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Wireless Clients not connecting on preferred standard

Posted on 2008-10-02
Medium Priority
Last Modified: 2013-11-09
I'm not sure if this has to do with the 802.11(a,b,g,n) standard, but the situation is this.  We have a wireless network that supports all of these standards using several Cisco Aironet 1200 series APs.  We also have a mix of HP NC6220, NC6400, and IBM T61 laptops.  The NC6400's have ABG cards but only seem to connect on G unless you specify under the card properties to only use A.  Once on A they work fine so I know the setup on the AP is correct.  The same thing happens with the T61's which have AGN cards.  They never connect to the 5GHz networks unless you tell them to specifically.  We've spent the money on AP's with 2.4 and 5GHZ radios, but we only ever seem to use the 2.4 range.  Just thought someone might know a tweek or reason for this.
Question by:yorkschool
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Expert Comment

ID: 22626994

Cisco Aironet 1200 support Network Standard are 802.11a, 802.11b, and 802.11g[only].

Non-overlapping channels in the 5 GHz band (802.11n).

So [Cisco Aironet 1200 Series Access Point] does not allow 5 GHz band (802.11n).

Great is our GOD.

Accepted Solution

pmwrightjr earned 750 total points
ID: 22643246
Uh... partially correct but somewhat misleading.  802.11a operates in the 5 GHz band and is supported by the 1200 series AP when equipped with the optional 802.11a radio while 802.11n can be either 2.4 or 5 although most implementations will be 5 GHz due to the greater availability of spectrum.

As far as the question that was asked, I guess if I wanted to make sure a card connected most of the time, I would program the driver to prefer the most common standard and only fall back to the less common standard if the other one was not available.  Also, everything else being equal, 802.11a will have less range than 802.11g for a variety of reasons from less efficient amplifiers to losses in antenna cables at the higher frequencies.  So I would guess that if you had an access point with both 802.11a and 802.11g radios in the same chassis, the 802.11g radio would have the stronger and higher-quality signal unless there were interference issues from adjacent 802.11g (or b) radios.

What happens when you take one of these laptops to an area where there is only 802.11a?  Does it connect then without being explicitly configured for 802.11a?

At any rate, I think the reason for A/B/G client equipment is so you can connect in any kind of environment, not so your equipment will always choose the best if they are all present.  Most environments, in my experience, do not operate A and G side-by-side so I don't think very many people experience the dilemma you are describing.

Similarly, I think the reason for combined A and G access points is to be able to talk to both A (only) and G (only) clients and not necessarily to choose the best path for a client that is able to talk on both.

Author Closing Comment

ID: 31503663
I guess we were hoping that half the clients would use G and the other half would use A and spread the demand over the 2 radios.  I will be looking at putting some of the clients on A only and see what happens.  You were right about the 1200 Aps we have 4 1200(g), 4 1220(a g), 2 1230 (a g), and 3 new 1250 (a g n).  since I don't have complete a coverage it's hard to put people on A only.  if you tell the card to connect to A only it connects right away and roams to other APs with A.  My overall goal was to distribute the loads but I see what you mean about overall quality of signal as a preferred network.



Expert Comment

ID: 22655388
Dan - Thanks for the additional information.  I think there might be a way to accomplish what you want to do by using a combination of group policy and some system-side programming.  Since your equipment is all Cisco, it seems like there should be a way to accomplish load-balancing even without a WLAN controller.  I'll give it some thought and post back to this thread if I have an idea.

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