Abbreviations and definitions to know about Frame-Relay

CIR – Committed Information Rate

a specified amount of guaranteed bandwidth (measured in bits per second) on a Frame Relay service

Local Access Rate

clock speed of theconnection CPE or last mile loop to the service providers frame switch, rate of speed that packets travel

VC Virtual Circuit

bi-directional path between network devices

PVC/SVW – Permanent Virtual Circuit / Switched Virtual Circuit

a permanently or switch circuit between a router and a frame-relay switch. when it is a switched path, it is established on-demand and torn down, when the transfer is complete. I it similar to an ISDN circuit.

A PVC is up all the time.

DLCI – Data Link Connection Identifier

assigned by the service provider. This number is used to identify the logical link between the router (DTE) and the frame relay switch (DCE). DLCI’s are only localy significant as they are only valid between the router and the frame-relay switch.

LMI – Logical Management Interface

Types: Ansi, Cisco, Q933a

it’s a signaling standard between the router and the service providers frame-relay switch. It manages the connection and maintains the status between devices. LMI messages will be send back and forth between the router and the switch. The status of the link can be:




it is a good idea to „debug frame-relay lmi“ to troubleshoot a connection.

Point-to-Point Connection

– talk only to one device

Multipoint Connection

– to more than one device

FECN – Forward Explicit Congestion Notification

sending FECN Packet if noticed congestion on the network

BECN – Backward Explicit Congestio Notification
if the frame-relay switch noticed congestion it send’s a BECN Packet


every 10 secound a keepalive is sent by the router. If no keepalive arrives, the link is assumed to be down.

usefull debug explanation for „debug frame-relay lm“

PVC information element, length, dlci, status, CIR in decimal, for PVC Status

Could be:

0x00 = added/inactive

the remote end is not able to receive traffic at this time

0x02 = added/active

both ends are up

0x04 = deleted

the end router is no longer receiving LMI from the CO

0x08 = new/inactive

0x0a = new/active

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