Before understanding the difference between H.323 and SIP, there are a few things which need to be put in perspective. Both of them are communication protocols and both of them were introduced around the same time and it must have happened around two decades ago. However, there certainly are some differences between the two protocols as far as their scope is concerned. This certainly widens the differences between the two as far as some features and functions are concerned.
SIP is the acronym for Session Initiation Protocol and it is basically like any application layer protocol. It is used for VoIP. It also plays a big role in controlling communication sessions where multimedia is used. Apart from VoIP, there are other areas too where SIP can be used. Hence when it comes to instant messaging, online games, video conferencing, file transfer or even fax over IP, SIP has a varied and wide usage. Ever since it was introduced in 1996 it has grown quite rapidly and it has now been standardized by the famous IETF or the Internet Engineering Task Force.
It is also important to find out the right answer to the question as to what is H.323. H.323 is also another application layer protocol and it is used for the purposes of VoIP. It finds a number of uses as far as video conferencing and audio conferencing is concerned. It however, is not used for other purposes like file sharing, application sharing or online games. It is mainly focused in areas of multimedia conferencing. It is less complex when compared to SIP. Hence when talking about H.323 vs sip, this important point should always be kept in mind. It also came into the market in 1996 and it was approved by the International Telecommunication Union. It has now become the standard as far as multimedia conferencing over IP is concerned. Unlike SIP, H.323 does not work on a text based protocol. It is basically a binary protocol. In other words, messages are transmitted using binary codes. It therefore could be very useful for narrowband connections. It has a high level of interoperability. It also has other benefits and features such as NAT traversal. It is perfectly suited for video conferencing, load balancing and for multiple addressing schemes.
Now that we have a reasonably good understanding of both the protocols, we can try and move away from the subject what is H.323 vs SIP. Instead we will try and list out the major areas of differences between the two protocols. Here are a few major areas of differences between H.323 and SIP:
SIP is suitable when it comes to instant messaging, file sharing, and multimedia communicating and also for the purposes of online gaming. It is also the most sought after protocol for multimedia conferencing. On the other hand, when we talk about H.323 it basically takes care of only multimedia conferencing. Therefore when there is a discussion on sip vs h.323 video conferencing, it has been found that SIP always has a better acceptability and is better when compared to H.323.
There is no doubt that H.323 has a much smaller scope of operation when compared to SIP. However, in terms of complexities and ease of use, many end users feel that H.323 could be a better option. Hence, this is an interesting point to be borne in mind while trying to find the difference between H.323 and SIP.
When it comes to interoperability, it has been proven time and again that H.323 is always a better choice. In terms of reliability too, H.323 could be better. This is mainly because it has inbuilt features to take care of failure of network connections and devices. This kind of recovery mechanism is found wanting in SIP.
It also would be pertinent to mention that SIP is a text based protocol. The messages are encoded using ASCII characters. When it comes to H.323 binary codes are used for messaging. In terms of readability there is no doubt that SIP scores quite heavily over H.323. However, in terms of bandwidth usage H.323 is always better because it uses binary coding system.
SIP does not have the capability of doing load balancing which H.323 provides. Further the addressing method used in H.323 is quite flexible and not as rigid as it is in SIP. SIP is capable of reading only URI. H.323 on the other hand is capable of supporting various other addresses such as E.164 numbers, email, mobile UIM, transport address and so on.
Both H.323 and SIP have their own unique features and advantages. Hence reputed service providers who offer the best of unified communication platforms make it a point to use both H.323 and SIP. If you visit sites like ezTalks video conferencing, you will find out that they use both the above protocols. This is because such service providers are strong both in video conferencing as well as instant text messaging and other services.
When it comes to evaluating H.323 vs SIP, both have their own pros and cons. While there is no doubt that SIP is the best option for multimedia communication and conferencing, when it comes to lowband connections, H.323 could always be a much better choice, because it uses binary codes.