Passive Optical Top-Of-Rack Interconnect for Data Center Networks

Optical networks offering ultra-high capacity and low energy consumption per bit are considered as a good option to handle the rapidly growing traffic volume inside data center (DCs). Consequently, several optical interconnect architectures for DCs have already been proposed. However, most of the architectures proposed so far are mainly focused on the aggregation/core tiers of the data center networks (DCNs), while relying on the conventional top-ofrack (ToR) electronic packet switches (EPS) in the access tier. A large number of ToR switches in the current DCNs brings serious scalability limitations due to high cost and power consumption. Thus, it is important to investigate and evaluate new optical interconnects tailored for the access tier of the DCNs. We propose and evaluate a passive optical ToR interconnect (POTORI) architecture for the access tier. The data plane of POTORI consists mainly of passive components to interconnect the servers within the rack as well as the interfaces toward the aggregation/core tiers. Using the passive components makes it possible to significantly reduce power consumption while achieving high reliability in a cost-efficient way. Meanwhile, our proposed POTORI’s control plane is based on a centralized rack controller, which is responsible for coordinating the communications among the servers in the rack. It can be reconfigured by software-defined networking (SDN) operation. A cycle-based medium access control (MAC) protocol and a dynamic bandwidth allocation (DBA) algorithm are designed for POTORI to efficiently manage the exchange of control messages and the data transmission inside the rack. Simulation results show that under realistic DC traffic scenarios, POTORI with the proposed DBA algorithm is able to achieve an average packet delay below 10 μs with the use of fast tunable optical transceivers. Moreover, we further quantify the impact of different network configuration parameters (i.e., transceiver’s tuning time, maximum transmission time of each cycle) on the average packet delay. The results suggest that in order to achieve packet-level switching granularity for POTORI, the transceiver’s tuning time should be short enough (i.e., below 30% of the packet transmission time), while for the case of a long tuning time, an acceptable packet delay performance can be achieved if the maximum transmission time of each cycle is greater than three times of transceiver’s tuning time.