Efficient time transfer using the Internet

The National Institute of Standards and Technology operates an ensemble of Internet time servers. The ensemble of servers receives about 450 million time-stamp requests per day (as of May, 2002). This demand is increasing at a compound rate of almost 9% per month, so that improving the efficiency of the time synchronization process is very important. In addition, these requests are not distributed uniformly among the servers, and the busiest servers are nearly saturated during peak periods. Therefore, the capacity of the system as a whole could be increased if the load were distributed more evenly, and we have investigated methods for achieving this active load balancing. We have also developed a number of algorithms based on the Network Time Protocol that try to make the best use of the time stamps and the available network bandwidth. In particular, the algorithms can be configured to trade off accuracy for cost (defined as the network bandwidth and computer cycles needed to realize a specific performance level), so that the many users who do not need the full accuracy of the system can receive satisfactory service at much lower cost.