draft-ietf-sip-199-06

Between Minneapolis and now, this document has become a lot more 
confusing, which I think bodes pretty ill for its hopes of being deployed.

For example, in section 5:

   If the received initial request contains an 199 option tag, the UAS
   SHOULD NOT send a 199 response for a dialog on which it intends to
   send a final response...

This reads as if sending a 199 response somehow absolves a UAS of 
sending a final response. Certainly this is not the intention of the 
draft (at least, not according to the text in section 7). Section 5 
needs to be re-phrased to indicate what is actually intended here.

In fact, on that topic, it's radically unclear to me how UASes fit into 
the entire scheme at all -- my understanding is that the 199 response is 
only sent by forking proxies. Given that a UAS is inherently an 
endpoint, the entirety of section 5 seems nonsensical. Either I'm 
missing something (in which case it needs some pretty explicit 
motivating text), or section 5 needs to be removed completely.

In section 6:

   When a forking proxy receives a non-2xx final response that it
   recognizes as terminating one or more early dialogs, if the proxy
   does not intend to forward the final response immediately (in
   accordance with rules for a forking proxy) and the UAC has indicated
   support for the 199 response code, the proxy SHOULD generate and send
   a 199 response upstream for each early dialog terminated on the
   downstream side by the non-2xx final response, except for any early
   dialog for which the proxy has previously received and forwarded a
   199 response.

What? On my best run at reading that, I made it to about the 81st word 
before the first predicate clause fell out of my head. If it's really as 
complicated as the structure of this sentence makes it seem, we need a 
flowchart or some other simplifying mechanism.


/a

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