RE: Network Reliability Engineering

Check out this book:

"High-Availability Network Fundamentals"
Cisco Press
ISBN 1-58713-017-3

Despite its Cisco Press origin, the book is 99% vendor-neutral and applies
to any equipment. It helps you calculate MTBF-based availability of entire
network paths, factoring in various types of redundancy. You're on your own
collecting actual MTBF data from vendors, but this book may help you put it
together into something sensible.