WSTS 2024 Summary & Trends

It was my first time at WSTS as Keysight team showcased brand new clock quality test platform – the Time Sync Analyzer (TSA). As a Product manager for Network Infrastructure Test, it was a great learning to see the components & technologies that brings the time and frequency information from the satellites to the timestamps in the Phy.

A good amount of presentation-time & grape wine discussion in the event was spent on time sync inside the data center networks. Timing accuracy became very important for the Telco networks especially disaggregated 5G RAN and propagating into 6G. Timing has always been present inside the data centers, but nobody talked about it as the accuracy needs were not as much as the telecom domain. The need for more stringent timing is being driven by the need to profile and improve the collective communication needed between AI clusters – the ultimate goal being to reduce any idle time for the CPUs or GPUs which are very expensive resources inside the data center.

The good thing is IEEE 1588 (PTP) is defined as a generic protocol that can work on higher interface speeds used in these data centers i.e. 400GE and 800GE PAM4 speeds. But there are challenges in terms of lack of specification on jitter etc. on the higher speeds. These specs will need to evolve in future as well the latency characteristics of pluggable optics, which are widely used inside a data center fabric, will need to be better standardized.

We have seen in OFC a month back, the proliferation of 400GE ZR,ZR+ optics. We demonstrated the 800GE ZR optics working with Keysight’s AresONE Dual Int 800GE platform. These coherent or ZR/ZR+ modules use colored DSPs to support longer distances. The colored optics and more complex DSP functions adds to the variability of the latency – raises the need for a proper benchmarking method and a specification in coming days.

The SmartNICs communicate inside the servers using PCIe interfaces. The timing information learned from the fabric using PTP over the ethernet interfaces needs to be transferred to CPUs or GPUs inside the server. Precision Time Measurement (PTM) is coming up as one of the technologies to propagate timing over PCIe interfaces. There has to be a dependable verification method to measure the time errors injected by these NICs while doing PTM. Keysight’s oscilloscopes or the Time Sync Analyzer can be used to compare 1pps references from the NIC and the CPU with the PTP reference.

We take Global navigation satellite system (GNSS) to be granted in our daily life and possibly can’t imagine a life without it. One of the talks showed that GNSS outage can cost $1B per day to the world economy. One can always debate the exact number but there is no doubt that it would be disruptive. Positioning, navigation, and timing (PNT) from low earth orbit satellite offers an alternative technology option. LEO (Low Earth Orbit) satellites are closer to earth and therefore can provide 1000 times stronger signal. They circle the earth faster and therefore claimed to be providing better coverage.

Security for time distribution has been a topic of discussion from last 2-3 years especially with the 5G disaggregated radio access network carrying the time for the radios to be synchronized. While encryption techniques like MACsec and IPsec are time tested methods for data transfers in the networking world, question remains how well suited those are for PTP. Alternatives like PTP integrated security using authentication TLVs are options that can become popular and provide a solution to get rid of the overheads of existing encryption techniques.

Time Synchronization over wireless networks comes with its unique challenges because of relatively unreliable media compared to wireline networks. Fine Timing Measurement (FTM) over Wifi and new 3GPP Release 17 specification for Time Sensitive Networking (TSN) over 5G are work in progress. We at Keysight has been working very closely with our industry partners to pave the stones for this technology to mature in near future.

It was fascinating to learn the technology and its evolution behind the atomic clocks and how Artificial Intelligence can have its blessings in compensating drift in oscillators. ?

As with any complex technology there is a need to test and benchmark to make it work at the system level and its more the case for a technology like timing which is sensitive to a lot of environmental parameters e.g. temperature, drift in atomic clocks etc. Allan deviation?(ADEV) is a widely used measure of frequency stability over longer period. There was presentations pointing out the importance of TDEV for GNSS receivers. The Keysight Time Sync Analyzer (TSA) is designed to do all these measurements over longer duration in addition to usual ITU-T compliance test. ?