The protocol testers may be used as an aid when testing the Message Transfer Part (MTP and the Signalling Connection Control Part (SCCP) of Signalling System No.7 (SS No.7), either when performing validation testing of an implementation or compatibility testing between two implementations. The tester’s main function is simulation of an ordinary user part or sub-system, as seen from the MTP or SCCP respectively, for the generation of test traffic.