TCP congestion control in datacenter optical packet networks on hybrid switches

Optical packet switching (OPS) has long promised performance and energy consumption improvements by doing away with optical-to-electronic conversions required by electronic packet switching; however, not having practical optical buffers makes OPS highly vulnerable to contention. This study reports on the possible and plausible use of OPS technology on datacenter networks by coupling two concepts: optical switches with shared electronic buffers, also known as hybrid switches, and the introduction of TCP congestion control algorithms (CCAs) to control transport of optical packets. The stop-and-wait (SAW) and the modified additive increase multiple decrease (mAIMD) CCAs families are reviewed. For SAW, a basic version and a modified one—stop-and-wait-longer, adapted for hybrid switches—are analyzed. As for mAIMD, a TCP selective acknowledgment (SACK) implementation and its simplified modification TCP mSACK are studied. It is successfully shown that these algorithms paired with the use of shared electronic buffers in hybrid switches significantly outperform bufferless all-optical switches and reach the level of all-electronic switches in datacenters and local area networks in terms of network throughput.