New technique may enable all-optical data-centre networks

TRANSNET members Dr Zhixin Liu and Kari Clark have developed a new technique that synchronises the clocks of computers to within a billionth of a second, publishing their findings in Nature Electronics. This work has the potential to create greater efficiency in data centres. 

Data centres, comprising tens or hundreds of thousands connected servers, are the underlying technology empowering everything we do online, from storing films and photos to serving up webpages and online services. However, they face rapidly rising demand, with server-to-server traffic increasing by 70% each year, which is increasingly hard to meet with existing technologies. All-optical networks that use light to both transmit and route data represent a promising alternative. However, their viability has been limited due to the need for each server to continuously adjust its clock time according to incoming data, which resulted in lower overall performance.

The study, published in Nature Electronics, shows that by synchronising clocks of all connected servers via optical fibre, and programming hardware to memorise clock phase values so clock time does not have to be re-checked, the time to “recover” the clock could be practically eliminated.

PhD candidate Kari Clark, of the Optical Networks Group at UCL and lead author of the study, said:

“Our research makes optical switching viable for the data centre for the first time by providing a solution to the clock synchronisation problem. It has the potential to transform communication between computers in the cloud, making key future technologies like the internet of things and artificial intelligence cheaper, faster and consume less power.”

Until now, cloud providers have been able to accommodate rapid growth in demand by relying on Moore’s Law for networking, whereby, about every two years, electronic switch integrated circuits double their data transmission speed at the same cost and power. However, the sustainability of this trend is increasingly being questioned due to the difficulty of continuing to be able to make silicon transistors smaller and faster.

Dr Zhixin Liu, TRANSNET Co-I and Kari's PhD supervisor, said:

“We started this work by investigating how to support future cloud services beyond the end of Moore’s law. By bringing the top minds from cloud operators and optical communication research, we propose a future-proof alternative using optics, helping data centres to cope with demand in the long term.”

Kari and Zhixin, working with in collaboration with researchers at Microsoft Research Cambridge, developed a prototype and found that their technique, called “clock phase caching,” could synchronise the clocks of thousands of computers in under a billionth of a second, or the time it takes for light to travel 30 cm in air. 

The authors demonstrated that reducing the clock recovery time to under a nanosecond resulted in a significant increase in performance of optical switching compared to state-of-the-art solutions, making it practical for data centres and unlocking its full potential.

This story was first published on UCL news.


Synchronous subnanosecond clock and data recovery for optically switched data centres using clock phase caching
Kari A. Clark, Daniel Cletheroe, Thomas Gerard, Istvan Haller, Krzysztof Jozwik, Kai Shi, Benn Thomsen, Hugh Williams, Georgios Zervas, Hitesh Ballani, Polina Bayvel, Paolo Costa and Zhixin Liu
Nature Electronics
doi.org/10.1038/s41928-020-0423-y

Image: Kevin Price/Detail Design Consultants/UCL.

For a full list of published TRANSNET research, including journal and conference papers, please take a look at our publications page.