Abstract: A communication system is provided which includes: a portable terminal; a mobility management device that manages mobility of the portable terminal; a first gateway that connects the portable terminal to a first network; and a second gateway that connects the portable terminal to a second network. Based on a result of determining whether to connect the portable terminal to the first network via the first gateway or connect the portable terminal to the second network via the second gateway, the mobility management device switches between causing the portable terminal to use first contract information for connection to the first network via the first gateway and causing the portable terminal to use second contract information for connection to the second network via the second gateway.

Abstract: A communication system is provided which includes: a portable terminal; a mobility management device that manages mobility of the portable terminal; a first gateway that connects the portable terminal to a first network; and a second gateway that connects the portable terminal to a second network. Based on a result of determining whether to connect the portable terminal to the first network via the first gateway or connect the portable terminal to the second network via the second gateway, the mobility management device switches between causing the portable terminal to use first contract information for connection to the first network via the first gateway and causing the portable terminal to use second contract information for connection to the second network via the second gateway.

Abstract: A plurality of nodes each including a transmitter, a receiver, and a controller is linked together via a network. The transmitter of a transmission node using multiple wireless interfaces sends a beacon message sending its own node identifier and wireless interfaces to at least one reception node, which in turn sends back a response message sending its own node identifier and at least one usable wireless interface. The controller of the transmission node determines the broadcast order based on the response message received by the receiver. The transmitter of the transmission node performs broadcasting or multicasting using the wireless interface, which is selected based on the broadcast order. Thus, it is possible to perform broadcasting or multicasting at an efficient usage of radio frequency while covering all reachable neighboring nodes in node-to-node wireless communications based on multiple wireless communication methods.