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Abstract

Optical data center networks (DCNs) are renovating the infrastructure design
for the cloud in the post Moore's law era. The fact that optical DCNs rely on
optical circuits of microsecond-scale durations makes nanosecond-precision time
synchronization essential for the correct functioning of routing on the network
fabric. However, current studies on optical DCNs neglect the fundamental need
for accurate time synchronization. In this paper, we bridge the gap by
developing Nanosecond Optical Synchronization (NOS), the first
nanosecond-precision synchronization solution for optical DCNs general to
various optical hardware. NOS builds clock propagation trees on top of the
dynamically reconfigured circuits in optical DCNs, allowing switches to seek
better sync parents throughout time. It predicts drifts in the tree-building
process, which enables minimization of sync errors. We also tailor today's sync
protocols to the needs of optical DCNs, including reducing the number of sync
messages to fit into short circuit durations and correcting timestamp errors
for higher sync accuracy. Our implementation on programmable switches shows
28ns sync accuracy in a 192-ToR setting.