d to the server after that 9 server request client_a to send media stream to the server and 10 client_a once received said request sends media stream a to the server in the same way 11 server requests client_b to send media stream to the server and 12 client_b sends media stream b to the server 13 14 once server has received media stream a and b mixes them with media streams c and d and 15 16 sends the mixed media stream from step 13 to client_c and media stream from step 14 to client_d respectively finally server sends 17 18 media stream c to client_a and client_b and 19 20 media stream d to client_a and client_b fig3 shows another embodiment of this invention in which sip protocol is now used in this case 1 client_n sends invite request to server with sdp session description as a body v 0 o alice 2890844526 2890844526 in ip4 127 16 70 1 s c in ip4 127 16 70 1 t 0 0 m audio 49170 rtp avp 97 a rtpmap 97 ilbc 8000 m video 51372 rtp avp 31 a rtpmap 31 h261 90000 in the invite request client capabilities preferences are described in contact header using according to rfc 3841 or in any other way media types and number of streams are indicated in sdp in this example the client is a pc and prefers.