In this sentence, is the second comma correct?
However, most operators are moving towards P2P networks, which do not have central servers.
From the hot tip on this site, I would think it is correct. I can remove the part starting with which and the sentence is perfectly useful to any reader who knows what a P2P network is.
EDIT: There are no P2P networks with central servers that I could refer to, so I think the comment answers the question.