LITERATURE REVIEW ON VoIP
2.0Background 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 Multimedia Teleconferencing Consortium (IMTC). However in 2003, there was a public hearing, with the purpose of gathering information on advancements, innovations, and regulatory issues related to VoIP services which was announced by the Federal Communications Commission (FCC) as a VoIP forum . 2.1What is VoIP?
Voice over Internet Protocol (VoIP) is the assembly of voice into IP data which can be transmitted over an IP network to an addressable (IP address) destination. VoIP calls are packet switched while analog calls are circuit switched. Packet switched data are data that can be routed through different routes on a network to reach a destination while circuit Switched is a connection where a physical path is dedicated between two end points .  Describe VoIP as the transport of voice over IP based data networks like WAN, MAN and LAN. In other words, it is a method for taking analog audio signals and turning them into digital data organized into packets that can be transmitted over the Internet.  Defines VoIP as the transmission of voice communications as datagram packets over IP networks. VoIP is a term used in IP telephony for a set of facilities for managing the delivery of voice information using the Internet Protocol (IP).Voice over IP is the technology of digitizing sound, compressing it, breaking it up into data packets, and sending it over an IP (internet protocol) network where it is reassembled, decompressed, and converted back into an analog wave form. The transmission of sound over a packet switched network in this manner is an order of magnitude more efficient than the transmission of sound over a circuit switched network . 2.2Basic Components of VoIP
According to  there are variety of equipment involved in executing VoIP, in general, though, the term Voice over IP is associated with equipment that provides the ability to dial telephone numbers and communicate with parties on the other end of a connection who have either another VoIP system or a traditional analog telephone. Demand for VoIP services has resulted in a broad array of products. The basic components of VoIP include gateway, IP phone, server, gatekeepers, Call Agents, multipoint control unit e.t.c. A simple diagram of how they are being interconnected is shown below.
Figure 2: Basic components of VoIP 
• Gateway: Interconnects or allows communications among devices that are not accessible within the IP network, e.g. call from or to analog phones. It converts the signals from the traditional telephony interfaces (POTS, T1/E1, and ISDN) to VoIP. Its main function includes voice packetization, compression/decompression, call routing and control signaling. • IP Phone: This can be divided into two, hard phones and soft phones. A hard phone has a terminal that has native VoIP support and can connect directly to an IP network. A soft phone on the other hand runs on software application on computers. They can also be installed on mobile devices that have the same base features as VoIP phones . • Server: Provides management and administrative functions to support the routing of calls across the network. • Gatekeepers: Is a centrally controlled entity that performs managemdr5ent...