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www.cisco.com/en/US/tech/tk652/tk701/technologies_white_paper09186a0080092947.shtml

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Posted by crouse

SIP Pros

* SIP works independently of the type of session, or the media used, giving it flexibility.
* It is an open standard, allowing multivendor support and integration. Applications can be written to customize SIP uses.
* SIP messages are clear text, making troubleshooting easier.
* SIP can accommodate multiple users with differing capabilities. For instance, in a conference that has some users with video capability and some only with audio capability, the video users can see each other. They do not have to drop down to audio only, as with other protocols.

SIP Cons

* Processing text messages puts a higher load on gateways. The router must translate that text into a language that the router can understand. Code for this must be in the Cisco IOS.
* SIP is a fairly new protocol, so fewer people understand it than the older protocols. Be sure you have trained support personnel if you intend to implement SIP within your network.
* When you are using both SIP and SCCP phones on the same network, you must convert between in-band and out-of-band DTMF tones.
* SIP features are still being developed, and many vendors have proprietary implementations of the protocol.

H.323
H.323 is an International Telecommunications Union (ITU) standard which was created in 1996
and updated in 1998. It provides a foundation for audio, video, and data communications across a
packet-based network infrastructure. H.323 provides standards for voice-encoding, simple
bandwidth management, admission control, address translation, call control and management,
and links to external networks. The voice over IP community has adopted H.323 standards in an
effort to foster the interoperability of equipment from multiple vendors. H.323 provides a solid
foundation for building multimedia networks and has become critical for developing large-scale
VoIP networks.

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Posted by sagitraz

A comparison between SIP and H.323 is shown below, illustrating the advantages and disadvantages of the two systems:
H.323:
- Robust but consumes more call set up time
- Requires about twelve packets for call-setup
- Provides floor control within a session
- Has more elaborate capability exchange (H.245)
- Provides a multipoint controller for conferences
- Requires both TCP and UDP during the call-setup
- Implementation is complex and time-taking

SIP :
- Simple, Scalable and Extensible
- Requires about four packets for call-setup
- Cannot provide
- Minimal capability exchange, enough for IP telephony
- Not required for SIP multicast conferences
- Basically runs on UDP. Reliability achieved through retransmissions. Supports TCP also, if UDP is not supported
- Easy to implement

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Posted by yogendra