We have a custom chat application(c#) which uses TCPClient. We are having problem on clients who are behind Firewall or proxy. We know that these client can browse the internet without a problem so we decided to change our TCPClient application so that It uses HTTP messages to communicate.

Will it be enough just to wrap our text massages with standard HTML tags and HTTP headers? We need a long lasting connection. Does keep-alive have a limit? Do firewalls or proxies have time limits for "alive" connections.