Precise latency measurement of unidirectional-data-flow network equipment

In regards to network performance measurements, many timing indices, such as latency, jitter, and one-way delay (OWD), are getting more attention because real-time applications and needs are pushing higher network capabilities. Data latency in a network can be measured by placing additional unidirectional-data-flow (UDF) devices, such as test access taps (TAPs), on the network path. However, this can create severe uncertainty to the timing measurement when sub-microsecond precision measurements need to be achieved. This paper proposes the Precision Time Protocol (PTP)-Based Measurement method for measuring latency of a UDF device based on traditional OWD measurements. In addition, we propose a Packet-by-Packet Precise Measurement method, which can further reduce the measurement uncertainty caused by the limit of precision in the PTP synchronization protocol in the PTP-Based Measurement method, by strictly calculating the latency for each packet.