H.323 and SIP - VoIP Protocols Comparison

H.323 and SIP - VoIP Protocols Comparison
By: Andrey J. Kanevsky

In recent years, the internet technology has grown in leaps and bounds. One major product of this technology is the Voice over Internet protocol (VoIP). VoIP is a technology that enables better audio and visual communication from our home computers. Through this, we can communicate easily from wherever we are and it is cheaper than the conventional telephone services. The upfront investment required for this is also very less. VOIP is still in its early stages and it has to undergo more development before it can substitute the regular telephone.

The two types of VOIP protocols used today are:
1. H.323
2. SIP

H.323
The more commonly used protocol.
This was created by the International Telecommunication Union for the purposes of multimedia communication over IP networks.
• It provides provisions for videoconferencing, data sharing, and audio transmission (VoIP)
• It merges the IETF and ITU-T protocols to form a unified system
• Though it is still in the early phases, it has been successful to some extent in matching the clarity and speed provided by PSTN networks

USES OF H.323
• Videoconferencing
• Voice over IP

It is been designed with a number of means to recover connection failures. It has a number of alternate gatekeepers and endpoints which help to pinpoint the source of connection failure.
H.323 performs a lot of functions like:
• Message encoding
• Load balancing
• Call signaling
• Address resolution

In the message encoding process, messages are encoded by H.323 into binary format and are decoded by using decoding machines. This binary format is suitable for both broadband and narrow band connections.

In load balancing process, endpoints report their total and available capacity to H.323, which distributes the calls equally across these gateways.

In call signaling process, the H.323 gatekeeper provides address resolution through RAS message exchange and routes the call signaling traffic.

In address resolution, the H.323 gatekeeper may use any number of protocols to discover the destination address of the callee, including LRQs to other gatekeepers, Annex G/H.225.0, TRIP, ENUM, and/or DNS.

New features are added to H.323 keeping in mind that backward compatibility is preserved.

SIP
The second type of VOIP protocol used is the SIP.
• SIP was designed to setup a “session” between two points
• It has no support for multimedia conferencing
• SIP has large number of problems and has been deployed successfully only in PSTN gateways
• Detection can only be done through timer expiration and re-establishment takes long periods

Like H.323, SIP also performs the functions of message encoding, load balancing, and address resolution.

In message coding, the message are coded into ASCII format and are too long. This makes it suitable only for broadband networks. Efforts are being made to encode SIP in binary format.

In the load balancing stage, SIP follows “trial and error” methods across different proxy servers available. If there is a timeout, then it shifts to another server.

In the process of address resolution, SIP has no address-resolution protocol.

DISADVANTAGES OF SIP
• The main disadvantage of SIP is that it has no means to detect network failures
• The processing requirements placed on the SIP proxy are higher than with H.323, which requires more message exchanges to pinpoint the position
• Another main problem with SIP is that all the new versions are not backward compatible, which causes operational problems

Hence we see that in many ways, H.323 protocol is vertical and complex, but actually SIP is horizontal and more open. So SIP protocol pretends to be more promising, despite of disadvantages.

Article Source: http://www.article-voip.com