Avaya Configuring Frame Relay Services Manual de usuario descargar pdf (Pagina 63)

Frame Relay Overview

117376-C Rev. 00

2-33

The parameters you can customize at the VC level are:

• wfFrCircuitShapedHiQueueLimit.

• wfFrCircuitShapedNormalQueueLimit

• wfFrCircuitShapedLoQueueLimit

For information on using the Technician Interface, see Using Technician Interface

Software.

FECN and BECN Notification Bits

The topic “Congestion Control” on page 2-22 explains that a specified number of

FECN and BECN bits received during a set time period indicate congestion.

When congestion occurs on a traffic shaped VC, the router either drops traffic,

throttles it, or throttles and then drops traffic, depending on the value of the

Congestion Method attribute or parameter.

The FECN and BECN notifications are part of the header in a frame relay data

packet. In a big pipe/little pipe topology (see Figure 2-11

), the central site router A

typically sends much more data than it receives. This means that the remote site

routers B, C, and D that receive a lot of traffic may be getting large numbers of

FECNs, while the central site router is getting relatively few data packets, and

therefore few BECNs, and is unaware than congestion is occurring. You may need

to fine tune the Congestion Counter parameter and the Congestion Timer

parameter (see Appendix A, “Site Manager Parameters”), from the default values

of 20 FECN or BECN counts per second to, for example, 10 counts per 5 seconds

to account for the differences in traffic volume from and to the central site.

Figure 2-11. FECNs and BECNs in Big Pipe/Little Pipe Topology

FR0015A

Remote site B

Remote site D

Remote site C

Flow of most traffic

Central site A

BECNs (few)

FECNs

(many)

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Avaya Configuring Frame Relay Services Manual de usuario Pagina 63