The reality (as the other thread shows) is that we just don't know. It's an erratic failure and some folk don't have the problem at all; their boards just seem to run until they reset them to change something. My experience is that it can be many hours before a failure and then sometimes two or three times in an hour. On the 5100 chip the buffers are on the chip itself. It has memory on board that is partitioned out for rx and tx buffers for 4 sockets. That's why that chip is so popular, it leaves the arduino memory available instead of using it up for buffers.