The invention is concerned with transmission of speech information over mixed networks, particularly over a segment using packet transmission in an otherwise circuit switched data transmission network. According to the invention, PCM transmission lines are connected with a packet based network such as an IP network in such a way, that data from one or more channels of a first PCM transmission line is collected in the payload part of a data packet. Further, the destination address of the data packet is constructed in such a way, that the packet network entity being connected to the second PCM transmission line can determine based on the destination address of the packet, to which channel or channels of the second PCM transmission line the data should be transmitted.