Daniel Collins has done a great job of explaining the latest VoIP technology. He uses a lot of call flow diagrams, which I find particularly useful in understanding how the various protocols work. In addition, his writing style is very clear, such that he makes it easy to understand what he is talking about. Not only does he address the most recent developments in the technology (eg. SIP, MGCP, MEGACO), he also does a good job of explaining how these technologies can fit with what is already in place (eg. H323 as well as traditional networks). In this regard, the chapter concerning SS7 is useful, although some focus on TALI as well as Sigtran would have been beneficial. - Overall, a good book that I would recommend to anyone who wants to understand VoIP.