What’s In the 2019 Edition of IEEE 1588?

Five Minute Facts About Packet Timing

By Doug Arnold

The new edition of IEEE 1588, IEEE 1588-2019 is finally available.  The name is based on the year it approved by the IEEE Standards Board, not the year it is published.

So, what’s there? Everything that was added or changed was for the purpose of:

• Making the standard clearer
• Adding flexibility to the protocol
• Adding robustness to the protocol
• Increasing accuracy

Some of these were shamelessly stolen from existing PTP profiles.  The authors of the PTP profiles have come up with some features which are just too good to hoard in a single industry.

Before I tell you what the new features are I need to quote The Hitchhiker’s Guide to the Galaxy, and say:

DON’T PANIC

The time and money you have spent on PTPv2 is not lost.  The new version will be backward compatible with the old.  We decided that this was so important that we wrote it into the bylaws of IEEE 1588 Working Group, which states:

“The working group shall ensure that the resulting draft has the highest degree of backward compatibility possible with the previous edition of IEEE 1588”

To make this clear we are referring to the new version of PTP as PTPv2.1.  Just a minor revision; no big deal.  But a minor revision with a lot of cool new options.   We define backward compatibility this way: You can take a PTPv2 device out of the network, and replace it with a PTPv2.1 device, and the network will work just as before.  Or you can take a PTPv2 device off the shelf and put it in a PTPv2.1 network, and it will work, as long as the older version device does not have to execute any of the new options.

Ok.  So, what are these options.  Here is a list.

Options for flexibility:

• Modular Transparent clocks. TCs which can be built in a blade server, or SFP architecture.
• Special PTP ports to interface to transport technologies which have their own built in timing mechanism, e.g. WiFi.
• Mixed Multicast/Unicast operation.  Usually this means that the Announce and Sync are multicast, and the DelayRequest and Delay Response is unicast.

Options for accuracy:

• Manual Port Configuration.  No BMCA, needed.  but be warned, we ‘re giving you all of the rope you need to hang yourself.
• Asymmetry calibration.  Including calibration of PHY asymmetry.
• Physical layer syntonization.  For example, Synchronous Ethernet.

These are three key additions for the White Rabbit extensions to PTP.  Using these feature the clever scientists at CERN were able to achieve sub-ns time transfer, using standard Ethernet PHYs.

Options for robustness:

• Profile isolation. Running incompatible profiles on the same network?  We got you covered.
• Inter-domain interactions Remember when I said that PTP domains are independent of each other?  Well, under some restrictive circumstances that is not always the case.
• Security.  We defined a security TLV for message and source integrity checking.  Plus a bunch of helpful guidelines on security.
• Standard performance metrics.  What if every PTP node on the network made performance statistics available in the same format…
• Slave port monitoring. Don’t just transfer time to the slave clock, prove you did it.

In upcoming posts, I will describe these options in more detail.  Until then, happy synchronizing.

If you have any questions about PTP, don’t hesitate to send me an email at doug.arnold@meinberg-usa.com or visit our website at www.meinbergglobal.com.