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3.2 Removing a Binding from the Registrar

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The SIP registrar SHOULD send a deregister NOTIFY to the UAC if it becomes necessary to remove a binding prematurely for any reason. Some of the reasons when this MAY happen are illustrated by the following examples, which are described in section 2.2.1.13.

  • The registrar enforces a quota on the number of endpoints from which a user MAY be registered. If this quota is exceeded, the registrar might use a policy of deregistering the oldest endpoint. In this case, the message body is set to "unregistered".

  • The administrator disables the user for policy reasons, such as when a user leaves the organization. In such cases, the registrar might automatically deregister all the endpoints of the user when the policy change is applied. The message body is set to "rejected".

  • The user is being moved across servers. This is possible if the system supports the notion of a dedicated "home server" for each user. In such cases, when the user is moved across servers, the existing endpoints in the previous server might be automatically deregistered. The message body is set to "deactivated".

  • The user is being moved across registrars. This is possible if the system supports the notion of a dedicated "home registrar" for each user. In such cases, when the user is moved across registrars, the existing endpoints in the previous registrar might be automatically deregistered. The message body is set to "preferred-registrar-change". The P-Preferred-Registrar header indicates the new home registrar for the user.<164>

  • The service responsible for presence of a user is unavailable and the endpoint has not indicated support for survivable mode. In such cases, the endpoints that do not indicate support are automatically deregistered. The message body is set to "userservices-unavailable".<165>

Note: These reasons are illustrative and the list of examples is not comprehensive.

When the registrar deregisters an endpoint, it SHOULD send a deregister NOTIFY to the UAC indicating that the registration has terminated.