Abstract: A method and circuit for mismatch detection in SDH-coded frame trace identifiers within a telecommunication network, wherein received trace identifiers are compared with expected trace identifiers in determined locations of the communication network, to detect if a misconnection event has occurred and generate a corresponding alarm signal. The method comprises the steps of: a) validating the received trace identifier (TI) and issuing a corresponding validation signal (CRC7, CNST); b) comparing the received trace identifier (TI) with an expected trace identifier (ETI) and issuing a corresponding validation signal (MTC1, MTC16); c) evaluating the validation signal (CRC7, CNST) and the match signal (MTC1, MTC16); and d) generating a matching state signal (SVAL1, SVAL16) according to the result of the evaluation as per step c), wherein steps a) and b) are executed in parallel.