frame Relay.

FERR

Framing Errors. FERR indicates the number of errors in the bits used to frame the DS3 signal. See also DS3 line.

Fiber Distributed Data Interface

See FDDI.

File Transfer Protocol

See FTP.

filter

A set of rules describing what action the MAX TNT should take when it encounters certain types of packets. A filter can apply to incoming packets, outgoing packets, or both. A packet filter applies to packets on an interface. A route filter applies to routes in Routing Information Protocol (RIP) update packets. See also packet filter, route filter.

filter persistence

A method of enabling a firewall to persist across connection-state changes. With filter persistence, the firewall rules stay in force even when a connection goes offline. Filter persistence applies only to interfaces you configure using the Command-Line Interface (CLI), such as Ethernet interfaces and virtual interfaces associated with Connection profiles. Filter persistence does not apply to interfaces built from RADIUS, TACACS, or TACACS+ profiles. See also CLI.

Filter profile

A profile containing parameters that set up filter rules. See also filter, packet filter, route filter.

firewall

See Secure Access Firewall.

flash card

See PCMCIA card.

flash memory

See NVRAM.

flat ASCII users file

A RADIUS users file in a flat, non-database format. Compare with DBM database. See also RADIUS, users file.

foreign agent

An Ascend unit that a mobile client dials into. The foreign agent is the starting point of the Ascend Tunnel Management Protocol (ATMP) tunnel. The foreign agent must be able to bring up an IP connection to the home agent, and it must authenticate the mobile client by means of a RADIUS user profile or Connection profile. See also ATMP, home agent, RADIUS, user profile.

Forward Explicit Congestion Notification

See FECN.

fractional T1 line

A T1 or ISDN BRI line that contains both switched and nailed-up channels. See also ISDN BRI line, nailed-up channel, switched channel, T1 line.

Fractional T1 Plus Switched Multilink Protocol Plus

See FT1-MP+.

frame

In Token Ring and Systems Network Architecture (SNA), a packet at the Data Link layer of the OSI Reference Model; in Frame Relay, a packet of fixed size; in Time Division Multiplexing (TDM), a sequence of time slots, each containing a portion of a multiplexed channel. A frame contains source and destination information, flags that designate the start and end of the frame, and information about the integrity of the frame. All other data, such as network protocol information and the actual payload of data, is first encapsulated in a packet. The system then encapsulates the packet in a frame. See also Data Link layer, Frame Relay, OSI Reference Model, packet, TDM.

framed protocol

A synchronous protocol that encapsulates data into frames. See also framing, protocol, synchronous transmission.

FrameLine card

A MAX TNT card that provides ten unchannelized T1 lines, each of which can be used for one nailed-up connection. Associated with each T1 line is a Serial Communications Adapter (SCA) responsible for receiving and transmitting HDLC frames. Because there is only one SCA per line, only one Point-To-Point Protocol (PPP) or Frame Relay link can be active per line. The Frame Relay link may use multiple Data Link Connection Indicators (DLCIs).

The FrameLine card provides the following PPP features:

1-24 DS0 channels per session
Noncontiguous channels
No MP or MP+ support
User authentication by local profile or RADIUS
No support for Stac compression

The FrameLine card provides the following Frame Relay features:

1-24 DS0 channels per session
Noncontiguous channels
Support for up to 120 DLCIs per card

The FrameLine card provides the following SNMP support:

The same DS1 status and management as the eight-port T1 card
The accounting MIB for session information

The FrameLine card supports the same RADIUS accounting and authentication features as the Digital Modem card. It supports only IP routing.

Unlike other slot cards, the FrameLine card does not use a Call-Route profile. The data pathway is directed to an on-board SCA device and cannot be routed to another host card. All packetization of data occurs locally.

The MAX TNT supports up to 15 FrameLine cards.

Frame Relay

A WAN architecture originally developed for ISDN lines. A Frame Relay network provides high throughput by handing monitoring functions to higher-level protocols. It is a very efficient standard, with a bandwidth of up to 2 Mbps. Frame Relay is ideal for situations in which periods of very high traffic are interspersed with idle periods. It is protocol independent, and performs routing over virtual circuits called Data Link Connection Indicators (DLCIs). See also DLCI, ISDN.

Frame Relay concentrator

A device that concentrates many low-speed, dial-in connections into one high-speed, nailed-up connection to a Frame Relay switch. When you configure the MAX TNT as a Frame Relay concentrator, it accepts incoming dial-in connections as usual and forwards them to a Frame Relay switch (Figure 16).

Figure 16. MAX TNT operating as a Frame Relay concentrator

The configuration contains the following elements:

A physical interface to the Frame Relay network (consisting of nailed-up WAN channels).
A logical interface to the Frame Relay network (defined in a Frame-Relay profile on the MAX TNT or a Frame Relay profile in RADIUS).
Connections forwarded to the Frame Relay network (defined in Connection profiles or RADIUS user profiles).

The MAX TNT must appear as a Frame Relay switch to both MAX TNT users and other Frame Relay switches. See also Frame Relay switch.

Frame Relay connection

A link between a dial-in user and the Frame Relay switch. The MAX TNT supports the following types of interfaces to the Frame Relay network:

User-To-Network Interface-Data-Circuit-terminating-Equipment (UNI-DCE)
User-To-Network Interface-Data Terminal Equipment (UNI-DTE)

Frame Relay profile

A profile that defines the logical link between the MAX TNT and a Frame Relay switch. See also Frame Relay, Frame Relay switch.

Frame Relay switch

A device that sends Frame Relay data out to the Frame Relay network. See also Frame Relay.

Frame Relay user profile

A RADIUS user profile that enables you to configure a Frame Relay connection for a user accessing a Frame Relay link. A Frame Relay user profile can specify one of three types of Frame Relay user connections: gateway, circuit, or direct. See also circuit connection, direct connection, Frame Relay, Frame Relay connection, gateway connection, user profile.

framing

At the Physical and Data Link layers of the OSI model, a method of fitting bits into a unit called a frame. A frame contains source and destination information, flags that designate the start and end of the frame, and information about the integrity of the frame. All other data, such as network protocol information and the actual payload of data, is first encapsulated in a packet. The system then encapsulates the packet in a frame. See also Data Link layer, encapsulation, OSI Reference Model, packet, Physical layer.

Framing Errors

See FERR.

FT1-MP+

Fractional T1 Plus Switched Multilink Protocol Plus. An FT1-MP+ connection begins as a nailed-up connection, but can later use switched channels, either to increase bandwidth or to provide a backup if the nailed-up channels go offline. When a nailed-up connection is temporarily down, the MAX TNT polls continuously while trying to re-establish the link. If an outgoing packet arrives while the nailed-up connection is still down, the unit replaces the nailed-up channel with a switched channel. See also fractional T1 line, MP+.

FTP

File Transfer Protocol. FTP is an Application-layer protocol that enables you to transfer files from one device to another over a network. See also Application layer.

full duplex

A type of communications configuration in which data can be transmitted in both directions at the same time. Compare with half duplex.

G

gateway

A device or program that provides mapping at all seven layers of the OSI model and translates between two otherwise incompatible networks or network segments. A gateway performs code and protocol conversion to facilitate traffic between data highways of differing architectures. See also OSI Reference Model.

gateway connection

A routing link in a Frame Relay configuration. In a gateway connection, the MAX TNT receives an incoming Point-To-Point Protocol (PPP) call, examines the destination IP address, and brings up the appropriate Connection profile or RADIUS user profile to the destination.

Figure 17 shows callers who dial into the MAX TNT to reach a distant IP network across the Frame Relay network.

Figure 17. Gateway connection

If the profile specifies Frame Relay encapsulation, a Frame Relay profile, and a Data Link Connection Indicator (DLCI), the MAX TNT encapsulates the packets in Frame Relay (RFC 1490) and forwards the data stream out to the Frame Relay switch. The Frame Relay switch uses the DLCI to route the frames. Compare with circuit connection, direct connection. See also Connection profile, DLCI, Frame Relay, Frame Relay connection, Frame Relay profile, Frame Relay switch, user profile.

gateway mode

An Ascend Tunnel Management Protocol (ATMP) configuration in which the home agent tunnels packets from the foreign agent to the home network across an open WAN connection. The WAN connection must be online. The home agent does not bring up a WAN connection to the home network in response to a packet it receives through the tunnel. For this reason, the home agent must have a nailed-up WAN connection to the home network. Compare with router mode. See also ATMP, foreign agent, home agent, home network, nailed-up circuit.

generic filter

A packet filter that examines the byte- or bit-level contents of a packet and compares them with a value defined in the filter. To use a generic filter effectively, you need to know the contents of certain bytes in the packets you wish to filter. Protocol specifications are usually the best source of such information. Compare with IP filter, IPX filter. See also call filter, data filter, packet filter.

Generic Routing Encapsulation

See GRE.

GGP

Gateway-To-Gateway Protocol. GGP is a TCP/IP protocol that transfers routing information between gateways. See also gateway, TCP/IP.

glare

A signal that the switch sends when you attempt to place an outgoing call and answer an incoming call simultaneously.

GloBanD

A European data service consisting of a single circuit whose bandwidth is a multiple of 64 Kbps. This circuit consists of one or more B channels. For example, if a caller requests 512-Kbps service, the line uses eight B channels to supply the requested bandwidth. GloBanD service is available over T1 PRI lines only. It differs from MultiRate in being an overlay network, rather than an integral part of the worldwide switched digital infrastructure. See also bandwidth, B channel, MultiRate, T1 PRI line.

GMT

Greenwich Mean Time. This term has been changed to Coordinated Universal Time (UTC). See UTC.

GRE

Generic Routing Encapsulation. GRE provides a simple, general-purpose mechanism for encapsulating an arbitrary Network-layer protocol in another arbitrary Network-layer protocol. When a system needs to route data, it first encapsulates the information in a GRE packet. The system then encapsulates the GRE packet in a protocol supported by the network and forwards the packet to its destination.

Greenwich Mean Time

This term has been changed to Coordinated Universal Time (UTC). See UTC.

H

H0 channel

In the Switched-384 data service, a circuit consisting of 6 B channels, or 384 Kbps. See also B channel, Switched-384.

H0 data service

See Switched-384.

H11 channel

In the Switched-1536 data service, a circuit consisting of 24 B channels, or 1536 Kbps. See also B channel, Switched-1536.

H11 data service

See Switched-1536.

half duplex

A type of communications configuration in which data can be transmitted in only one direction at a time. Compare with full duplex.

hardware address

An address assigned by the hardware manufacturer and unique to a device.

hardware interface

A hardware link between two devices. A hardware interface has electrical, physical, and functional specifications that determine how two devices communicate. An electrical specification defines the characteristics of the electrical signals. A physical specification might define the number of pins and wires required, and the order in which the pins and wires are laid out. The functional specification instructs the hardware on how to interpret the electrical signals. Examples of commonly used hardware interfaces are RS-232 and V.24. See also interface, RS-232, V.24.

HDLC

High-Level Data Link Control. HDLC is a synchronous, bit-oriented Data Link layer protocol for data transmission. Frame Relay is an example of an HDLC-based packet protocol. HDLC offers half- or full-duplex communications over circuit- or packet-switched networks, allows point-to-point and multipoint configurations, and provides transmission over both wires and wireless media. See also circuit switching, Data Link layer, Frame Relay, full duplex, half duplex, HDLC channel, multipoint link, packet switching, point-to-point link.

HDLC card

High-Level Data Link Control card. On the MAX TNT, an HDLC card provides support for 128 HDLC sessions. Each ISDN call and each channel of a nailed-up connection requires an HDLC channel to process the data received from or destined for a WAN interface. You must install an HDLC card if your system uses an eight-port E1 card, an eight-port T1 card, or a T3 card.

Each HDLC card contains six HDLC controller chips. Each of these chips can handle a maximum of 32 channels. Because nailed-up connections cannot span controller chips, each nailed-up link cannot contain more than 32 channels.

An HDLC card is also known as a Hybrid Access card. See also E1 card, HDLC channel, T1 card, T3 card.

HDLC channel

High-Level Data Link Control channel. Vital to call routing on the MAX TNT, HDLC processing removes encapsulation from high-speed incoming data calls, such as those from ISDN Terminal Adapters (TAs). After removing the link's encapsulation, the HDLC channel passes the data stream to the router. One 128-channel HDLC card supports all switched channels on an eight-port T1 card. See also HDLC, HDLC card, T1 card.

