Connect to a specific AP541N in a cluster system, and issue with cluster+WDS

Unanswered Question
Apr 2nd, 2010

We are running with four AP541N in a cluster (connected to a SA540), where they all broadcast on the same SSID and channel (9). If we forces one offline by unplugging the power, a client is automatically connected to another AP in the cluster. But we have a few questions:

1) For testing purpose, is it possible from Vista/Win7/XP to force connection onto a specific AP in the cluster? Only one network is shown in the list, and the AP with best signal seems to be the one automatically choosen.

2) One problem we have found is that two of the APs have a WDS connection between them (one is at a location where we could not easily cable it). This also seems to basically work fine with clustering, but if the wired part of the WDS goes offline, the clients already connected to the wireless WDS AP does not get kicked out, but do of course loose their connection to the network. Even worse, clients connected to the wired WDS AP (which "went down"), might be transferred to the wireless AP with no network connection since the signal from this might be the best...! Any way to solve this, so that APs depending on the WDS kicks out their clients if the WDS is broken....?

We do also seem to be biten by the "speed degrade" issue of the APA541N now-and-then, particulary on the AP beeing the wired part of the WDS. Using WPA-PSK, and having set the recommended "key refresh" setting to 0, without seeming to help anything at all. Running FW 1.8.0, and really hoping for a new FW fixing this issue to appear soon!

- Ola

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David Hornstein Sat, 04/03/2010 - 01:09


Seems like this is your topology.

LAN Switch-------- AP541  (  (  (    WDS    )  )   )  AP541----switch--PC remote

Hmmm and you want to have another backup link from the remote AP541 in case the LAN connected AP541 fails.

It would be very interesting to see If RSTP could be used in your scenario to block the redundant link. I wish I had three AP's to try it out, looks interesting.

But anyway that third AP would not be in AP mode but just there to provide a WDS link to the remote AP.

So it would be acting as a spare to provide a backup link to the remote AP.

On that train of thought, If you therefore have a AP acting as a spare, just keep one on the shelf and use it if one of the AP fails.

LAN Switch-------- AP541  (  (  (    WDS    )  )   )  AP541----switch--PC remote

                 |                                                                  |

                 |----/----AP541  (  (  (    WDS    )  )   ) -----

Why specifically do you need to have WDS running , what is the nature of the problem with cat5e connectivity to the remote AP ?

Is it CAT5e distance related, can't run cable to that location  or what,  I have a idea, but have to better understand what problem you are facing.

regards Dave

opresterud Sat, 04/03/2010 - 08:04

Thanks Dave!

The setup is like this:



|- AP#1

|- AP#2  ( ( ( WDS ) ) )  AP#3

|- AP#4

|- + printer

The network is intended mostly for laptops which uses wireless network. The implementation is on a sports arena, and to get good enough coverage we had to put AP#3 in a tower across the outdoor space. It have free sight with only glass windows between to where AP#2 is (which is also quite high), but AP#3 then helps to cover the ground area which AP#2 did not properly do alone. So AP#3 is connected to AP#2 with WDS, and acts like a repeater. No equipment is connected to the ethernet port of the AP#3. We are not able to acheive the same coverage from any place where AP#3 could have been cabled, so WDS from AP#2 is our only option here.

If AP#2 goes down (as in forced down by unplugging the power when testing), clients connected to AP#3 is left untouched but looses their connection with the network. Non of the other cabled AP's are in such a postition that they can set up a another WDS to AP#3 (as it seems is possible with AP541N, to have several WDS connections on one unit, without me investigating further into this). The best would be that AP#3 would kick out the connected clients if WDS goes down, since most of the potential clients might be able to get a useable connection to AP#1 instead.

Problem 2 here is that error recovery on this should hopefully happen automatically, since there might not be any technicians around at all the time this is beeing used.

Even that it is announced to be so, we find the loss of speed with WDS to be quite noticeable. Sitting with a laptop at the same location as AP#3, and getting a 3of5 bar signal from AP#2 with a 11g laptop, we get max internt speed (which is ~10Mbps). But then booting the AP#3 and connecting to this instead, we only get speed in the range 3-4Mbps. Should the WDS and the AP acting as repeater drop the speed this much? WDS is configured with WPA-PSK and spanning tree enabled. All the AP's are running in 11bgn mode, and the regular broadcasted net is using WPA-PSK too.

- Ola

opresterud Mon, 04/05/2010 - 13:32

Partially found solutions now:

1) This can be achieved by using "WIFI Studio", which scans for all WLANs beeing broadcasted, and lists them with MAC. You can then choose exactly which AP Vista/Win7 should connect too. Extremely usefull! Link:

2) We will try to set up a triangle with WDS here, so that two cabled AP's both have a WDS connection to the single non-cabled AP. It seems like this can work, but havn't investigated deeply into this yet.

- Ola


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