*[Bits, Signals, and Packets: An Introduction to Digital Communications and Networks](http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-02-introduction-to-eecs-ii-digital-communication-systems-fall-2012/readings/)
*[Code Connected vol.1](http://hintjens.wdfiles.com/local--files/main%3Afiles/cc1pe.pdf)(PDF)(book on ZeroMQ)
*[Computer Networking : Principles, Protocols and Practice](http://cnp3book.info.ucl.ac.be/1st/html/index.html)(HTML, ePub, PDF, Kindle)
*[Computer Networks: A Systems Approach](https://book.systemsapproach.org) - Larry Peterson and Bruce Davie (HTML, epub, mobi, PDF)