VoIP protocols
- an overview or tutorial of the different VoIP protocols that are used to
enable voice communication over IP networks.
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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