The PTP parameters for a processing blade can be adjusted from the Synchronization → PTP sub-pages (in HOME's Advanced parameters). These options become relevant if the Mode Select option on the Synchronization page is set to PTP (as described earlier).

There is one main page with global parameters plus several sub-pages that address the ports.

The first option to check is Slave Only as this defines the PTP mode.

  • If Slave Only is enabled, then the processing blade is forced to operate as a PTP slave at all times. In this mode, the blade looks for an incoming PTP signal from the media network (e.g. from an external grandmaster).
  • If Slave Only is disabled, then the processing blade will operate as either a master or slave, depending on the PTP priorities set within the device itself and the other streaming nodes.

In each case, you can choose which port(s) are listening for, or transmitting, PTP using the Enable Port PTP options. To configure redundancy, you must enable at least two ports.

The other parameters define the PTP priorities of the blade. How they should be configured depends on the network architecture and PTP profile in use. More information can be found in the Lawo IP Networking Guide.

In order for PTP to work correctly, and to avoid configuration mistakes, we strongly recommend using the same values for all PTP-capable devices, masters and slaves.

Global Parameters

Synchronization → PTP

Clock Status

Shows the status of the PTP clock source (arriving from the network).

PTP Process Status

Shows the status of the internal PTP processes within the blade.

Port Enables

Shows which port(s) are listening for, or transmitting, PTP. You can add or remove port(s) using the Enable Port PTP options.

Domain

Defines the domain number. The recommended value for this field will vary depending on the PTP profile in use. Please refer to the Lawo IP Networking Guide.

DSCP

Defines the DSCP (differentiated services code point) or quality class. The default value for PTP is 56.

Priority 1 and Priority 2

These options set the PTP priorities of the processing blade as follows.

PTP uses a master-slave approach in which all master-capable devices elect the best master, called the grandmaster, according to a common algorithm known as the Best Master Clock Algorithm (BMCA). The algorithm compares the following parameters in turn:

  • Priority 1 - the lower the number, the higher the priority of the device.
  • Clock Class
  • Priority 2 - as for Priority 1.
  • MAC Address

For example, if there is no Priority 1 available, then all devices on the network look at the Clock Class, then Priority 2 and finally the MAC Address.

Note that only the Priority 1 and Priority 2 values can be adjusted for .edge. The Clock Class cannot be adjusted but may be used by a third-party grandmaster if one is installed. The MAC Address (for the transmitting port) can be viewed in HOME's Network Ports tab.

In order to sync properly, the Priority values must be configured according to the system design. In particular, a Slave Only device will not sync properly unless its priority is lower than that of the desired grandmaster.

Slave Only

This option defines the PTP mode: ON = Slave Only; OFF = master-slave.

TimeToLive

Defines the PTP Time To Live (TTL). The value determines how many "hops" the PTP clock streams may navigate. Each time a stream traverses a network switch, the TTL is reduced by one.

All Port Parameters

Synchronization → PTP → All Ports

The All Ports sub-page includes more global parameters that affect all media network ports: Announce Receipt Timeout, Delay Mechanism, Log Announce Interval, Log Min Delay Request Interval, Log Sync Interval.

The recommended values will vary depending on the PTP profile in use. Please refer to the Lawo IP Networking Guide.

Individual Port Parameters

Synchronization → PTP → Ports → QSFP

Enable Port PTP

The Enable Port PTP options can be used to define which ports are listening for PTP from the media network (or transmitting PTP if the blade is running as master).

The available ports depend on the operating mode of the system: either 4 x 25GbE (SFP 1 to 4) or 2 x 100GbE (QSFP 1 & 2). In each case, select a port (on the left) and then set the option using the on/off slider.

Path Delay

For diagnostic purposes, you can turn on the Enable PathDelay Updates option to monitor the Path Delay. This is the delay caused by the time taken for packets to travel between the PTP master and slave device. 

Other Fields

The other fields are for informational purposes.