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Frame Relay

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Objectives

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Frame Relay Operation

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Frame Relay Switches

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Frame Relay Concepts

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Virtual Circuits

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Local Significance of DLCIs

The data-link connection identifier (DLCI) is stored in the Address field of every frame transmitted.

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Terminology

• The connection through the Frame Relay network between two DTEs is called a virtual circuit (VC).

• Virtual circuits may be established dynamically by sending signaling messages to the network. In this case they are called switched virtual circuits (SVCs).

• Virtual circuits can be configured manually through the network. In this case they are called permanent virtual circuits (PVCs).

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Frame Relay Stack Layered Support

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Frame Relay Functions

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Bandwidth and Flow Control

Bit counter Example 1

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Frame Relay Concepts

Queue

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Frame Relay Concepts

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Frame Relay Concepts

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Star (Hub and Spoke)

Full Mesh

Partial Mesh

Selecting a Frame Relay Topology

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LAPF Frame – Address Field

6-bits

4-bits

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Data Link Control Identifier

• The 10-bit DLCI associates the frame with its virtual circuit

• It is of local significance only - a frame will not generally be delivered with the same DLCI with which it started

• Some DLCI’s are reserved

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Local Management Interface (LMI)

• Three types of LMIs are supported by Cisco routers:

Cisco — The original LMI extensions

Ansi — Corresponding to the ANSI standard T1.617 Annex D

q933a — Corresponding to the ITU standard Q933 Annex A

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LMI Frame Format

LMI MessageFlag FlagFCS

1 2 1

Address

2 1

Control

1

PD

1

CR

1

MT

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Stages of Inverse ARP andLMI Operation #1

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Stages of Inverse ARP and LMI Operation #2

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Configuring Basic Frame Relay

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Configuring a Static Frame Relay Map

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Reachability Issues with Routing Updates in NBMA

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Reachability Issues with Routing Updates in NBMA

By default, a Frame Relay network provides nonbroadcast multiaccess (NBMA) connectivity between remote sites. An NBMA environment is treated like other multiaccess media environments, where all the routers are on the same subnet.

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Frame Relay Subinterfaces

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Configuring Point-to-Point Subinterfaces

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Verifying Frame Relay

• The show interfaces command displays information regarding the encapsulation and Layer 1 and Layer 2 status. It also displays information about the following:

The LMI type

The LMI DLCI

The Frame Relay data terminal equipment/data circuit-terminating equipment (DTE/DCE) type

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The show interface Command

LMI Type

LMI DLCI

LMI Status

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The show frame-relay lmi Command

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The show frame-relay pvc Command

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The show frame-relay map Command

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Troubleshooting Frame Relay The debug frame-relay lmi Command

PVC Status0x2 – Active0x0 – Inactive0x4 – Deleted

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Summary