VoIP telephony
for all of those that are starting to make first steps with VoIP, or believe know everything - i’d like to highly recommend my fathers book that was just published via BTC publishing house. it covers both H.323 and SIP protocols, along with all auxiliary topics - like integration, and signaling over middleboxes like packet filters and stateful firewalls: Telefonia VoIP. Multimedialne sieci IP, Marek Bromirski, ISBN: 83-60233-07-1