HDSL

High Data Rate Digital Subscriber Line. HDSL is a technology that enables modems on either side of two copper twisted-pair wires to transmit data at T1 or E1 speeds. HDSL provides 1.544 Mbps of bandwidth each way at distances of up to 12,000 feet. T1 data rates require two lines. E1 data rates require three lines. Compare with ADSL, SDSL.

High Data Rate Digital Subscriber Line

See HDSL.

High-Level Data Link Control

See HDLC.

High-Speed Serial Interface

See HSSI.

home agent

An Ascend unit that represents the terminating part of the Ascend Tunnel Management Protocol (ATMP) tunnel. It must be able to communicate with the home network directly, through another router, or across a nailed-up WAN connection. See also ATMP, home network, nailed-up circuit, router.

home network

A private corporate network in an Ascend Tunnel Management Protocol (ATMP) configuration. A private network is one that cannot communicate directly on the Internet, such as an IP network with an unregistered network number. See also ATMP, IP network, IPX network, IP network number.

hop

A single message or packet transmission between host and a router, or between two routers. See also hop count, host, router.

hop count

The number of routers through which a packet passes to get from its source to its destination. See also hop, host, router.

host

A computer on a network, also called a node or a station.

host number

The portion of an IP address that denotes an individual node on a network. The class of an IP address determines which portion of the address belongs to the network number and which portion belongs to the host number. See also IP address, IP network number.

host port

A High-Level Data Link Control (HDLC) channel or a digital modem on the MAX TNT. The MAX TNT routes each call it receives to the appropriate host port. See also digital modem, HDLC channel.

host route

An IP address with a subnet mask of 255.255.255.255, representing a single host rather than a remote router. A host route requires a static IP address. Figure 18 shows a sample connection in which a dial-in host with an ISDN modem card calls into the MAX TNT and requires a static address for a host route.

Figure 18. Dial-in host requiring a static IP address (a host route)

host-route connection

A connection that enables the dial-in host to keep its own IP address when logging into the MAX TNT IP network. See also host route.

host-side address

The interface address of the device that terminates the WAN circuit for an incoming call to the MAX TNT. An analog-encoded call handled by a digital modem and a digital call handled by an HDLC circuit are two examples of a route to a host-side address. Compare with network-side address. See also call routing, call-routing database.

HSSI

High-Speed Serial Interface. HSSI is a serial interface that operates at speeds of up to 52 Mbps, and at distances of up to 50 feet. It is similar to the RS-232 and V.35 serial interfaces, but operates at a higher speed. See also RS-232, SWAN card, V.35.

hub

A device that serves as a termination point for multiple hosts, sending signals onto the proper paths. Typically, a hub contains four to eight connectors. In addition to providing connectors for hosts, many hubs include connectors that you can use to link one hub to another.

hunt group

A group of channels that share the same phone number. When a call comes in using the phone number assigned to the hunt group, the switch hunts for an available channel in the group. See also channel, switch.

Hybrid Access card

See HDLC card.

hybrid LAN

A network in which some links are capable of sending and receiving analog signals, while others handle digital signals. See also analog signal, digital signal.

I

ICMP

Internet Control Message Protocol. ICMP is an error-reporting mechanism integral to the TCP/IP protocol suite. Gateways and hosts use ICMP to send reports of datagram problems to the sender. ICMP also includes an echo request/reply function that tests whether a destination is available and responding. See also gateway, host, TCP/IP.

idle connection

A connection between endpoints in which no data is being transmitted.

idle disconnect

A disconnect that occurs when no data is transmitted on a link for a specified period of time. See also idle timer.

idle timer

A timer that measures how long a session can remain idle before the MAX TNT disconnects it. By default, any traffic across an active connection resets the connection's idle timer. When you apply a call filter, its forwarding action determines which packets can initiate a connection or reset a session's timer. When a session's idle timer expires, the MAX TNT terminates the session. The idle timer is set to 120 seconds by default, so if a connection is inactive for two minutes, the MAX TNT terminates the connection. Compare with inactivity timer. See also call filter.

IDRP

Inter-Domain Routing Protocol. IDRP is an International Standards Organization (ISO) protocol for routing packets between disparate administrative domains. It is based on the Border Gateway Protocol (BGP). See also BGP, ISO.

IDSL card

ISDN Digital Subscriber Line card. The IDSL card supports high-bandwidth applications such as remote access, Internet access, intranet access, and telecommuting. By installing the IDSL card into the MAX TNT, you can cost-effectively support a wide range of analog, ISDN, Frame Relay and IDSL services on a single, manageable platform. Any existing ISDN U-interface device, such as a Terminal Adapter (TA) or Ascend Pipeline, can connect to a MAX TNT equipped with an IDSL card.

The IDSL card provides the following features:

ISDN BRI (2B1Q) signaling
2 DB37 connectors, each providing 16 IDSL sessions
128-Kbps data rate over a two-wire subscriber loop
Line Termination (LT) mode
No switch requirements
Data calls only
Point-to-point transmission
Support for both switched and nailed-up channels (including Ascend's SuperDigital 128)
Support for such maintenance functions as the BRI-U interface-monitoring commands, loopback, and out-of-band management

Compare with ADSL, HDSL, RADSL card, SDSL, SDSL card. See also ISDN BRI line, LLB, LT mode, nailed-up channel, out-of-band management, SuperDigital 128, switched channel, TA, two-wire subscriber loop.

IEC

Interexchange Carrier. An IEC is a type of telephone service that provides long-distance links between local telephone companies. Well-known IECs include AT&T, MCI, and Sprint. Compare with LEC.

IEEE

Institute of Electrical and Electronics Engineers. The IEEE is an organization that maintains the standards for 10Base-T and other communications specifications. See also 10Base-T.

IGMP

Internet Group Management Protocol. IGMP is a protocol implemented by multicast clients and routers. The MAX TNT responds as a client to IGMP packets it receives from a Multicast Backbone (MBONE) router. The packets may use IGMP version-1, IGMP version-2, or IGMP Multicast Trace (MTRACE). MAX TNT clients wanting MBONE service must implement IGMP. See also MBONE, multicast, multicast network, router.

IGP

Interior Gateway Protocol. IGP transmits routing information internal to a network. See also routing.

immediate mode

A terminal-server access mode in which the terminal server does not display the command-line prompt or a menu of hosts, but immediately directs a dial-in user to a designated host by means of TCP, Rlogin, or Telnet. When you use Telnet to initiate the connection to the host, you can configure the terminal server to pass the call to the host before authentication. In this case, the responsibility for authentication belongs to the Telnet host. See also Rlogin, TCP, Telnet.

inactivity timer

A timer that determines the number of minutes that an Ascend Tunnel Management Protocol (ATMP) home agent maintains an idle tunnel before disconnecting it. Compare with idle timer.

inband signaling

A type of signaling in which a line uses 8 Kbps of each 64-Kbps channel for WAN synchronization and signaling. The remaining 56 Kbps handle the transmission of user data. When a line is configured for inband signaling, the MAX TNT does not receive bearer-capability information from the carrier. Therefore, it does not know whether a call uses voice service or digital service. For call-routing purposes, the MAX TNT assumes that all calls on an inband-signaling line are digital. Another term for inband signaling is robbed-bit signaling. Robbed-bit refers to the 8 Kbps of each channel used for signaling. Compare with ISDN D-channel signaling.

incoming call

A call the MAX TNT receives from a remote user or device.

index

A name, physical address, or interface address that identifies a specific profile of a particular type. See also interface address, physical address.

input filter

A filter applied to an incoming packet. See also filter, packet filter, route filter.

Institute of Electrical and Electronics Engineers

See IEEE.

Integrated Services Digital Network

See ISDN.

Inter-Domain Routing Protocol

See IDRP.

Interexchange Carrier

See IEC.

interface

A connection between two devices, programs, or program elements. See also hardware interface.

interface address

A profile address composed of a physical address and logical-item number in the following format:

{{shelf slot item} logical-item }

The {shelf slot item} portion specifies the physical address. The logical-item portion specifies a logical item number. The logical item number is 0 (zero), except when the device is further divided, such as for a channelized T1 line. For a T1 line, each channel can have its own logical item number (1-24).

An IP-Interface profile is an example of a profile indexed by interface address. In addition, some lines or ports contain subdivisions, such as the individual channels on a T1 line. These items have an interface address in the MAX TNT as well. See also channelized T1 PRI/E1 PRI, item number, logical item number, physical address, shelf, slot, T1 line.

interface-based routing

An IP-routing method in which each physical or logical interface on the unit has its own IP address. The interface becomes a numbered interface. Reasons for using numbered interfaces include troubleshooting nailed-up point-to-point connections and forcing routing decisions between two links going to the same final destination. More generally, interface-based routing allows the MAX TNT to operate more as a multihomed host behaves.

You can configure each link as numbered (interface-based) or unnumbered (system-based). If no interfaces are numbered, the MAX TNT operates as a purely system-based router. Compare with system-based routing, unnumbered interface. See also IP routing, multihomed host, numbered interface, point-to-point link.

interface table

A table containing the addresses of each Ethernet, IP, and IPX interface on the MAX TNT. Each packet-handling slot card operates as a router subsystem with its own local interface table and route cache. To view the interface table, enter the Netstat command with the -in argument, as shown in the following example:

admin> netstat -in

Name     MTU  Net/Dest          Address        Ipkts  Ierr Opkts  Oerr

ie0      1500 12.65.212.0/24    12.65.212.227  107219    0 54351     0

lo0      1500 127.0.0.1/32      127.0.0.1        4867    0  4867     0

rj0      1500 127.0.0.2/32      127.0.0.2           0    0     0     0

bh0      1500 127.0.0.3/32      127.0.0.3           0    0     0     0

wan4     1500 10.122.99.1       -                   0    0     0     0

ie1-12-1 1500 11.168.6.0/24     11.168.6.227   430276  651     0     0

ie1-12-2 1500 10.122.72.0/24    10.122.72.1         0    0     0  3144

ie1-12-3 1500 10.122.73.0/24    10.122.73.1         0    0  3142     0

ie1-12-4 1500 10.122.74.0/24    10.122.74.1         0    0  3141     0

The columns in the interface table contain the following information:


Column name	Description
`Name`	The name of the interface: `ie0` or `ie[`shelf`]-[`slot`]-[`item`]` is an Ethernet interface. `lo0` is the loopback interface. `rj0` is the reject interface, used in network summarization. `bh0` is the blackhole interface, used in network summarization. `wan`N is a WAN connection, entered as it becomes active. `wanabe` indicates an inactive RADIUS dialout profile.
`MTU`	(Maximum Transmission Unit) The maximum packet size allowed on the interface.
`Net/Dest`	The network or the target host this interface can reach.
`Address`	The address of this interface.
`Ipkts`	The number of packets received.
`Ierr`	The number of packets that contain errors.
`Opkts`	The number of packets transmitted.
`Oerr`	The number of transmitted packets that contain errors.

Field	Indicates
Destination	Target address. To send a packet to this address, the MAX TNT uses the route. Note that the router uses the most specific route (having the largest subnet mask) that matches a given destination.
Gateway	Address of the next-hop router that can forward packets to the destination. Direct routes do not show a gateway address.
IF	Name of the interface through which the MAX TNT sends a packet addressed to the destination.
Flg	Flag values describing the route: C (A directly connected route, such as Ethernet) I (An ICMP Redirect dynamic route) N (A route placed in the table by the SNMP MIB II) O (A route learned from OSPF) R (A route learned from RIP) r (A transient RADIUS-like route that will disappear when the connection drops) S (A static route) ? (A route of unknown origin, which indicates an error) G (An indirect route through a gateway) P (A private route) T (A temporary route) M (A multipath route) * (A backup static route for a transient RADIUS-like route)
Pref	Preference value of the route.
Metric	RIP-style metric for the route, with a valid range of 0-16. Routes learned from OSPF show a RIP metric of 10. OSPF Cost infinity routes show a RIP metric of 16.
Use	Count of the number of times the route was referenced since it was created. (Many of these references are internal, so this is not a count of the number of packets sent using the route.)
Age	Age of the route in seconds. It is used for troubleshooting, and to determine when routes are changing rapidly.

J

Java

An object-oriented programming language developed by Sun Microsystems, Inc. You can use Java to create applets for distribution on the World Wide Web. Java programs run inside a Java-enabled Web browser or inside a Java Virtual Machine (JVM).

Java Virtual Machine

See JVM.

JVM

Java Virtual Machine. A JVM is an abstract computer that runs compiled Java code. The JVM is virtual because it is software that runs on top of a hardware platform and an operating system. All Java programs are compiled for a JVM. See also Java.

