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Realizing the Optical Transport Networking Vision in the 100 Gb/s EraSilvano Frigerio, Alberto Lometti, Juergen Rahn, Stephen Trowbridge, and Eve L. VarmaAfter a half-decade hiatus, stimulated by dramatic service-driven increases in backbone network bandwidth requirements, industry focus has once again turned to realizing a vision of optical transport networking (OTN). In the timeframe since the rst OTN standards were stabilized, technology has continued to evolve, and additional new service requirements have materialized. The ability to provide optimized support for gigabit Ethernet services, ranging from 1Gb/s to 100 Gb/s, has become a high priority. This paper examines how evolving OTN standards provide a multi-service capable backbone infrastructure supporting lambda and sub-lambda services with guaranteed quality, the role of optical control plane technology in realizing dynamically congurable OTN and Internet Protocol (IP) over optical transport networking solutions, and emerging technology enablers. The paper concludes by providing a vision of optical transport network infrastructure evolution in the 100 Gb/s era. 2010 Alcatel-Lucent.

IntroductionBandwidth demand continues to grow worldwide, fueled by new Internet Protocol (IP)-based services and multimedia applications. The availability of higher bandwidth service offerings, coupled with applications needing higher speeds, has resulted in dramatic increases in access rates in order to enable faster consumer access to these services. This dramatic increase in access rates has created a domino effect, rippling through metro networks and ultimately driving dramatic increases in backbone network bandwidth requirements. With higher volume, lower revenue service mixes driving the need for increased protability, there has been increased service provider attention towards converging multiple services onto a future-proof next-generation optical transport network (NG-OTN) infrastructure positioned to support emerging ultra-high bit rate services (e.g., IEEE 100GBASE-R, 40GBASE-R). Leveraging optical control plane advances, dynamically congurable OTN and IP-over-OTN solutions deliver on the promise of rapid provisioning, increased automation, and richer sets of service functionality. The control plane enabled OTN opens the door to new services, similar to how signaling system 7 (SS7) opened up the possibilities for advanced intelligent networking (AIN) for the public switched telephony network (PSTN). IP-over-OTN solutions not only provide a dynamically congurable optical layer responsive to IP networking demands, but enable multi-layer optimization with superior service resiliency. This paper examines OTN standardization advances and how OTN-based networking helps service providers

Bell Labs Technical Journal 14(4), 163192 (2010) 2010 Alcatel-Lucent. Published by Wiley Periodicals, Inc. Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/bltj.20410

Panel 1. Abbreviations, Acronyms, and Terms 3RReshape, retime, retransmit AINAdvanced intelligent networking AISAlarm indication signal AMPAsynchronous mapping procedure APSAutomatic protection switching ASICApplication-specic integrated circuit ASONAutomatically switched optical network ASSPApplication specic standard product ATMAsynchronous transfer mode BERBit error rate BIPBit interleaved parity BoDBandwidth on demand CAPEXCapital expenditure CBRConstant bit rate CDRClock and data recovery CMConnection monitoring CMOSComplementary metal-oxide semiconductor DCDirect current DPSKDifferential phase shift keying DQPSKDifferential quadrature phase shift keying DWDMDense wavelength division multiplexing E-NNIExternal network-network interface FDIForward defect indication FECForward error correction GbEGigabit Ethernet GFPGeneric framing procedure GFP-FGFP-framed GFP-TGFP-transparent GMPGeneric mapping procedure GMPLSGeneralized multiprotocol label switching HOHigher order IEEEInstitute of Electrical and Electronics Engineers IaDIIntra-domain interface IPInternet Protocol IrDIInter-domain interface ITUInternational Telecommunication Union ITU-TITU Telecommunication Standardization Sector LANLocal area network LCASLink capacity adjustment scheme LHLong haul LOLower order LOSLoss of signal MIIMedia independent interface MPLSMultiprotocol label switching NENetwork element NG-OTNNext-generation OTN NMSNetwork management system NOCNetwork operations center OADMOptical add/drop multiplexer OAMOperations, administration, and maintenance OChOptical channel ODUOptical channel data unit O/EOptical/electrical OEOOptical-electronic-optical OMSOptical multiplex section ONEOptical network element OOKOn-off keying OPEXOperating expenses OPSMnkOptical physical section multilane (n number of lanes) OPUOptical channel payload unit OSCOptical supervisory channel OSNROptical signal-to-noise ratio OSSOperations support system OTLCOptical transport lane carrier OTLCGOptical transport lane carrier group OTMOptical transport module OTNOptical transport network OTSOptical transport section OTUOptical channel transport unit P2PPoint-to-point PCSPhysical coding sublayer PDHPlesiochronous digital hierarchy PHYPhysical layer PMDPolarization mode dispersion PSTNPublic switched telephony network PXCPhotonic cross connect QoSQuality of service QPSKQuadrature phase shift keying ROADMRecongurable optical add/drop multiplexer SDHSynchronous digital hierarchy SESpectral efciency SLAService level agreement SONETSynchronous optical network SRLGShared risk link group SS7Signaling system 7 STMSynchronous transfer mode TCMTandem connection monitoring TDMTime division multiplexing TOADMTunable optical add/drop multiplexer ULHUltra long haul UNIUser network interface VCATVirtual concatenation VCGVCAT group VLANVirtual local area network VPVirtual path VTVirtual tributary WANWide area network WDMWavelength division multiplexing WSSWavelength selective switch WXCWavelength cross connect

