Quicktime Multicast Broadcast locks-up/crashes Airports

Question

We are experimenting with QT Broadcast which works like a charm in unicast mode. However, what we really need to do is generate a couple of streams of h.264 video in multicast. We have managed to get it working fairly easily, however the multicast seems to cause our assorted Airports (all extremes, some of .11n) to lockup. The freeze usually lasts 20 to 30 seconds. The problem will ping pong around the network as long as the multicast is up.
The topology is roughly 25 Airports on a moderately sizable campus network with a dozen or so switches running 10/100 mbps. we are using a 10.x.x.x address space internally with not particular subnetting. I've tried fiddling with things like the packet size (the TTL is set to 1) with no particular improvement. We are using the default multicast address settings provided by QTB.
I would love some suggestions on getting this to work.

Answer 1

And, piggybacking on tjk's queries:
Do you have one AC adapter that stays in the office and another that travels with the Powerbook outside the office?
Does the office have any sort of power-conditioning equipment installed, i.e. to smooth voltage irregularities, filter out noise, etc?
Is your use of the PB at the office subtly different from your use elsewhere, i.e. are there keystroke combinations you use more often elsewhere, and not at the offfice? Particularly ones involving the left Command key? How many other places have you used the Powerbook in, where the problems have occurred? Are we talking about two or three other places, or a dozen?
Unless an odd power-supply issue is in play, it seems exceedingly strange that the office should provide immmunity from whatever affects the PB everywhere else (except at the Apple Store, of course). Are you quite sure these freezes never happen at the office?
I've never heard of any aspect of one's wireless configuration (or malfunction of same) causing a whole computer to freeze, so I strongly doubt that your networking arrangements in any location are implicated here.
If your computer were freezing up unpredictably wherever it goes, tjk and I would both immediately have urged you to look into the Orange Ribbon Cable Issue/Fix, as it has come to be known around here. Unless your PB is the 400MHz or 500MHz model, which don't suffer from that problem, I suggest that you try the free, quick and easy ribbon cable fix just to see whether it makes any difference.
Please keep us posted on your progress.