K

K56flex

A 56-Kbps modem specification developed by Rockwell and Lucent for calls between a digital modem and an analog modem. K56flex allows 56-Kbps data transfers on the downstream portion of a call, and 33.6-Kbps data transfers on the upstream portion. The Ascend Series56 Digital Modem card includes the K56flex technology. See also digital modem, modem, Series56 Digital Modem card.

L

LAN

Local Area Network. A LAN is a network in which two or more computers, located within a limited distance of one another, are connected in order to share files and resources. A PC-based LAN consists of a dedicated server running a network operating system and attached to several workstations. A host-based LAN consists of one or more hosts and terminals. Examples of LAN architectures are Ethernet, ARCnet, Fiber Distributed Data Interface (FDDI), and Token Ring. See also ARCnet, FDDI, Token Ring.

LAN adapter

See NIC.

LAN packet display

A display of packet performance over a specified time, measured graphically or by counters.

LAN/WAN connectivity

The ability to link Local Area Networks (LANs) and Wide Area Networks (WANs). A wide range of tools, from translation protocols to communications features to support services, make a remote-access device like the MAX TNT an effective link between LANs and WANs.

LAP

Link Access Procedure. LAP is a protocol containing a subset of High-Level Data Link Protocol (HDLC) features. In order to maintain compatibility with HDLC, LAP was changed to create LAPB. See also LAPB.

LAPB

Link Access Procedure, Balanced. LAPB is a protocol for B channels that use packet-switching mode. See also B channel, packet switching.

LAPD

Link Access Procedure, D channel. LAPD is a protocol for the D channel. It provides the mechanism for combining multiple channels into a single logical link, and for monitoring and controlling the flow of data over the B channels. See also B channel, D channel.

LAPF

Link Access Procedure, Frame. LAPF is a protocol for Frame-mode bearer services. See also bearer service.

LAPM

Link Access Procedure, Modem. LAPM is an error-detection protocol for correcting data communication errors occurring on the link between two modems.

latency

For a communications channel, the amount of time before the channel is available for a transmission; for data transmissions, the amount of time it takes for a packet to reach its destination. The following elements contribute to latency:

The type of physical media in use.
Physical interference from noise or other signals.
Required setup and teardown times.
Signal interfaces. Ethernet consumes a minimum of 0.3 milliseconds (ms). A 28.8 modem takes about 300 times longer.
Bottlenecks, such as the 50 ms it takes to move data through a serial port.
Data conversion, such as the conversion from digital to analog data required by a modem.
Compression.

Once latency is present, it cannot be optimized. You must remove the cause. To maximize throughput, use the highest bandwidth available. All services go as fast as the medium allows. For example, if the medium is copper, the speed of the electrical signal through the copper does not vary with the type of line in use. A T1 line is considered faster than a single analog line only because its bandwidth is greater.

LCP

Link Control Protocol. LCP sets up, manages, and tears down a connection between two Point-To-Point Protocol (PPP) endpoints. See also PPP.

LCV

Line Code Violations. In the line-statistics display, LCV indicates that the MAX TNT detected either a Bipolar Violation or Excessive Zeroes on the DS3 or E1 line, indicating that one of the low-level rules for encoding data was violated on the receive signal. See also DS3 line.

leased circuit

See nailed-up circuit.

leased line

See nailed-up line.

LEC

Local Exchange Carrier. An LEC is a local telephone company. See also IEC.

line

A physical interface to the WAN. A line consists of one or more channels, each of which can transmit data. See also channel.

Line Code Violations

See LCV.

Line Loopback

See LLB.

line-status window

The status window in which T1, E1, and T3 line- and channel-status information appears. The status information can fill the upper-right portion, the lower-right portion, or the entire right side of the status window. The line-status information consists of a line identifier in shelf/slot/line format, and a two-character code indicating the line's link status. A single-character code indicates channel status. See also DS3 line, E1 line, T1 line, T3 line.

Line Quality Monitoring

See LQM.

Line Termination Mode

See LT mode.

Link Access Procedure

See LAP.

Link Access Procedure, Balanced

See LAPB.

Link Access Procedure, D Channel

See LAPD.

Link Access Procedure, Frame

See LAPF.

Link Access Procedure, Modem

See LAPM.

link compression

A process that removes waste and redundancy from the data on a connection, enabling faster throughput. For the MAX TNT to use link compression, both sides must be configured to use the same compression method. You can use Stac compression (an Ascend-modified version of draft 0 of the CCP protocol), Stac-9 compression (the method specified by draft 9 of the Stac LZS compression protocol), or Microsoft Stac compression (the method implemented by Windows 95). See also CCP, slot compression, VJ compression.

Link Control Protocol

See LCP.

link state

The condition of an Open Shortest Path First (OSPF) link. See also OSPF.

Link-State Advertisement

See LSA.

link-state database

A database that contains Open Shortest Path First (OSPF) routing information. Link-state routing algorithms require that all routers within a domain maintain identical link-state databases, and that the databases describe the complete topology of the domain. An OSPF router's domain may be an Autonomous System (AS) or an area within one.

Based on the exchange of information among routers, OSPF routers create a link-state database, which is updated based on packet exchanges among the routers. Link-state databases are synchronized between pairs of adjacent routers. In addition, each OSPF router uses its link-state database to calculate a self-rooted tree of shortest paths to all destinations. The routing table is built from these calculated shortest-path trees. Externally derived routing data is advertised throughout the AS but is kept separate from the link-state data. Each external route can also be tagged by the advertising router, enabling the passing of additional information between routers on the boundary of the AS.

For example, suppose you have the network topology in Figure 22.

Figure 22. Sample OSPF network topology

The following information appears in the link-state databases of the three routers:

Router-1

Router-2

Router-3

Network-1/Cost 0

Network-2/Cost0

Network-3/Cost 0

Network-2/Cost 0

Network-3/Cost0

Network-4/Cost 0

Router-2/Cost 20

Router-1/Cost 20

Router-2/Cost 30

Router-3/Cost 30

Router-1	Router-2	Router-3
Network-1/Cost 0	Network-2/Cost0	Network-3/Cost 0
Network-2/Cost 0	Network-3/Cost0	Network-4/Cost 0
Router-2/Cost 20	Router-1/Cost 20	Router-2/Cost 30
	Router-3/Cost 30

Each router builds a self-rooted shortest-path tree, and then calculates a routing table stating the shortest path to each destination in the AS (Figure 23, Figure 24, and Figure 25).

Figure 23. Shortest-path tree and resulting routing table for Router-1

Destination

Next hop

Metric

Network-1

Direct

0

Network-2

Direct

0

Network-3

Router-2

20

Network-4

Router-2

50

Figure 24. Shortest-path tree and resulting routing table for Router-2

Destination

Next hop

Metric

Network-1

Router-1

20

Network-2

Direct

0

Network-3

Direct

0

Network-4

Router-2

30

Figure 25. Shortest-path tree and resulting routing table for Router-3

Destination

Next hop

Metric

Network-1

Router-2

50

Network-2

Router-2

30

Network-3

Direct

0

Network-4

Direct

0

	Destination	Next hop	Metric
Network-1	Direct	0
Network-2	Direct	0
Network-3	Router-2	20
Network-4	Router-2	50

	Destination	Next hop	Metric
Network-1	Router-1	20
Network-2	Direct	0
Network-3	Direct	0
Network-4	Router-2	30

	Destination	Next hop	Metric
Network-1	Router-2	50
Network-2	Router-2	30
Network-3	Direct	0
Network-4	Direct	0

Field	Description
`Name`	Hostname.
`IP address`	IP address. An asterisk (*) indicates that the entry has been automatically updated by a DNS query.
`# Reads`	Number of accesses since the entry was created.
`Time of last read`	Time and date the entry was last accessed. The time and date appear only if Simple Network Time Protocol (SNTP) is in use. If SNTP is not in use, the field contains a row of hyphens.

Type	Description
Type 1 (RTR)	Router-LSA that describes the collected states of the router's interfaces.
Type 2 (NET)	Network-LSA that describes the set of routers attached to the network.
Types 3 and 4 (STUB)	Summary-LSA that describes point-to-point routes to networks or Area Border Routers (ABRs).
Type 5 (ASE)	AS-external-LSA that describes routes to destinations external to the AS. An AS-external-LSA can also describe a default route for the AS.

M

MAC

Media Access Control. In the IEEE's Local Area Network/Reference Model, MAC denotes a sublayer below the Logical Link Control (LLC) sublayer. Combined, the LLC and MAC sublayers are equivalent to the Data Link layer in the OSI Reference Model. They give higher-level protocols access to the physical media. See also LLC, MAC address, OSI Reference Model.

MAC address

The 6-byte hexadecimal address that the manufacturer assigns to the Ethernet controller for a port. See also hardware address, MAC.

Management Information Base

See MIB.

manager

An application that receives Simple Network Management Protocol (SNMP) information from an agent. An agent and manager share a database of information, called the Management Information Base (MIB). An agent can use a message called a traps-PDU to send unsolicited information to the manager. A manager that uses the Ascend Enterprise MIB can query the MAX TNT, set parameters, sound alarms when certain conditions appear, and perform other administrative tasks. See also agent, community name, MIB, SNMP, traps-PDU.

mask

In a generic filter, a 12-byte value the MAX TNT applies to a packet before comparing its contents to the value you indicate in a filter specification. The mask hides the bits that appear behind each binary 0 (zero). A mask of all ones (FF:FF:FF:FF:FF:FF:FF:FF) masks no bits, so the full specified value must match the packet contents. See also generic filter.

master shelf controller

The shelf controller that is responsible for maintaining the routing tables, and for managing each of the slot cards in the system. Compare with slave shelf controller. See also shelf controller.

Maximum Receive Unit

See MRU.

Maximum Reconstructed Receive Unit

See MRRU.

Maximum Transfer Unit

See MTU.

MAX TNT

A multiprotocol WAN access switch that enables carriers, Internet Service Providers (ISPs), corporations, and major network providers to offer a variety of access services, such as analog, ISDN, nailed-up T1 and E 1, and Frame Relay. The MAX TNT has a scalable, modular card-and-backplane architecture that lets users design solutions that satisfy the specific application and bandwidth requirements of any customer.

The MAX TNT system hardware consists of one, two, or three shelves, a shelf controller, and redundant, load-balancing power supplies. The backplane consists of three distinct buses: Cell, Time Division Multiplexing (TDM), and Packet. It supports up to 720 simultaneous digital modem, ISDN, or 56/64-Kbps Frame Relay sessions. A single MAX TNT shelf can terminate up to 150 nailed-up T1/E1 Frame Relay lines. The system terminates a T3 and routes a full channelized T3 interface (with 720 DS0 timeslots) on a multiple-shelf system.

You can enhance the base system by adding one or more slot cards, such as a FrameLine or Analog Modem card. A single shelf can support up to 16 cards. See also analog data, Analog Modem card, Digital Modem card, DS0 channel, DS3 line, E1 line, FrameLine card, ISDN, Series56 Digital Modem card, T1 line, T3 line.

MBONE

Multicast Backbone. The MBONE is a virtual network layered on top of the Internet to support IP multicast routing across point-to-point links. Because multicasting is a fast and inexpensive way to communicate information to multiple hosts, the MBONE is used for transmitting audio and video on the Internet in real time.

The MBONE consists of groups of networks called islands. These islands are connected by tunnels and support IP. When the MAX TNT accesses an MBONE network, it starts receiving MBONE multicasts. It resends the multicast packets to all of its own clients connected to it for MBONE service. The clients wanting MBONE service must implement Internet Group Membership Protocol (IGMP).

To the MBONE, the MAX TNT looks like a multicast client. It responds as a client to IGMP packets it receives from an MBONE router. The MBONE router can reside on the MAX TNT unit's Ethernet interface or across a WAN link. If the router resides across a WAN link, the MAX TNT can respond to multicast clients on its Ethernet interface as well as across the WAN.

To multicast clients on a WAN or Ethernet interface, the MAX TNT looks like a multicast router, although it simply forwards multicast packets on the basis of group memberships. See also multicast, multicast forwarding, multicast heartbeat, multicast network, multicast rate limit, point-to-point link.

MBONE interface

The location on the MAX TNT that connects to an MBONE router. See also MBONE router.

MBONE router

A router that directs multicast packets to a group of clients on a subscription list. See also MBONE, MBONE interface, multicast, multicast forwarding, multicast heartbeat, multicast network, multicast rate limit.

