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The server is required to support incoming subscriptions to three types of presence document formats; however, the order of preference that follows is to be used if the subscriber indicates support for all three:
Enhanced presence (Content-Type: application/msrtc-event-categories+xml)
MSRTC (Content-Type: text/xml+msrtc.pidf)
PIDF (Content-Type: application/pidf+xml)
That is, for every incoming dialog-creating SUBSCRIBE request, the server searches the Accept header for these presence document formats in this order. When a match is found, the SUBSCRIBE request is terminated using the matched format. Subsequent SUBSCRIBE refresh requests indicate support for the same presence document formats.
The server supports the generation of PIDF documents for SIP subscription. The server does not support the PIDF and Rich Presence Extensions to the Presence Information Data Format (RPID), as described in [RFC4480], data formats in their entirety, but only the subset required for interoperability with federated presence clouds.
The PIDF document contains a single PIDF tuple that contains attributes from basic PIDF, as well as the following attributes from the RPID and Contact Information in PIDF (CIPID), as described in [RFC4482], extensions:
Available/activity: Activity is an RPID extension that allows SIP protocol clients that provide presence information, called presentities, to attach information about what the presentity is actually doing.
display-name: A CIPID attribute that provides the friendly name of the user.
The server passes these attributes in a single PIDF tuple.
The PIDF document can also contain a list of linked identities of the user. The linked identities let the consumers know all of the URIs that could represent the same presentity. The cid field contains a unique contact ID for the presentity.
In addition to PIDF, the server supports MSRTC subscriptions. For details about the MSRTC presence document format, see [MS-SIP].