Patent ID: 7707286

Claim:
A method for updating presence information between a first user equipment (UE) and a second UE over a Push-to-Talk over Cellular (PoC) communications network, the method comprising: publishing a first presence status with a presence server by the second UE, wherein the first presence status indicates that the second UE is available; subscribing with the presence server by the first UE, wherein the first UE is subscribed as a watcher to the second UE; while the first presence status incorrectly indicates the second UE is available, on an INVITE message delivery failure to the second UE from the first UE, sending a first PUBLISH message on behalf of the second UE to a presence server by a POC communications server indicating that the second UE IS unavailable; sending a NOTIFY message to the first UE by the presence server indicating that the second UE is unavailable; and setting the first presence status by the presence server to indicate that the second UE is unavailable; and sending a NOTIFY message by the presence server to all watchers of the second UE indicating that the second UE is unavailable.