On Aug 21, 2008, at 9:38 PM, Dwight, Timothy M (Tim) wrote:
I'm sorry but it seems pretty far-fetched to try and blame SIP
shortcomings on "Bell-heads". Since when have they (we) been that
influential?
Since we were busy defining the SIP-PSTN interworking model back in
about 1998, and came up with the "early media" approach. Mots of us
working on SIP back then were bell-headed, even if we didn't think so
at the time. It's a matter of accepting the preconceived notions that
the telephone system was reasonable. I'm quite guilty of it myself.
Remember, Henry and I were sponsored by MCI back then, and our mission
was to make something that interopped with the PSTN and that the
business people could understand how to make a business out of.
A lot of the insanity here stems back to obtuseness on my part at the
interim meeting we held with the DCS cable team back in 1999, where we
came up with the idea of QOS preconditions negotiated with reliable-
provisionals rather than just using a two-stage invite. We should have
had a first INVITE for QoS, and a re-invite for media, and probably
would have if we hadn't had people thinking that the first 200 OK
meant "start billing", or if we had realized that gateway/precondition
forking really requires a B2BUA, not a proxy. But JDR and I really
believed in proxies back then . . .
See:
http://www.softarmor.com/sipwg/meets/interim-nov-1999/
My point to Henry was just that this "problem" is not specific to PSTN
gateways; so it wouldn't be appropriate to confine its solution to
such
a device. The need for media interaction prior to call completion
(which as Martin notes can be 2-way) arises from the intermediated
service model; which is as applicable to VoIP as to circuit switched
networks.
So we need to be able to differentiate the "intermediated" session
from the "non-intermediated" session. Insisting that the "session"
hasn't started (despite the fact that media is flowing) until some
arbitrary downstream event has occurred is just silly.
We've massed layers of complexity (early media, early session,
preconditions) onto the rather elegant base protocol just to
compensate for this misunderstanding. And frankly, it hasn't helped
things all that much -- implementations are now insanely difficult,
I'm confused by it, and AFAIK, nobody's stuff actually works 100% to
the specs. Why should we be happy with this? As (I think it was
Douglas Adams that said) it is easy to become blind to the essential
uselessness of these things due to the sense of wonder and fulfillment
one gets from getting them to do anything at all.
--
Dean
_______________________________________________
Sip mailing list https://www.ietf.org/mailman/listinfo/sip
This list is for NEW development of the core SIP Protocol
Use [EMAIL PROTECTED] for questions on current sip
Use [EMAIL PROTECTED] for new developments on the application of sip
