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The network delivers this excess data with a lower probability of success than
committed burst size data. Set the Be to a value greater than zero only if you are
willing to accept the risk of discarded data and its effect on higher-layer protocol
performance. The Be should equal the value set up with the network provider.
Use the add permanent-virtual-circuit, change permanent-virtual-circuit, add
switched-virtual-circuit or change switched-virtual-circuit commands during
frame-relay configuration to set the excess burst size. You can also use the set
circuit console command to dynamically change the excess burst size. Orphan
circuits will receive a default excess burst size equal to the value set in the set
CIR-defaults command. If you configure 0 for CIR, then you must configure a
nonzero value for the excess burst (Be) size. You can also set the default excess
burst size for all Frame Relay circuits on this interface using the set CIR-defaults
command.
Line Speed
The
line speed
is the interface’s line speed.
The FR interface’s line speed is configured using the set line-speed configuration
command. The line speed must be configured when internal clocking is used.
However, it is recommended that you configure a line speed for external clocking
since the router uses the line speed as the maximum information rate when
congestion monitoring is enabled. Also some of the protocols use an interface’s
configured line speed when calculating a route’s cost.
The line speed is not configurable on a Frame Relay dial circuit interface. If the dial
circuit is mapped to an ISDN base interface, 64 Kbps is used as the line speed.
For dial circuits using Channelized T1/E1 as the base net, the line speed is 64
Kbps times the number of timeslots assigned or 56 Kbps if you set the bandwidth of
the Channelized circuit to 56 Kbps. For example, if you set the number of timeslots
for a Channelized circuit to 3, the line speed is 192 Kbps (3 * 64 Kbps).
If the dial circuit is mapped to a V.25bis base interface, the line speed of the
V.25bis interface is used for the FR dial circuit.
Minimum Information Rate
The
minimum information rate (IR)
is the minimum data rate for a VC that the router
throttles down to when it is notified of congestion. You set the minimum IR as a
percentage of CIR using the set ir-adjustment configuration command. It can be
dynamically changed using the set ir-adjustment console command. If you
configure CIR equal to 0, the minimum IR is 1500 bps.
Maximum Information Rate
The
maximum information rate
is the maximum data rate at which the router
transmits for a VC. If the CIR monitoring feature is enabled and CIR and Bc are
nonzero, the maximum information rate is calculated using CIR, Bc, and Be as
follows:
( Bc + Be ) per Tc interval
If the CIR monitoring feature is enabled and CIR and Bc are configured equal to 0,
the maximum information rate is equal to the excess burst size (Be) per second.
Using Frame Relay
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MRS V3.2 Software User’s Guide
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