The textbook for COMP476 Networked Computer Systems is
Computer Networks and Internets, 5th edition, by Douglas E. Comer,
Prentice Hall, 2009,
The textbook is available at the A&T Bookstore for $127.00 new
You can also find the textbook at many online bookstores. The following search engines will locate the text at several online bookstores
If you buy the textbook online, I strongly suggest you pay extra for fast shipping.
The 5th edition of the textbook moves and improves the chapters from the 4th edition. A rough mapping of the chapters between the 4th and 5th editions can be found here.