TSN-PTP: A Real-Time Network Clock Synchronizing Protocol

In a network containing multiple nodes, the need for synchronization between the various nodes is not just instrumental but also a complicated and highly complex process. This process becomes even more tricky if we synchronize the clocks between the Manager and the Peripheral. As we know, in a real-time network, some of the nodes would behave like Managers while some would be a Peripheral. If we must make the communication process smooth, then the local clocks of these nodes must be synchronized.

The problem with this synchronization is that we have the clock running in the Manager as well. If we send the value of the Manager clock to the Peripheral, the synchronization doesn’t happen as we have a propagation delay of the messages, along with the propagation delay of the electronic circuits of Manager and the Peripheral.

The cherry on the cake is that these electronic circuit propagation delays are not random and remain constant, so we can add a time offset to it to match the clock. To tackle this challenge, IEEE has come up with a protocol named “Precision Timing Protocol.”

Operation of PTP

To synchronize the clocks, a Sync message is sent by the Manager to the Peripheral, which then timestamps the receiving time of the same. Following this, a ‘Follow up’ message is issued by the Manager stating the timestamp at which the Sync message was sent.

The Peripheral then finds the difference between the two values and adds this to its current time. After this, the time difference between the Manager and the Peripheral narrows down to only the propagation delay of the messages.

To overcome this, the Peripheral issues a ‘Delay Request’ to the Manager, and the Manager, in turn, issues a ‘Delay Response.’ Both these messages have the timestamp of when they were issued. The time at which they are received is then noted. Since two messages are sent, one from the Peripheral and the other from the Manager, there are two propagation delays. Then half of this value is our propagation delay.

The Peripheral then adds this propagation delay to its clock, and hence the clock gets synchronized.

Advantages of PTP

1. It provides accurate time stamping.
2. It is a well-known clock synchronization protocol.
3. It provides intensified security inside the premises.
4. It provides the possibility of setting coordinated actions and synchronized communication.

There are various versions of PTP that have been developed over time, namely PTPv1, PTPv2, PTPv2_1, and the latest, PTP-AS.

Cadence Verification IP for Ethernet is available to support the newer version of PTP, allowing simulation of the device for efficient IP, SoC, and system-level design verification. Semiconductor companies can start using it to fully verify their controller design and achieve functional verification closure on it within no time.