A communication system comprising: a communication terminal (10, 10a, 10b, 10c), a counterpart communication terminal (10, 10a, 10b, 10c) and a management system; the communication terminal (10, 10a, 10b, 10c) is connectable to the counterpart communication terminal (10, 10a, 10b, 10c) and the management system via a network, the communication terminal (10, 10a, 10b, 10c), comprising: a plurality of client communication applications (1031, 1032), wherein each client communication application is associated with a distinct identification, wherein each of the plurality of client communication applications (1031, 1032) is in communication with a respective client communication application (1031, 1032) of the counterpart communication terminal (10, 10a, 10b, 10c) of the same distinct identification; a publish-subscribe, pub/sub, data transmitter and receiver configured to transmit, at a prescribed timing, first information to the management system that manages communication between the communication terminal and the counterpart communication terminal (10, 10a, 10b, 10c) and configured to transmit to the management system second information to be sent from the management system to the counterpart communication terminal (10, 10a, 10b, 10c) connected to the management system through the network, when the management system does not receive the first information for a prescribed length of time, wherein the first information is used by the management system to determine whether the communication terminal (10, 10a, 10b, 10c) is connected to the network, wherein the second information is a disconnection message, the disconnection message including presence information of each of the plurality of client communication applications (1031, 1032) that operate in the communication terminal (10, 10a, 10b, 10c), characterized in that the communication terminal further comprises an integrated client application configured to implement the publish-subscribe, pub/sub, data transmitter and receiver and configured to manage the presence information that indicates the status of each of the plurality of the client communication applications (1031, 1032) based on the information sent from each of the plurality of client communication applications (1031, 1032). a plurality of client communication applications (1031, 1032), wherein each client communication application is associated with a distinct identification, wherein each of the plurality of client communication applications (1031, 1032) is in communication with a respective client communication application (1031, 1032) of the counterpart communication terminal (10, 10a, 10b, 10c) of the same distinct identification; a publish-subscribe, pub/sub, data transmitter and receiver configured to transmit, at a prescribed timing, first information to the management system that manages communication between the communication terminal and the counterpart communication terminal (10, 10a, 10b, 10c) and configured to transmit to the management system second information to be sent from the management system to the counterpart communication terminal (10, 10a, 10b, 10c) connected to the management system through the network, when the management system does not receive the first information for a prescribed length of time, wherein the first information is used by the management system to determine whether the communication terminal (10, 10a, 10b, 10c) is connected to the network, wherein the second information is a disconnection message, the disconnection message including presence information of each of the plurality of client communication applications (1031, 1032) that operate in the communication terminal (10, 10a, 10b, 10c), characterized in that the communication terminal further comprises an integrated client application configured to implement the publish-subscribe, pub/sub, data transmitter and receiver and configured to manage the presence information that indicates the status of each of the plurality of the client communication applications (1031, 1032) based on the information sent from each of the plurality of client communication applications (1031, 1032).