Media Access Control

See MAC.

menu mode

A mode in which the terminal server presents a banner message and a menu of hosts. In menu mode, a user cannot enter terminal-server commands, but can connect by means of Telnet, Rlogin, or raw TCP to the hosts you specify. The MAX TNT authenticates the user's login name and password, and then displays a text-based menu such as the one shown in Figure 26.

Figure 26. Menu mode

Users can Telnet to the specified host by pressing 1, 2, 3, or 4, or can quit the menu by pressing Q. Quitting the menu terminates the connection.

If you configure the menu locally, you can specify up to four hosts. If you configure the menu in RADIUS, you can configure up to ten. Compare with command mode, immediate mode.

message

Data transmitted from one location to another with a header field, information field, and trailer. Often used interchangeably with packet and frame.

metric

A value that determines how quickly a packet can reach its destination. Routing Information Protocol (RIP) and the Open Shortest Path First (OSPF) protocol use different types of metrics.

RIP is a distance-vector protocol, which uses a hop count to select the shortest route to a destination network. RIP always uses the lowest hop count, regardless of the speed or reliability of a link.
OSPF is a link-state protocol. OSPF can take into account a variety of link conditions, such as the reliability or speed of the link, when determining the best path to a destination network.

MHRP

Mobile Host Routing Protocol. MHRP is a protocol designed to support the mobility of a host. Using MHRP, a developer can design a product allowing continuous network connectivity for traveling computer users.

MIB

Management Information Base. A MIB is a Simple Network Management Protocol (SNMP) database of information available to network management programs. An agent creates a MIB. A network manager queries the MIB for information, and might create a MIB of its own. The MIB on the agent contains machine-specific information. The manager's MIB has more general information. The MAX TNT supports SNMP MIB II, T1 MIB, and Ascend Enterprise MIBs. See also agent, manager, SNMP.

Microcom Networking Protocol

See MNP.

Microsoft CHAP

See MS-CHAP.

Microsoft Stac

The version of the Stac LZS compression method implemented by Windows 95. Compare with Stac compression, Stac-9 compression.

MNP

Microcom Networking Protocol. MNP is a communications hardware protocol developed by Microcom, Inc. Used by many high-speed modems, MNP supports several classes of communication. A modem can support more than one class.

Class 4 provides error detection, and can vary the modem's transmission speed in accordance with the quality of the line. Class 5 offers data compression, and can enable a device to double its transmission speed. Class 6 tries to detect the highest transmission speed supported by the modem at the other end of the connection, and then attempts to transmit data at that speed. The most commonly used MNP classes are Class 4 and Class 5, also called MNP-4 and MNP-5, respectively.

N

nailed-up channel

A channel on a line rented from the phone company for exclusive use, 24 hours per day, seven days per week. See also nailed-up circuit, nailed-up line.

nailed-up circuit

A permanent connection between endpoints over which two parties exchange data. The number of nailed-up channels must be the same at both ends of the connection. For example, if there are five nailed-up channels at the local end, there must be five nailed-up channels at the remote end. However, channel assignments do not have to match. For example, channel 1 may be switched at the local end and nailed up at the remote end. A nailed-up circuit is also known as a private circuit or a leased circuit. See also nailed-up channel, nailed-up line.

nailed-up line

A line rented from the phone company for exclusive use, 24 hours per day, seven days per week. The connection exists between two predetermined points and cannot be switched to other locations. A nailed-up line is also called a leased line. See also nailed-up channel, nailed-up circuit.

name and password authentication

A form of authentication in which the MAX TNT attempts to match a caller's user name and password to the parameters or attributes specified in a profile. If name and password authentication is required, the MAX TNT first attempts to match the caller's name and password to a local Connection profile. If authentication succeeds using a local Connection profile, the MAX TNT uses the parameters specified in the profile to build the connection.

If it cannot find a matching Connection profile, the MAX TNT looks for a RADIUS, TACACS, or TACACS+ profile containing a matching name and password. If authentication succeeds using a RADIUS user profile, the MAX TNT uses the specified RADIUS attributes to build the connection. The MAX TNT can then forward the call to its router or other destination. If authentication succeeds using a TACACS or TACACS+ profile, the MAX TNT must make a request to the server for information about the resources and services the user can access.

NAS

Network Access Server. An NAS is a device that provides LAN and WAN access for network hosts. The MAX TNT is an example of an NAS.

NCP

NetWare Core Protocol. NCP is a protocol that allows an IPX server to respond to client requests. See also IPX server.

NCP

Network Control Protocol. NCP is a collection of protocols for setting up and configuring Network-layer protocols (such as AppleTalk) over PPP. See also PPP.

Near-End Block Error

See NEBE.

NEBE

Near-End Block Error. A signal that the remote end sends to indicate that it has detected an error in the data it has transmitted. A block error is detected each time the calculated checksum of the data does not correspond to the control checksum transmitted in the successive superframe. One block error indicates that one superframe has not been transmitted correctly. No conclusion with respect to the number of bit errors can be drawn. Compare with FEBE.

NetBIOS

Network Basic Input/Output System. NetBIOS is a protocol developed by IBM that provides network access to upper-layer programs. NetBIOS functionality includes the Session, Presentation, and Application layers of the OSI Reference Model, and provides naming services, connectionless best-effort datagram delivery, and support for virtual circuits. See also OSI Reference Model.

NetWare Core Protocol

See NCP.

NetWare server

See IPX server.

network

A group of computers, often called hosts, nodes, or stations, that are connected to each other for the purpose of sharing files and other resources. Each computer has a Network Interface Card (NIC) that enables it to gain access to the network. Each host can have one or more peripherals (such as a fax modem or printer) attached to it. Each peripheral can be shared with other network users, or can remain private to the individual computer.

Network Access Server

See NAS.

network adapter

See NIC.

network address

An address shared by all the hosts on the same physical network.

network alignment

A method of setting up IP address pools for pool summary. When you perform network alignment, you make sure that the first address in the pool is the first host address, and that the maximum number of entries you specify is two fewer than the total number of addresses in the pool. See also IP address, pool summary.

Network Basic Input/Output System

See NetBIOS.

network board

See NIC.

Network Control Protocol

See NCP.

Network File System

See NFS.

Network Information Center

See InterNIC.

Network Information Service

See NIS.

Network Interface Card

See NIC.

Network layer

A layer in the OSI Reference Model. The Network layer provides address resolution and routing protocols. Address resolution enables the Network layer to determine a unique network address for a node. Routing protocols allow data to flow between networks and reach their proper destination. Examples of Network-layer protocols are Address Resolution Protocol (ARP), Datagram Delivery Protocol (DDP), Internet Control Message Protocol (ICMP), Interior Gateway Protocol (IGP), Internet Protocol (IP), Internetwork Packet Exchange (IPX), and Packet Layer Protocol (PLP). See also ARP, DDP, ICMP, IGP, IP, IPX, OSI Reference Model, routing.

network number

See IP network number, IPX network number.

network port

A T1 or E1 channel. The MAX TNT always places or receives calls on a network port.

network range

A contiguous range of integers (from 1 to 65, 199) assigned to an AppleTalk network. Each network range must be unique. No two networks can use the same range, and no two network ranges can overlap.

In order for the MAX TNT to receive calls from dial-in AppleTalk Remote Access (ARA) clients, you must define a virtual AppleTalk network by specifying a network range. Each number in the range can be associated with up to 253 nodes, so the range determines how many AppleTalk clients can dial into the MAX TNT. For example, a network with a range from 1000 to 1002 could support up to 2 x 253, or 506 clients.

network-side address

The interface address of the line on which the MAX TNT sends an outgoing call. A call switched to a local ISDN BRI line is an example of a route to a network-side address. Compare with host-side address. See also call routing, call-routing database.

Network-To-Network Interface

See NNI.

Network Virtual Terminal

See NVT.

Network Virtual Terminal ASCII

See NVT ASCII.

NFAS

Non-Facility Associated Signaling. NFAS is a special case of ISDN signaling in which two or more T1 PRI lines use the same D channel, and you can add a backup D channel. It is required for the Switched-1536 data service. Because all 24 channels of the T1 PRI line carry user data, the D channel must be on another line. See also D channel, Switched-1536, T1 PRI line.

NFS

Network File System. NFS is an Application-layer protocol, developed by Sun Microsystems, for sharing and transferring remote files on UNIX or other types of networks. See also Application layer.

NIC

See InterNIC.

NIC

Network Interface Card. A NIC enables a PC to connect to a network. The NIC uses drivers to communicate with the host's networking software, and interacts with the physical media that connects the host to other computers. A NIC is also called a LAN adapter, network adapter, or network board.

NIS

Network Information Service. Along with the Network File System (NFS), the NIS is a method of creating a distributed database system in order to centralize common configuration files, such as the UNIX password file (/etc/passwd) and the hosts file (/etc/hosts). An NIS server manages copies of the database files, and NIS clients request information from them. NIS was developed by Sun Microsystems. See also NFS.

NNI

Network-To-Network Interface. A standard that defines the interface between two Frame Relay switches located in a private or public network. Both switches must reside in the same type of network. The User-To-Network Interface (UNI) standard defines the interface between a public switch and private one. NNI operation enables the MAX TNT to act as a Frame Relay switch communicating with another Frame Relay switch.

Figure 31 illustrates an NNI interface.

Figure 31. NNI interfaces

Compare with UNI. See also Frame Relay.

node

See host.

node number

A value assigned to a host on a network. The node number can be hardcoded in the Network Interface Card (NIC), or assigned by means of jumper settings. It is unique among all the hosts on a local, physical network. The address for a host also contains the network address shared by all the hosts on the local network. See also host, network address, NIC.

Non-Facility Associated Signaling

See NFAS.

nonseed router

An IPX or AppleTalk router that acquires its network configuration from another router on the network. Compare with seed router. See also AppleTalk routing, IPX router.

Nonvolatile Random Access Memory

See NVRAM.

normal area

An Open Shortest Path First (OSPF) area that allows Type-5 Link-State Advertisements (LSAs) to be flooded throughout it. Area Border Routers (ABRs) advertise external routes as Type-5 LSAs. A normal area is the default for the MAX TNT. If you change the default for one interface on the unit, you must change it for all interfaces, because the MAX TNT does not currently perform ABR functions. Compare with NSSA, stub area. See also ABR, area, ASE Type-5, external route, LSA, OSPF, router, routing.

Not So Stubby Area

See NSSA.

NSSA

Not So Stubby Area. An NSSA is an Open Shortest Path First (OSPF) area that does not receive or originate Type-5 Link-State Advertisements (LSAs), and that imports Autonomous System (AS) external routes in a limited fashion. OSPF version 2 defines a new Type-7 LSA for NSSAs.

For NSSAs, all routes imported to OSPF have the P-bit set (P stands for propagate). When the P-bit is enabled, Area Border Routers (ABRs) translate Type-7 LSAs to Type-5 LSAs, which can then be flooded to the backbone. These external routes are considered Type-7 LSAs. They may be routes defined in local Connection profiles or RADIUS profiles, or static routes defined in IP-Route profiles.

Compare with normal area, stub area. See also area, AS, ASE Type-5, ASE Type-7, external route, LSA, OSPF.

NT1

Network Terminator Type 1. An NT1 is a terminating device for an ISDN BRI line. Installed at the subscriber's location, an NT1 provides line maintenance, timing, and echo cancellation. An NT1 can be a standalone device, or it can be built into other types of equipment. See also ISDN BRI line.

numbered interface

In interface-based IP routing, a unique address assigned to one side of a connection. Assignment of a unique address is a requirement for some applications, such as Simple Network Management Protocol (SNMP). Figure 32 shows a local interface with two addresses, one of which is used for a numbered interface connection.

Figure 32. How numbered interfaces work

Reasons for using numbered interfaces include troubleshooting nailed-up point-to-point connections and forcing routing decisions between two links going to the same final destination. More generally, interface-based routing allows the MAX TNT to operate more as a multihomed Internet host behaves. Compare with system-based routing, unnumbered interface. See also interface-based routing, IP address, multihomed host, point-to-point link, SNMP.

NVRAM

Nonvolatile Random Access Memory. NVRAM is a type of memory that maintains its data contents across resets and power cycles. It is useful for storing configuration information across sessions. Data is written and erased in blocks, rather than byte-by-byte.

The MAX TNT unit's system configuration is stored in the onboard NVRAM. Some error conditions may require that you clear the MAX TNT configuration and reboot. When you clear NVRAM, the system is re-initialized and comes up unconfigured, just as it was when you first installed it. You can then restore the configuration from a recent backup.

