An oxygen storage capacity monitoring system for a vehicle having a catalytic converter includes an inlet oxygen sensor that generates an inlet sensor signal based on an oxygen content of exhaust flowing into the catalytic converter. A PWM reference signal generation unit generates a PWM reference signal. In one embodiment, each reactor subsection includes a respective coolant flow for manipulating the operating temperature of the respective subsection. Through this resource allocation, the terminal can efficiently transmit uplink signals. The multi-call VoIP terminal and a multi-call service method can realize packet relaying through IP address conversion without an expansion or modification to a server, so that a multi-call service can be provided to users in a simple fashion. A first client node, upon switching to or joining a new channel, transmitting S2 a channel update message to said associated group, said channel update message comprising an identity of said first client node, an identity of said new channel and a topological indication for said channel.