I had been developing a p2p videochat app in flex with rtmfp and had been having video freeze after 2 seconds of playback, but only when using two computers on the same network, and only certain networks. one of them was my house after comcast put in an arris tm722 modem. We were using a POS dynex for a router.

Bought a new motorola sb6010 and a cisco / linksys e2110L, called comcast to provision it, and had it working on the windows 7 netbook i had plugged into the router.

Hung up with comcast, power cycled the modem, and plugged it into the router. nothing - couldn't get the signal to transfer.

Replugged the netbook - it got online fine.

After a lot of wasted time, what it took was:

Manually releasing the DHCP with the netbook connected to the modem online with:

ipconfig /release

powercycling the modem ( unplugging adn waiting 1min ) to reset it completely
restarting the router
plugging the modem back in

..and then i had a signal across the cisco.

all leading, in the end, to a much faster network. moreover, it DID fix the rtmfp problem i had been having. I suspect there was a double NAT with the arris tm722. not so with the sb6010. very relieved all this hassle was worth it in the end :)