NVRAM is also called flash memory. Compare with DRAM, EEPROM, RAM.

NVT

Network Virtual Terminal. An NVT is a bidirectional character device with a printer and a keyboard. The printer responds to incoming data, and the keyboard produces outgoing data sent over a Telnet connection. The code set is seven-bit ASCII in an eight-bit field. See also NVT ASCII, Telnet session.

NVT ASCII

The ASCII character set used with a Network Virtual Terminal (NVT). See also ASCII, NVT.

O

Octet

Eight data bits, also called a byte.

odd parity

See parity.

Open Shortest Path First

See OSPF.

Open Systems Interconnection Reference Model

See OSI Reference Model.

OSI Reference Model

Open Systems Interconnection Reference Model. The OSI Reference Model describes the layers of a network, details the functions of each layer, and explains how to connect communications devices on a LAN or WAN. Each layer provides services for the layer above it, and uses the services of the layer below it. The seven layers are:

Layer

Description

Application

Provides applications with access to the network. File transfer, email, and network management software are examples of Application-layer programs. Protocols such as Simple Network Management Protocol (SNMP), Telnet, Rlogin, File Transfer Protocol (FTP), and File Transfer, Access, and Management (FTAM) provide Application-layer services.

Presentation

Responsible for presenting information in a format understandable to users and their applications. Data conversion, special graphics, compression, and encryption are some of the functions implemented at the Presentation layer.

Session

Synchronizes the data in a network connection, maintains the link until the transmission is complete, handles security, and makes sure that the data arrives in the proper sequence. Gateway communications are implemented at the Session layer. Examples of Session-layer protocols are AppleTalk Data Stream Protocol (ADSP), NetBEUI (an extension of NetBIOS), NetBIOS, and Printer Access Protocol (PAP).

Transport

Provides data transfer at the proper speed, quality, and error rate, ensuring reliable delivery. Protocols include Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Sequenced Packet Exchange (SPX).

Network

Provides address resolution and routing protocols. Address resolution enables the Network layer to determine a unique network address for a node. Routing protocols allow data to flow between networks and reach their proper destination. Examples of Network-layer protocols are Address Resolution Protocol (ARP), Datagram Delivery Protocol (DDP), Internet Control Message Protocol (ICMP), Interior Gateway Protocol (IGP), Internetwork Packet Exchange (IPX), Internet Protocol (IP), and Packet Layer Protocol (PLP).

Data Link

Creates, sends, and receives data packets appropriate for the type of network in use. Protocols include High-Level Data Link Control (HDLC), Link Access Procedure, Balanced (LAPB), Link Access Procedure, D channel (LAPD), Point-To-Point Protocol (PPP), and Serial Line Internet Protocol (SLIP).

Physical

Defines the electrical properties of the physical medium, and converts the data into a series of 0s and 1s for digital transmission. Examples of Physical-layer specifications include RS-232, RS-422, RS-423, RS-449, IEEE 802.3, and IEEE 802.5.

Layer	Description
Application	Provides applications with access to the network. File transfer, email, and network management software are examples of Application-layer programs. Protocols such as Simple Network Management Protocol (SNMP), Telnet, Rlogin, File Transfer Protocol (FTP), and File Transfer, Access, and Management (FTAM) provide Application-layer services.
Presentation	Responsible for presenting information in a format understandable to users and their applications. Data conversion, special graphics, compression, and encryption are some of the functions implemented at the Presentation layer.
Session	Synchronizes the data in a network connection, maintains the link until the transmission is complete, handles security, and makes sure that the data arrives in the proper sequence. Gateway communications are implemented at the Session layer. Examples of Session-layer protocols are AppleTalk Data Stream Protocol (ADSP), NetBEUI (an extension of NetBIOS), NetBIOS, and Printer Access Protocol (PAP).
Transport	Provides data transfer at the proper speed, quality, and error rate, ensuring reliable delivery. Protocols include Transmission Control Protocol (TCP), User Datagram Protocol (UDP), and Sequenced Packet Exchange (SPX).
Network	Provides address resolution and routing protocols. Address resolution enables the Network layer to determine a unique network address for a node. Routing protocols allow data to flow between networks and reach their proper destination. Examples of Network-layer protocols are Address Resolution Protocol (ARP), Datagram Delivery Protocol (DDP), Internet Control Message Protocol (ICMP), Interior Gateway Protocol (IGP), Internetwork Packet Exchange (IPX), Internet Protocol (IP), and Packet Layer Protocol (PLP).
Data Link	Creates, sends, and receives data packets appropriate for the type of network in use. Protocols include High-Level Data Link Control (HDLC), Link Access Procedure, Balanced (LAPB), Link Access Procedure, D channel (LAPD), Point-To-Point Protocol (PPP), and Serial Line Internet Protocol (SLIP).
Physical	Defines the electrical properties of the physical medium, and converts the data into a series of 0s and 1s for digital transmission. Examples of Physical-layer specifications include RS-232, RS-422, RS-423, RS-449, IEEE 802.3, and IEEE 802.5.

OSPF

Open Shortest Path First. OSPF is the next generation Internet routing protocol. The Open in its name refers to the fact that OSPF was developed in the public domain as an open specification. The Shortest Path First portion refers to an algorithm developed by Dijkstra in 1978 for building a self-rooted shortest-path tree from which routing tables can be derived. As a link-state protocol, OSPF an take into account a variety of link conditions, such as the reliability or speed of the link, when determining the best path to a destination network. OSPF uses a link-state database of the network and propagates only changes to the database. See also link-state database, route, router, routing.

outgoing call

A call that the MAX TNT places to another device.

out-of-band management

A management method that uses a separate channel for diagnostic and administrative purposes (rather than a portion of each data channel).

out-of-band signaling

See ISDN D-channel signaling.

out-of-frame condition

A condition in which the DS3 line or DS2 stream cannot receive or transmit data because the MAX TNT has lost the frame alignment on the received signal. See also DS3 line.

output filter

A filter applied to an outgoing packet. See also filter, packet filter, route filter.

P

packet

A block of information containing a header, data, and trailer. Packets created at one level of the OSI Reference Model are inserted into lower-level packets. The format of a packet depends upon the protocol that creates it. A packet can be transmitted over a network or phone line. Compare with frame. See also OSI Reference Model, packet field.

packet buffering

In a TCP dial-in session that does not require V.120 processing, a method of buffering and transmitting raw TCP data as TCP packets, rather than as a continuous data stream. Unless V.120 processing is required, raw TCP WAN data goes directly to the HDLC interface, rather than to the terminal-server subsystem. If V.120 processing is required, the terminal server processes the call. See also Raw TCP.

packet field

A portion of a packet that contains a specific kind of information. For example, the data field in a packet contains the data being transmitted between applications. The header field can contain information identifying the packet type and any error-checking mechanisms. See also packet.

packet filter

A series of rules stating how the MAX TNT is to handle certain types of packets. Each rule specifies a condition and an action to be taken if the condition is met. The MAX TNT compares data in the packet to each condition, one condition at a time, until it finds a match between the data and one of the conditions. It then forwards or drops the packet, depending on the action specified for the condition.

When no filter is in use, the MAX TNT forwards all packets. But when you apply a filter to an interface, you reverse that default. For security purposes, the unit no longer forwards non-matching packets automatically. It requires a rule that explicitly allows those packets to pass.

You can apply a packet filter to incoming packets, outgoing packets, or both. In addition, you can specify that the MAX TNT forward or drop those packets that match the rules, or all packets except those that match the rules.

The MAX TNT supports three types of packet filters: generic, IP, and IPX. You can apply a generic, IP, or IPX filter as either a data filter or a call filter. The MAX TNT applies a data filter before a call filter.

Compare with route filter. See also call filter, data filter, generic filter, IP filter.

packet switching

A mode of data transfer in which packets are transmitted from a specific source to a specific destination using any available circuit. Packets may take different paths at the same time, and may not arrive in the order in which they were sent. Compare with circuit switching.

PAP

Password Authentication Protocol. PAP uses a two-way handshake method of establishing a caller's identity. Used only during the initial establishment of the data link, PAP is not a strong authentication method. Passwords travel across the line as plain text, so they are subject to eavesdroppers using software that monitors network information. Use PAP authentication only when the dial-in device does not support a stronger authentication method, such as Challenge Handshake Authentication Protocol (CHAP), or when the remote device requires a plain text password.

An extension of PAP adds the U.S. Data Encryption Standard (DES) cipher to data transmissions. The caller applies the encryption algorithm to a PPP packet and places the resulting cipher text in the information field of another PPP packet. The receiving end applies the inverse algorithm and interprets the resulting plain text as if it were a PPP packet that had arrived directly on the interface.

Compare with CHAP. See also authentication, DES, password, PPP.

PAP-Token authentication

An extension of Password Authentication Protocol (PAP) authentication. In PAP-Token authentication, the user authenticates his or her identity by entering a password (called a token). The token is derived from a hardware device, such as a hand-held token card. The MAX TNT prompts the user for the token, possibly along with a challenge key. The MAX TNT obtains the challenge key from a token-card server that it accesses through RADIUS. The token travels in the clear, but because it is a one-time-only password, the security risk is usually not serious. To authenticate the base channel of the connection, the token-card server uses the token that the user sends in response to the challenge.

PAP-Token is appropriate for single-channel, dial-out calls. It is not practical for multichannel calls, because any time that bandwidth requirements cause another channel to come up, the MAX TNT challenges the user for another token.

Compare with PAP, PAP-Token-CHAP authentication. See also RADIUS, token, token card, token-card authentication, token-card server.

PAP-Token-CHAP authentication

An authentication method that uses PAP-Token to authenticate the base channel of Multilink Protocol Plus (MP+) call, and then a Challenge Handshake Authentication Protocol (CHAP) password to authenticate additional channels. The advantage of a PAP-Token-CHAP call over a PAP-Token call is that you need to verify only the initial connection by means of a hand-held token card. In a PAP-Token-CHAP call, the MAX TNT uses CHAP to verify any additional channels. Compare with CHAP, PAP, PAP-Token authentication. See also MP+, token, token card, token-card authentication, token-card server.

parallel dialing

A way for the MAX TNT to add channels to an outgoing call in multiples, rather than one at a time.

parity

In 7-bit communication, a way for a device to determine whether it has received data exactly as the sending device transmitted it. Each device must determine whether it will use even parity, odd parity, or no parity.

The sending device adds the 1s in each string it sends and determines whether the sum is even or odd. Then, it adds an extra bit, called a parity bit, to the string. If even parity is in use, the parity bit makes the sum of the bits even. If odd parity is in use, the parity bit makes the sum of the bits odd. For example, if a device sends the binary number 1010101 under even parity, it adds a 0 (zero) to the end of the byte, because the sum of the 1s is already even. However, if it sends the same number under odd parity, it adds a 1 to the end of the byte in order to make the sum of the 1s an odd number.

The receiving device checks whether the sum of 1s in a character is even or odd. If the device is using even parity, the sum of 1s in a character should be even. If the device is using odd parity, the sums of bits in a character should be odd. If the sum of the bits does not equal the parity setting, the receiving device knows that an error has occurred during the transmission of the data.

For special ASCII characters (128-256), eight bits are necessary to represent the data. In 8-bit communication, no parity bit is used. See also ASCII.

parity bit

An extra bit added to a string in 7-bit communication. The sending device adds the 1s in each string it sends and determines whether the sum is even or odd. Then, it adds the parity bit to the string. If even parity is in use, the parity bit makes the sum of the bits even. If odd parity is in use, the parity bit makes the sum of the bits odd.

password

A text string that a user must enter during the login process. Entering the proper password identifies the user as a person authorized to access network resources. Compare with token.

P-bit Parity Errors

See PERR.

PCM

Pulse Coded Modulation. PCM is a sampling technique for encoding a digital stream so that it contains a digitized version of the analog waveform sent by a device attached to a modem. The MAX TNT can also convert outgoing data into analog waveforms, change these waveforms into a PCM-encoded digital stream, and send them to the network over a digital line. The network presents the data to the receiving modem in analog form over an analog line. The data looks exactly as it would appear if it had been sent by an analog-based modem.

There are two standards for coding the sample level. The U-Law standard is common in North America and Japan. Elsewhere, the A-Law standard is typically in use.

PCMCIA

Personal Computer Memory Card International Association. PCMCIA is a standard that supports the devices on a credit-card-sized board. The 1990 PCMCIA version 1.0 specification supports Type I cards for RAM, ROM, or NVRAM. The 1991 PCMCIA version 2.01 specification supports Type II cards for network and fax/modem functionality, and Type III cards. A Type III card provides a miniature hard drive for wireless networks. See also NVRAM, RAM, ROM.

