802.11b/g AP association

[vramanaiah]

I have a question regarding the client association to the AP.

As i roam across the campus, i expect the client adapter to associate to its nearest AP (Obviously due to better signal strength). However, we observe the client continues to be associated to the original AP although the signal quality level are much much lower than the nearest AP.

Just want to know, if this is the normal behaviour as per standards? Also want to know, if there is any threshold setting that we can do on client adaptor where we can configure to choose a better AP when the SQ goes down with the associated AP.

Note that, i can associate to the nearest AP, if i disable my client radio and enable it again...

[vramanaiah]

Well, i guess, this has something to do with the AP Selection method

of the wireless client..

I could not locate a good reference on this... Does anyone have a good

link explaining the AP selection process...?

Would appreciate if you can share it..

[rwyates_2]

Here is the information ont eh Cisco client. I do not know what client you are using, but it should be the same.

http://www.cisco.com/en/US/partner/products/hw/wireless/ps4555/products_qanda_item09186a0080094cdc.shtml#assoc

[vramanaiah]

Hi, That was a useful link, however it does not answer my question fully. Basically i am not convinced that the client will not choose an AP with better signal quality. This is going to result in poor throughout for mobile clients... Hope you agree.. Is there a solution to this issue?

May be if i restrict data rates, it will swithover, will try it and update.

[rwyates_2]

You are correct. By restricting data rates you will cause the clients to change more frequently because it will not have as much range.

[eallan]

By the description in your post I would assume that you are using Microsoft Wireless Zero config as the client on your laptop. You need to move to the software client that comes with your card (Cisco, Dell, Linksys). Currently Windows is not smart enough to look at signal strength and noise levels to know when to move to another AP. The client software that comes with most wireless cards will be able to "roam" like you are looking to do. We have had great luck with the Dell mini PCI 1350 and 1370 cards.

[john.preves]

The problem you describe usually is attributed to the fact that the power

is too high and your cells are too large. The result is the client doesnt see a weak enough signal to roam

until it is far beyond the next few cells.

Using lower powered cells (and client cards!!) will enable you to physically load balance the wireless infrastructure.

Of course this means more AP's to cover the area but you will eliminate the problem you have

and a few you haven't mentioned yet, such as having some AP's with the bulk of the associations while other

AP's are under-utilized, which in turn will improve aggragate throughput across the network.

Lower power, smaller cells, better load balancing and troubleshooting and increased aggragate throughput.

[vramanaiah]

I was using the lowest possible power settings...

[ethiel]

This is mainly a function of the client adapter. As mentioned above, most clients will not roam unless they drop below a certain signal strength.

If you post what client you are using, we may be able to give more specifics. For instance, the Intel driver allows you to tweak the "Roaming aggressiveness". To do that, you can click "configure" next to "Connect using", and choosing "Advanced".

[vramanaiah]

Yes, you are correct.. This is purely a client adapter behaviour..

I was using Cisco Aironet 350 Adapter. It did not switchover as expected.

However, i was checking with a 7920 ip phone and i saw this one switching over as expected..

Unfortunately, no vendor documents this behaviour, although some of them allow you tweak some parameters that will influence the selection process..

[estein]

In the 350's Aironet Client Utility, if you Edit the work profile and click the RF Network tab, there is a 'Scan for a better Access Point' section. It is by default set to roam when the Signal Strength is less than 50 I think. You might want to try modifying that setting to see if it improves roaming for your users.

[mmatulevich]

We are having similar roaming problems with various clients. While turning down the mW power on the b/g and a bands have resulted in improvement, I think the roaming sensitivity is still a big issue due to having such a dense lwapp environment. What version of the ACU has this tab, as I thought we were on the latest and I don't clearly see the RF Network tab you mentioned? Thanks in advance for info

[wififofum]

Are you using Aironet extensions on the APs? Are you enforcing client transmit power to match the AP transmit power via the "power client" command?

You should also eliminate data rates below 11.0Mb/s. This has an impact on cell ize as well. Remember also when you use a low basic data rate, higher-rate-connected clients have to down-shift to allow for lower-rate clients accessing the medium.