Voice over IP, VoIP protocols

- an summary or tutorial about the protocols used with Voice over IP, VoIP networks and systems.

Voice over Internet Protocol, VoIP tutorial includes:

    •  VoIP technology tutorial
    •  VoIP protocols
    •  VoIP testing & monitoring

Voice over Internet Protocol, VoIP, has seen an enormous level of growth in recent years and it is likely that this with continue, or even increase in the foreseeable future. The reason for this level of growth in the use of VoIP results from the cost savings it provides, the increase in flexibility, and the fact that the same network can be used for voice and data.

Although the first VoIP networks started to appear as early as 1995, and these VoIP networks used proprietary protocols to enable the IP data to be exchanged. However with the rapid growth, and the need for VoIP traffic to be routed globally, the need for established standards to control the exchange of data arose. In view of the fact that there were a number of different requirements, several standards were developed and are in use today.

Although it may be surprising at first sight that there are several VoIP protocols, these different protocols are required for different reasons and they have been deployed in many systems. Even though the concept of one unified VoIP protocol or set of protocols would seem ideal, this is unlikely to happen in view of the extent to which the different protocols have already been deployed. Additionally different companies and organizations will use the VoIP protocol which best meets their requirements and accordingly, they will want to maintain what they are currently using. This will mean that there will be resistance to any change, especially as interfaces have been devised to enable interoperability.

VoIP protocols overview

Although working together, there are a number of different organizations and bodies that are mentioned when referring to VoIP protocols:

• IETF     This is the Internet Engineering Task Force. It is a community of engineers that defines some of the prominent standards used on the Internet (including VoIP protocols) and seeks to spread understanding of how they work.
• ITU     the International Telecommunication Union. This is an international organization within the United Nations System used by where governments and private sector companies to coordinate and standardize telecommunications networks, services and standards on a global basis.

In addition to the organizations involved, there is also a variety of different VoIP protocols and standards.

• H.248     H.248 is an ITU Recommendation that defines "Gateway Control Protocol" and it is also referred to as IETF RFC 2885 (Megaco). It defines a centralized architecture for creating multimedia applications and it extends MGCP. H.248 is the result of a joint collaboration between the ITU and the IETF and it is another VoIP protocol.
• H.323     This is ITU Recommendation that defines "packet-based multimedia communications systems." H.323 defines a distributed architecture for multimedia applications, and it is thus a VoIP protocol.
• Megaco     This is also known as IETF RFC 2885 and ITU Recommendation H.248. H.248 defines a centralized architecture for creating multimedia applications.
• Media Gateway Control Protocol (MGCP)     This is also known as IETF RFC 2705. It defines a centralized architecture for creating multimedia applications, and it is therefore a VoIP protocol.
• Real-Time Transport Protocol (RTP)     This VoIP protocol is defined under IETF RFC 1889 and it details a transport protocol for real-time applications. RTP provides the transport mechanism to carry the audio/media portion of VoIP communication and is used for all VoIP communications.
• Session Initiation Protocol (SIP)     This is also known as IETF RFC 2543 and it defines a distributed architecture for creating multimedia applications.

Centralised and distributed architectures

One of the advantages of VoIP is that it does not legislate for the architecture of the network that carries the data. Early telecommunications networks used a centralised structure where all the intelligence was contained at the switching station or exchange. With the advent of packet technology, the routing and intelligence can be distributed to where it is most convenient to locate it. This may be by having a distributed architecture, or a centralised one.While both architectures can be employed with VoIP, the type of architecture does have an impact on the optimum VoIP protocols to use. This is one of the reasons why a number of VoIP protocols are used, and will remain to be used.

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