PCMCIA card

A card on the shelf controller that contains code for the slot cards, shelf-controller run-time code, and profiles. A PCMCIA card is also called a flash card. See also PCMCIA, PCMCIA card code, PCMCIA slot.

PCMCIA card code

Code written to make use of PCMCIA-card functionality. See also PCMCIA, PCMCIA card, PCMCIA slot.

PCMCIA slot

A slot on the MAX TNT shelf controller into which you can install a PCMCIA card. The MAX TNT contains two PCMCIA slots. See also PCMCIA, PCMCIA card, PCMCIA card code, shelf controller.

PDU

Protocol Data Unit. A PDU is a packet created at any one of the OSI layers. See also OSI Reference Model.

peripheral

A device attached to a network, server, or workstation. Peripherals include CD-ROM drives, fax machines, hard drives, modems, optical drives, printers, and tape drives.

permission level

A specification that governs the commands you can use at the MAX TNT Command-Line Interface (CLI). You set permission levels in a User profile. See also CLI, User profile.

PERR

P-bit Parity Errors. In the line-statistics display, PERR indicates the number of times that the P-bit parity check failed on the DS3 line. Compare with CPERR. See also DS3 line.

Personal Computer Memory Card International Association

See PCMCIA.

per-user accounting

A way for network reseller to direct accounting information about specific users to a RADIUS server belonging to a particular ISP. A network reseller can serve many different ISPs, each with a different access policy. The reseller carries traffic for individual users, and must bill for usage according to the policies of the appropriate ISP. Per-user accounting facilitates this process. See also accounting, ISP, RADIUS.

per-user default route

The default route for IP packets coming from a particular user. The MAX TNT uses the per-user default under either of the following circumstances:

The next-hop address in the MAX TNT unit's routing table is the default route for the system (destination 0.0.0.0).
The normal routing logic fails to find a route and there is no system-wide default route.

The direct route can take place by means of a profile or an Ethernet connection. If the Ascend unit does not have a direct route, it drops the packets on the connection. The default value is 0.0.0.0. If you accept this value, the Ascend unit routes packets as the routing table specifies, using the system-wide default route if it cannot find a more specific route.

The per-user default route applies to all packets the MAX TNT receives for a given profile, regardless of the specific IP source address. Therefore, you can use this feature when the profile belongs to another router, and all hosts behind that router use the default gateway. The MAX TNT handles packets from other users or from the Ethernet network in the usual fashion. The global routing table is not altered. Therefore, when you diagnose routing problems with a profile that implements a per-user default route, an error in a per-user gateway address is not apparent from inspection of the global routing table.

physical address

The location of a device within the MAX TNT system. The physical address has the format {shelf slot item}. The following table lists each element of the syntax:

Syntax element

Indicates

shelf

Shelf in which the item resides. If you are using a single-shelf system, the shelf number is always 1. For call-routing purposes, a value of 0 (zero) or any-shelf specifies any shelf.

slot

Number of the item's slot. Physical slots are numbered from 1 to 16, starting with 1 for the slot just below the shelf controller. The slot value 17, controller, or c specifies the shelf-controller card. For call-routing purposes, a value of 0 (zero) or any-slot specifies any slot.
For example, to address the first slot on shelf 1:

{ 1 1 0 }

item

Item on the slot card, such as a digital modem or T1 line. Items are numbered starting with #1 for the leftmost item on the card. An item number of 0 denotes the entire slot.
For example, to address modem #48 on a modem card in slot #2 on shelf 1:

{ 1 2 48 }

Syntax element	Indicates
shelf	Shelf in which the item resides. If you are using a single-shelf system, the shelf number is always 1. For call-routing purposes, a value of 0 (zero) or `any-shelf` specifies any shelf.
slot	Number of the item's slot. Physical slots are numbered from 1 to 16, starting with 1 for the slot just below the shelf controller. The slot value 17, `controller`, or `c` specifies the shelf-controller card. For call-routing purposes, a value of 0 (zero) or `any-slot` specifies any slot. For example, to address the first slot on shelf 1: `{ 1 1 0 }`
item	Item on the slot card, such as a digital modem or T1 line. Items are numbered starting with #1 for the leftmost item on the card. An item number of 0 denotes the entire slot. For example, to address modem #48 on a modem card in slot #2 on shelf 1: `{ 1 2 48 }`

Interface	Description
The reject interface (rj0)	The reject interface has an IP address of 127.0.0.2. When you specify this address as the router to the destination pool network, the MAX TNT rejects packets to an invalid host on that network, appending an ICMP Host Unreachable message.
The blackhole interface (bh0)	The blackhole interface has an IP address of 127.0.0.3. When you specify this address as the router to the destination pool network, the MAX TNT silently discards packets to an invalid host on that network.

Q

quiesce

To gracefully take a line or modem out of service.

R

R2 signaling

An ITU-T standardized signaling protocol for establishing and clearing 64-kbps switched circuits on E1 digital trunks. Signaling is performed through a combination of A/B bit manipulation in channel 16 of the E1 frame, and inband MF tone generation and detection. The relevant specifications are found in ITU-T recommendations Q.400 to Q.490. R2 signaling is widely implemented in international markets in which ISDN PRI signaling is not yet available. See also E1 line, ITU-T.

RADIUS

Remote Authentication Dial-In User Service. Using RADIUS, end users can have access to secure networks through a centrally managed server. RADIUS provides authentication for a variety of services, such as login, callback, Serial Line Internet Protocol (SLIP), and Point-To-Point Protocol (PPP). It also enables you to set up accounting. You can keep records on the number of packets the MAX TNT transmitted and received, the protocol in use, the user name and IP address of the client, and other system information.

In Figure 36, the RADIUS server performs both authentication and accounting.

Figure 36. RADIUS authentication and accounting

In a RADIUS query, the MAX TNT provides a user ID and password to the server. The server sends back a complete profile, which specifies routing, packet filtering, destination-specific static routes, and restrictions specific to the user. In addition, the MAX TNT can use the data in the RADIUS database to create and advertise static routes, and to place outgoing calls.

The communications channel between a RADIUS client and server is provided by UDP/IP, with messages acknowledged. The primary advantage in using RADIUS to authenticate incoming calls is that you can maintain all user information offline on a separate UNIX-based server. The server can accept authentication requests from many machines, which makes swapping out one dial-in network server for another much easier.

RADIUS accounting

See accounting.

radiusd

The RADIUS daemon that runs with a flat ASCII users file.

RADIUS daemon

The daemon that provides users with RADIUS authentication and accounting. Ascend provides a RADIUS daemon that runs with a flat ASCII users file, and one that runs with a UNIX DBM database. The radiusd daemon runs with a flat file. The radiusd.dbm daemon runs with a UNIX DBM database.

radiusd.dbm

The RADIUS daemon that runs with a UNIX DBM database.

RADIUS server

The machine on which the RADIUS daemon is running. A single RADIUS server can administer multiple security systems, maintaining profiles for thousands of users. See also RADIUS, radiusd, RADIUS daemon, radiusd.dbm.

RADSL card

Rate Adaptive Asymmetric Digital Subscriber Line card. A RADSL card supports high-bandwidth applications such as remote access, Internet access, intranet access, and telecommuting. Using RADSL allows the MAX TNT to detect the noise level on the line and automatically adjust the data-transfer rate for optimum performance. RADSL supports the following asymmetric transfer rates:


Upstream rate	Downstream rate	Distance
544 Kbps	640 Kbps	17,000 feet (5.18 km)
1.088 Mbps	2.560 Mbps	12,000 feet (3.66 km)
1.088 Mbps	7.168 Mbps	10,000 feet (3.05 km)

RAI

Remote Alarm Indicator. An RAI indicates that a device on the DS3 line or DS2 stream is detecting framing-error conditions n the signal it receives. An RAI is also called a Yellow Alarm signal. See also DS3 line.

RAM

Random Access Memory. RAM is computer memory that holds data temporarily. See also DRAM, NVRAM.

Random Access Memory

See RAM.

RARP

Reverse Address Resolution Protocol. RARP is a TCP/IP protocol that learns a workstation's hardware address and maps it to an IP address. See also ARP.

rate adaption

A data-transmission method that enables the MAX TNT to send and receive data moving at a rate of 56 Kbps over a 64-Kbps channel. For incoming calls, the MAX TNT automatically adapts the data received at 56 Kbps to the 64-Kbps channel. For outgoing calls, the MAX TNT sets the data rate to either 64 Kbps or 56 Kbps.

For example, suppose a network consists of five switches, one of which uses a 56-Kbps line. The MAX TNT sends data at 56 Kbps over the 64-Kbps line that connects the switch to the network. In doing so, the router drops one of the 8 bits of data and sends only 7 bits at a time. V.120 is a rate-adaption standard. See also V.120.

Rate Adaptive Asymmetric Digital Subscriber Line card

See RADSL card.

Raw 802.3

See 802.3.

Raw TCP

Raw Transmission Control Protocol. Raw TCP is a method of supporting encapsulation performed by an application that runs on top of TCP. Raw TCP must be understood by both the login host and the caller. As soon as the connection is authenticated, the MAX TNT establishes a TCP connection to the host specified in the Connection profile or RADIUS user profile.

In a TCP dial-in session that does not require V.120 processing, the MAX TNT can buffer and transmit data as TCP packets, rather than as a continuous data stream. In addition, unless V.120 processing is required, raw TCP WAN data goes directly to the HDLC interface, rather than to the terminal-server subsystem. If V.120 processing is required, the terminal server processes the call.

Raw TCP is also known as TCP-Clear. See also HDLC card, TCP, V.120.

Raw Transmission Control Protocol

See Raw TCP.

RBOC

Regional Bell Operating Company. An RBOC is one of seven companies created after the breakup of AT&T. The RBOCs are Ameritech, Bell Atlantic, Bell South, NYNEX, Pacific Telesis, Southwestern Bell, and U.S. West.

RDP

Reliable Data Protocol. RDP provides a reliable data transport service for packet-based applications. It is simple to implement, and works efficiently in environments that have long transmission delays and non-sequential delivery of message segments.

Read-Only Memory

See ROM.

Red Alarm signal

A signal indicating that an out-of-frame condition has lasted for more than 2.23 msec on the DS3 line, or more than 9.9 msec on the DS2 stream. See also DS3 line, out-of-frame condition.

redundancy

A method of safeguarding against line and equipment failure during a transmission. Each method for transmitting signals has inherent error rates, and all physical media is subject to damage. In the event of hardware failure, a redundant line or unit can take over at any time. You should always have a redundant (backup) module for multiplexers and other critical equipment.

reject interface

An interface that enables the router to handle packets whose IP address matches an unused IP address in a summarized address pool. The reject interface has an IP address of 127.0.0.2. When you specify this address as the router to the destination pool network, the MAX TNT rejects packets to an invalid host on that network, appending an ICMP Host Unreachable message. See also pool summary.

Reliable Data Protocol

See RDP.

Remote Alarm Indicator

See RAI.

Remote Authentication Dial-In User Service

See RADIUS.

remote device

A unit that resides across the WAN.

remote LAN Access

The process of allowing branch offices, telecommuters, and traveling computer users to access the corporate LAN backbone over digital or analog lines. The lines can be switched or nailed up. See also analog line, digital line, nailed-up line, switched line.

remote management

A MAX TNT management feature that uses bandwidth between sites over a management subchannel. Any Ascend unit can control, configure, and obtain statistical and diagnostic information about any other Ascend unit. Multilevel security assures that unauthorized personnel do not have access to remote-management functions.

remote network

A network to which the MAX TNT connects over the WAN.

Remote Port Module

See RPM.

Remote Procedure Call

See RPC.

remote profile

A user profile configured in RADIUS, TACACS, or TACACS+, as opposed to a Connection profile configured on the Ascend unit. See also user profile.

remote user

A user at a device not connected directly to the Ascend unit and not residing on the local Ethernet.

replay attack

A strategy for gaining illegal access to a system. During a replay attack, an unauthorized user records valid authentication information exchanged between systems, and then replays it later to gain entry. Token-card authentication protects your system against replay attacks. Because the token is a one-time-only password, replay is impossible. See also token-card authentication.

Request For Comments

See RFC.

Request To Send

See RTS.

Reservation Protocol

See RSVP.

Reverse Address Resolution Protocol

See RARP.

