ABSTRACT
This chapter addresses clock synchronization in distributed systems in general and gives particular insight into two state-of-the-art synchronization protocols, namely, the Network Time Protocol (NTP) and the Precision Time Protocol (PTP). Clock synchronization based on the exchange of time information encapsulated in data packets is one of the widely used synchronization techniques due to its seamless integration into existing network and communication technique. NTP and PTP emerged in different application contexts, but their basic operation is very similar as they both essentially rely on the two-way synchronization principle using round-trip delay measurements. NTP, with its strictly distributed and fault-tolerant approach of finding a good agreement between several time servers, is ideally suited for large-scale networks such as the Internet with unclear and changing topologies. PTP, using a simpler master-slave approach, is better suited for smaller-scale networks with clear, well-maintained topology where synchronicity is more essential than in IT environments and thus resynchronization takes place much more frequently.
