Precision Time Protocol

The Precision Time Protocol (PTP) feature is used to synchronize the clocks on the network to which the receiver is connected.

Configuring PTP

The general use and configuration of a PTP network is beyond the scope of this document. The following is an overview of the steps to configure an OEM7 receiver to be part of a PTP network.

1. Configure the Ethernet settings on the receiver. Refer to Ethernet Configuration for information about configuring the receiver.

   If using a dynamic IP address, ensure the network switch has DHCP enabled.

2. Use the PTPMODE command to enable PTP on the receiver.

   PTPMODE ENABLE

3. Use the PTPPROFILE command to select the PTP profile used by the receiver.

4. Use the PTPTIMESCALE command to select the time scale used on the PTP network.

Configuration Notes

• Configure all of the PTP clocks to be synchronized on the network, so the transport mechanism, domain number, delay mechanism, best master clock algorithm, sync interval, and announce interval match.

• The receiver clock is never changed to be synchronized with another master clock. The difference between the receiver clock and the master clock is reported in the PTPDELTATIME log.

• Configure the values of priority1 and priority2 for each PTP clock to ensure that the appropriate clock is selected as the best master under the appropriate conditions.

• For best synchronization performance, all PTP clocks must be connected only to PTP aware networking appliances (hubs, switches and routers). Specifically, all connections must be made via PTP boundary or transparent clocks.

  At a minimum, all networking appliances must support the distribution of PTP multicast messages. Failing to use PTP boundary or transparent clocks for all interconnections will reduce the synchronization accuracy. However, the PTP protocol will continue to synchronize the clocks within the limits of the variability of PTP message transit times.

  Consult the user documentation for the networking appliances to determine if the devices support PTP and how to configure them for PTP support.

• If PTP is enabled on multiple receivers and all receivers are reset, it is expected that all receivers will report MASTER for a few seconds before having all but one receiver switch to report PASSIVE/SLAVE in the PTPDELTATIME log.

• If the master clock is not configured using the PTPPROFILE command (i.e. the PTPPROFILE command is left at the default value), the PTP algorithm will decide which device is the master regardless of which device is connected first.

• A peer-to-peer PTP network is designed to work with 2 clocks per subnet. Having more than two clocks will cause issues with PTP.

• If using any ITU profile, which is a forced PTP MASTER state, it is normal to see other receivers with the MASTER state. PTP will still only synchronize to the best clock.

Monitoring the PTP Status

The status of PTP on the receivers is monitored using the PTPDELTATIME log. To check the status of PTP:

1. Collect the PTPDELTATIME log on each receiver.

2. Check the PTP State field of the PTPDELTATIME log for each receiver to ensure that only one device is reporting MASTER and all other devices are reporting PASSIVE or SLAVE (unless multiple masters have been specifically configured on the system).

3. Check the Time Offsets Valid field of the PTPDELTATIME log. All of the receivers should report a value of TRUE.

4. It is also beneficial to collect the TIME log and confirm the clock status of each receiver.

Troubleshooting

Networking issues are a primary cause of the PTP network not working as expected. While troubleshooting networking issues is beyond the scope of this manual, the following tips can be helpful starting points.

• Ensure that all receivers/devices are connected to the switch and are on the same subnet.

• Ensure IGMP snooping is turned off on the network switches (if that feature is available on the switches).

• Check the multicast address groups (IGMP querying) on the network switches.

• Network monitoring applications (such as the free program Wireshark) can be used to filter and view PTP specific messages. This can help to determine which devices are connected and sending PTP messages.