Using Wds; Using Wds To Fill Coverage Gaps - Extreme Networks Summit WM Technical Reference Manual

The third reason to keep the number of hops as small as possible is that the maximum throughput
●
decreases proportionally with the depth of the WDS tree. In a WDS tree, the frame is transmitted
multiple times over the same channel. For N WDS hops, each frame will be transmitted N+1 times.
Due to collisions and congestion, the maximum throughput over N hops will be smaller than 1/
(N+1) of the maximum throughput over one hop.
It is recommended to keep the width of the WDS tree as small as possible. Within a WDS WM-AD,
●
the parent sends broadcast frames by converting them to unicasts and sending each frame to every
one of its children. This is optimal for narrow trees (each parent has only few children) since the
unicasts are sent with the higher PHY rate than the broadcasts which are sent with the minimum
Basic Rate. However, this may become a problem for wider trees so it should be considered when
designing the WDS tree.
Due to the above limitations, it is recommended to limit the number of APs participating in a WDS
●
tree to 8. This limit guarantees decent performance in most typical situations.
Other limitations
The WDS feature is not supported on the Scalance W788 or the Altitude 802.11n AP.
●
The APs used for WDS cannot be used for a rogue AP scan, because a rogue scan would force the
●
WDS link out of service. Therefore, APs that are configured in a WDS WM-AD (regardless of radio
or the actual role) are not listed on the Summit WM series Spy Scan Groups page of the Summit
WM GUI. In addition, if an AP has been configured for a rogue scan, none of its radios can be
assigned to a WDS WM-AD.
The Summit WM GUI does not allow the user to disable a WDS WM-AD on an AP that is operating
●
as a WDS child. This prevents the user from erroneously cutting the WDS uplink. To disable a WDS
WM-AD on a child AP, the AP must be connected to the wired infrastructure, either via Ethernet or
via a different WDS WM-AD.
The Summit WM GUI does not allow the user to rename the SSID or enter a different Pre-shared key
●
for the WDS WM-AD. This prevents the risk of cutting the WDS uplink for the APs acting as
children. In order to change the SSID or the Pre-shared key, the user must follow the steps below:
Define a new WDS WM-AD and apply it to the same APs with the same roles as the current
●
WDS WM-AD.
Disable the old WDS WM-AD on all APs.
●
Wait until the new configuration is propagated to all APs. The first one to receive and accept the
●
new configuration will be the root, and then its children will follow, and so on.

Using WDS

Using WDS to fill coverage gaps

No matter how good the initial site survey is, it is possible to have coverage gaps in the final
deployment. For example, furniture location has changed, people movement, etc. For those
circumstances, moving APs is typically not an option and adding an extra AP can be difficult due to a
lack of Ethernet cabling. For those situations, WDS can be used in conjunction with DC power bricks to
provide an effective solution to resolve coverage gaps.
Summit WM Technical Reference Guide, Software Version 5.1
97