The invention relates to establishing trust between parties prior to a multi-party communications session over the Internet or the like. This is achieved by the exchange of messages describing participant roles required to be performed during a session, and the assumption of the described roles by the parties to a session. The assumption of a role is non-repudiable via the use of digital signatures, in that a party must digitally sign the message or part thereof which indicates that it intends to assume a role. The roles relate to control functions to be performed during the session, such as Quality of Service determiner, or Quality of service signaller.