VoIP Voice and Fax Signal Processing

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VoIP OVERVIEW AND INFRASTRUCTURE

This chapter presents an overview of VoIP and its supporting infrastructure. VoIP services operate on an Internet protocol (IP) to transmit compressed voice samples as frames and messages as a group of bytes over an IP data network. VoIP can be achieved on any data network that uses IP-based networks like the Internet, intranets, and local area networks (LANs). In residential applications, voice from front-end telephone lines is converted into a suitable signal level, digitized, compressed as voice payload, and sent as IP packets. Signaling protocols are used to set up and tear down calls. Signaling packets carry information required to locate users, negotiate capabilities, create call establishing, and set up call features. Fax calls also work similarly to voice calls. The payloads of packets are the fax-compressed bytes. Initially, a fax call operates like a voice call, on fax tone detection, switches to fax, and continues with fax messages. The popular VoIP signaling protocols are the Session Initiation Protocol (SIP), Media Gateway Control Protocol (MGCP), and ITU-T-H.323 (2006). Many initial deployments have used H.323. Other standards like MGCP, ITU-T-H.248 (2005)/Megaco, and SIP evolved after the release of H.323. SIP has been mainly adapted for recent deployments. Major extensions in VoIP signaling were happening on SIP signaling during writing of this book. SIP is relatively simple and is favored by many engineers and service providers. ...