I am roughly halfway through this book right now by Douglas E. Comer. The book is called Internetworking with TCP/IP Vol.1: Principles, Protocols, and Architecture (4th Edition). I am finding it a good read so far. It talks about the history of the Internet with ARPA-net and NSF-net and describes most of the protocols that have been used and that are used today. It has some good explanations on TCP where it describes TCP slow start and other features of TCP. As a part of my studies for the CCIE I am keeping a count of how much time I study. If anyone is interested I will post the numbers later on. So far I have done about 15 hours of reading.
Halfway through Internetworking with TCP/IP