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Frame Relay

This chapter covers the following topics:
Using the MAX TNT as a Frame Relay concentrator
Configuring a physical link for a Frame Relay interface
Configuring the Frame Relay data link
Configuring Frame Relay gateway connections
Configuring Frame Relay Switching
Configuring Frame Relay Direct connections

Using the MAX TNT as a Frame Relay concentrator

In a Frame Relay network, every access line connects directly to a Frame Relay switch. In the past, most connections to the Frame Relay network were relatively high speed, such as full T1 or E1 lines. With recent changes in Frame Relay pricing, providers now want to concentrate many low-speed dial-in connections into one high-speed nailed connection to a Frame Relay switch. You can configure the MAX TNT as a Frame Relay concentrator, as shown in Figure 3-1. It then accepts incoming dial-in connections (shown at the right of Figure 3-1) as usual and forwards them out to the Frame Relay network.

Figure 3-1. Frame Relay concentrator

The main elements of this configuration are:

Configuring a physical link for a Frame Relay interface

The MAX TNT requires a nailed connection to the Frame Relay network (a switch or other Frame Relay device). Each Frame-Relay profile requires its own nailed physical link. For example, you could set all 24 channels on a T1 to the same nailed group number to dedicate a T1 line to Frame-Relay, or you could configure the link on another line card that supports sufficient nailed bandwidth.

Note: NNI operations are supported for HDLC and channelized T1 cards, and for DSL cards in the 2.0.0 release. Support for NNI on Frameline and SWAN cards will be provided in a subsequent release.

Following is an example that shows how to define one physical link by configuring all channels of a T1 line for nailed usage and assigning them to the Nailed-Group number 11:

For details about configuring lines and channels, see the MAX TNT Hardware Installation Guide.

Configuring the Frame Relay data link

To define the interface between the MAX TNT and the Frame Relay network, you configure a Frame-Relay profile. Following are the parameters contained in a Frame-Relay profile, shown with their default settings:

Link types

 The MAX TNT supports both User-to-Network Interface (UNI) and Network-to-Network Interface (NNI) specifications.

UNI operations include Data Communications Equipment (DCE) or Data Terminal Equipment (DTE) configurations. DCE refers to a device that connects computers to a data communications service, such as Frame Relay. (A Frame Relay switch performs DCE operations.) When it is operating as DCE, the MAX TNT acts as a Frame Relay end-point for DTE devices. DTE refers to a computer that is the source or destination of the data traversing the service (for example, a user's PC accessing a router or switch). When it is operating as DTE, the MAX TNT forwards data out to a DCE device on the Frame Relay network.

NNI is a mode of operation in which the MAX TNT acts as a Frame Relay switch communicating with another Frame Relay switch. Following are important differences in NNI as opposed to UNI operation:

Note: On DTE and NNI interfaces, the MAX TNT is able to query the device at the other end of the link about the status of DLCIs on that interface. If a DLCI becomes unusable, and its Connection profile specifies a Backup connection, the MAX TNT dials the Connection profile specified by the Backup parameter in the Session-Options subprofile. For details, see the description of the Backup parameter in the MAX TNT Reference Guide.

Specifying the physical link to use

Each Frame-Relay profile uses a dedicated nailed connection to the Frame Relay network. The Nailed-Up-Group parameter specified the number assigned to that nailed bandwidth. (See Configuring a physical link for a Frame Relay interface.)

DTE configuration for connecting to a DCE switch

In Figure 3-2, the MAX TNT operates as a DTE device connecting to a Frame Relay switch that performs DCE link management functions. The data link for this interface will be configured as a DTE data link in the MAX TNT. This example shows how to configure a Frame-Relay profile for a DTE interface.

Figure 3-2. Frame Relay DTE interface

The following example shows how to configure a Frame-Relay profile for DTE operations. It includes Link-Mgmt and status report parameters, which must match the specifications on the DCE device:

DCE configuration for connecting to DTE equipment

 In Figure 3-3, the MAX TNT operates as a DCE device. It connects to Customer Premise Equipment (CPE) that operates as a DTE device, forwarding data from its local users to the MAX TNT as a Frame Relay network end-point. This example shows how to configure a Frame-Relay profile for a DCE interface.

Figure 3-3. Frame Relay DCE interface

The following example shows how to configure a Frame-Relay profile for DCE operations:

NNI configuration for Frame Relay switching

 In the example data link connection shown in Figure 3-3, the MAX TNT must perform NNI operations to communicate with another switch on the Frame Relay network. This example shows how to configure a Frame-Relay profile for a NNI interface.

Figure 3-4. Frame Relay NNI interfaces

Note: NNI operations are not required for the MAX TNT to operate in switched mode using Frame Relay circuits. However, to make an NNI interface useful for passing data, it must be paired with another interface to complete a switch circuit. For an example of an NNI configuration integrated with paired interfaces to enable the MAX TNT to switch data, see Configuring Frame Relay Switching.

The following commands define a Frame-Relay profile to FR-Asnd-A in Figure 3-3:

Configuring Frame Relay gateway connections

A Frame Relay gateway connection routes incoming PPP calls out on the Frame Relay network. The calls are routed at layer 3 (such as IP).

When the MAX TNT receives an incoming PPP call, it brings up the Frame Relay gateway connection based on the packets' destination address. It then encapsulates the packets in Frame Relay (RFC 1490) and forwards the data stream out to a Frame Relay switch, assigning the DLCI specified in the Frame Relay gateway profile.

The incoming calls are ordinary PPP connections, as described in Chapter 2, WAN Connections.

