The Bliss IE draft for Shared Appearances (http://tools.ietf.org/id/draft-ietf-bliss-shared-appearances-03.txt) requires proxies to add an Alert-Info header into INVITEs sent to shared users (5.4):
"The Appearance Agent MUST be able to communicate with the forking proxy to learn about incoming calls and also to pass the appearance number to the proxy to insert in the Alert-Info header field." Can anyone comment on this requirement and how we might implement it? It seems to me that it would force the SAA and the Proxy to be co-resident, and an authplugin in the Proxy would have to communicate with the SAA process on every outgoing INVITE. In http://tools.ietf.org/id/draft-anil-sipping-bla-02.txt (which is what SAA currently implements), this header is mentioned but is not marked as Required, and in the current implementation of SAA, we do not insert this header. The Polycom sets select an appearance-number (called x-line-id in this version of the draft) and duly report it to the SAA without the Proxy knowing or caring. The purpose of this field is to attempt to force all UAs to present the call on the same "line" key, as a shared line may have several appearances on a UA. Then users can communicate to each other to say, for example, "pick up the call on line 2". I personally have a lot of trouble with this idea, since "line 2" doesn't map to anything concrete - it does not mean a physical button labelled "line 2", it means the second appearance of this particular registration; and it might be in different places on different sets; it might even share a line key if a set has only one key for the appearance group... I am not entirely convinced that the Proxy needs to be involved, or should be involved, in telling UAs where to present a call. Any other opinions out there? Thanks, Carolyn
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