1. In a communication system having a service adapted to execute defined operations and extended operations and a client adapted to request execution by the service of defined operations and extended operations, a method performed by the client for invoking at least one of the extended operations, comprising the steps of: transmitting by the client to the service an extended operation invocation request identifying the at least one extended operation; and receiving by the client from the service in response to the request an extended operation invocation response having a result obtained through execution by the service of the at least one extended operation.