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Frame Relay. Objectives. Frame Relay Operation. Frame Relay Switches. Frame Relay Concepts. Virtual Circuits. Local Significance of DLCIs. The data - link connection identifier (DLCI) is stored in the Address field of every frame transmitted. Terminology.
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Local Significance of DLCIs The data-link connection identifier (DLCI) is stored in the Address field of every frame transmitted.
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).
Bandwidth and Flow Control Bit counter Example 1
Frame Relay Concepts Queue
Selecting a Frame Relay Topology Full Mesh Partial Mesh Star (Hub and Spoke)
LAPF Frame – Address Field 6-bits 4-bits
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
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
LMI Frame Format 1 2 1 1 1 1 2 1 Flag Address Control PD CR MT LMI Message FCS Flag
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.
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
The show interface Command LMI Status LMI DLCI LMI Type
Troubleshooting Frame RelayThe debug frame-relay lmi Command PVC Status 0x2 – Active 0x0 – Inactive 0x4 – Deleted