Precise packet delay measurement in an Ethernet network

• We built a device for precise packet delay measurement using IEEE 1588 protocol.
• One common clock for master and slave port guarantees high measurement accuracy.
• Device was calibrated using known Ethernet cables and network delay simulator.
• Measurement method can be used to determine path delay asymmetry.
• Method eliminates an influence of separate slave clock synchronization mechanism.

Node synchronization can be implemented in an Ethernet network using time protocols; e.g. IEEE 1588 [1]. Active network components like switches and routers influence the accuracy of synchronization because they affect a packet delay variation in the network. Therefore, the delay is not constant and, as well, the delay in one direction is not equal to the delay in the opposite direction.This paper presents a low-cost device that can measure the packet delay with high accuracy in both communication directions and, at the same time, calculate network parameters including a packet delay variation, path asymmetry and dependency of the delay in opposite directions.The measurements can be used for the estimation of synchronization accuracy within the tested network. Some network elements have an unexpectedly large variability of path delays and large asymmetry. This behavior can be measured directly and therefore it is possible to eliminate these devices from the network. The results can be also used for the manual calibration of end nodes. It is not recommended, however, as it is vulnerable to network topology changes.