Specifications

Sample Scenarios 65
Figure 33. Frame Relay LMI
When FR interface receives a packet for encapsulation, it looks in its address
resolution protocol (ARP) cache. If the ARP cache contains the local DLCI
number that matches the network address, the FR protocol encapsulates that
packet into a frame and transmits the frame over its specified local DLCI. If the
ARP cache does not contain a match, the FR protocol sends out an ARP request
over all configured PVCs on the interface.
When the appropriate endpoint responds with an ARP response, the FR protocol
adds its local DLCI that received the ARP response to the ARP cache.
Subsequent data packets directed to the same network address are then
encapsulated into a frame and sent out over its local DLCI. Protocol addresses
can be either mapped statically to PVC addresses or discovered dynamically
through Inverse ARP or ARP.
4.1.4 Committed Information Rate (CIR)
The CIR is the data rate that the network commits to support for the PVC under
normal, uncongested conditions. Any PVC that is configured or is learned is
provided a CIR (by the FR service provider). The CIR is a portion of the total
bandwidth of the physical link reserved for the PVC. A value of 64 kbps for a
single DS0 channel is most common.
2212
DLCI = 16
DLCI = 20
DLCI = 18
2212
2212
DLCI = 16
DLCI = 17
DLCI = 18
STATUS ENQ
STATUS
Frame Relay Network
2212
DLCI = 16
DLCI = 20
DLCI = 18
2212
2212
DLCI = 16
DLCI = 17
DLCI = 18
STATUS ENQ (Full)
Frame Relay Network
STATUS (Full)
DLCI = 16 OK
DLCI = 17 OK
DLCI = 18 NG