VoIP Standards And Internet Protocols
Just like the name suggests, voice over IP (VoIP) uses the Internet Protocol (IP) to send/receive voice as data packets over an IP network. By using a VoIP protocol, voice communications can be achieved on any IP network regardless of the fact that it is Internet, Intranets or Local Area Networks (LAN). In a VoIP enabled network, the voice signal is first digitized, compressed and converted to IP packets and then sent over the IP network. A VoIP signaling protocol is used to set up and tear down calls, carry information required to locate users and negotiate capabilities (such as
bandwidth. A known advantage of VoIP is the very low
cost of the phone call. But others, such as the integration of voice, data and video on one network as well as new services available on the converged network and simplified management of end user terminals, are just as important.
Mainly there are a few important VoIP protocol stacks which have derived from various standard bodies and vendors, namely H.323,
SIP, MEGACO and MGCP.
H.323
H.323 is the ITU-T standard. It was originally created for multimedia conferencing on LANs, but due to its high implementation the company decided to expand its horizon, thus, H.323 was later extended to cover Voice over IP. The Voice over IP standard has the ability to handle both point to point communications and multipoint conferences. In fact, H.323 defines four logical
components:
Terminals,
Gateways,
Gatekeepers and Multipoint Control Units (MCUs). Terminals, gateways and MCUs are commonly known as endpoints.
Session Initiation Protocol (SIP)
Session Initiation Protocol (SIP) is the IETF standard for establishing a
Voice over IPconnection. SIP is an application layer control protocol for creating, modifying and terminating sessions with one or more participants (it can be used for conferences as well). As to what regards its structure, this Voice over IP standard is similar to that of HTTP (a client-server protocol). Data requests are generated by the client and sent to the server. The server processes the requests and then sends back data packets containing a response to the client. A request and the responses for that request make a transaction.
Media Gateway Control Protocol (MGCP)
Media Gateway Control Protocol (MGCP) is a
Cisco and Telcordia proprietary
Voice over IP protocol that sustains communication between call control elements (Call Agents or Media Gateway) and telephony gateways. MGCP is a control protocol (just like SIP), allowing a central operator (generally, a server) to monitor and analyze events in IP phones and gateways and instruct them if necessary to send media to specific addresses. In the MGCP structure, the call control intelligence is located outside the gateways and is handled by the call control elements (the Call Agent). Also the call control elements (Call Agents) will synchronize with each other so that they will be able to send commands to the gateways under their control.
New VoIP standard
United Nations-affiliated telecommunications group has approved a new standard ...
