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Energy-Efficient Solutions for 10Gbps Ethernet Yury Audzevich, Alan Mujumdar, Philip Watts, Andrew W. Moore MSN 2012 workshop Friday, July 13th, 2012 Introduction Energy-efficiency of transmission systems is one of the key priorities with respect to the next generation of networking equipment. Open questions: What is the power contribution of the ‘lower layer’ transmission protocols? What is the power impact of Servers vs Network for a Google cluster (fat trees topology) the encoding blocks? (Energy proportional datacenter networks, Abts et al. ISCA 2010) The focus of the research Which effect DC-balanced codes do have on the optical transmission system? …and in particular: what is - the effect on optical power requirement? - front-end power contribution, like PMA and PMD? - the power consumption of line coding block itself? ??? ??? 10Gb/s optical link simulations Optical link – transmission system: • 219 bits PRBS is used as an input, the baud rate is adjusted after encoding Optical link parameters: • 100m Single Mode Fibre with parameters satisfying requirements for 10Gbps Ethernet over SMF Optical link – receiving system: • Optical receiver with direct detector and AC coupling achieved using High Pass Filter • BER is calculated using the complementary error function 10Gb/s optical link simulations (cont.) better better • The transmission system is relatively insensitive to the DC-balanced codec choice • Taking 100MHz HPF cut-off frequency and assuming 20dB link budget, the laser power requirement is lower for encoded sequences (0.3mW of savings) in comparison to PRBS Physical Coding Sublayer – 8B10B (and 64B66B) 8B10B line code: 1) Encoder/Decoder – implemented 3B4B and 5B6B codes plus disparity control check for DC-balance 64B66B line code: 1) Encoder/Decoder – decoding from XGMII into 10GBASE-R format 2) Scrambler/Descrambler – mixing of data to avoid long sequences of 0s/1s • Codecs were implemented in Verilog HDL and Synthesized using 90nm and 45nm technical process libraries • Industry standard estimation tools were used for power measurements Early-days results – 8B10B PCS power 10Gb/s link results: obtained for 30 microseconds simulation periods, with a symbol clock frequency of 625MHz for both 45nm and 90nm tech. process Inverse of energy-proportionality • IDLE sequences costs MORE to encode • Low leakage 45nm library provides decrease in power by a factor of 2 Power estimates – 64B66B PCS 10Gb/s link results: Identical pattern sent for 30 microseconds of simulation periods, with a symbol clock frequency of 156.25 MHz 64B66B 10GBASE-SR / 10GBASE-LR (commonly used) 8B10B 10GBASE-LX4 (less common) • Power consumption of 64B66B codec is actually more data proportional • Scrambling & gearbox modules have a fixed power cost (~1.5-2.5 times larger power dissipation than the combination of encoder & decoder power) Physical Medium Attachment – 8B10B and 64B66B PMA components are built using both CMOS and MCML logic families • CMOS designs were synthesized using standard cell libraries • MCML designs were built, optimized and analysed using HSPICE tools PMA power – 8B10B and 64B66B 64B66B • MCML power is independent of the operating frequency but is strongly related to the optimization criteria • At high clock frequencies MCML designs become more power efficient than their CMOS counterparts • Even well power-optimized PMA designs may require 5x-10x times higher power than the corresponding PCS blocks! Implications • Our recent analysis of realistic trace data(10Gbps) showed average link utilization of only 8.79% - in concordance with [1]. • The majority of the networks are overprovisioned to sustain peak loads and underutilized most of the time • Current implementations of Ethernet standards require continuous transmission of IDLE code words (even in the absence of MAC traffic) So… May be, we need a system that has good energy-proportionality and can quickly restart Sounds like we need a new MAC… [1] T. Benson, A. Akella, and D. A. Maltz. Network traffic characteristics of data centers in the wild. In Proceedings of ACM IMC '10, pp. 267-280, New York, USA, 2010. Or an old energy-efficient MAC Remember this one? Ethernet – CSMA/CD Many features/ideas we don’t want, but one we do: • Preambles give clocks valuable re-sync. time and allow photonic systems to turn back on Energy-efficient MAC Where do we get energy-savings from: Powering down the codecs when no data is present Using a synchronization preamble prior to data transmission for fast CDR Is the protocol going to make a difference? 89% 93% 93% 87% With avg. Ethernet frame size of 1150bytes and 64bits of preamble, the effective energysaving is ~93% Key take-aways Optimal laser power is independent of the DC-balanced codec chosen Codec power consumption is not always data-proportional Serialization/deserialization power dominates over all the other power groups New MACs (off when idle) do save significant power How do we test, build, trial? regular NICs don’t help Need something programmable but FAST… Thank you! QUESTIONS?