RFC

Request for Comments. RFC denotes the document series, begun in 1969, that describes the Internet suite of protocols and related experiments. Not all RFCs describe Internet standards, but all Internet standards are written up as RFCs. The RFC series of documents is unusual in that the proposed protocols are distributed by the Internet research and development community, acting on its own behalf. The protocols do not go through the formal review and standardization process promoted by organizations such as ANSI. A complete list of RFCs resides at http://www.internic.net/rfc/.

RI

Ring Indicate. RI is a signal that indicates that a call is coming into a unit.

Ring Indicate

See RI.

RIP

Routing Information Protocol. RIP is a distance-vector protocol found in both the NetWare and TCP/IP protocol suites. The protocol keeps a database of routing information that it gathers from periodic broadcasts by each router on a network.

IPX routers broadcast RIP updates periodically and when a WAN connection is established. The MAX TNT receives IPX RIP broadcasts from a remote device, adds 1 to the hop count of each advertised route, updates its own RIP table, and broadcasts updated RIP packets on connected networks in a split-horizon fashion.

The MAX TNT follows standard IPX RIP behavior for routers when connecting to non-Ascend units. However, when it connects to another Ascend unit configured for IPX routing, both ends of the connection immediately exchange their entire RIP tables. In addition, the MAX TNT maintains those RIP entries as static until the unit is reset or power cycled.

The MAX TNT recognizes network number -2 (0xFFFFFFFE) as the IPX RIP default route. When it receives a packet for an unknown destination, the MAX TNT forwards the packet to the IPX router advertising the default route. If more than one IPX router is advertising the default route, the unit makes a routing decision based on the hop and tick count. For example, if the MAX TNT receives an IPX packet destined for network 77777777 and it does not have a RIP table entry for that destination, the MAX TNT forwards the packet towards network number FFFFFFFE, if available, instead of simply dropping the packet.

Rlogin

An Application-layer, remote-login service provided by Berkeley UNIX. On the MAX TNT, Rlogin is available only from an asynchronous dialup session to the terminal server. See also Application layer.

ROM

Read-Only Memory. ROM is computer memory whose contents can be read and executed, but not modified. See also EEPROM, PROM.

rotary

A type of hunt group in which the incoming call hunts on a rotating basis for an available channel to ring and answer the call. See also hunt group.

rotary switch

See Shelf-Select rotary switch.

route

The path that data takes from its source network to its destination network. See also IP route, IPX route.

route cache

See IP route cache.

router

A device that determines a path from a host on one network to a host on another. The networks may be in close proximity, or may be separated by long distances. A router has access to the three lowest OSI layers, and generally operates at the Network layer. To route a packet, a router uses the logical address specified as the packet's destination field, and determines the next router (if any) to which the packet must travel to reach its destination. All routers share information about the current topology and state of the network, maintaining routing tables that reflect the latest information. See also IP router.

router mode

An Ascend Tunnel Management Protocol (ATMP) configuration in which the home agent's routing module forwards packets it receives from the foreign agent onto the local network. The network can be the home network, or it can support another router that can connect to the home network. In either case, packet delivery relies on a routing mechanism, such as a static or dynamic route, and not on a WAN connection. Compare with gateway mode. See also ATMP, dynamic route, foreign agent, home agent, home network, static route.

route filter

A type of filter containing rules for the action to take on routes in Routing Information Protocol (RIP) update packets. When you apply a route filter to an IP interface, the MAX TNT monitors RIP packets on the interface and takes one of the following actions when a route matches the filter rules:

No action (the default).
Accept the route by allowing it to affect the routing table.
Deny the route by not allowing it to affect the routing table.
Add the value set in the Add-Metric parameter to the route metric and accept the route.

The filter can apply to incoming packets, outgoing packets, or both. When you apply a route filter to an interface, the MAX TNT applies all defined input and output filters to RIP update packets until it finds a match. If it does not find a match for a route, the default action is to deny the route. RADIUS does not support route filters. Compare with packet filter. See also IP route, IP routing table, RIP.

routing

A method of determining how to forward a data packet to the proper destination. See also IP routing, IPX routing, OSPF, RIP, route, router.

Routing Information Protocol

See RIP.

routing table

See IP routing table.

RPC

Remote Procedure Call. An RPC is a method in which a program on one device can transparently use a procedure on another device. RPCs are often used in client-server architectures.

RPM

Remote Port Module. An RPM is an Ascend unit that enables you to extend data, signaling, and control ports to local applications over Unshielded Twisted Pair (UTP) cable. See also UTP cable.

RS-232

An EIA standard that specifies various electrical and mechanical characteristics for interfaces between Data Terminal Equipment (DTE) and Data Circuit-terminating Equipment (DCE) devices. The standard applies to both synchronous and asynchronous binary data transmission at rates below 64 Kbps. RS-232 is also known as EIA/TIA-232. Compare with RS-422, RS-423. See also asynchronous transmission, DCE, DTE, synchronous transmission.

RS-422

A standard EIA interface for connecting serial devices. Along with RS-423, RS-422 replaces the RS-232 standard. RS-422 supports higher data rates than RS-232, and offers greater protection against electrical interference. All Apple Macintosh computers contain an RS-422 port that you can use for RS-232 communication. RS-422 supports multipoint connections, while RS-423 does not. RS-422 and RS-423 are often referred to collectively as EIA-530. Compare with RS-232, RS-423. See also EIA, multipoint link.

RS-423

A standard EIA interface for connecting serial devices. Along with RS-422, RS-423 replaces the RS-232 standard. RS-423 supports higher data rates than RS-232, and offers greater protection against electrical interference. All Apple Macintosh computers contain an RS-423 port that you can use for RS-232 communication. Unlike RS-422, RS-423 supports only point-to-point connections. RS-422 and RS-423 are often referred to collectively as EIA-530. Compare with RS-232, RS-422. See also EIA, point-to-point link.

RS-449

A standard EIA Physical-layer interface. RS-449 is a a faster version of RS-232, and allows longer cable extension. RS-449 can run at speeds of up to 2 Mbps, and is also known as EIA/TIA-449. Compare with RS-232.

RSVP

Reservation Protocol. RSVP enables a router to reserve bandwidth for time-sensitive data transmissions, resulting in smooth reception of voice and video data. A client can use RSVP to request that a router set aside a certain amount of bandwidth to handle the incoming call. If sufficient bandwidth does not exist, the request enters a queue and remains there until the appropriate amount of bandwidth becomes available.

RTS

Request To Send. RTS is a signal that a transmitter sends to a receiver in order to indicate that it wants to begin sending data. If the receiver is ready for the transmission, it responds with a Clear To Send (CTS) signal. See also CTS.

S

SafeWord AS

See Enigma Logic SafeWord server.

SafeWord authentication

A form of token-card authentication in which RADIUS forwards a connection request to an Enigma Logic Safeword server, a type of authentication server. The SafeWord server sends an Access-Challenge packet back through the RADIUS server and the MAX TNT to the user dialing in. The user sees the challenge message, obtains the current password from his or her token card, and enters the current password (called a token).

The token travels back through the MAX TNT and the RADIUS server to the SafeWord server. The SafeWord server sends a response to the RADIUS server, specifying whether the user has entered the proper user name and token. If the user enters an incorrect token, the SafeWord server returns another challenge, and the user can again attempt to enter the correct token. The server sends up to three challenges. After three incorrect entries, the MAX TNT terminates the call.

SafeWord token

A randomly generated access code that a user obtains from a token card when using a SafeWord authentication server. See also SafeWord authentication.

SAM

Secure Access Manager. SAM gives you a high degree of centralized control over the security functions of an entire network. Through this Windows-based application, you can configure Secure Access Firewall(s) offline, and download the configuration to remote locations. See also Secure Access Firewall.

SAP

Service Access Point. A SAP is a defined location through which a procedure at one OSI layer can provide services to the next layer above it. Each SAP has a unique address in hexadecimal format. See also DSAP, OSI Reference Model, SSAP.

SAP

Service Advertising Protocol. SAP is a NetWare protocol that operates at the Transport layer and enables servers to inform other devices about the services they have available. Each server advertises its services using a SAP packet. Each router on the network retrieves the SAP packets and builds a database of all the servers it knows about. The router then broadcasts this information to other routers, either at a set interval or whenever the database changes.

The MAX TNT follows standard SAP behavior for routers when connecting to non-Ascend units across the WAN. However, when it connects to another Ascend unit configured for IPX routing, both ends of the connection exchange their entire SAP tables, so all remote services are immediately added to the MAX TNT unit's SAP table.

When a NetWare client sends a SAP request to locate a service, the MAX TNT consults its SAP table and replies with its own hardware address and the internal network address of the requested server. This behavior is analogous to the use of proxy ARP in an IP environment. The client can then transmit packets whose destination address is the internal address of the server. When the MAX TNT receives those packets, it consults its Routing Information Protocol (RIP) table. If it finds an entry for that destination address, it brings up the connection (unless it is already up) and forwards the packet. See also IPX router, IPX server, proxy ARP, RIP.

SAP filter

Service Advertising Protocol filter. A filter that determines which SAP advertisements the MAX TNT forwards or drops. Each IPX-SAP-Filter profile contains up to eight input filters and output filters, numbered from 1 to 8, which are defined individually and applied in order to the packet stream.

The router examines incoming and outgoing SAP packets to see whether certain fields in the packet match the filter. The MAX TNT applies input filters to all SAP packets it receives. Input filters screen advertised services and exclude them from (or include them in) the MAX TNT service table. The MAX TNT applies output filters to SAP response packets it transmits. If it receives a SAP request packet, the MAX TNT applies output filters before transmitting the SAP response, and excludes services from (or includes them in) the response packet.

A SAP filter enables you to control the size of resident SAP tables and reduce bandwidth usage. You can also use a SAP filter to restrict a user's view of services on the network. By turning off IPX SAP, you can prevent the MAX TNT from sending its SAP table or from receiving a remote site's SAP table.

Subnet mask	Number of host addresses	Ascend notation
255.255.255.0	254 hosts + 1 broadcast, 1 network base	/24
255.255.255.128	126 hosts + 1 broadcast, 1 network base	/25
255.255.255.192	62 hosts + 1 broadcast, 1 network base	/26
255.255.255.224	30 hosts + 1 broadcast, 1 network base	/27
255.255.255.240	14 hosts + 1 broadcast, 1 network base	/28
255.255.255.248	6 hosts + 1 broadcast, 1 network base	/29
255.255.255.252	2 hosts + 1 broadcast, 1 network base	/30
255.255.255.254	Invalid subnet mask (no hosts)	/31
255.255.255.255	1 host (a host route)	/32

Message type	Format	Description
Level 4 (warning) Level 6 (informational)	date time ipaddr shelf`/`slot`: [`shelf`/`slot`/`line`/`port_channel`]` text `[MBID` num`]`	The date, time, IP address, and device address (shelf, slot, line, and port or channel), followed by warning or informational text and a session identifier.
Level 5 (notice)	call-event-ID event-description slot-n port-n data-svc phone-n	The call-event-ID and event-description specify the event ID and its description. The slot-n port-n address indicates the serial port, which is suppressed when it is not applicable or unknown. data-svc indicates the data service in use. phone-n is the phone number of the calling party.
Disconnect cause and progress codes	[name,]c=xxxx,p=yyyy,[ipaddr]	name specifies the name of a profile (incoming calls only). xxxx is the disconnect cause code. yyyy is the connection progress code. ipaddr is the login host's IP address for Telnet and raw TCP connections (if applicable).
Error messages	Various formats	An error message associated with a session can contain the following information: `[`shelf`/`slot`/`line`/`channel`]` indicates a physical channel identifier. `[MBID` xxx`]` indicates a session identifier. `[`name`]` indicates the authenticated user name. `[ calling -> called ]` indicates the calling number, the called number, or both.
Backoff queue error message	Backoff Q full, discarding user username	Accounting records are kept until they are acknowledged by the accounting server. Up to 100 unacknowledged records are stored in the backoff queue. If the unit never receives an acknowledgment to an accounting request, it will eventually run out of memory. In order to keep this situation from the occurring, the unit deletes the accounting records and displays the error message in the `syslog` file.
Messages generated by a Secure Access Manager (SAM) firewall	date time router-name ASCEND: interface message	date indicates the date the message was logged by Syslog. time indicates the time the message was logged by Syslog. router-name indicates the router that sent the message. interface is the name of the interface, or `call` if the packet is logged by the call filter as it brings up the link. The message format has a number of fields, one or more of which may be present, as described in the next table.

