How to do Presence Aggregation, when there are more than one devices with the same SIP URI. I couldn't find any useful, for deciding, what to show to the others, if more clients has the same SIP URI and everyone of them has different presence status.
Should I show the weakest presence status (like available) as the aggregated presence, or should I show the strongest (like busy), or sort by priority? Or for example create a management web page, where users can change the priority or the policy? Or or or...
And if I got an aggregated presence status, which device should I ring in a click-to-call system? All availables, last changed to available, most prior available, most prior weakes etc. Is there an RFC or a standard for this?
I found 2 solutions for multiple devices with same SIP URIs:
1.) using SIP-Etag and SIP-If-Match headers in SIP messages
2.) using more tuple tags with different id, per PIDF XML document, like shown in RFC3863's examples. And if using PIDF with multiple tuple tags, can XLite decide the aggregated presence?
I can make somekind of an aggregated presence using 1.) and/or 2.), but I don't know will it be compatible with SIP clients.