Gateway connection parameters

Following are the parameters required to configure a gateway connection to the Frame Relay network. The following parameters are shown with their default settings:

      encapsulation-protocol = frame-relay

      fr-options

            frame-relay-profile = ""

            dlci = 16

      ip-options

            ip-routing-enabled = yes

            remote-address = 0.0.0.0/0 






 Parameter



 Effect




 Encapsulation-Protocol



 Specifies Frame-Relay encapsulation for gateway connections.




 Frame-Relay-Profile



 Specifies the name of the Frame-Relay profile to use to send the connection's data out to the Frame Relay network.




 DLCI



 Specifies a Data Link Connection Indicator (DLCI) to use for this connection on the Frame Relay network.This number must be obtained from a Frame Relay provider.




 Routing parameters



 Routing must be enabled and the destination address specified for the MAX TNT to bring up the gateway profile.

Example of a gateway connection

 In gateway mode, the destination IP address lies at the end of a Permanent Virtual Circuit (PVC), whose first hop is known by the DLCI named in the Connection profile. The MAX TNT does not allow you to enter duplicate DLCIs, except when they are carried by separate physical links specified in different Frame-Relay profiles.

Figure 3-5 show three callers who dial into the MAX TNT to reach a distant IP network across the Frame Relay network. The callers have regular PPP Connections profiles that enable IP routing. The gateway connection is between the MAX TNT and the CPE on a remote network.

Figure 3-5. Gateway connection to Frame Relay CPE

Following is an example of how to configure a gateway connection to the remote CPE in Figure 3-5.

Configuring Frame Relay Switching

The MAX TNT supports a switched mode of operation between Frame-Relay interfaces (as opposed to routed or bridged operation). When a Frame Relay circuit has been specified in two Connection profiles, the MAX TNT switches data received on one of the paired interfaces to the other paired interface. Circuit switching occurs at layer 2 based on the assigned DLCIs. The layer 3 IP router never receives the packets.

A circuit is a Permanent Virtual Circuit (PVC) segment that consists of two DLCI endpoints, and typically uses two different Frame-Relay profiles. The Frame-Relay profiles can specify any supported UNI or NNI link type.

Frame Relay circuit parameters

Following are the related parameters, which are shown with sample settings:

Example of a circuit between UNI interfaces

 Figure 3-6 shows a circuit configuration in the MAX TNT. In this example, assume that the two T1 lines in the MAX TNT are configured for nailed usage. The channels of the T1 line connecting to the Pipeline 130 labeled P130-East are in Nailed-Group 33, and the channels of the T1 line connecting to the MAX are in Nailed-Group 11 (see Configuring a physical link for a Frame Relay interface).

Figure 3-6. Frame Relay circuit with UNI interfaces

The following commands define a Frame-Relay profile to the MAX in Figure 3-6:

The following commands define a Frame-Relay profile to P130-East in Figure 3-6:

The following commands configure a Connection profile to send or receive data to or from the MAX on DLCI 71:

The following commands configure a Connection profile to send or receive data to or from P130-East on DLCI 90:

Example of a circuit between NNI interfaces

 Figure 3-3 shows a circuit configuration that uses NNI interfaces. In this example, assume that the lines connecting the MAX TNT to each of the switches have been configured for nailed usage. For this example, the line connecting to the switch labeled FR-Asnd-A is in Nailed-Group 52, and the line connecting to the switch labeled FR-Asnd-B is in Nailed-Group 128.

Figure 3-7. Frame Relay circuit with NNI interfaces

The following commands define a Frame-Relay profile to FR-Asnd-A in Figure 3-3:

The following commands define a Frame-Relay profile to FR-Asnd-B in Figure 3-3:

The following commands configure a Connection profile to send or receive data to or from the switch named FR-Asnd-A on DLCI 55:

The following commands configure a Connection profile to send or receive data to or from the switch named FR-Asnd-B on DLCI 23:

Configuring Frame Relay Direct connections

Frame Relay Direct connections are PPP calls that are forwarded out on the Frame Relay network based solely on the FR-Direct configuration.The MAX TNT does not examine the destination IP address within the packets. The assumption is that another device will route them.

For a Frame Relay Direct connection, the MAX TNT removes the PPP header from the layer 3 packet (such as IP), encapsulates the packet in Frame Relay (RFC 1490), and forwards it using the specified FR-DLCI number and FR-Profile name.

Many Frame Relay Direct connections can share the same FR-DLCI number. When it is forwarding packets without examining the destination IP address, the MAX TNT sends all of the packets on a single PVC.

However, it's important to note that a Frame Relay Direct connection is not a full-duplex tunnel between a PPP dial-in and a far-end device. The PPP connections must enable routing to allow the MAX TNT to choose the proper destination for packets coming back across the connection from a far-end device. When the far-end device responds, the MAX TNT must use its router software to send the packets back to the appropriate PPP caller.

Frame Relay Direct parameters

Following are the related parameters, which are shown with sample settings:

Example of two Frame Relay Direct connections

 Figure 3-8 shows two Frame Relay Direct connections. The callers dial in using PPP software, and the MAX TNT forwards the data stream out to the Frame Relay network using DLCI 72.

Figure 3-8. Frame Relay Direct connections using the same DLCI

Following is an example of how to configure a Frame Relay Direct connection for caller-1 in Figure 3-8:

The following example shows how to configure a Frame Relay Direct connection for caller-2 in Figure 3-8:

Note: Both Connection profiles enable FR-Direct and specify the same DLCI.


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