Filter
Top Products
switched-virtual-circuit configuration command. You can also dynamically change
the CIR with the set circuit console command. You can also set the default CIR for
all Frame Relay circuits on this interface using the set CIR-defaults command.
Some Frame Relay switches allow a value of 0 to be configured for CIR. When CIR
is equal to 0, little or no bandwidth is reserved in the Frame Relay network
backbone for the VC, and the VC’s traffic uses non-reserved bandwidth.
Orphan Permanent Virtual Circuit CIR
The router assigns a CIR to orphan circuits based on the CIR defaults configured at
the interface level. If you are relying on the orphan circuit to route important data
and the CIR, Bc, and Be values from the network provider are different from the
values configured at the interface level, it is recommended that you define a PVC
instead of an orphan circuit. Doing this, you can assign a CIR that the network
commits to support.
Committed Burst (Bc) Size
The
committed burst (Bc) size
is the maximum amount of data (in bits) that the
network commits to deliver during a
calculated time (Tc) interval
. The Tc is equal to
the Bc divided by the CIR (Tc = Bc / CIR). If you configure 0 for CIR, Frame Relay
uses a value of 1 second for Tc..
For example, if you set a VC’s CIR to 9600 bps and the committed burst size to
14 400 bits, the time period is 1.5 sec. (14 400 bits / 9600 bps = 1.5 sec). This
means that the VC is allowed to transmit a maximum of 14 400 bits in 1.5 seconds.
Note: The minimum Tc supported by FR is .1 second.
This parameter is important because of the relationship between the committed
burst size and the maximum frame size. If the maximum frame size in bits is
greater than the committed burst size, the network may discard frames whose size
exceeds the committed burst size. Therefore, the committed burst size should be
greater than or equal to the maximum frame size. It should also equal the burst size
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 configuration
commands to set the committed burst size. The set circuit console command can
be used to dynamically change the committed burst size. You can also set the
default committed burst size for all Frame Relay circuits on this interface using the
set CIR-defaults command.
The device assigns orphan circuits a committed burst size based on the default you
set with the set CIR-defaults command. If you configure 0 for CIR, then the
committed burst (Bc) size also equals 0.
Excess Burst (Be) Size
The
excess burst (Be) size
is the maximum amount of uncommitted data the router
can transmit on a PVC in excess of the Bc during the Tc (Tc = Bc / CIR) when CIR
and Bc are nonzero. When CIR = 0, Frame Relay used a value of 1 second for Tc.
Using Frame Relay
Chapter 30. Using Frame Relay Interfaces 397
|
|
|
|
|
|
|
|
|
||
|
|
|
|
|
|