The Berkeley UNIX 4.3BSD Time Synchronization Protocol

The Time Synchronization Protocol TSP has been designed for specific use by the program timed, a local area network clock synchronizer for the UNIX 4.3BSD operating system Timed is built on the DARPA UDP protocol and is based on a master slave scheme. TSP serves a dual purpose. First, it supports messages for the synchronization of the clocks of the various hosts in a local area network. Second, it supports messages for the election that occurs among slave time daemons when, for any reason, the master disappears. The synchronization mechanism and the election procedure employed by the program timed are described in two other documents 1,2. While some messages need not be sent in a reliable way, most communication in TSP does require reliability. Reliability is achieved by the use of acknowledgements, sequence numbers, and retransmission when message losses occur. When a message that requires acknowledgment is not acknowledged, the time daemon which has sent the message will assume that the addressee is down. This document will not describe the details of how reliability is implemented, but will only point out when a message type requires a reliable transport mechanism The message format in TSP is the same for all message types however, in some instances, one or more fields are not used. The next section describes the message format. The following sections describe in detail the different message types, their use and the contents of each field.