[Asterisk-Users] Need an explanation about different protocols

[Nicholas Bachmann]

Larry Keyes wrote:

>>>Is there someody who can explain me the meaning of these sentence.
>>>"Sip is philosophically horizontal and H.323/MGCP are vertical"
>>>      
>>>
>
>
>Hi, Ignace, 
>
>I think this refers to the fact that SIP is "lightweight", relative to
>H.323. My favorite reason, though, is that you can easily "see" what is
>going on with SIP, when doing debugging and tracing, (in Ethereal, say,)
>whereas H.323 seems to me to a lot more work. Also, the RFC's related to SIP
>are a model of clear explanation...there can be understood by mere mortals.
>Since the H.323 stuff is IETF
>
You mean H.323 is ITU... SIP is IETF.

>, you have to even go through hoops just to get
>to the standards documents. 
>
>
>Although H.323 and SIP provide many of the same services, they evolved from
>different protocol families. The roots of H.323 are in the circuit-switched
>world, while SIP evolved from newer standards such as HTTP and SMTP. In
>their comparison of the two protocols, Schulzrinne and Rosenberg (link
>below)	who were instrumental in developing SIP highlight several
>differences:   	
> 
>.	H.323 is considerably more complex than SIP. The specifications for
>H.323 run to 736 pages for the base definition. The base SIP specification
>is 128 pages. Part of the reason for the complexity is that H.323 remains
>backward compatible with early versions of the specification, while SIP is
>designed to jettison older or obsolete features when new versions of the SIP
>specification are issued. 
>
>.	SIP has specific support for certain call control features common in
>business telephone systems, including call transfer, hold, and park. 
>
>.	SIP is extensible. In particular it allows for the addition of media
>codecs via SDP. Codecs are limited in H.323 to ITU approved codecs, of which
>several are proprietary and require licensing.  
>  
>
The other important difference is that H.323 is not a telephony protocol 
but a general media protocol.  SIP is designed more specifically for 
telephony, while H.323 was designed to carry video over ISDN and has 
evolved into a general media signaling & transport protocol.  H.323 
integrates the transport as part of the protocol, while SIP disjoins the 
two and only negotiates (but does not carry) the RTP session; this seems 
backwards for ITU/IETF standards.  SS7 (and ITU-adopted standard) is 
like SIP, with a separation of signaling and media transport, while 
H.323 is more like IETF standards that would keep the two bundled.

Nick