A method of negotiation of media between a source communication device and a destination communication device for multiplexing multiple media types on an IP transport address comprises the source communication device generating an offer message comprising an extension to the ICE protocol according to RFC 5245 to specify the IP transport address whereon the multiple media types can be multiplexed, wherein the offer message comprising the extension indicates support for both the multiplexing and a non-multiplexing of the multiple media types, and sending the offer message from the source communication device to the destination communication device.