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A comparison and description of SIP and H.323

In selecting a protocol standard to be used for a corporate-wide VoIP implementation, what are the basic factors to consider in favor of or against H.323 versus SIP? My understanding is that SIP is a newer, less complex, more secure and fast emerging standard. Are there any compelling reasons to choose H.323?

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This question would be answered very differently depending on whether you are implementing an entirely new system or upgrading/supplementing an existing system.

But either way -- H.323 was the first protocol around. H.323 is actually an old multimedia protocol and not all of the stack is used for plain-jane voice transmissions. The problem with some of the H.323 systems, and even some of the new SIP systems, is interoperability between like-protocol systems and with each other -- for instance: H.323 → SIP. For the most part, vendors seem to be developing the newer equipment around SIP technology.

The main advantages to SIP are speed and the virtual session it works in. Some of the older protocols could route packets any way they wanted which caused problems for reassembly. We have overcome a lot in both worlds, but in future terms, my opinion is that SIP is gaining ground. That is not to say that if you have an H.323 system, or one that can interface to an existing PBX that uses H.323, that you will be wasting your money. Both are very mature solutions these days and any inadequacies in the protocols can now be assisted by a solid infrastructure of active components. SIP does reuse the HTTP ports, so it may be a bit easier to work with for novice end users.

This was first published in July 2006

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