802.11 b/g compatibility?

Hi wireless fans... long time listener, first time caller...

We've enjoyed a nice wireless LAN with a Linksys BEFW11S4 (firmware v

1.45z, an 802.11b router) providing a gateway to cable internet, serving a few laptop PC's: (1) Windows XP home, internal Broadcom 802.11g adapter (2) Windows XP home, external Linksys WPC11 (802.11b) adapter (3) Windows XP pro, internal LanExpress 802.11b adapter (4) Windows XP home, internal 802.11g adapter .... and a couple wired clients

The router is configured for MAC address filtering, but no WEP.

Everything was groovy for almost a year. Typical throughput was on the order of 1200 bps on all clients. Recently, pc (1) started getting terrible throughput, say 120 kbps, rather spontaneously. I tried the usual suspects: reset the router, reboot PC's, reinstall drivers on pc (1), reset TCP/IP, all to no avail. All the other PC's meanwhile were fine. Digging deeper, I did a "repair" install of Windows on (1). No joy.

Since PC (1)'s throughput's rate was killed so suddenly I suspected either some crazy software was installed, the internal adapter on (1) was going south, or there was something screwed with TCP/IP. I could not find any suspicious software on (1), so I installed (and plugged in) the Linksys external "b" adapter in (1). It worked great: 1200 bps.

Thinking this confirmed my suspicions about the internal adapter on (1), I bought a new external Linksys g adapter for (1). To my amazement, not only did the throughput on (1) NOT improve with this new adapter, installing the same adapter on PC's (2) and (3) also brought them down to pitiful throughputs.

So my conclusion is, this Linksys BEFW11S4 (802.11b) is not really compatible with some 801.11g adapters, including some Linksys wireless adapters.

I've read some other posts, mostly old, that poo-poo the idea of incompatibility between b and g equipment. Any ideas here? I will probably acquire a "g" WAP in the near future -- in part to test my theory, and in part to satiate PC (1) who has terrible throughput at the moment...

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I think you meant 1200 Kbps (1.2Mbps), right? That would be an aggregate throughput of of 4.8 Mbps, about what you'd expect for 802.11b.

If you haven't changed the configuration on the router or any of the clients, then something has to have changed in the operating environment - host hardware problems, host processor overload, some other network interfering, something new between the client and the router that absorbs the signal, etc.

Did you check the site survey to see if any new networks are showing up? Did you try changing the network's center channel? Have you recently bought a

2.4 Ghz cordless phone or some other device that uses 2.4 Ghz (like a video sender, for example)?

Your instinct is right, that something environmental changed.

This conclusion is incompatible with the fact the the Broadcom G adapter worked fine for a year. The fact that the Linkys B adapter worked but the Linksys G did not proves nothing. Those two adapters probably differ in more ways than just B vs. G. They may have been made by different vendors (resold by Linksys), using different antennas, and may have different receiver sensitivities. It sounds to me like you have some new source of interference that pushed the old Broadcom card over the edge, but your old Linksys B card happens to be able to tolerate it.

Let's define compatibility. According to the standards, it means that a G access point supports a mix of B and G clients, by design. It does *not* mean there is no performance penalty. There is always a penalty. If the B clients are very quiet, the G clients can operate at full G bitrates, with only a little throughput penalty for certain messages used to co-ordinate between the different client types. If the B clients generate even moderate traffic, all clients will be dragged down to B bitrates.

If your access point is configured to support a B network, then *all* clients will connect as B clients, whether they are capable of G or not. A B access point cannot support or even recognize a G client. The G client recognizes B, and switches to that mode when associating with the access point.

If you buy a G router, and host 1 goes back to full throughput, it still doesn't prove the theory that G is incompatible with B. It probably just proves that your new router has a higher transmit power, better antennas, or both.

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I would also reset the router; not just reboot, but clear out the settings and start over. The wireless router software can get messed up it seems from what I have read. And I have had an access point go bad on me, such that the throughput dropped considerably, though that does not necessarily explain this situation.

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Jim Fox

Well duh me... what's a factor of 1000 between friends?

There is no new equipment and no changes on my network. Nothing new as far as electronics in the house (unless you count Christmas tree lights? ... but those were installed after the problems began (^: )

Interesting question about new networks... PC(1) does not see any new networks. However PC(4) routinely sees 2 or 3 foreign networks, and occasionally prefers to connect to one of them even though my AP is certainly the closest. Both (1) and (4) have internal G adapters, and my AP is strictly B so I think I can understand (4)'s preference, however (1) does not see the same opportunities.

The other thing I neglected to mention about (1) is its curious ping results. Even when (1)'s throughput was normal, a typical ping (say, to

formatting link
would show 25-50% dropouts. The successful packets had times consistent with other machines on this network. Same is true pinging any machine on the LAN. Pinging the loopback address is always

100% successful. Now that the throughout is poor, pings have not really changed: still 25-50% dropouts pinging any other host, and still normal timing on returned packets. This profile is also observed when (1) uses the external B adapter. Since the ping behavior does not vary with connection quality or method, it seems doubtful the high dropout rate and poor throughput share the same cause, but it seems unusual enough to warrant a mention.

Thanks for your input.

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