Difference between SIP and H.323

Question

What is the difference between SIP and H.323, I mean what are the salient features between them? To start with ,

1. SIP is text based while H.323 is binary.
2. SIP is by IETF while H.323 by ITU.
3. SIP is basically request-response based like HTTP, while H.323 is not like that(is based on session).

What were the motivating factors which led to SIP's development?

How is one advantageous from other?

Answer 1

Both are relatively the same on the technical side - there are differences, but you can use both to run a VoIP service. They both started at about the same time to develop, with H.323 gaining more traction in the beginning and SIP taking center stage in the past several years.

The main advantages of H.323 is the level of interoperability it provides in existing video conferencing equipment - something that can't be matched by SIP today (yet), and the fact that it holds most of the deployments of video conferencing in enterprises.

The main advantages of SIP is a larger ecosystem and dominance in voice calls and PBX systems. And the fact that it is viewed as the future of VoIP (at least to some extent).

I also wrote about it in the past in my company's blog: http://blog.radvision.com/voipsurvivor/2011/03/24/ask-an-expert-which-protocol-do-you-prefer-sip-or-h323/

Answer 2

H323 is familiar to telecommunications people. It reuses many concepts, terms and protocols from ISDN. SIP is familiar to internet people. It's a lot like HTTP, re-uses all the response codes and standards like URI-s, uses the DNS well, etc.