A boundary clock is an IEEE 1588 component that allows the synchronization of IEEE 1588 clocks across subnets defined by a router or other devices that blocks the transmission of all IEEE 1588 messages. A boundary clock serves to eliminate the large fluctuations in communication latency typically generated by routers and similar devices.
An IEEE 1588 Boundary Clock serves as a time transfer standard between the subnets defined by the router or other network device. The router or other device must be configured to block all IEEE 1588 messages. The boundary clock has a network connection to each of the subnets. When viewed from a subnet the boundary clock appears exactly like any other (ordinary) 1588 clock in the system. Within a subnet the ordinary clocks and the portion of the boundary clock visible from the subnet synchronize with each other as though they were all ordinary clocks. The boundary clock itself resolves all of the times of the several subnets by establishing a parent child hierarchy of clocks. In a system with a single IEEE 1588 Boundary Clock, the boundary clock will typically be the at the root of this hierarchy and will be the master clock for all of the clocks in each of the subnets.
In addition to the synchronization functionality, an IEEE 1588 Boundary Clock provides for the appropriate retransmission of 1588 management messages.