SIP and H.323
SIP is, more or less, equivalent to the Q.931 and H.225 components of H.323. These protocols are responsible for call setup and call signalling. Consequently, both SIP and H.323 can be used as signalling protocols in IP networks.
A comparison:
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SIP |
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H.323 |
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PHILOSOPHY | ||
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"New World" - a relative of Internet protocols - simple, open and horizontal |
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"Old World" - complex, deterministic and vertical |
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IETF |
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ITU |
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Carrier-class solution addressing the wide area |
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Borne of the LAN - focusing on enterprise conferencing priorities |
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CHARACTERISTICS | ||
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A simple toolkit upon which smart clients and applications can be built. It re-uses Net elements (URLs, MIME and DNS) |
H.323 specifies everything including the codec for the media and how you carry the packets in RTP | |
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Leaves issues of reliability to underlying network |
Assumes fallibility of network - an unnecessary overhead | |
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SIP messages are formatted as text. (Text processing lies behind the web and email) |
Binary format doesn't sit well with the internet - this adds complexity | |
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SIP allows for standards-based extensions to perform specific functions. |
Extensions are added by using vendor-specific non-standard elements | |
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Hierarchical URL style addressing scheme that scales |
Addressing scheme doesn't scale well | |
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Minimal delay - simplified signalling scheme makes it faster |
Possibilities of delay (up to 7 or 8 seconds!) | |
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Slim and Pragmatic |
The suite is too cumbersome to deploy easily | |
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SERVICES | ||
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Standard IP Centrex services |
Standard IP Centrex services | |
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Ability to 'fork' calls |
Not possible in the existing standard | |
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User profiling |
- | |
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'Unified messaging' |
- | |
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Presence management |
- | |
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Unique ability to mix media (e.g. IVR) |
Cannot mix media within a session | |
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URLs can be embedded in web browsers and email tools |
H.323 has no URL format | |
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Works smoothly with media gateway controllers controlling multiple gateways - crucial in a multi-operator environment |
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"Shoehorn" interworking with SS7 is problematic - H.323 has trouble connecting calls to and from PSTN endpoints |
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Seamless interaction with other media - services are only limited by the developers imagination |
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Services are nailed-down and constricted - voice only ceiling |
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STATUS | ||
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Industry endorsed |
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Popularity due to the fact that it was the first set of agreed-upon standards |
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Many vendors developing products |
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The majority of existing IP telephony products rely on the H.323 suite |