[Stox] Review for stox-7248bis-02

["Isomaki Markus (Nokia-TECH/Espoo)" <[e-mail]>]

Hi Peter, all,

I did a review for the 7248bis-02 draft and unless I'm missing something, there seem to be still a few confusing things  about the message flow diagrams and the terminology about SIP-to-XMPP and XMPP-to-SIP gateways. (The reason to go for 7248bis was indeed to fix the message flows so they are really the main part of it.)

A minor issue:
- In the diagrams abbreviations S2X GW and X2S GW are used. While most readers can guess what they mean, it would be good to open them explicitly, perhaps in Section 3, Terminology. 

Bigger issues:
- The diagram in Section 4.2.1: It looks weird that the SIP server already generates the (F7) 200 OK message, while the (F8) NOTIFY does not get any response. Shouldn't it be that the 200 OK is generated by the "X2S GW" and then passed forward by the SIP server? 
- The text in 4.2.1 is somewhat confusing as well, as it first (understandably) talks about XMPP-to-SIP GW as shown in the diagram ("S2X"), but then (after Example 2) talks a few times about SIP-to-XMPP GW as well. I believe this is coming from 7248, which does have the two GWs as explicit entities in the diagram. But in 7248bis they are merged, and the current text makes the reader wonder if SIP-to-XMPP GW refers to the same entity as XMPP-to-SIP GW as shown, or whether there is another implicit/invisible GW function included. 
- The same issue occurs in 4.3.1 in reverse. There, the diagram only has "S2X GW" but the text contains both SIP-to-XMPP and XMPP-to-SIP. 

So we have gotten rid of the double gateways of 7248 in the diagrams, but they still somehow loom in the text and terminology. I think there are a couple of options to clarify this: Either always refer to the gateway as XMPP-to-SIP (X2S) in those sections that are about XMPP-to-SIP, and vice versa. Or, make the gateway direction neutral and just call it something like SIP-XMPP GW everywhere. Or, explain some more about the directions.

Sorry to be late about this, but I guess this is the last chance and we should definitely get the gateways right this time :-O

Markus