Advances in Computer Network Timekeeping


from Alice's Adventures in Wonderland, Lewis Carroll

Researchers involved: David Mills, Judah Levine (NIST), graduatestudents

Funding: National Science Foundation

Importance of the Problem

The speeds of both computers and networks and the sizes of things has risen dramatically in the last few years. It has been necessary to continuously improve the accuracy, stability and reliability of computer network time synchronization technology to match. This requires timely re-examination of the architecture, protocol and implementation issues on which these qualities depend.

Brief Description of Work and Results

The work involves refining the Network Time Protocol (NTP) for greater precision and new service paradigms, such as multicast and manycast, and developing security mechanisms specialized to the needs of the protocol and the new paradigms. We have designed and implemented NTP multicast and manycast service in the NTP Version 4 implementation for Unix, VMS and Windows, which is now in widespread use on the Internet. We have defined a security model specifically for NTP and designed and implemented the Autokey cryptographic authentication scheme. We are currently documenting this work and revising the NTP protocol specification for NTP Version 4.

We have worked with NIST on dissemination means for International Atomic Time (TAI) using NTP. We have designed and implemented Autokey extensions to provide this capability and deployed it in UDel and CAIRN routers for testing.

We have developed or integrated NTP drivers for several new types of radio clocks, including those built by Hewlett Packard, Motorola and Arbiter, for a total of about three dozen. These include DSP drivers for shortwave time and frequency services WWV/WWVB Boulder and CHU Ottowa. These operate with a workstation audio codec and inexpensive shortwave radio. We have designed and implemented several enhancements to existing NTP algorithms, in particular, algorithms to improve the accuracy and reliability of the local clock discipline.

As part of this work, we have participated in deployment exercises designed to install NTP primary servers in the Americas Europe and Pacific Rim. In particular, NIST has installed redundant Automated Computer Time Service (ATCS) primary servers in the Boulder and Seattle areas, and USNO has installed redundant Global Positioning Service (GPS) servers at 15 places in the US, Alaska and Hawaii. Additional deployments are expected as well. The DARTnet community has installed primary servers at 9 places in the US. We have recently assisted groups in the UK, Italy, Norway, Germany, Brazil, Mexico, Singapore and Japan in deploying primary servers synchronized to national standards laboratories. Many of these servers are monitored on a regular basis using our own monitoring systems, as well as those of other operators.

Future Plans

We plan to continue collaboration projects with USNO and NIST and other agencies as interest develops. Development of NTP Version 4 will continue, as well as refinements to the authentication, configuration and precision capabilities of the protocol and implementation.

Selected Publications

  1. Levine, J., and D. Mills. Using the Network Time Protocol to transmit International Atomic Time (TAI). Proc. Precision Time and Time Interval (PTTI) Applications and Planning Meeting (Reston VA, November 2000). Paper: PostScript | PDF
  2. Mills, D.L., and P.-H. Kamp. The nanokernel. Proc. Precision Time and Time Interval (PTTI) Applications and Planning Meeting (Reston VA, November 2000). Paper: PostScript | PDF, Slides: PostScript | PowerPoint
  3. Mills, D.L. Public key cryptography for the Network Time Protocol. Electrical Engineering Report 00-5-1, University of Delaware, May 2000. 23 pp. Abstract: PostScript | PDF, Body: PostScript | PDF
  4. Mills, D.L., A. Thyagarajan and B.C. Huffman. Internet timekeeping around the globe. Proc. Precision Time and Time Interval (PTTI) Applications and Planning Meeting (Long Beach CA, December 1997), 365-371. PostScript | PDF
  5. Mills, D.L. The network computer as precision timekeeper. Proc. Precision Time and Time Interval (PTTI) Applications and Planning Meeting (Reston VA, December 1996), 96-108. PostScript | PDF