Literature Review on Voice over Internet Protocol. by Lawal Babatunde from Tai Solarin University of Education

3467 Words Aug 27th, 2012 14 Pages
CHAPTER TWO
LITERATURE REVIEW ON VoIP
2.0 Background of VoIP
The first implementation of transmitting voice over the network was in 1973 through Network Voice Protocol (NVP) which was invented for Advanced Research Projects Agency Network (ARPANET). In 1990’s, there were a lot of VoIP applications that faced the problem of incompatibility due to fundamental differences between different vendors. Therefore, standards, specifications and interoperability guidelines were founded in May 1996 to standardize VoIP technology, which was a consortium of major equipment vendors and technology organizations including Cisco, Vocal Tec, 3Com, Microsoft, US Robotics and Net Speak. Nowadays, the VoIP forum is operating under the umbrella of international
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It provides two distinct and independent services; * Call Routing: This is the process in which a name or phone number is being resolved into an IP address and, * CAC (Call Admission Control): It grants permission for a call setup attempt by determining if the network has enough bandwidth for the call.
• IP network: This can be a private network, an Intranet or the public network such as the Internet.
• IP PBX: Internet Protocol private branch exchange (IP PBX) is a telephone switching system situated within the enterprise that switches calls between VoIP users on a local line while enabling users to share some certain number of external phone lines [2].
• Audio & Video Codecs: This is the compression and decompression of the transmitted signal. It is done by the digital signal processor (DSP) which has been embedded in the gateway through utilization of different codec algorithms such as G.729 (8/13kbit/s), G.728 (16kbit/s), and H.263 (for 64kbps and below) etc.
2.4 VoIP Protocols Stack
Around 1996 industry standards bodies started to ratify early protocol standards that specified how these various entities should communicate and interact with each other. Today there are many protocols that exist within the IPT arena not just for voice but also for video telephony [7]. The following are some of the key protocols and standard bodies: H.323, SIP, MEGACOP, MGCP etc.
2.4.1 H.323
It was developed by Study Group 16 of the ITU-T