C-Through: Part-time Optics in Data centers Aditi Bose, Sarah Alsulaiman

Evaluation Joke – Didn’t construct a real such data center -Simulation on electrical switching data center and on only 16 servers & 2 Ethernet switches. – They omit implementation details. – Network management overhead huge for big data centers.

Effective use of optical Network – Estimate cross-rack traffic demand – Configure the optical circuit – Configure ToR switch to demultiplex traffic into correct path – Method used increases configuration complexity

Application Requirements..? – Topology aware – Doesn’t sound very practical – Increases complexity of applications. – Communication Requirements – Traffic pattern – Not useful for apps with small sized data units(e.g. Hadoop) – Frequency of synchronization – Suitable for apps with loose or no synchronization.

New Protocols! – Why Still use TCP – High app latencies. – Wouldn’t newer protocols be more appropriate(e.g. DCTCP)?

Fault Tolerance – What if fiber is cut? – How it affects network?

Limitations of Optical circuit switch – Need to reconfigure faster – Catch short, bursty flows.

Cost ? – Practical today? – Heat dissipation

Overcrowding – Retains complete packet switch network.

Handling Latency Sensitive Applications – Traffic de-multiplexing only based on Destination Rack & not on latency – sensitivity of applications. – Applications studied are not sensitive to latency.