[Standards-JIG] SIP jep?

CORVOYSIER David FTRD/DMI/REN david.corvoysier at francetelecom.com
Wed Mar 10 09:37:21 UTC 2004


> The TINS jep makes sense. it merges basics of SIP and SDPng, 
> although i 
> can imagine a pure SDPng-embedding approach as well. What i 
> like about 
> the JEP is the use SDPng instead of plain ASCII sdp.
> 

Yup, except that SDPng was supposed to be a mid-term replacement for
SDP, but for some reasons noone seems to care anymore. And as you will
see when you try to actually implement it, it's far from being complete.
For that reason, I think Joe Hildebrand is now considering supporting
SDP in TINS.

> But, TINS only works for one-to-one use cases and misses all those 
> functionalities used for administration of i.e. a conference.
> 
> It would be great to end up with a merged JEP, fitting both 
> one-to-one 
> and conference use cases.

We did it in my project (mixing TINS and MUC) but it was not a generic
solution because our conference bridge acts rather as a multiplexer than
as a mixer (so we had to advertize for every single RTP flow exchanged
in the conference).
Now, the only thing I can say about it is that it was a bit clumsy, with
a huge TINS packets overhead exchanged between conference members, thus
leading to clients implementing weird rules to drop most of them. I
could post a brief protocol description if you want (but perhaps using
the Jabber Wiki would be a better idea).   

> 
> [1] * http://www.iptel.org/sip/siptutorial.pdf - great 
> in-depth overview

Yes. It outlines in particular some of the main differences between SIP
and XMPP:
- Complex Client vs Simple Client,
- Peer-to-peer vs client-server,
- Stateless vs Statefull,
- UDP vs TCP.
Why these differences ? Mainly because SIP has been designed to do IP
Telephony (and as a consequence is based on a connectionless mode
transmission model), as XMPP has been designed to do near-realtime
notification (and as a consequence is based on a connection-oriented
mode transmission model).

What do I learn from that ?
1. VoIP could probably be done simpler in XMPP than in SIP (see if we
can get rid of these extra trying, ringing and acks, especially in
conference mode)
2. SIP is probably a better protocol than XMPP to interface with the
PSTN
3. XMPP is probably a better protocol than SIMPLE/UDP for exchanging
presence (actually most implementers of SIMPLE use a custom,
session-oriented version of SIMPLE over TCP) ... But that's a different
story !

David



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