SIP: Understanding the Session Initiation Protocol, Second Edition
Alan B. Johnston is a distinguished technical member at MCI and an adjunct assistant professor of electrical engineering at Washington University in St. Louis. He holds a B.E.(Hons) in electrical and electronic engineering from the University of Melbourne, Australia and a Ph.D. in electrical engineering from Lehigh University.  He is a co-author of the new SIP specification RFC 3261 and several other SIP-related RFCs.