Avaya Configuring Frame Relay Services Manual de usuario descargar pdf (Pagina 36)

Configuring Frame Relay Services

2-12

Congestion Control

Network congestion can degrade network performance. Congestion occurs when

a node receives more frames than it can process, or sends more frames than the

transmission line can handle. The Frame Relay network informs the nodes of

congestion conditions so that they can reduce the amount of trafﬁc across the

network.

In the Frame Relay packet header, there are two bits that the network sets to alert

nodes of network congestion. These bits, as deﬁned by the Frame Relay

speciﬁcation, are the FECN (Forward Explicit Congestion Notation) bit and the

BECN (Backward Explicit Congestion Notation) bit.

If the network detects congestion, it alerts the router in the same direction as the

received frame by changing the frame’s FECN bit from 0 to 1. For nodes in the

opposite direction of the received frame, it changes the frame’s BECN bit from 0

to 1 (Figure 2-7).

Figure 2-7. Detecting and Controlling Network Congestion

Congestion

Direction

BECN

FECN

Frame Relay

Network

Node

Frame Relay

Network

Node

Frame Relay

Network

Node

FR0010A

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Avaya Configuring Frame Relay Services Manual de usuario Pagina 36