A method of communication between a first node and a second node for a system where a plurality of different channels is provided between said first and second node. The method comprises the step of calculating an integrity output. The integrity output is calculated from a plurality of values, some of said values being the same for said different channels. At least one of said values is arranged to comprise information relating to the identity of said channel, each channel having a different identity. After the integrity output has been calculated, Information relating to the integrity output is transmitted from one of said nodes to the other.