Extreme Networks Summit WM Technical Reference Manual page 96

WDS – Wireless Distribution Service
Performance limitations with WDS
The average packet delay with WDS is equal to the average delay introduced by every hop,
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multiplied by the number of hops. As with any WLAN system, if the wireless medium is free, the
latency is negligible, but when the medium becomes busy the latency increase will be amplified by
the number of hops. The figure below depicts how this delay may become very significant for a
large number of hops. It is essential to keep the number of hops — the depth of the tree — as small
as possible.
Figure 21: Delay dependency on number of hops
Another reason to keep the number of hops — the depth of the tree — as small as possible is that
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the packet loss is amplified by the number of hops. In order for a packet to be successfully
forwarded from a satellite AP to the root AP, the packet must be transmitted successfully at every
hop. The figure below shows how the overall goodput depends on the number of hops. Increasing
the number of retries may help reduce the packet loss and increase the goodput, but it does not help
(it actually hurts) when the packet loss is actually caused by congestion.
Figure 22: Goodput dependency on number of hops
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Delay dependency on no. of hops
no. of hops
Goodput dependency on no. of hops
no. of hops
Summit WM Technical Reference Guide, Software Version 5.1