Information Technology Reference
In-Depth Information
(in bps) at which the network guarantees to transfer data over a time T. Traffic can burst at rates
above the CIR depending upon use within the carriers network. Traffic can burst above the CIR
for an agreed upon amount of time.
Some parameters that define the allowable burst rate and amount of time a burst of traffic can
be transmitted are T, B
c
, and B
e
. T is the time allowed to transmit B
c
or B
c
+B
e
traffic. B
c
is the
committed burst size; the maximum number of data that can be transmitted during time T. B
e
is the maximum number of uncommitted data bits that the network carries during time T.
Local Management Interface (LMI)
LMI is a set of enhancements to the original Frame Relay specification. The LMI extensions
include global addressing, virtual-circuit status messages, and multicasting. With LMI, control
messages are sent between the DTE and DCE proving status information about the switch
and PVCs.
The LMI type is significant between the local router and connecting Frame Relay switch. The
remote router-switch pair can implement a different LMI format.
NOTE
There are three types of LMI implementations. The LMI type can be set per serial interface with
the following command:
frame-relay lmi-type {ansi | cisco | q933a}
Cisco routers perform autosensing of the LMI type with IOS 11.2 or higher. The
lmi-type
command does not need to be configured on routers running newer code.
Data Link Connection Identifier (DLCI)
Frame Relay uses the DLCI to identify VCs. Each DLCI has local significance. The DLCI
number at Router A can be different than the DLCI number at Router B for the same PVC. As
shown in Figure 5-6, each router uses the local DLCI number to reach another through the
Frame Relay network. Router A uses DLCI 200 to reach Router B, DLCI 300 to reach Router
C, and DLCI 400 to reach Router D.
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