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Re: [Sip] INFO considered harmful



At 12:48 AM 12/31/2002 -0500, Jonathan Rosenberg wrote:
Orit Levin wrote:
The big huge difference I have been trying to point out is that EVENTS
DEFINES SEMANTICS, whereas INFO doesnt.
MIME provides semantics and syntax that are independent of the type.
SIP events provides semantics and syntax that are independent of the
package.
INFO provides nothing.
INFO provides "minimal" but very important semantics: asynchronous data
reliably follows the established SIP path.
Huh?

Every new SIP method is reliable, it inherits the SIP transaction state machine for non-invite. Follows the established path? Every in-dialog method would have this property, it is method independent. Asynchronous? You can send any method at any time.

Thus, nothing you have pointed out above is different between INFO and any other new method we might introduce.
I think the key point is that there is a difference between transport protocol semantic and application semantic. The transport protocol semantic expressed in INFO is "Here is some data that will be used by the application. It is not important to the transport protocol, except that the transport protocol is expected to deliver it reliably". INFO says NOTHING about the APPLICATION level semantic -- that's up to what goes IN the INFO payloads. The question is -- do we try to rigidly define application-level semantics here? Do we define that there ARE no such applications possible? Or do we design a framework by which application-level semantics can be expressed outside of the protocol definition?

And as for "Just add another method to your SIP stack". Let's say I have a mobile phone and the SIP stack is burned into ROM and exposes only a simplistic transactional API. This is only likely to happen, oh, 100 million times or so over the next two years . . . Now, just exactly how is my BREW or JTME application going to go about extending the SIP stack to support another method? Will the evil wireless operator networks even pass another method? Neither is happening anytime soon, I think . . .

--
Dean


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