Very interesting question. Since my ansewer to that would be yanked straight from the RFC's, I thought I would just suggest some *light* reading to you that should resolve a lot of your questions.
If you are not already familiar with the RFC's, they are the best technical references on the net if you ask me. And best of all they will save you a lot of money on technical books.
Suggested reading:
RFC791 Internet Protocol
RFC815 IP Datagram Reassembly Algorithms
RFC814 Names, Addresses, Ports, and Routes
RFC768 User Datagram Protocol
RFC793 Transmission Control Protocol
RFC813 Window and Acknowledgment Strategy in TCP
RFC896 Congestion Control in IP/TCP Internetworks
you can get them all at
http://www.rfc-editor.org/rfc.html
Hope this helped.
