10. Provisioning Considerations

UAs can automatically discover if this feature is active for an AOR by looking for the 'shared' Event header field parameter in a response to a dialog package SUBSCRIBE to the AOR, so no provisioning for this is needed.

The registrar will need to be provisioned to accept either first or third party registrations for the shared AOR. First party registration means the To and From URIs in the REGISTER request are the shared AOR URI. Third-party registration means the To URI is the shared AOR URI and the From URI is a different AOR, perhaps that of the individual user. Either the credentials of the shared AOR or the user MUST be accepted by the registrar and the Appearance Agent, depending on the authorization policy in place for the domain.

If the Appearance Agent needs to subscribe to the dialog state of the UAs, then the Appearance Agent and the UAs need to be provisioned with credentials so the UAs can authenticate the Appearance Agent.

In some cases, UAs in the shared appearance group might have a UI limitation on the number of appearances that can be rendered. Typically, this will be hard-phones with buttons/lamps instead of more flexible UIs. In this case, it can be useful for the Appearance Agent to know this maximum number. This can allow the Appearance Agent to apply policy when this limit is reached, e.g., deny a call. However, this mechanism does not provide any way to discover this by protocol means.