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Pros and cons of H.323 and SIP [2022]

February 20, 2019
Alina Krukova

Alina Krukova


H.323 has been holding a central position in the world of video conferencing for a long time, but recent market statistics show that SIP is becoming increasingly popular. It is already supported by many major manufacturers, including Polycom and Cisco solutions. But what is the difference between them?

In this review we will consider the features of SIP and its differences from H.323 in implementation of video conferencing software.


H.323 is recommended by the ITU Telecommunication Standardization Sector (ITU-T), which defines a set of standards for the transmission of packet multimedia data over networks. These guidelines establish the function of user terminals in networks with shared resources without a guarantee of the quality of service (QoS).

The H.323 standard does not necessarily require the use of an IP protocol, but most implementations are based on this protocol.

SIP (Session Initiation Protocol) is a transfer protocol that articulates a method for establishing and terminating user online sessions, including multimedia content exchange (video and audio conferencing, instant messaging, online games). This protocol was developed and standardized by the Internet Engineering Task Force (IETF) and by the IETF MMUSIC Working Group in RFC 3261. What is SIP for Video Conferencing?

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Along with H.323, SIP refers to a Voice over Internet Protocol (VoIP). Recently, the H.323 IP telephony has increasingly been replaced by the SIP protocol.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 trunking

SIP and H.323 Comparison

Both SIP and H.323 are quite dated. SIP and H.323 were both initiated in 1996. The last RFC 3261 for SIP was approved in 2002, and H.323v6 was approved in 2006. Although, SIP still gets new RFCs that expand its functionality – for example, SIMPLE and DualVideo.

H.323 works with bitfields that – in ideal conditions of implementation (not online) – rations network traffic when 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 a human-readable protocol, so SIP is simpler than H.323 when developing and supporting software. Google Trends information also confirms the popularity of this protocol.

Can SIP Completely Replace H.323?

Yes! Every H.323 extension already handles an SIP extension. 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 protocols.

Basically, H.323 and SIP are functionally equivalent when it comes to video conferencing solutions development.

Nevertheless, the transition to SIP is not a panacea for the problems of incompatibility between the solutions made by different producers (during functional fixes). This problem is inherent in any protocol on the video conferencing market, including H.323.

Manufacturers are not particularly interested in the compatibility of proprietary extensions. They cannot 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 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 simpler implementation as compared to H.323, SIP has become a popular VoIP service provided by many Internet telephony service providers. It connects PABXes to the public switched telephone network (PSTN) over the Internet. Nevertheless, H.323 is still a widespread protocol and it can barely be replaced by SIP in the near future. Thus, both SIP and H.323 have a strong position on the video conferencing market nowadays.

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