Congestion Control - HP auroraTempo User Manual

aurora Tempo - User Guide

Congestion Control

Congestion occurs when multiple users contend for the
same physical resources, at the same time. Minimizing
congestion is a key factor in maintaining a high quality
service because, when congestion occurs, the network
begins to discard frames, resulting in the end user devices
having to retransmit.
When congestion occurs Frame Relay employs a
mechanism to notify the end devices that congestion
exists within the network.
• The network notifies the destination device of
congestion by setting the FECN (Forward Explicit
Congestion Notification) bits in frames bound for
this destination.
• The network notifies the source device of
congestion by setting the BECN (Backward Explicit
Congestion Notification) bits in frames bound for
the source device.
The end user devices, on receiving the congestion
notification, reduce their traffic accordingly, allowing the
congestion to subside.
The following diagram shows the congestion mechanism in
operation:
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