Abstract: A communication device includes: a first monitoring unit that monitors a first lifetime until a data amount transmitted through a first encryption communication path established between the communication device and another communication device exceeds a first threshold, a second monitoring unit that monitors a second lifetime until the data amount transmitted through the first encryption communication path exceeds a second threshold that is larger than the first threshold, a communication path establishing unit that establishes a second encryption communication path different from the first encryption communication path between the communication device and the another communication device when the first lifetime has expired, and a communication path deleting unit that deletes the first encryption communication path when the data amount transmitted through the second encryption communication path exceeds a remaining data amount of the second lifetime.

Abstract: This is a method for transmitting packets. The transmission method includes measuring a time taken for feedback indicating that a packet including context information has been lost; and switching between a first mode and a second mode based on the measured time taken for the feedback, the first mode being a mode for periodically transmitting a packet including the context information and the second mode being a mode for transmitting a packet including the context information in response to the feedback indicating that a packet including the context information has been lost.

Abstract: When being triggered by a call setting request that has been made, dummy information that is different from information to be transmitted and is information used for creating a path on which encrypted communication is to be performed is generated. The path on which the encrypted communication is to be performed is established by using the generated dummy information. A responding process of responding to the call setting request is performed after the path on which the encrypted communication is to be performed has been established. Thus, in the case where information that is obtained after the responding process of responding to the call setting request is encrypted and transmitted, it is possible to transmit the information while maintaining the real-time characteristics of the information to be transmitted.

Abstract: A first apparatus includes a sending unit which attaches a sequence number which is numbered for each priority of QoS set in a first packet, the sequence number is numbered for each priority of QoS set in the first packet, and sends the first packet with the sequence number. A second apparatus includes a storage unit which stores, for each priority, a history of sequence numbers attached to packets received, a determining unit which receives the first packet from the first apparatus, identifies the sequence number of the first packet, and determines whether the first packet has been previously received by comparing the identified sequence number with the history of sequence numbers according to the priority of QoS set in the first packet stored in the storage unit, and a unit which discards, when the determining unit determines the first packet has been previously received, the first packet.