POTORI: A Passive Optical Top-of-Rack Interconnect Architecture for Data Centers

Abstract

Abstract-Several optical interconnect architectures inside data centers (DCs) have been proposed to efficiently handle the rapidly growing traffic demand. However, not many works have tackled the interconnects at top-of-rack (ToR), which have a large impact on the performance of the data center networks (DCNs) and can introduce serious scalability limitations due to the high cost and power consumption. In this paper, we propose a passive optical ToR interconnect architecture (POTORI) to replace the conventional electronic packet switch (EPS) in the access tier of DCNs. In the data plane, POTORI relies on a passive optical coupler to interconnect the servers within the rack and the interfaces toward the aggregation/core tiers. The POTORI control plane is based on a centralized rack controller responsible for managing the communications among the servers in the rack. We propose a cycle-based medium access control (MAC) protocol to efficiently manage the exchange of control messages and the data transmission inside the rack. We also introduce and evaluate a dynamic bandwidth allocation (DBA) algorithm for POTORI, namely Largest First (LF). Extensive simulation results show that, with the use of fast tunable optical transceivers, POTORI and the proposed LF strategy are able to achieve an average packet delay below 10 µs under realistic DC traffic scenarios, which outperforms conventional EPSs. On the other hand, with slower tunable optical transceivers, a careful configuration of the network parameters (e.g., maximum cycletime of the MAC protocol) is necessary to obtain a good network performance in terms of the average packet delay.Index Terms-Optical interconnect architectures, data center networks, medium access control (MAC), dynamic bandwidth allocation (DBA).

PULSE: Optical circuit switched Data Center architecture operating at nanosecond timescales

“…Distributed and centralized MAC protocol based heuristics have also been proposed to control optical switches. In the 64-port POTORI (coupler based) switch, a centralized and tailored MAC protocol uses Largest First (LF) and iSLIP scheduling heuristics, which were shown to incur a latency of 10 ms above 80% workload [14]. The c-MAC control scheme in the AWG-based petabit switch architecture has an estimated latency of 5 µs (also for 64-port AWG) for offered network loads above 70% [64].…”

“…However, a major challenge faced when scaling an optical switch is the scalability of the central scheduler [12]. Hence, many optical switch technologies resolve to softwarebased scheduling to simplify switch configuration [9], [10], [13], [14]. Nevertheless, software based control systems take milliseconds to compute switch configurations.…”

SDN enabled flexible optical data center network with dynamic bandwidth allocation based on photonic integrated wavelength selective switch

“…The scalability of wired OSA architecture is limited by the switch port radix, just supporting 2560 servers. POPI and POTORI DCN architectures can provide dynamic bandwidth to serve the various traffic [22,23]. However, the hundreds of microseconds server-to-server latency do not satisfy the latency-sensitive applications.…”

Multi-Node All-Optical Interconnect Network Routing for Data-Center Parallel Computers

“…The high cost and high-power consumption characteristics of traditional data centers introduce severe scalability limitations. A passive optical top-of-rack (ToR) interconnect architecture is proposed to replace the traditional electronic packet switch (EPS) in the data center networks (DCNs) access layer [16]- [18]. Meanwhile, an optical interconnection structure based on a fiber link is proposed to realize long-distance optical interconnection transmission [19], [20].…”