Synchronization protocols work in one or more association modes, depending on the protocol design. In this mode, a client synchronizes to a stateless server as in the conventional RPC model. NTP also supports symmetric mode, which allows either of two peer servers to synchronize to the other, in order to provide mutual backup. DTSS and NTP support a broadcast mode which allows many clients to synchronize to one or a few servers, reducing network traffic when large numbers of clients are involved. In NTP, IP multicast can be used when the subnet spans multiple networks.
Configuration management can be a serious problem in large subnets.
Various schemes which index public databases and network directory services are used in DTSS and NTP to discover servers. Most computers include a quartz resonator-stabilized oscillator and hardware counter that interrupts the processor at intervals of a few milliseconds. At each interrupt, a quantity called tick is added to a system variable representing the clock time. The clock can be read by system and application programs and set on occasion to an external reference. Once set, the clock readings increment at a nominal rate, depending on the value of tick .