1. A charging system for a communication system, the charging system comprising: a plurality of network elements ( 103 , 105 , 107 , 109 ) of a fixed network of the communication system; a plurality of user equipments ( 101 ) of the communication system, at least some of the plurality of network elements ( 103 , 105 , 107 , 109 ) and the plurality of user equipments ( 101 ) comprising a charging proxy ( 205 ); and a charging server ( 111 ) comprising: a topic controller ( 305 ) for initializing charging topics, each charging topic being associable with charging data, a publication controller ( 307 ) for, for each of the charging topics, registering proxies of the charging proxies as publishing proxies, a subscription controller ( 309 ) for, for each of the charging topics, registering proxies of the charging proxies as subscribing proxies, a receiver ( 301 ) for receiving charging data messages from proxies, a charging data receiver ( 311 ) for validating a first set of charging data belonging to a first charging topic in response to a first set of charging proxies registered as publishing proxies for the first charging topic, and a transmitter ( 313 ) for transmitting the first set of charging data to a second set of charging proxies registered as subscribing proxies for the first charging topic.