Avaya Configuring Frame Relay Services Bedienungsanleitung PDF herunterladen (Seite 46)

Configuring Frame Relay Services

1-24

308624-14.10 Rev 01

When configuring the CIR, consider the following:

•CIR of 0

You can contract with a carrier for a CIR of 0, which yields best-effort service

at low cost. The carrier transmits data, but does not commit to providing a

specified throughput. To configure a CIR of 0, set both the throughput (which

is the CIR) and the committed burst (B

) to 0, and set the excess burst (B

) to

a value greater than 0. For more information about burst rates, see the next

section, “Committed Burst Rate and Excess Burst Rate

.”

• Maximum CIR

The maximum CIR should not be greater than the speed of the access line on

the slower end of a virtual circuit. In a big pipe/little pipe topology (Figure 1-8

on page 1-20

), likely CIRs at the remote sites would be 32 Kb/s, 56 Kb/s, or

64 Kb/s. If you configure CIRs for these virtual circuits at the central site, you

can use CIR enforcement (described in the next topic) to prevent the big pipe

from sending traffic that exceeds the PVC CIRs.

• CIR enforcement

CIR enforcement means restricting the speed of outbound traffic to a rate no

faster than the CIR. It is the major component of traffic shaping. You can

configure CIR enforcement to operate over Synchronous, High-Speed Serial

Interface (HSSI), T1, E1, and Integrated Services Digital Network (ISDN)

lines, for frame relay backup, demand, bandwidth-on-demand, and leased

lines at the virtual circuit level. CIR enforcement operates on whole frames

only. It controls congestion either by bringing down the virtual circuit, or by

throttling the traffic.

Committed Burst Rate and Excess Burst Rate

The committed burst rate (B

) defines the number of bits that the router can

transmit over a specified time interval (T

) when congestion is occurring. The

excess burst (B

) defines the number of extra bits that the router attempts to send

over the T

when there is no congestion. Both the B

and the B

are values that

you configure.

The sum of the B

and the B

is the maximum amount of traffic that can travel

across the network per T

when there is no congestion. If you set the B

to a value

greater than zero, the router can send traffic exceeding the CIR. To enforce the

CIR, that is, to limit traffic that the router can send to the amount of the CIR, set

the B

to 0.

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