Understanding the Impact of Arbitration in MZI-based Beneš Switching Fabrics

Javier Navaridas, Markos Kynigos, Jose a. Pascual, Mikel Luján, Jose Miguel-Alonso, John Goodacre

Research output: Contribution to journalArticlepeer-review


Top-of-rack switches based on photonic switching fabrics (PSF) could provide higher bandwidth and energy efficiency for datacenters (DC) and high-performance computers (HPC) than these with traditional electronic crossbars. However, because of their bufferless nature, PFS are affected by contention much more drastically than traditional packet-switched electronic networks where traffic can advance towards its destination, getting buffered upon encountering contention and resuming transmission once resources are freed. In contrast, PSFs stop the injection of all traffic that generate contention. Consequently, it is important to understand how the order in which flows are serviced affects performance metrics. Our contribution is to quantify this impact through a comprehensive simulation-based evaluation focusing on a recently fabricated PSF prototype. Our experiments include configurations with three routing algorithms, two switching methods, three ToR switch sizes and 9 representative workloads from the DC and HPC domains. We found that the effect of arbitration on raw throughput is negligible but, when considering more realistic loads, selecting an appropriate arbitration policy can improve communication time and energy efficiency. Indeed, the communication time can be reduced by between 10% and 30% by employing appropriate arbitration. Switching energy efficiency can also be improved between 4% and 13%. Finally, insertion loss is barely affected, with differences below 2%. LFU and ARR were found to obtain the best results. LFU is very good with regular workloads but one of the worse with irregular workloads. ARR obtains good results regardless of the type of workload.
Original languageEnglish
Pages (from-to)338-348
Number of pages11
JournalIEEE Transactions on Parallel and Distributed Systems
Issue number2
Early online date28 Nov 2023
Publication statusPublished - 1 Feb 2024


  • Top-of-Rack Photonic Switches
  • arbitration
  • Mach-Zehnder Interferometers
  • performance evaluation
  • simulation


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