IEEE 1588v2 PTP Boundary Clock Overview

IEEE 1588v2 PTP Boundary Clock

Starting with Junos OS Release 17.3R1, IEEE 1588v2 boundary clock is supported on QFX10002 switches. An IEEE 1588v2 boundary clock has multiple network connections and can act as a source (primary) and a destination (client) for synchronization messages. It synchronizes itself to a best primary clock through a client port and supports synchronization of remote clock clients to it on primary ports. Boundary clocks can improve the accuracy of clock synchronization by reducing the number of 1588v2-unaware hops between the primary 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 primary.

The boundary clock intercepts and processes all PTP messages and passes all other traffic. The best primary clock algorithm (BMCA) is used by the boundary clock to select the best configured acceptable primary clock that a boundary client port can see. To configure a boundary clock, include the boundary statement at the [edit protocols ptp clock-mode] hierarchy level and at least one primary with the master statement and at least one client with the slave statement at the [edit protocols ptp] hierarchy level.

ACX5448 router supports PTP boundary clocks for phase and time synchronization using IEEE-1588 Precision Timing Protocol (PTP). The ACX5448 router supports the following features:

• PTP over IPv4 (IEEE-1588v2)

• PTP ordinary and boundary clocks

• One step clock mode operation for PTP Primary

• 10Mhz and 1PPS output for measurement purpose

All PTP packets uses the best-effort queue instead of network control queue.

If clksyncd-service restart is initiated, then the show ptp lock status detail CLI command output of Clock reference state and 1pps reference state fields shows incorrect information. The following is a sample of output for show ptp lock status detail:

Figure 1 illustrates two boundary clocks in a network in which the clock flow is from the upstream node (BC-1) to the downstream node (BC-2).

Figure 1: Boundary Clocks in a Network

The first boundary clock—BC-1—has four ports. Each port is configured as follows:

• BC-1 P-1 and BC-1 P-4 are boundary client ports connected to two reference clocks—OC-1 and OC-5. The reference clocks are included as the clock sources in the client port configurations. From the packets received on the client ports, BC-1 selects the best primary, synchronizes its clock, and generates PTP packets, which are sent over the primary ports—BC-1 P-2 and BC-1 P-3—to the downstream clients.

• BC-1 P-2, a primary port, is connected to OC-2, an ordinary remote client. OC-2 is included as a clock client in BC-1 P-2’s primary configuration, and so receives PTP packets from BC-1 P-2.

• BC-1 P-3, a primary port, is connected to BC-2 P-1, a remote boundary client port. In this situation, the primary port—BC-1 P-3—is included as a clock source in the configuration of the boundary client port—BC-2 P-1. In addition, the boundary client port—BC-2 P-1—is included as a clock client in the configuration of the primary port—BC-1 P-3. With this configuration, the boundary client—BC-2 P1—receives PTP packets from BC-1 P3.

The second boundary clock—BC-2—has three ports. Each port is configured as follows:

• BC-2 P-1 is a boundary client port connected to the upstream primary port—BC-1 P3. As described previously, BC-2 P-1 receives PTP packets from BC-1 P3. The primary ports—BC-2 P-2 and BC-2 P-3—synchronize their time from the packets received from BC-2 P1.

• BC-2 P-2 and BC-2 P-3, boundary primary ports, are connected to ordinary remote slaves—OC-3 and OC-4. OC-3 and OC-4 are included as clock clients in the configuration of the primary ports—BC-2 P2 and BC-2 P-3. Both slaves receive PTP packets from the primary boundary port to which they are connected.

In this example, the boundary clock synchronizes its clock from the packets received on its client ports from the upstream primary. The boundary clock then generates PTP packets, which are sent over the primary port to downstream clients. These packets are timestamped by the boundary clock by using its own time, which is synchronized to the selected upstream primary.

Clock Clients

A clock client is the remote PTP host, which receives time from the PTP primary and is in a client relationship to the primary.

An device acting as a primary boundary clock supports the following types of downstream clients:

• Automatic client—An automatic client is configured with an IP address, which includes the subnet mask, indicating that any remote PTP host belonging to that subnet can join the primary clock through a unicast negotiation. To configure an automatic client, include the subnet mask in the clock-client ip-address statement at the [edit protocols ptp master interface interface-name unicast-mode] hierarchy level.

• Manual client—A manual client is configured with the manual statement at the [edit protocols ptp master interface interface-name unicast-mode clock-client ip-address local-ip-address local-ip-address] hierarchy level. A manual client does not use unicast negotiation to join the primary clock. The manual statement overrides the unicast negotiation statement configured at the [edit protocols ptp] hierarchy level. As soon as you configure a manual client, it starts receiving announce and synchronization packets.

• Secure client—A secure client is configured with an exact IP address of the remote PTP host, after which it joins a primary clock through unicast negotiation. To configure a secure client, include the exact IP address in the clock-client ip-address statement at the [edit protocols ptp master interface interface-name unicast-mode] hierarchy level.