| 摘要 |
In the course of a half-duplex telecommunication session, such as a push-to-talk (PTT) session, a message 305 has a message validity information item added to it and, if appropriate, a check is performed to determine whether or not the message is valid 310. The message validity information item may be a prescribed time period after whose expiry the message needs to be erased 311 if a recipient has not retrieved the message. Alternatively, the message validity information item may be spatial information such that the message is erased 311 if a recipient is not within the local area, or it may be a subject-related information item such that the message is erased 311 if the recipient has no information regarding the indicated subject, or the message may be erased 311 if the recipient is not registered or ready to receive the message. |
