Reading the RFCs for popular protocols is also a good start. Several of the RFCs also document many years of learning from operating networks. A good place to start is the RFC index - http://www.rfc-editor.org/rfc-index2.html
For the past 8 years I been using the Tanenbaum book for teaching my university networking class.
That book is really starting to show a bit of age (the author also recently retired). The Peter Dordal Creative Commons approach needs a bit more polishing. Just did a browse through and comparison, it goes quite deep (e.g. TCP Westwood). However, Tanebaum more applications and uses, including telnet to port 80, audio compression threshold of hearing and runlength encoding.
btw please put the slides online used to present this to students.. Every professor needs to make their own now.
I haven't read the linked book, so I can't comment on which is a better introduction.
I will say that having read the Tannenbaum book, it is a very thorough, bottom-up survey, and you will certainly know quite a lot about computer networking after reading it.
Just browsed through this, looks like a great book. Two suggestions:
1. Put your ToC on the home screen as well.
2. It'd be nice if you covered low-power IoT protocols like ZigBee, Thread, 6loWPAN, etc. Stuff based on the 802.15.4 stack
I've been looking for clear statement of IPv6 --- it's not sticking in my head yet and I get a lot of questions about schema design around IPv6 --- this looks like it might finally give a clear view.
The scope of networking, at an introductory level, is large. It's increasingly important too, as more and more systems become distributed, and rely on the network. For example, HDD's with ethernet interfaces!
(eg HTTP/1.1 is RFC 2616)