Bitcoin traffic and memory usage

[CODERsp]

Hi, community! I have one problem using Bitcoin. I installed bitcoind on server. When all blocks had been downloaded something mysterious was happening. Memory usage of bitcoind process was about 250 MB and traffic was low, but sometimes traffic suddenly increased to 2 GB per one hour and then it decreased to low values again. I saw such problem 2 times per day. How do you think, why?

[Stephen Gornick]

but sometimes traffic suddenly increased to 2 GB per one hour and then it decreased to low values again.

A peer may be connecting to you and downloading the blockchain from you.  You can configure your client to not accept incoming connections (-nolisten) if operating a node with open access to other nodes to connect becomes a problem.