Intermittent inability to "see" other machines on WLAN
I'm having a strange problem with my WLAN.
Environment:
Frame house
Cable modem and SMC WBR14-G router upstairs in master bedroom (fairly central), with Hawking external flat antenna
Laptop in room with router with IBM a/b/g card
Laptop on main floor, directly below router with Hawking PCMCIA card (also has crap Intel 2200b card in it, disabled)
Desktop in basement, also pretty well directly below router with Hawking PCI card in it
All machines are XP SP2 with all current service, using Wireless Zero Configuration service.
This is one of those "nothing changed" scenarios: it all worked a treat for a long time. Recently, however, I've started being unable to "see" machines from within the WLAN -- can't VNC to them, can't ping.
Repeated ping attempts often start working suddenly, but just as suddenly quit.
Network Stumbler shows no other signal on that channel and good signal strength, so I don't *think* it's an interference issue. Using channel 11 at the moment.
The router shows all the machines happily connected, and indeed, they are able to surf happily while unable to see each other. And I can always get to the router while I can't see the other machines.
SMC website doesn't list any updated firmware for the router; all of the wireless cards are current on drivers.
My understanding is that peer-to-peer communication is direct anyway -- that the machines don't go through the router to talk to each other. Is that correct?
Windows' Event Viewer shows nothing.
Any ideas? I'm stumped...I've had wireless for 8 years, starting with the Proxim proprietary, pre-b stuff, and haven't seen anything quite like this, nor have any of my friends (some of whom are far more network-savvy than I).
...phsiii (who is more than willing to find out he's missing something obvious!)
The clients use the AP to connect to each other and some APs/routers have an option to disable wireless client to client communication. It might be worth checking that this hasn't be accidentally enabled in the router settings.
Even if you don't pick up any other APs, it might be worth changing the channel (use 6 or below to ensure adequate separation from 11) just in case any interference is coming from a non-Wifi device such as a cordless phone. The clients shouldn't need reconfiguring if you do this.
The last option I'd try if it were possible is to test a different router.
Intermittent inability to "see" other machines on WLAN 
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