Chow, Hungkei

Duque, Alex

Suvakovic, Dusan

Torfs, Guy

Van Praet, Christophe

Verbeke, Marijn

Vyncke, Arno

Yin, Xin

English

Ghent University Academic Bibliography

A Low Power 40Gbit/s Cascaded Extension toBit-Interleaving Optical Networks EnablingNext-Generation Metro/Access ConnectivityA. Vyncke1, G. Torfs1, M. Verbeke1, C. Van Praet1,H.K. Chow2, D. Suvakovic2, A. Duque2, and X. Yin11 Ghent University - iMinds - imec, Department of Information Technology (INTEC),Sint-Pietersnieuwstraat 41, B-9000 Ghent2 Bell Laboratories, Alcatel-Lucent, Murray Hill, NJ 07974, USAOptical networks in use today were not designed to accommodate the needs of new tech-nologies such as cloud services and the Internet of Things. Features as flexible bandwidthallocation and low packet-delay variation, which are of crucial importance, are still miss-ing in current metro/access networks. In this paper the solution known as CBI-PON ishighlighted. CBI-PON is a cascaded extension of the BiPON protocol offering thesefeatures, while lowering the network’s power consumption. A 40 Gbit/s implementationof the electrical part is presented, showing 80× (Repeater) and 6× (End-ONT) powerconsumption reduction compared to currently available commercial equipment.IntroductionThe demand for higher bandwidths has been steadily rising over the last few years [1].To satisfy this demand, a divergent collection of access technologies has been developed.Particularly interesting are the Passive Optical Networks (PONs), since they are generallyconsidered as a cost-effective and energy efficient option.Furthermore, upcoming technologies such as the Internet-of-Things and cloud servicespose new challenges such as a need for highly flexible dynamic bandwidth allocation andlow packet-delay variation. On top of these new challenges, the environmental impact ofcommunication networks is becoming more and more significant: in 2012 an estimated1.8 % of the global power consumption was attributed to communication networks [2].Therefore, next-generation networks should try to reduce their power consumption.In this paper, the Cascaded Bit-Interleaving PON (CBI-PON) is introduced as a solutionto all these challenges. First, the Bit-Interleaving PON (BiPON) is introduced, followedby its extension CBI-PON. Subsequently, the CABINET implementation is presented.Finally, the predicted power consumption figures illustrate the potential of the concept.Bit-Interleaving PON ProtocolIn 2010 the Bit-Interleaving PON Protocol was introduced [3, 4]. Traditional PONs usea packet-based TDM: bits intended for a single Optical Network Unit (ONU) are sentconsecutively and are grouped in packets, as shown in Figure 1a. This has some impor-tant implications on the receiver side. In short, the receiver front-end must operate at ahigh frequency and must recover all bits, which is a power hungry operation. The MACprocessor then continues to process all bits, including those addressed to other ONUs.This energy efficiency was mitigated by introducing a paradigm-shift and moving to abit-based TDM: bits are sent one at a time, with bits for other ONUs in between. A clari-fying schematic representation is given in Figure 1b.Packet-based Time Division MultiplexingONUOLTONUONUSplitter(a) Packet-based TDMBit-based Time Division MultiplexingOLT ONUONUONUSplitter(b) Bit-based TDMFigure 1: Time-Division MultiplexingFurthermore, bits are sent in the form of a BiPON Frame, which contains a frame header.This header allows receiver configuration on a frame-per-frame basis, which enables ahighly flexible dynamic bandwidth allocation scheme. For a more elaborate descriptionof the protocol the reader is referred to [3, 4]. The BiPON concept was demonstratedin a 10 Gbit/s implementation with power consumption measurements showing reductionfactors from 35× up to 180× depending on the specific configuration.Cascaded BiPONIn an effort to further decrease communication networks’ power consumption, the Cas-caded BiPON (CBI-PON) concept was developed. A Cascaded BiPON is a multi-levelPON network where each level consists of a self-contained BiPON. A 3-level implemen-tation is shown in Figure 2, where the 3 levels (L1, L2, L3) are clearly indicated. Withthe exception of the lowest level (L3), each level consists of two types of CBI Devices:CBI Repeaters and CBI End-ONTs.R2Core routerCoreMeshR1N1 N2InterleaverEnterpriseNetworkEnterpriseNetworkN3N3N3Nx: Level-x End-ONTRx: Level-x RepeaterMetro/EdgeL1 PONDS: 40 GbpsAccessL2 PONDS: 10 GbpsHomeL3 PONDS: 2.5 GbpsFigure 2: Cascaded Bit-Interleaving