Experimental verification of the egress and ingress latency correction in PTP clocks

Precise time synchronization using the Precision Time Protocol (PTP, IEEE 1588-2008) is based on time-stamping of data packets on egress and ingress. The accuracy of the time-stamps is highly affected by the ingress and egress latencies of the PTP node. For an accurate synchronization it is therefore crucial to know the characteristics of these latencies. In our paper we present a measurement setup that enables the direct measurement of both the ingress and egress latencies of a PTP clock. In contrast to our earlier work, the principle utilizes standard PTP peer delay mechanism messages. It can therefore be applied to any PTP clock that supports the peer delay mechanism. It can thus verify whether the egress and ingress latencies of commercially available devices are correctly compensated. In our contribution we give a detailed description of the measurement setup. We demonstrate the feasibility of the system by presenting results for several devices with different time-stamping hardware.