Abstract: Telecommunications systems embody means for establishing communications links between entities within that telecommunications system. These links are usually established following an exchange of digital messages in accordance with a communications protocol. Communications protocols are often sophisticated, involving a sequence of complex message exchanges. Known protocol analysers for testing communications protocols involve the use of data bases, which are pre-programmed with all possible combinations of messages sequences which correspond with the protocol to be tested. This is time consuming, expensive and inflexible. By using a neural network within the protocol analyser, a sequence of messages exchanged in accordance with a correctly operating communications protocol may be learned, obviating the need for a data base.