IEEE 1588 applied in the environment of high availability LANs

Abstract

High availability applications typically count on the network's ability to reconfigure in case of a failure. Since the precision time protocol (PTP) measures the delay of communication paths, it has to cope with network topology changes. The concept of peer-to-peer transparent clocks (TC), introduced with PTP version 2, facilitates the handling of path switchover by measuring the link delays from each node to its neighbors in advance. The parallel redundancy protocol (PRP) follows a different approach from the well-known reconfiguration protocols. It makes use of two independent Ethernet networks. Frames are replicated by the sending node and transmitted over both networks. Duplicates are discarded by the receiving node. There is no distinction between a working and a backup path. The combination of PTP and PRP is studied in this paper. Different models are presented and evaluated with respect to synchronization switchover and implementation issues. An experimental implementation is outlined. The results show that master clock failure as well as network failures can be handled with very low impact on synchronization quality.