Are questions about Internet Protocols (like TCP) on topic for Computer Science Stack Exchange? I think they should be.
In principle, questions about computer networks and internet protocols are on-topic here, especially if they are asked from a theoretical or protocol design perspective.
However, this may not be the best place for practical problems when working with them. For those questions, SU (for consumer networks) or Network Engineering (for professional/business computer networks) may be a better fit.
Also, we don't appear to have many experts in those topics active on CS.SE, so it may take a while for questions to be answered.