A communication system is disclosed, in which a mobile telephone has a control-plane connection to a first base station and communicates user data using at least one communication bearer provided via a second base station. The base stations are configured to exchange information relating to the data rate required for the mobile telephone via the second base station. The first base station derives, based on the exchanged information, an aggregated maximum bit rate (AMBR) parameter specific to the second base station and provides the derived AMBR parameter to the second base station for use in data rate enforcement for the mobile telephone's communications via the second base station.