How to Distribute GPS-Time over COTS-based LANs

This paper shows how to distribute GPS-time with s-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 avours: 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 s-range. Still, memory-based timestamping requires network controllers that cannot store entire packets on-chip, and the available connguration 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 s-range.