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Client's roaming decision

I have heard this question before from customers and have had mixed replies from Cisco and instructors at Gigawave who worked for Aironet.

Q1 How does the CB21AG using the Aironet Desktop Utilty 4.2.0.269 determine which 1242-LWAP AP to associate to? Can I debug the decision it made?

Q2. How does the Microsoft Wireless Zero Configuraiton (WZC) determine which 1242-LWAP AP to associate to? Can I debug the decision it made?

If you have a answer I'll also ask for a url reference.

8 REPLIES
Silver

Re: Client's roaming decision

Hi Jason!

Well, I don't have a URL reference... but there's a good reason why. The reason you aren't getting any answers out of Cisco or Gigawave is because, well, there's no good answer.

There is nothing at all about roaming in the 802.11 standards. As such, all wireless adapters have their own algorithms for determining when to roam. And companies tend to keep these algorithms secret, because it's company IP.

As far as I know, you cannot debug either Windows or Cisco client adapters when they roam. There is no way to receive insight as to why they roamed, and this is by design.

This isn't exactly what you wanted to hear, but it's how it works I guess.

Jeff

Green

Re: Client's roaming decision

I pretty much agree with what you posted, but wanted to point out that Intel have (had?) settings for their wireless NICs/Drivers that let you adjust some of the roaming parameters.

IIRC it was a window / tab from their "Advanced" settings screen.

FWIW

Scott

Re: Client's roaming decision

Most higher quality chipsets have the ability to adjust roaming aggressiveness. If they don't, we pretty much recommend a newer chipset. The chipset manufacturers base their algorithms on basically 3 factors. 1. Signal strength. 2. SNR, 3. Client load on the existing AP. If the threshold for any of these are violated the client chipset goes into active scan mode and seeks a better AP. If none is found it will stay where it is. If a better AP is found the process of reassociation and reauthentication (if needed, not needed with LWAPP solutions usually) to the new AP.

Re: Client's roaming decision

I wanted to share a book i am in the middle of reading. Its "Secure Roaming in 802.11 networks"

Its a great book ... talks about the driver, chipset, clients, etc ...

__________________________________________________________________________________________ "Satisfaction does not come from knowing the solution, it comes from knowing why." - Rosalind Franklin ___________________________________________________________
Cisco Employee

Re: Client's roaming decision

You can tune the CB21AG's roaming behavior - see:

Optimize CB21AG/PI21AG Roaming Behavior

http://www.cisco.com/en/US/products/hw/wireless/ps4555/products_tech_note09186a008074fed9.shtml

There's no user accessible way to debug a driver's roaming decisions - this typically involves running a driver in some kind of debug mode, which is quite tricky.

Hall of Fame Super Gold

Re: Client's roaming decision

Q1 How does the CB21AG using the Aironet Desktop Utilty 4.2.0.269 determine which 1242-LWAP AP to associate to? Can I debug the decision it made?

Using the (Aironet) Cisco Desktop Utility, you can configure which AP's you want to associate in a particular order. Otherwise, the CB21AG card will associate on the AP with a stronger and stable signal.

Does this help?

Silver

Re: Client's roaming decision

Be careful about using the Preferred AP function. This forces the client to stay attached to that AP as long as possible, which can result in roaming issues.

Bronze

Re: Client's roaming decision

Jason,

Lookup LinkMon on the web. Its a great little client utility that performs a low-level diagnostic trace (logs signal level, data rate, retries, and roaming events) with the CB21AG.

--Bruce Johnson

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