SynUTC - high precision time synchronization over ethernet networks

This article describes our SynUTC (Synchronized Universal Time Coordinated) technology, which enables high-accuracy distribution of GPS time and time synchronization of network nodes connected via standard Ethernet LANs. By means of exchanging data packets in conjunction with moderate hardware support at nodes and switches, an overall worst-case accuracy in the range of some 100 ns can be achieved, with negligible communication overhead. Our technology thus improves the 1 ms-range accuracy achievable by conventional, software-based approaches like NTP by 4 orders of magnitude. Applications can use the high-accuracy global time provided by SynUTC for event timestamping and event generation both at hardware and software level. SynUTC is based upon inserting highly accurate time information into dedicated data packets at the media-independent interface (MII) between the physical layer transceiver and the network controller upon packet transmission and reception, respectively. As a consequence, every node has access to the local time information of any communication peer and can therefore re- adjust its local clock accordingly. This enables both simple solutions based upon synchronizing with a (GPS-equipped) master node as well as elaborate fault-tolerant clock synchronization algorithms. Each node must be equipped with a special network interface card (NIC) for this purpose, which extends standard NIC chipsets by a custom hardware encapsulated in a single IC plugged into the MII. This chip contains primarily a high-precision adjustable adder-based clock and timestamping registers as well as an uC core executing the synchronization algorithm. Our technology is generic, in the sense that our hardware support can be used with any NIC chipset based upon the MII. Moreover, since clock synchronization, except a simple service that broadcasts messages on a regular basis, is performed by the on-chip uC, standard NIC device drivers and protocol stacks can be used without changing. Last but not least, the principle underlying SynUTC is not limited to Ethernet-based networks but is applicable for any packet-oriented data network as well. To verify the feasibility of our approach, a research prototype has already been developed and evaluated successfully. Currently, a multi-node demonstration system is being built to facilitate the transfer of our SynUTC technology in commercial applications. (12 refs).