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IEEE 1588v2 Precision Timing Protocol (PTP) on ACX Series Universal Access Routers

The IEEE 1588v2 standard defines the Precision Time Protocol (PTP), which is used to synchronize clocks throughout a packet-switched network. This synchronization is achieved through packets that are transmitted and received in a session between a master clock and a slave clock or remote clock client. The clocks used for the distribution of accurate time are in an hierarchical master/slave architecture, which includes boundary clocks, ordinary clocks, and grandmaster clocks. A boundary clock is both a clock source and a clock client. An ordinary clock is either a clock source or a clock client. However, a grandmaster clock is always a clock source. An ordinary clock on an ACX Series router is always a clock client. In addition, User UDP over IPv4 and unicast mode are used to transport PTP messages.

• Boundary clock—A boundary clock has multiple network connections and can act as a source (master) and a destination (slave or clock client) for synchronization messages. It synchronizes itself to a best master clock through a slave port and supports synchronization of clients to it on master ports. Boundary clocks can improve the accuracy of clock synchronization by reducing the number of 1588v2-unaware hops between the master and the client. Boundary clocks can also be deployed to deliver better scale because they reduce the number of sessions and the number of packets per second on the master.
• Ordinary clock—The PTP ordinary clock has a single network connection and can act as a source (master) or destination (slave or clock client) for synchronization messages. On ACX Series routers, the ordinary clock is a slave, which receives synchronization reference messages from a master, either a grandmaster or a master boundary clock. You cannot configure an ordinary master on an ACX Series router. However, a boundary clock can provide time to the ordinary slave.
• PTP grandmaster clock—The PTP grandmaster clock communicates time information to destination or slave ports. The grandmaster clock is an external device to which the boundary or ordinary clock synchronizes. You cannot configure a grandmaster clock on an ACX Series router. However, a boundary clock slave or an ordinary clock slave can receive time from a grandmaster clock.
• Clock source—A clock source is the PTP master clock to which the slave synchronizes. The clock source is included in the configuration of the slave clock.

  Note: The term master is sometimes used to refer to the clock source.

• Clock client—A clock client is the remote PTP host, which receives time from the PTP master. The clock client is included in the configuration of the master clock.

  Note: The term slave is sometimes used to refer to the clock client.

• PTP over UDP over IPv4—The IEEE1588v2 standard specifies different transport protocols for carrying PTP packets. For example, PTP over Ethernet, PTP over UDP over IPv4, and PTP over UDP over IPv6. ACX Series routers support PTP over UDP over IPv4.
• Unicast mode (IPv4 on Gigabit Ethernet interfaces only)—Unicast mode is a user-to-user protocol used to send a datagram to a single recipient. Unicast mode is used for transporting PTP messages.