Wireless outage (IP only) for 5 minutes, every 15 minutes

Question

Hey everyone,
I recently moved to the UK from the US, and in the process gave up my Airport Base Station for the much less friendly BT Home Hub. Since doing so, I have been having some very annoying problems with the wireless connection that I did not have before.
Essentially, what happens is that I lose IP connectivity (cannot ping the gateway, or get to the internet), but the Airport menu icon/Network Connect reports I am still connected to the wireless network, and there is no change in reported signal strength. I took a look at it with iStumbler, and there is pretty much no difference in signal/noise or any other readouts when the dropout occurs - the "wireless network" appears to be up, I just don't have IP connectivity.
Turning the Airport card on and off restores connection, but doing this every 15 minutes is very annoying, of course. If I wait 5 minutes with no IP connectivity, it comes back, once again with no corresponding change in signal strength.
This may be a result of the change in wireless access points, but there are some things about my particular situation that makes me wonder if it might be something related to my PowerBook/Airport card. Firstly, while I was moving, I was housesitting for friends, using a wired ethernet connection, when I installed the Airport security update and iTunes 7, so my configuration has changed since the last time I knew it to work well (I have since upgraded to OS X 10.4.8 and iTunes 7.0.1 over my intermittent wireless connection, but I have had this problem since before doing so).
Secondly, and more importantly, I have noticed an incredibly regular pattern to the outages. Specifically, the times I mentioned above are pretty much exact and consistent. Since I started having the problem, I opened a terminal window and ran a continuous ping of the gateway, and my results are as follows:
Every 895-900 pings (i.e. seconds), there is an outage, which lasts for 296-297 pings/seconds. So, for example, there is an outage at icmp_seq=1025 (895 sec after the last outage), and the ping command then recieves its next response at icmp_seq=1321 (296 sec). There is then subsequently an outage at 2221 (900 sec after the last outage) which resumes at 2517 (296 sec), etc., etc.
What makes this especially interesting is that, as I mentioned above, if I turn the Airport card on and off I get connectivity back. The connection then lasts for 900 seconds from when I turned the card back on, not from the last outage. So the outage seems come specifically after 15 minutes of having the Airport card on and connected, rather than the WAP giving up the ghost every 15 minutes regardless of what's connected to it.
The WAP is running in 802.11g mode with WPA security using WPK encryption. The SSID is not being broadcast. This is a modification of the original BT Home Hub settings (64-bit WEP encryption? No thanks) but pretty similar to what I had on my Airport Base Station. The WAP's event log shows nothing out of the ordinary, and looking at the device during the outage doesn't really show any problems. If I plug into the wired port while I'm having one of these 5 minute outages, it works.
I have also tried changing the wireless channel it runs on, but this has no affect.
I don't have any other computers/devices in the flat so I can't test whether this outage is universal or specific to my computer, but I was wondering if anybody else has experienced a similar problem? Is there any way I could narrow it down more between the WAP and the PowerBook? The regularity of the outage, and the fact that IP gives out, but I don't get disconnected from the wireless network seems to two very tantalizing clues.
Thanks,
Andrew
PowerBook G4 15-inch (FW800)   Mac OS X (10.4.8)   2GB RAM, 1.67 GHz G4

Answer 1

I am still having this problem and am starting to get really annoyed by it. Since my last posting, the following things have happened:
1) Last Thursday, I turned my Powerbook on and experienced a full day of work at home with a consistent wireless connection. Nothing had changed in configuration on either the router or the Powerbook. Then, at night, I turned my computer off, turned it on Friday morning, and again experienced dropouts every 15 minutes, for 5 minutes exactly.
2) By this time I had already called BT and complained, and they were kind enough to send me a new hub. I got it today, took the old one down and set it up (via ethernet cable) with the exact same settings as the old one, and then connected to it via wireless - I was able to connect successfully with no interruptions. Then, I shut my computer down to go out for a few hours. I am now back, and since booting my computer, I now once again only stay connected for 15 minutes at a time!
So, it now seems to be only 95% consistent, instead of 100% consistent, but I am really beginning to suspect my Powerbook, since it seems to be behaving differently on different boots! Please help? What can I do to isolate this problem? As I have demonstrated in my previous posts, I have already looked at iStumbler, etc. and am still having the same exact problems, even with new hardware!