Avaya Configuring Frame Relay Services Instrukcja Użytkownika Pobierz pdf (Strona 44)

Configuring Frame Relay Services

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308624-14.10 Rev 01

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, 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 forward explicit congestion notation (FECN) bit and the

backward explicit congestion notation (BECN) 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 1-9)

Figure 1-9. Detecting and Controlling Network Congestion

If you enable congestion control, you can specify the number of FECN/BECN bits

the router receives in a given time period before it stops transmitting frames.

While frames are going across the network, the frame relay interface checks

received packets for FECN and BECN bits set to 1. If the interface receives the

specified number of bits during the designated time period, frame relay drops all

traffic destined for the PVC where there is congestion. When the interface no

longer receives these congestion notifications, the router resumes transmission.

Congestion

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FR0010A

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Avaya Configuring Frame Relay Services Instrukcja Użytkownika Strona 44