Xpress: What’s new in Xelerated’s precision time solution?

Tord Haulin: We have added a Precision Time Unit to every Ethernet MAC embedded on the NPU. This is a piece of flexible time stamping and time correction logic, which allows advanced synchronization services. The precision time unit has one-step time stamping capability and offloads the CPU from latency calculation tasks.

Xpress: What is One-step PTP?

TH: One-step PTP is quickly becoming a key requirement for synchronization services to base stations in Carrier Ethernet mobile backhaul networks.  It allows to fully utilize the advantages provided by PTPv2-2008. With one-step time stamping each PTP event packet gets its latency time added ‘on-the-fly’, before the PTP packet is further forwarded to the next node towards the base station. Although this adds to the processing of PTP packets, we have implemented a solution that actually improves the time stamp precision.

Xpress: How precise is the solution?

Johan Bäck: To achieve high accuracy, time stamping has to be done as close to the wire as possible. We have paid close attention to jitter, and even managed to reach nanosecond time stamp accuracy for the higher link speeds. You won’t find anything better than that in the market.

Xpress: What about customers who want to support other PTP profiles, like legacy two-step PTP?

TH: The precision time solution supports PTPv1 and all clock modes in PTPv2-2008.

Xpress: What about Synchronous Ethernet?

TH: Synchronous Ethernet is of course also supported. You can flexibly monitor and select links for locking the frequency of the real time clock embedded on the NPU.

Xpress: Can other applications benefit from the new precision time unit?

JB: Sure.The technology has been developed for superior flexibility. We see One-step PTP as an important use case of course, but having time logic in the MAC increases the overall capability of the network processor. The most obvious area for other usages is OAM and performance monitoring.

Interested to understand more about Xelerated Precision Time Solution? Check out our Precision Time white paper.

Note! PTP is short for Precision Time Protocol. This is an IEEE standard initially developed for the automation industry in mind, but was re-engineered in 2008 to support wide scale carrier deployments. The updated standard is referred to PTP IEEE 1588-2008.

• Synchronous Ethernet and PTP are the standards gaining a lot of momentum, and all players are eagerly putting support for these on to their products. (Yes, Xelerated is one of them.)
• There is no need to bet on which of these technologies will actually will become most popular. As some of the big fives in Europe have backed Synchronous Ethernet, it is likely it will find its way to the market. One of the comments at the break was that BT is planning to use Synchronous Ethernet in Open Reach, the UK model for local loop undbundling. If this is the case, all major vendors must support it. And PTP is already in trials with a number of operators.
• PTP v2/2008 is likely to be rolled out in trials with limited on-path support. I see this as an interim solution, while waiting for switch and router vendors to support PTP in hardware. At that point, not too far away, the technology has the scale and reach to depend upon for synchronization services.
• Operators are actively looking for a solution that allows them to can their TDM synchronization services. The pace of adoption will vary widely of course. Expect alternate providers to pave the way.
• Time stamping in hardware is being asked for not only for synchronization services, but also for performance monitoring. I will revisit this area, but as a general point, it is obvious for anyone that router and switch vendors have been getting away with limited capabilities in this area. Integrated probe functionalities have been more of a tick in the box, and haven’t propelled up to the show stopper level in the technical evaluation processes. This is about to change.

There was a good mix of people at the seminar – some representing the vendor side and an equal share from the larger Swedish operators. Notably most of them haven’t been focusing on synchronization for the last ten years, but are now actively getting their heads around the strategies for years to come. Packet technologists and TDM architects are now coming together.  And in a few years, we will know the outcome.

• Network vendors want to comply to two important evolving standards: Packet-based Precision Time Protocol, PTP 1588, and physical layer frequency synchronization defined by Synchronous Ethernet in ITU G.8261.
• A good PTP implementation rely heavily on accurate time stamping. This can be obtained by having all incoming packets time stamped as close as possible to the physical interface. Similarly, outgoing PTP packets should be time stamped as close as possible to the outgoing interface.
• There are a range of configuration options, why hardware support must be both broad and flexible. Programmable designs will help support future amendments to these standards.
• Calculations show that PTP can achieve an accuracy in the range of 50 nano seconds, well in line with demands for mobile backhaul applications.

Synchronization is important for many applications. Requirements for these are collected by the IETF TICTOC work group.

Stay tuned for more updates on the synchronization topic.