Frame Relay

Frame Relay is packet switched technology it works based on virtual circuits between two locations.Virtual circuits are identified using DLCI(Data Link Connection Idendifier).Frame Relay switches makes decision based on DLCI.There are two virtual circuits,

Permanent Virtual Circuits(PVC)
Switched Virtual Circuits (SVC)

Permanent virtual circuits is always kept active and Switched virtual circuit is created only when we send a data, once communication completed circuit will become down.

Frame Relay encapsulation,

There are two types of encapsulation

IETF(standardized) Internet Engineering Task Force

Frame Relay LMI(Local Management Interface)

LMI is a signaling type used between our router and frame relay switch,Inverse ARP uses LMI to update the Routers about the DLCI and PVC from the frame relay switch.There are three types of LMI we can use,


By default lmi enabled in router with 'cisco ' we no need to configure this, if we want to change the lmi type we can chage by using above command in serial interface.LMI must be same in frame relay switch as well as Router.

Important Terms in Frame Relay,

CIR-Committed Information Rate

Committed Information Rate is the maximum speed in bits gauranteed by the ISP for the virtual Circuits under normal condition.The traffic rate above CIR will be Discard Eligible(DE).

AR-Available Rate

This is the maximum traffic rate decided by the physical interface using clock rate command or by frame relay service provider.

Min CIR - Minimum Comitted Information Rate

This is the minimum traffic rate the router speed will drop down when congestion occurs on a frame relay network.Min CIR is half of the speed in a CIR.

DE -Discard Eligible

A bit that is set for traffic sent above the CIR will be Discard Eligible (DE).

BC-Commited Burst

The amount of bits sent during a specific interval,measured as Time committed(Tc).Time Committed is measured in milliseconds(default is 125ms 8 intervals per second).

CIR=Bc X 1000/Tc

BE-Excess Burst

Bits that exceeding the committed burst is Excess Burst(BC) and it is marked a Discard Eligible.

Trouble Shooting Commands

HO# show frame-relay pvc

HO# show frame-relay map

HO# show frame-relay lmi

HO# debug frame-relay lmi

HO# debug frame-relay

HO# debug frame-relay packet

Freame Relay Configurations in Different Type of Networks

Frame Relay  Point to Point 

Frame Relay Multi Point Hub and Spoke

Frame Relay Multi Point Hub and Spoke Fully Mesh

Frame Relay Configuration with Sub Interfaces Point to Point and Multi Point 

Frame Relay Using Routing Protocols

Frame Relay Traffic Shaping

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