| 摘要 |
Instant messaging clients transmit, to a server, presence information indicating that the respective client is in a communicative state in which the client is receptive to communicating with the other clients. A server determines, for each client, that the respective client is in a communicative state if presence information was received from the client over a preceding predetermined time period, and that the client is in an unknown state if presence information was not received from the client over the preceding predetermined time period. The communicative state and the unknown state are possible presence states of the clients. The server transmits a notification to a second client of the presence state of a first client when both the first client and the second client are in a communicative state. But the server refrains from transmitting the notification to the second client when the first client is in the unknown state.
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