Solving the Ultimate Sync Challenge – Oscilloquartz

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Solving the Ultimate Sync Challenge

Kenneth Hann, Senior Director, Research & Development, Oscilloquartz


Synchronization is now an enabler for many high-value services. In the case of new mobile technologies, it’s even a prerequisite for service availability. Quite simply – if you don’t have sync you don’t have service!

Synchronization enables business and if ever the flow of dollars is stopped someone will pay. With this kind of value attached, it’s no surprise that there’s so much interest both in the provision of synchronization as a service and in monitoring the service quality.

Delivering and Monitoring Time at the Same Time
In ten years of attending and speaking at the annual Workshop on Synchronization and Timing Systems (WSTS), I’ve focused on how to provide synchronization as a service over the transport network. Well, last year my focus changed from delivery to monitoring.

Let’s consider operator “A”, who uses Oscilloquartz grandmasters to provide synchronization throughout his network. It may also install Syncjack™ equipment to provide independent monitoring of the synchronization network. Operator “B” may purchase a synchronization service from “A” and may choose to install a separate monitoring solution to verify his synchronization service meets SLA commitments.

The Poacher and Gamekeeper
What if we built delivery and monitoring of timing into the same equipment? Could one device perform these different roles? Could we trust a gamekeeper who is also a poacher? In a traditional synchronization network, the gamekeeper checks the sync but doesn’t provide it. Meanwhile, the other guy is responsible for delivering it accurately but wouldn’t normally be considered an unbiased monitor. That’s why separate equipment and separate management are normally the only way to be sure of accuracy. But this demands multiple kit in the network. Can these roles be combined? Could one box deliver both functions properly at the same time?

The basic problem here involves independence, credibility, and cost effectiveness. In an extreme case, operator “A” uses a device to deliver a service to operator “B” and operator “B” uses a separate, but similar device to monitor the delivered quality of that synchronization service.

The use of additional equipment for service monitoring ultimately increases the cost of the service. Especially so if monitoring is installed and managed separately by both the service provider and the service subscriber. So, what can be done to provide monitoring, traceability and security direct from the synchronization delivery network?

Successful Timing in the Brownfield
Packet-based timing can’t be assured when we can’t measure and compensate for asymmetry in the physical path. There are three solutions to the asymmetry problem:

  • Install full on-path support. This solves the problem in newer managed network scenarios but isn’t possible in brownfield installations and isn’t always economically feasible.
  • Shorten the path by bringing the grandmaster closer to the slave. This is the best workaround when legacy equipment adds latency and doesn’t support PTP. If fixed asymmetries need to be compensated for and impairments can’t be avoided then a shorter path reduces the problem.
  • Make sure it’s monitored. You want to know how well your workaround is working. By installing sync probes to monitor performance, any issues can be quickly resolved.

Assisted Partial Timing Support Does Double Duty
Clocks that use Assisted Partial Timing Support (APTS) can both deliver and monitor timing. When GNSS is available, APTS supports the local time base, allows monitoring of Precision Time Protocol (PTP) and calculates asymmetry. Total/constant/dynamic time error is compared to predefined thresholds and maximum time interval error is evaluated against a predefined mask. This level of monitoring and data analysis helps with early detection of errors.

Should GNSS fails, PTP maintains the local time base, using the asymmetry compensation values previously calculated. So when things are going well, you have two sources of timing information GNSS and PTP slave.

In fact, all of the following are in the same physical APTS box:

1. An edge grandmaster – providing sync service to base stations
2. A sync probe – monitoring the quality of PTP (slave) at the network edge
3. An APTS function which uses a PTP slave for back-up

Sync Monitoring Is New and Advancing
But can we do even better than this? What if we could add embedded sync probes at every Ethernet port and so have delivery and monitoring coexist at every Ethernet interface. Of course whatever technologies and techniques are employed must be based on agreed standards and any missing components introduced for future standardization.

Combining functionality will provide the efficiencies needed for the advanced networks of tomorrow. The ultimate solution for synchronization delivery and assurance certainly looks likely to involve the poacher also doing gamekeeper duty.

At Oscilloquartz, we continue to advance synchronization solutions that not only deliver time accuracy, but provide simultaneous probing across the network. It’s about making monitoring easy, cost-effective and unobtrusive so the networks of today grow quickly to support the fully connected world of the future.

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