There's no one book that you could read... I've been a network engineer/developer/administrator for over a decade, got some pretty high level qualifications from a number of hardware manufacturers and I'm still learning new stuff every day.
Anyone who says they're an expert in all fields of networking is telling fibs.
Best thing to do is start with some basic training, e.g. Cisco CCNA. Learn Subnetting, The 7 layer Model, get some routers and switches to play with (it's amazing how well you can simulate a large WAN with just a decent layer 3 switch, a few Linux boxes and GNS3.)
It's also only through experience that you learn which carriers are good, and which ones to avoid, for example BT, Verizon, Level3, XO all are great and want to do well by their customers. Avoid DTAG (Deutsche Telekom / T-systems) And Orange (France Telecom) like the plague... They seemingly deliberately oversubscribe their peering links meaning that you experience unexplained packet loss that they just blame on you - this is a plot to get you to purchase high bandwidth links direct from them in other countries to avoid your traffic going through their peer links.
And please don't get me stated on Airtel in India. I mean none of the carriers there are particularly good, but these guys happily drop your traffic left right and centre, do nothing about it except to say they can't see any problem, then immediately close the ticket when the transient event had passed instead of getting us a Reason For Outage, or providing any info on what has happened.
One of the things we're currently working on is intelligent load sharing (NOT load balancing) across multiple unreliable links... e.g. take a few 4g cards, a couple of DSLs and maybe an enterprise circuit or two and use them all together like one big virtual link back to your NAP. Works great, but hellishly complicated.