Abstract: The magnitude of a pulse in a signal having both positive and negative polarity pulses (for example, a ternary PDH signal) is determined by measuring the magnitude of multiple samples of the signal. A reference level for the signal is determined from a plurality of these sample magnitudes, and the magnitude of a pulse in the signal is determined from the sample magnitudes and the reference level.

Abstract: The invention provides a method of identifying framing bits in order to correctly frame a test signal comprising a data payload in the form of a pseudo random binary sequence (PRBS), split into frames by a number of framing bits, after disruption and re-establishment of transmission of the test signal. The method comprises comparing the test signal to a comparison PRBS, and determining the position of the framing bits, or other non-payload data, based on the position of mismatches between the incoming test signal and the comparison PRBS. Errors may be deliberately introduced before transmission of the test signal, in a predetermined position relative to the non-payload data bits, so that analysis of the payload data is used to identify the framing elements.