PTP/IEEE-1588 FAQ
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What is PTP?
Precision Time Protocol (PTP) is a relatively new protocol that was developed to improve the time
synchronization accuracy
that is obtainable over a Local Area Network (LAN). Specifications for PTP are defined in the
IEEE-1588 standard. In PTP terminology, the Grandmaster is the distributor of accurate time and the Slave
is the receiver of this time. The Slave synchronizes itself to the Grandmaster.
The most common network timekeeping protocol is the Network
Time Protocol (NTP). In NTP terminology, the Server is the distributor of accurate time and the Client is the
receiver of this time. The Client synchronizes itself to the Server.
With NTP you can get client synchronization accuracies in the millisecond range.
With PTP you can get slave synchronization accuracies in the nanosecond or microsecond range. Synchronization
accuracy depends not just on the PTP Grandmaster, but also on the network
topology such as switch and slave hardware. For an explanation of PTP and how it is implemented in the
EndRun products read this white paper:
Precision Time Protocol.
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What is the accuracy of EndRun's PTP?
On an existing LAN, with no specialized network or slave hardware, PTP as implemented in the EndRun products,
is capable of synchronizing multiple clocks (slaves) to better than 10 microseconds RMS.
For more information read this white paper: Precision Time Protocol.
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Do your products use version 1 or version 2? What is the difference?
EndRun products have both PTPv2 (IEEE-1588-2008) and PTPv1 (IEEE-1588-2002) available and you can
select which one you want to use. Following is a very brief summary of the two versions:
IEEE-1588-2002 V1
Version 1 is primarily targeted for test & measurement and industrial automation. It is a multicast
protocol for use on a LAN with performance exceeding the capability of NTP.
IEEE-1588-2008 V2
Version 2 is an enhancement to version 1. The versions are incompatible - you need to use one or the other, not both.
Enhancements include unicast messaging, shorter frames,
higher message rates, and profiles such as the Default Profile, Telecom ITU-1 G.8265.1 Profile and Power IEEE-C37.238 Profile.
Shorter frames from 165-octet to 44-octet reduced network bandwidth.
Here are some features of EndRun's PTPv2 implementation:
Default profile.
Multicast messages.
Two-step clock.
Peer-to-peer (P2P) or end-to-end (E2E) delay mechanism.
Sync Interval: 1 or 2 seconds.
Delay Request Interval: 1, 2, 4, 8 or 16 seconds.
Transport: UDP/IPv4.
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I want to put my Grandmaster on one subnet, with my servers and workstations on
another subnet. How will that work?
The Grandmaster user interface allows you to modify the TTL Value (time-to-live value) in order to
accomplish this. You will also need to modify the TTL Value on your PTP Slave.
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What is the difference between hardware and software timestamping?
The main difference is in the synchronization accuracy that is achievable. With software timestamping as
typically implemented (software-only approach), you can see slave synchronization accuracies between 10 and 100 microseconds.
With software timestamping as implemented on an EndRun product (software-hardware hybrid) you can see slave
synchronization accuracies of less than 10 microseconds. You can achieve this level of accuracy with commonly
used network hardware such as standard switches, and computers with software PTP slaves.
With hardware timestamping it is possible to achieve time synchronization accuracies below 1 microsecond. However, in order
to get this level of accuracy, both the Grandmaster and the Slave must be capable of hardware timestamping.
This means you will need to purchase specialized hardware to install in each Slave. In addition, special
PTP-enabled network switches must be used.
For more information on the software, hardware and hybrid implementations of PTP read this white paper: Precision Time Protocol.
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Can PTP operate over a wide area network (WAN)?
PTP Version 2 has been designed to span over a WAN. However, performance is dependent on the network
configuration. For example, a router on the network would need to be 1588-aware to realize the superior
synchronization capability. Otherwise, if the router is not 1588-aware, synchronization of PTP becomes
equivalent to NTP.
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Can PTP be installed in the field?
Yes. All Tempus LX and Unison Time Servers are capable of operating PTP.
PTP is a relatively low-cost option that can be installed by you at any time. All that is needed from
you is the ethernet address (MAC) and we can supply you with instructions for turning on PTP. For older products,
you may need to upgrade your software first.
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Where can I get PTP Slave software?
That question is answered here: PTP Slave Software.
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How many PTP Slaves can your Grandmaster support?
Over 2000.
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