Communication system and communication method

A communication method for implementing a chat between/among Instant Messaging (IM) clients by using:

• an IM presence management server which manages presence information indicating a state of each of the IM clients;
• a VoIP communication connection management server which manages a connection for voice chatting using VoIP (Voice over Internet Protocol);
• and
• a media server which implements multi-party voice communication by mixing voice data,
• wherein, the IM presence management server performs processing of:
• managing, as to each of the IM clients, the presence information, information regarding media (including text and voice) usable for chatting, and user information of the IM client;
• providing, in accordance with an instruction from one of the IM clients, said one IM client with the presence information, the information regarding media usable for chatting and the user information of each of the IM clients which are set as buddies of said one IM client;
• managing, in accordance with information of each of IM clients (called as text participating clients) participating in a text chat, which is notified from one of the IM clients, a connection between/among the text participating clients and the IM presence management server;
• and
• merging text data sent from each of the text participating clients to distribute the result to each of the text participating clients,
• wherein the VoIP communication connection management server performs processing of:
• managing a connection between/among each of the voice participating clients and the media server in accordance with information of each of the IM clients (called as voice participating clients) participating in a voice chat, which is notified from one of the IM clients or the IM presence management server, and
• wherein the media server performs processing of:
• as to each of the voice participating clients, mixing voice data sent from the voice participating clients except for the client in question (called as a focused client) to distribute the result to the focused client.