PONThe sole purpose of CBI Repeaters is to repeat CBI Frames to lower level BiPONs, whichexplains why they are not present on the lowest level. To this end, only the headers ofthe incoming CBI Frames are processed by the CBI Repeaters. According to the config-uration of the CBI Repeater and the header data, the appropriate part of the payload isrepeated to the lower level BiPON. The processing complexity of the CBI Repeaters isdeliberately kept to a minimum to reduce the power consumption of these devices.CBI End-ONTs act as the leaf nodes of the BiPON on each level. Based on the informa-tion parsed from the frame header, all necessary processing is performed on the payloadand the output data is sent to the FPGA which provides a standard Ethernet interface tothe end user.CABINET ImplementationThe CABINET Application-Specific Integrated Circuit (ASIC) was developed to demon-strate the concept of the CBI-PON and its power consumption reduction potential. TheCABINET chip is a multi-mode, multi-rate device: it can act both in Repeater mode asin EndONT mode, and it supports input line rates of 40 Gbit/s, 10 Gbit/s and 2.5 Gbit/s.This allows the CABINET chip to be used to implement any CBI Device in the pre-sented 3-level CBI-PON, reducing cost of deployment for the network operator. A systemoverview of the CABINET ASIC is shown in Figure 3. It consists of an analog front-endthat sub-samples the incoming data, recovers the clock and retimes the data. Subse-quently, this data is processed by the MAC pre-processor. The physical implementationis shown in Figure 4a and the testboard is shown in Figure 4b.PD88dsCDRDownstreamcoreControl logicCP LF VCOFDFigure 3: CABINET System Overview(a) CABINET ASIC(b) CABINET TestboardFigure 4: CABINET ImplementationPower Consumption ReductionThe first prototype of the CABINET ASIC had some issues, causing some modes to onlyfunction partly. Combining the simulated power consumption and the measured powerconsumption of the functional parts, the total power consumption was estimated. Theseextrapolated results are presented in Table 1.Table 1: Extrapolated CABINET power consumptionCBI RepeaterSimulated ExtrapolatedL1 126 mW 187.63 mWL2 86.5 mW 120.48 mWL3 - -CBI End-ONTSimulated ExtrapolatedL1 106 mW 162.55 mWL2 66.5 mW 94.55 mWL3 50.88 mW 60.51 mWWithin the GreenTouch project, a reference architecture was defined to compare powerfigures. The access network is defined as a 40 Gbit/s ring of Remote Nodes with an ag-gregation switch combining 32 2.5 Gbit/s PONs with an average of 73.36 ONUs per PON.This aggregation switch (201 mW/ONU) is equivalent to 32 L1 Repeaters (2.56 mW/ONU),resulting in an 80× power reduction.The leaves of the access network are ONUs (1.481 W/ONU) containing a small internalPON to support 2 Ethernet ports. An L3 Repeater and 2 L3 End-ONTs would be equiva-lent, but since there is no L3 Repeater implemented, the power number of the L2 Repeaterwill be used. This configuration is estimated to consume 241.5 mW/ONU, which trans-lates to a more than 6× power reduction.ConclusionIn this paper, the Cascaded Bit-Interleaving PON was presented as a way to mitigate thechallenges that are appearing for next-generation metro/access networks. To demonstratethe potential of this solution, the CABINET was developed: a 40 Gbit/s ASIC that canimplement both CBI Repeaters as CBI EndONTs. Compared to commercial equipment,the estimated power consumption of the CABINET shows reduction factors of 80× (Re-peater) and 6× (EndONT).References[1] Cisco. Cisco Visual Networking Index: Forecast and Methodology, 2014–2019. Cisco VNI WhitePaper, 2015.[2] S. Lambert, W. Van Heddeghem, W. Vereecken, B. Lannoo, D. Colle, and M. Pickavet. Worldwideelectricity consumption of communication networks. Optics Express, 20(26):B513–B524, 2012.[3] C. Van Praet, H.K. Chow, D. Suvakovic, D. Van Veen, A. Dupas, R. Boislaigue, R. Farah, M.F. Lau,J. Galaro, G. Qua, et al. Demonstration of Low-Power Bit-Interleaving TDM PON. Optics Express,20(26):B7–B14, 2012.[4] C. Van Praet, G. Torfs, Z. Li, X. Yin, D. Suvakovic, H.K. Chow, X.Z. Qiu, and P. Vetter. 10 Gbit/sBit-Interleaving CDR for Low-Power PON. Electronics letters, 48(21):1361–1363, 2012.

A low power 40 Gbit/s cascaded extension to bit-interleaving optical networks enabling next-generation metro/access connectivity

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A low power 40 Gbit/s cascaded extension to bit-interleaving optical networks enabling next-generation metro/access connectivity

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