Avaya Configuring Frame Relay Services Manual de usuario descargar pdf (Pagina 42)

Configuring Frame Relay Services

2-22 117376-A Rev. A

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

Interface Software.

FECN and BECN Notiﬁcation Bits

The earlier section, “Congestion Control,”explained 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 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 F

igure 2-10), the central site router

typically sends much more data than it receives. Therefore, the remote site routers

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 and Congestion Timer parameters (see A

ppendix A), from

the default values of 20 FECN or BECN counts per one second to, for example,

10 counts per 5 seconds to account for the differences in trafﬁc volume from and

to the central site.

Figure 2-10. 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 42