Abstract: Known apparatus for measuring jitter in a signal under test employ narrowband filters and limiters that have technological limitations when the bit rate of the signal under test is around 40 Gbps. The present invention avoids the use of the above-mentioned elements by firstly wideband filtering an extracted clock signal and mixing the filtered clock signal down to baseband using a quadrature demodulator to yield a complex baseband signal. Prior to conversion of the complex baseband signal to the digital domain, the quadrature components of the complex baseband signal are low-pass filtered. Subsequently, digitized signals are converted to a polar form having an amplitude and phase, the phase being weighted by the amplitude prior to measurement of the phase in order to incorporate a measure of confidence in the phase relating to a density of transitions in the signal under test.

Abstract: A multi-channel network monitoring apparatus has input connectors for network signals to be monitored and four channel processors in a rack-mountable chassis/enclosure for receiving and processing a respective pair of incoming signals to produce monitoring results. Each processor operates independently of the others and is replaceable without interrupting their operation. LAN connectors enable onward communication of the monitoring results. A cross-point switch routes each incoming signal to a selected processor and can re-route a channel to another processor in the event of processor outage. Each processor has a self-contained sub-system of processing modules interconnected via a CPU-peripheral interface in a backplane, which provides a separate peripheral interface for each processor.

Abstract: Known apparatus for measuring jitter in a signal under test employ narrowband filters and limiters that have technological limitations when the bit rate of the signal under test is around 40 Gbps. The present invention avoids the use of the above-mentioned elements by firstly wideband filtering an extracted clock signal and mixing the filtered clock signal down to baseband using a quadrature demodulator to yield a complex baseband signal. Prior to conversion of the complex baseband signal to the digital domain, the quadrature components of the complex baseband signal are low-pass filtered. Subsequently, digitised signals are converted to a polar form having an amplitude and phase, the phase being weighted by the amplitude prior to measurement of the phase in order to incorporate a measure of confidence in the phase relating to a density of transitions in the signal under test.

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.