H.323 had held a leading position in video conferencing for a long time. But the latest market statistics show that SIP becomes increasingly popular and is already supported by many major manufacturers, including Polycom and Cisco solutions.
In this review we will consider the features of SIP and its differences from H.323 in implementation of video conferencing software.
We will try to answer the main question – “What kind of protocol is more promising for organizing video conferencing over the Internet?”
H.323 is recommended by ITU Telecommunication Standardization Sector (ITU-T), which defines a set of standards for the transmission of packet multimedia data over networks. This guidelines establish the functioning of the user terminals in networks with shared resource without a guarantee of the quality of service (QoS).
The H.323 standard does not necessarily require the use of IP protocol, but most implementations are based on this protocol.
SIP (Session Initiation Protocol) is a transfer protocol, which describes a method for establishing and terminating user online session, including multimedia content exchange (video and audio conferencing, instant messaging, online games). This protocol has been developed and standardized by Internet Engineering Task Force (IETF) and by IETF MMUSIC Working Group in RFC 3261.
Along with H.323, SIP refers to Voice over Internet Protocol (VoIP). Recently, the H.323 IP telephony has increasingly been replaced by SIP protocol.
According to the report of www.infonetics.com, the global VoIP services market, including residential and business VoIP services, gained $63 billion in 2012, which is 9% higher than in 2011.
As predicted by Infonetics, VoIP market as a whole will rise up to $82.7 million in 2017.
SIP and H.323 Comparison
Both SIP and H.323 are quite dated, though. SIP and H.323 were both initiated in 1996. Last RFC 3261 for SIP approved in 2002, H.323v6 approved in 2006. Although, SIP still gets new RFCs that expand its functionality. For example, SIMPLE and DualVideo.
H.323 works at bitfields that in ideal conditions of implementation (not online) saves network traffic as compared to SIP. However, in modern conditions of the rapid spread of broadband Internet, this advantage does not look so important.
SIP is an application layer protocol for the OSI model.
Principles underlying SIP protocol:
- Simplicity: includes only six methods.
- The independence of the transport layer. It may use UDP, TCP, ATM, etc.
- Personal mobility of users. Users can move within a network without any restrictions due to the assignment of a unique identifier for each user.
- Network scalability. Network structure based on the SIP protocol makes it easy to expand and increase its number of components.
- Extensibility. The protocol is characterized by the possibility to supplement it with new features when new services appear.
- Integration into the existing Internet protocol stack. SIP is part of a global multimedia architecture developed by the IETF. The architecture also includes RSVP, RTP, RTSP, SDP protocols.
- Interaction with other signaling protocols. SIP protocol can be used in conjunction with other IP telephony protocols, PSTN protocols, and to communicate with the smart grid.
SIP is human readable protocol, so SIP is simpler than H.323 in developing and supporting software. Google Trends information also confirms the popularity of this protocol.
Can SIP Completely Replace H.323?
Yes, and even more than that! Every H.323 extension has an SIP extension to deal with. Session Initiation Protocol is more flexible in this respect (for example, when adding a new field, if someone does not understand it, it is simply ignored). Major hardware solutions support both.
Basically, H.323 and SIP are functionally equivalent when it comes to video conferencing solutions developing.
Nevertheless, the transition to SIP is not a panacea for the problems of incompatibility between the solutions made be different producers (during functional fixes). This problem is inherent in any protocol on video conferencing market, including H.323.
Manufacturers are not particularly interested in the compatibility of proprietary extensions. They can not afford to be completely incompatible, but try to limit the maximum compatibility. A good example is Microsoft Lync: SIP connections are limited to CIF at much higher theoretical possibilities.
One of the most important points is to provide security of the transmitted data. One of the sections of RFC 3261 is dedicated to the security concerns of SIP. Traffic signal encryption via TLS is possible at the transport layer. In addition, a standard SIPS, imposing additional agreements on the safe transfer of data through SIP. For multimedia content SRTP encryption protocol is used.
Let’s Sum Up
Due to a more simple implementation, compared to H.323, SIP communication has become a popular VoIP service provided by many Internet telephony service providers. It connects the PABX to the public switched telephone network (PSTN) via the Internet.