Field	Description
protocol	Four-hexadecimal digit Ethernet type, or one of the following network protocol names: `arp`, `rarp`, `ipx`, `appletalk`. For IP protocols, protocol indicates either the IP protocol number (up to 3 decimal digits) or one of the following names: `ip-in-ip`, `tcp`, `icmp`, `udp`, `esp`, `ah`. In the special case of ICMP, the field also includes the ICMP Code and Type (`[`Code`]/[`Type`]/icmp`).
local	For non-IP packets, the source Ethernet MAC address of transmitted packets and the destination Ethernet MAC address of received packets. For IP protocols, the IP source address of transmitted packets and the IP destination address of received packets. In the case of TCP or UDP, local also includes the TCP or UDP port number (`[`IP-address`];[`port`]`). On a WAN connection, the two MAC addresses are all zeroes.
direction	An arrow (<- or ->) showing the direction in which the packet was traveling. A left arrow indicates an incoming packet. A right arrow indicates an outgoing packet.
remote	For non-IP protocols, the same format as local for non-IP packets, but shows the Ethernet MAC destination address of transmitted packets and the source Ethernet MAC address of received packets. For IP protocols, the same format as local, but shows the IP destination address of transmitted packets and the IP source address of received packets.
length	The length of the packet in octets (8-bit bytes).
frag	Reports whether the packet has a non-zero IP offset or whether the IP More-Fragments bit is set in the IP header.
log	Reports one or more messages based upon the packet status or packet header flags. The packet status messages include: `corrupt`-The packet is internally inconsistent. `unreach`-The packet was generated by an "unreach=" rule in the firewall. `!pass`-The packet was blocked by the data firewall. `bringup`-The packet matches the call firewall. TCP flag bits that will be displayed include `syn`, `fin`, `rst`. `syn` is displayed only for the initial packet, which has the SYN flag and not the ACK flag set.
tag	Indicates any user defined tags specified in the filter template used by SAM.

T

T1 card

A MAX TNT card that provides eight ports, each of which can be connected to a T1 PRI line, a fractional T1 line, or an unchannelized T1 line. When the MAX TNT detects a T1 card, it creates a default T1 line profile for each of the eight lines on the card. See also fractional T1 line, T1 channel, T1 line, T1 PRI line, unchannelized service.

T1 channel

One of 24 channels on a T1 line. See also fractional T1 line, T1 card, T1 line, T1 PRI line, unchannelized service.

T1 line

A line that supports 24 64-Kbps channels, each of which can transmit and receive data or digitized voice. The line uses framing and signaling to achieve synchronous and reliable transmission. The most common configurations for T1 lines are ISDN Primary Rate Interface (T1 PRI) and unchannelized T1, including fractional T1. See also fractional T1 line, T1 card, T1 channel, T1 PRI line, unchannelized service.

T1 PRI line

T1 Primary Rate Interface line. A T1 PRI line has a total bandwidth of 1.544 Mbps. It uses 23 B channels for user data, and one 64-Kbps D channel for ISDN D-channel signaling, The B channels can be all switched, all nailed up, or a combination of switched and nailed up. The T1 PRI line is a standard in North America, Japan, and Korea. You can connect this type of line to standard voice, Switched-56, Switched-64, Switched-384, Switched-1536, and MultiRate data services. Compare with E1 PRI line, ISDN BRI line, unchannelized service. See also B channel, D channel, MultiRate, nailed-up channel, PCM, Switched-56, Switched-64, Switched-384, Switched-1536, T1 card, T1 channel, T1 line.

T1 Primary Rate Interface line

See T1 PRI line.

T3 card

A MAX TNT communications circuit composed of seven DS2s, each of which consists of four DS1s, each of which consists of 24 DS0s, for a total of 720 DS0 channels. On the T3 card, DS2 #1 includes DS1 lines 1-4, DS2 #2 includes DS1 lines 5-8, and so on. Each DS1 is similar to a T1 line, except that on the T3 card, a DS1 only functions if the DS2 and DS3 that contain it are up and in frame. You can think of the T3 card as a collection of 28 T1 lines, because the card provides 28 independently configurable DS1 lines. See also DS0 channel, DS1 channel, DS2 channel, DS3 line.

T3 line

A digital transmission link consisting of 28 T1 lines with a total bandwidth of 44.736 Mbps. See also T1 line, T3 card.

TA

Terminal Adapter. A TA is a protocol converter that adapts non-ISDN equipment (such as a phone, fax, or modem), and enables each device to work over an ISDN connection. A TA has two functions. First, it must change the format of transmitted data to match the V.120 standard for asynchronous transfer over a B channel. Second, it must provide a way of setting up and clearing calls, usually by means of Hayes AT commands. A TA is to an ISDN line what a modem is to an analog telephone line. However, some of the D-channel information does not pass through the TA, so non-ISDN equipment cannot take full advantage of ISDN facilities, such as Calling-Line ID (CLID). See also ISDN, V.120.

TACACS

Terminal Access Concentrator Access Control Server. TACACS is a very simple query/response protocol that enables the MAX TNT to check a user's password in order to grant or prevent access. A TACACS server supports only the basic password exchanges that Password Authentication Protocol (PAP) uses. It does not support Challenge Handshake Authentication Protocol (CHAP). See also CHAP, PAP.

TACACS+

Terminal Access Concentrator Access Control Server Plus. TACACS+ is a proprietary Cisco enhancement to the Terminal Access Concentrator Access Control Server (TACACS) protocol. TACACS+ handles the transfer of authentication and authorization information between a Network Access Server (NAS) and an authentication server, encrypting password information and forwarding it over the network. TACACS+ supports AppleTalk Remote Access (ARA), Challenge Handshake Authentication Protocol (CHAP), Password Authentication Protocol (PAP), Point-To-Point Protocol (PPP), Serial Line Internet Protocol (SLIP), and Telnet. In addition, TACACS+ uses the TCP protocol to transmit accounting information to an accounting server. See also CHAP, PAP, PPP, SLIP, TCP, Telnet.

tag

An Open Shortest Path First (OSPF) method of flagging a route as external-that is, as having been imported into the OSPF database from outside the router's Autonomous System (AS). See also AS, external route, OSPF.

tariff

A document filed by a regulated telephone company with a state public utility commission or the Federal Communications Commission. A tariff details services, equipment, and pricing publicly offered by the telephone company.

TCP

Transmission Control Protocol. TCP operates at the Transport layer, providing connected-oriented services. It uses IP to deliver packets. See also IP.

TCP-Clear

See Raw TCP.

TCP/IP

Transmission Control Protocol/Internet Protocol. TCP/IP is a family of protocols that defines the format of data packets sent across a network, and is the communications standard for data transmission between different platforms. The TCP/IP family consists of the following protocols and services:

Protocol name

Description of service

Transmission Control Protocol (TCP)
User Datagram Protocol (UDP)

Transport protocols that control data transmission between computers

Internet Protocol (IP)
Internet Control Message Protocol (ICMP)
Routing Information Protocol (RIP)
Open Shortest Path First (OSPF)

Routing protocols that control addressing and packet assembly, and determine the best route for a packet to take to arrive at its destination

Border Gateway Protocol version 4 (BGP)
Gateway-To-Gateway Protocol (GGP)
Interior Gateway Protocol (IGP)

Gateway protocols that enable networks to share routing and status information

Domain Name System (DNS)
Address Resolution Protocol (ARP)
Reverse Address Resolution Protocol (RARP)

Network-address services and protocols that handle the way each computer on a network is identified

Boot Protocol (BOOTP)
File Transfer Protocol (FTP)
Telnet

User services that provide applications a computer can use

Network File System (NFS)
Network Information Service (NIS)
Remote Procedure Call (RPC)
Simple Mail Transfer Protocol (SMTP)
Simple Network Management Protocol (SNMP)

File-transfer, mail, and management services

Protocol name	Description of service
Transmission Control Protocol (TCP) User Datagram Protocol (UDP)	Transport protocols that control data transmission between computers
Internet Protocol (IP) Internet Control Message Protocol (ICMP) Routing Information Protocol (RIP) Open Shortest Path First (OSPF)	Routing protocols that control addressing and packet assembly, and determine the best route for a packet to take to arrive at its destination
Border Gateway Protocol version 4 (BGP) Gateway-To-Gateway Protocol (GGP) Interior Gateway Protocol (IGP)	Gateway protocols that enable networks to share routing and status information
Domain Name System (DNS) Address Resolution Protocol (ARP) Reverse Address Resolution Protocol (RARP)	Network-address services and protocols that handle the way each computer on a network is identified
Boot Protocol (BOOTP) File Transfer Protocol (FTP) Telnet	User services that provide applications a computer can use
Network File System (NFS) Network Information Service (NIS) Remote Procedure Call (RPC) Simple Mail Transfer Protocol (SMTP) Simple Network Management Protocol (SNMP)	File-transfer, mail, and management services

TCP/IP header compression

See VJ compression.

TDM

Time Division Multiplexing. TDM is a scheme that uses time-slot assignment, enabling information from multiple channels to use bandwidth on a single line.

TE

Terminal Equipment. A TE is any ISDN-compatible device attached to a network, such as a telephone, fax machine, or computer.

Telecommunications Industry Association

See TIA.

telecommuter

A work-at-home computer user who connects to the corporate LAN backbone by means of remote-access technology. For example, a telecommuter can establish a link with the LAN by means of a modem connected to an analog line, an ISDN Terminal Adapter (TA) or router connected to an ISDN line, or a Channel Service Unit/Data Service Unit (CSU/DSU) connected to a Switched-56 line. See also analog line, CSU, DSU, ISDN line, modem, TA.

Telnet

A protocol that links two computers in order to provide a terminal connection to the remote machine. Instead of dialing into the computer, you connect to it over the Internet using Telnet. When you issue a Telnet session, you connect to the Telnet host and log in. The connection enables you to work with the remote machine as though you were a terminal connected to it. If your MAX TNT has an Ethernet card installed, you can remotely manage it by establishing a Telnet session to the MAX TNT from any Telnet workstation on the network.

Telnet session

A terminal connection to a remote machine by means of the Telnet protocol. After you set up a basic IP configuration for the MAX TNT, users can Telnet into the MAX TNT command line. Each user can initiate a Telnet session to the MAX TNT from a local workstation or from a WAN connection. In both cases, the MAX TNT authenticates the session by means of a User profile, which defines a permission level for the user logging in. In addition to the password required by a User profile, you can specify that Telnet requires its own password authentication, which occurs prior to any User profile authentication. See also User profile.

terminal

A computer that does not have its own processor and that must connect to a terminal server in asynchronous mode to use its Central Processing Unit (CPU). VT100, ANSI, and TTY are all types of terminals.

Terminal Adapter

See TA.

Terminal Access Concentrator Access Control Server

See TACACS.

Terminal Access Concentrator Access Control Server Plus

See TACACS+.

terminal emulation program

See terminal emulator.

terminal emulator

A program that makes your computer look like a terminal so that you can connect to a terminal server. Your computer acts like a terminal during the connection. All processing is taking place remotely. A terminal emulator is also called a terminal emulation program.

Terminal Equipment

See TE.

terminal mode

A terminal-server access mode in which the MAX TNT negotiates a user-to-host session. Instead of providing only the login name and password required to authenticate a Connection profile or RADIUS user profile, you can set up an expect-send script that also includes the terminal-server prompt and a command, such as PPP, SLIP, TCP, Telnet, or Rlogin. In this way, the session with a host comes about as part of the login process, so the user never actually sees the terminal-server command-line prompt. Alternatively, you can provide access to the command line and restrict the commands you make accessible to the user. See also expect-send script, PPP, Rlogin, SLIP, TCP, Telnet, terminal server.

terminal server

A terminal server is a computing device to which a terminal can connect over a LAN or WAN link. A terminal communicates with the terminal server over an asynchronous serial port (typically an RS-232 port) through a modem. A terminal converts the data it receives from the terminal server into a display and does no further processing of the data. A terminal also converts the operator's keystrokes into data for transmission to the terminal server.

The MAX TNT terminal-server software receives asynchronous calls after they have been processed by a digital modem. Typically, a modem or V.120 Terminal Adapter (TA) dials these calls. V.120 and TCP calls are enabled by default. If the caller does not send Point-To-Point Protocol (PPP) packets immediately, the terminal server starts a login sequence.

Figure 38 shows an incoming modem call. A PC running SoftComm initiates the connection. (SoftComm is a program that causes the user's modem to dial into the MAX TNT.) The MAX TNT directs the call to its digital modem, and then forwards the calls to its terminal-server software. In Figure 38, the MAX TNT immediately directs the call to a Telnet host.