Volume 1: The Protocols
After a brief introduction to TCP/IP, Stevens takes a bottom-up approach by describing the protocol from the link layer and working up the protocol stack.
Volume 2: The Implementation
500 illustrations, combined with 15,000 lines of actual code from the 4.4BSD-Lite release, serves as concrete examples of the concepts covered in Volume 1.
Volume 3: TCP for Transactions, HTTP, NNTP, and the Unix Domain Protocols
This volume goes into detail on four topics:
T/TCP (TCP for Transactions)
HTTP (Hypertext Transfer Protocol)
NNTP (Network News Transfer Protocol)
Unix Domain Protocols (see Unix domain socket)