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In the IMS public user identities are used to reach the recipient and single public user identity can be shared among a number of devices under single subscription (see Sections 3.5.3 and 3.7). This means that it is not possible to identify a specific device when more than one device has been registered with the same public user identity.

To reach a particular device a specific identifier called a Globally Routable User Agent URI (GRUU) must be used. For example, user Joe has a shared public user identity and his presence status indicates that he is willing to play games with UE1 and and he is willing...


Cover of THE IMS: IP Multimedia Concepts and Services, 3rd Edition