Hi,
This is about iChat being cut off at th router due to some sort of Protection feature.
Most likley this is DoS (Denial of Service)
This is threshold based and will have changed from SNow Leopard as iChat can not use HD camera if the computer has one (meaning more pixels per frame and therfore more data being sent.)
The Protection then cuts the one port it thinks is getting too much data.
It may be before you did not reach the Threshold but now you do.
(could be that the Buddy has just got a faster Service).
In iChat > Preferences > Video Section on both computer set the Bandwidth to 500kbps.
This should keep it below the threshold.
Alternativley turn the feature off in the router's set up pages.
The Log (Open the Send to Apple Pop up and see the whole log) may well list that Pings are not being sent
This could be that the call gets cut off before this or that the router is Blocking Pings.
If you need to copy the log and post the first two sections here (that is in fact all of It except the bit below the Line "Binary Images for iChat")
9:55 PM Thursday; February 2, 2012
Please, if posting Logs, do not post any Log info after the line "Binary Images for iChat"
iMac 2.5Ghz 5i 2011 (Lion 10.7.2)
G4/1GhzDual MDD (Leopard 10.5.8)
MacBookPro 2Gb (Snow Leopard 10.6.8)
Mac OS X (10.6.8),
"Limit the Logs to the Bits above Binary Images." No, Seriously