Telephone system, gateway for telephone system, and redundancy switching method

A telephone system, which comprises a plurality of gateways used to convert each other's protocols of a first network of a packet-switched type and a second network of a circuit-switched type, and in which one of the plurality of the gateways selectively serves as a main gateway, and the other gateways serve as slave gateways which are controlled by the main gateway, each of the plurality of gateways comprising:

• a control channel management module configured to control, when the control channel management module included in the one of the plurality of gateways that is the main gateway, speech data individually sent and received by the plurality of gateways, based on a control signal of a control channel of the second network;
• an operation controller configured to control redundancy switching between the plurality of gateways upon occurrence of a fault;
• and
• a determination module configured to determine whether the fault is associated with the control channel,
• wherein when the fault is associated with the control channel, the determination module notifies one of the slave gateways of an invocation instruction message used to activate the control channel management module of the one of the slave gateways via the first network.