[updated 2010-01-24]
There are four new sections about SIP: Introduction to SIP, SIP Messages, SIP Call Flow, and SIP — Session Description Protocol.
The other pieces cover digitization of voice, audio codecs, codec latency vs. bandwidth optimization, audio jitter, the Real Time Protocol, introduction to H.323, description of H.323 call flow, and H.323 call signalling optimizations.