a b c are u201c multimedia pcs u201d that is to say computers which are connected to a network and which are set up to reproduce and accept audiovisual useful data instead of the multimedia pcs it is also possible to use other network components which can be used as a communication terminal instead for example ip telephones the clients a b c can interchange control data signaling information and useful data with one another via the directly communicating communication network which is in the form of a voice data network voip communication network and which interchanges data voice data useful data in line with the internet protocol ip protocol tcp ip udp ip the arrows shown in figure la and in the other figures visualize the transmission or interchange of messages between the clients which are used to set up a communication link in this case the arrows have been provided with reference symbols which can be repeated in the individual figures provided that the respective message or control information is a respective message with the same function similarly the clients a b c and further clients are shown repeatedly in the figures provided that their functionality is not changed between.