Charging method and system for push-to-talk over cellular system

A charging method for a Push-to-Talk over Cellular (PoC) system, comprising:

• receiving an initial online charging request sent by a PoC server;
• sending to the PoC server an initial online charging response message that carries a downlink channel type switching trigger variable;
• and
• receiving an online charging request that is sent, after a change of a type of a downlink channel used by a PoC service is detected according to the downlink channel type switching trigger variable, by the PoC server, wherein the online charging request comprises a switched type of the downlink channel.

A Push-to-Talk over Cellular (PoC) server, comprising:

• a first sending module, configured to send an initial online charging request to an Online Charging System (OCS);
• a first receiving module, configured to receive an initial online charging response message that is sent by the OCS and carries a downlink channel type switching trigger variable;
• and
• a monitoring module, configured to monitor a type of a downlink channel used by a PoC service according to the downlink channel type switching trigger variable;
• wherein
• the first sending module is further configured to send an online charging request to the OCS if the monitoring module detects switching of the type of the downlink channel used by the PoC service, wherein the online charging request comprises a switched type of the downlink channel.

An Online Charging System (OCS), comprising:

• a second receiving module, configured to receive an initial online charging request sent by a Push-to-talk over Cellular (PoC) server;
• and
• a second sending module, configured to send to the PoC server an initial online charging response message that carries a downlink channel type switching trigger variable;
• wherein
• the second receiving module is further configured to receive an online charging request that is sent, after a change of a type of a downlink channel used by a PoC service is detected according to the downlink channel type switching trigger variable, by the PoC server, wherein the online charging request comprises a switched type of the downlink channel.