SIP understanding the Session Initiation Protocol 由 Johnston, Alan B.

How to save on phone bills the basics of internet telephony 由 Zayco, Herbert M.

Deploying Cisco voice over IP solutions

CISCO IP telephony 由 Lovell, David

Developing Cisco IP phone services 由 Deel, Darrick

Cisco CallManager fundamentals

Voice over IP systems and solutions

Available for University of the Philippines Diliman via IET Digital Library. Click here to access
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Computer telephony demystified putting CTI, media services, and IP telephony to work 由 Bayer, Michael (Michael Thomas)

The voiceXML handbook understanding and building the phone-enabled web 由 Edgar, Bob

Carrier grade voice over IP 由 Collins, Daniel