evolve to a unied, optimized layer of high-capacity, high-reliability bandwidth management, providing solutions for delivering existing and emerging packetbased services with guaranteed quality.

HistoryDuring the late 1990s, the telecommunications industry became swept up in a desire to capitalize on an unprecedented demand for network capacity, mostly driven by rapidly growing packet-based servicesin particular, by Internet/Intranet-based applications. The industry view was that transport networks would need to become optimized for much larger capacity channels carrying broadband data, voice, and video. At the same time, driven by the vision of virtually innite information bandwidth and transport in the optical domain, research thrusts accelerated in exploring sophisticated photonic devices and techniques to allow the transport and routing of signals in the optical domain [1]. While these early visions focused upon optical transparency, it became clear that practical visions for optical networking involved the use of optoelectronics to support carrier grade transport capabilities. The optical transport network was born out of this recognition, leveraging industry synchronous digital hierarchy (SDH)/synchronous optical network (SONET) experience and considering optical technology factors, and was considered the next step beyond SDH/SONET in supporting data-driven needs for bandwidth and the emergence of new broadband services [26]. The industry was swept up in a wave of standardization initiatives to create a suite of OTN recommendations. It was expected that optical transport networks would quickly evolve from dense wavelength division multiplexing (DWDM) remedies for capacity exhaust, to DWDM optical networking solutions optimized for support of fully transparent Gb/s services. However, with the bursting of the Internet bubble, bandwidth requirements were lower than predicted with little demand surfacing for wavelength leased lines, and client signals remained predominantly at the sub-SDH and synchronous transfer mode (STM)16 rates. Exacerbating the situation, there was a significant amount of installed excess capacity in

long-haul networks that had been laid in the expectation of its imminent need. The market downturn in succeeding years resulted in deferred deployment of new photonic networking technologies. Thus, in the timeframe during which the OTN standardization effort came to fruition, the market stalled. In the past few years, the anticipated bandwidth demands have nally materialized, as exemplied by intensive Institute of Electrical and Electronics Engineers (IEEE) standards initiatives for specication of 100 GbE/40 GbE. Concurrently, packet-based services optimization demands have driven interest in OTN capabilities well down into the sub-lambda ranges. These forces have triggered OTN evolution initiatives, expanding its scope from 1 Gb/s through 100 Gb/s, with further upward growth towards 400 Gb in the next decade.

OTN DriversDrivers for evolution from SDH/SONET to OTN have evolved over the timeframe from its conception to its rebirth. A case in point is the meaning and role of OTN transparency, referring to the set of characteristics of a client signal that are preserved when that client is carried over the OTN. Examples of types and levels of transparency include dark ber, wavelength, bit, symbol or codeword, Ethernet (media independent interface [MII], frame plus preamble, frame), and timing. As noted previously, the early optical transparency visions of transport of arbitrary client signals over wavelengths of a ber-optic network were found problematic given the various impairments (e.g., chromatic and polarization mode dispersion, attenuation) that occur when traversing various ber types and optical components. There can also be challenges in preserving the same set of client characteristics when a client is transported on a dedicated wavelength versus when that same clien