How to distributed GPS-time over cots-based lans

摘要

This paper shows how to distribute GPS-time with mus-accuracy and below even in Ethernet-based distributed systems. Our SynUTC-approach~1 is based upon a simple network controller-level hardware for timestamping data packets as they leave and arrive at a node, which comes in two flavors: The memory-based timestamping method exploited by our Network Time Interface (NTI) M-Module timestamps data packets as the network controller accesses them in memory. This technique can be used for virtually any type of network and network controllers. For 10 Mb/s Ethernet, for example, our experimental evaluation revealed a time distribution accuracy down to the mus-range. Still, memory-based timestamping require network controllers that cannot store entire packets on-chip, and the available configuration parameters must be carefully chosen in order to cope with the various hidden sources of timing uncertainty. To escape from those limitations, we recently developed a novel MII-based timestamping method that can be used in conjunction with almost any modern 10/100 Mb/s Ethernet chipset. The timestamping hardware sits at the standard MII-interface between network controller and transceiver here, and will allow a time distribution accuracy well below the mus-range.