Pbt article packet-optical-integration_vishal_05-08-12


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Since the photonic layer is the cheapest on a per-bit, per-function basis, and since
the key imperative before operator's today is to bridge the yawning gap between
exponentially increasing data traffic on the one-hand, and flat-to-declining revenues
on the other, a tighter coupling between the packet and optical layers to derive
operational, management, and deployment efficiencies, has...

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Pbt article packet-optical-integration_vishal_05-08-12

  1. 1. PTB >>Packet-Optical IntegrationThe operator’s paradox for the past several years has been that while there is an explosion in datatraffic volumes to the tune of 45-65% yearly, the corresponding revenue growth is in the single digits atbest. To bridge this gap, providers must assess how to better architect their networks to reduce thetransport-cost per bit, conserve space and power, and improve network performance to lower the opex.(Statistics show that service providers spend almost 5 opex dollars for each capex dollar![1]). They mustalso optimize their networks to efficiently carry high growth services like Internet access, packet trafficfrom 3G/4G wireless networks, and video. Achieving this efficiency entails a tighter integration betweenthe packet and the optical/photonic layers, since the photonic layer is the cheapest perbit, per function, thusmotivating the packet-opticalintegration.Major Solution Drivers Figure 1. Neilsen’s Law of Internet Bandwidth,Technological advances (e.g. cloud predicted in 1998, has shown accurate and consistent forcomputing, remote diagnostics, over a decade (From Jakob Neilsen’s Alertboxmultimedia collaboration), http://www.useit.com/alertbox/980405.html ).bandwidth in tensive applications(e.g. video services with HD,Carrier Ethernet enterpriseservices, remote data backup anddisaster recovery), and fastconnection speeds, whichaccording to Nielsen’s Lawdouble every 21 months (Figure 1),lead to a proliferation of datapackets and drive the demand for abetter networking solution. Inaddition, some key enterprisetrends contribute to this traffic. Forinstance, almost 95% of enterprisetraffic is now Ethernet-based.Indeed, business Ethernet portdemand was up 43% in 2008alone. Further, almost 80% oftraffic now leaves the enterprise(the reverse of what it was just alittle over a decade ago) implying a much greater load in the metro and core[2]. Thus, a key impetus forcarriers is to increase the effectiveness and efficiency of transporting these packets over an optical transportnetwork in the WAN environment.Today, the IP/Ethernet packets are wrapped into SONET/SDH or G.709 TDM circuits, and transportedover wavelengths on an optical infrastructure. One disadvantage of this is that when all switching occurs ina Layer 3 router/switch rather than judiciously leveraging Layer 2 Ethernet or Layer “2.5” MPLSswitching, the cost of the network begins to increase. Con sequently, control layer mechanisms, such asMulti- Protocol Label Switching-Transport Profile, MPLS-TP (e.g. RFCs 5654, 5317, 5718, 5860;[3]), orProvider-Backbone Bridging-Traffic Engineering, PBB-TE (IEEE 802.1Qay standard), are becoming
  2. 2. important. Plus, the transport of IP/Ethernet over optical infrastructure is moving to sending nativeIP/Ethernet over wavelengths via WDM, which requires newer packet-optical solutions. The particularsolution adopted will be dictated by a number of factors. For example, the balance between the extent ofconnection-oriented (TDM) traffic and pure datagram traffic; the exist ing capital investment inSONET/SDH ADMs, ROADMs, switches and routers; the degree of equipment consolidationneeded/desired to reduce opex; desire to use the wavelengths better; the OAMP&T (operations,administration, maintenance, performance and troubleshooting) provided by the deployed technologies; andwhether IP/MPLS expertise and transport expertise resides in a common team or in different parts of theFigure 2. Conceptual Operation of a Wavelength Selective Switch.providers’ organization.Characteristics of a Packet- Optical SolutionSo what are the key ingredients being looked upon by operators in a packetoptical solution? It turns out thatthe following 4 elements are becoming table stakes:• Reconfigurable Optical Add/Drop Multiplexer (ROADM) infrastructure with support for routingwavelengths at multi-degree junctions, as well as the simpler two degree nodes [4].• The ability to efficiently carry existing SONET/SDH services without compromising support for high-growth packet and OTN traffic.• Connection-oriented Layer 2 Ethernet switching and aggregation.• Carrier-grade OAM — merging what exists in the optical domain with what exists in the packetdomain to give an operator a comprehensive view of the network. Thus a general industry consensus isemerging on the requirements of a Packet-Optical Transport System (POTS).
  3. 3. Three Key Areas of AdvancementThe development of packet-optical solutions has involved advancements in 3 key areas: subsystems such asROADMs and PICs; systems and ASICs (such as Packet-Optical Transport Systems); and control andmanagement plane software.1) ROADMs & PICsROADMs have played a key role in moving the transport network toward greater agility/flexibility byreducing the manual intervention needed to set up new lightpaths. A ROADM is composed of a number ofsub-systems such as Wavelength Selective Switches (WSSs), optical amplifiers, optical channel monitors,transponders, and control and management software. A ROADM eliminates costly optical-to-electricalconversions at intermediate nodes by allowing wavelengths to pass intermediate nodes in the opticaldomain. First generation ROADM’s allowed a lightpath’s direction to be changed, while itswavelength remained fixed. They were typically 2-dimensional nodes that enabled ring architectures. Subsequent ROADMs had higher degrees of between 4-8, allowing for mesh architectures. Second generationROADM’s used tunable lasers and wavelength selective switches (WSSs), allowing both the directionand the wavelength of a lightpath to be changed. WSS modules are the building blocks for ROADMs thatcan handle any wavelength on any port (and so are known as ‘colorless’) and can connect signalsflowing in any direction on any port to any other port (hence ‘directionless’).The next-generation of ROADMs will be gridless and contentionless. A contentionless ROADM allowsmultiple copies of a given wavelength (coming from different directions) to be dropped at a node, while agridless ROADM has the capability to accommodate wavelengths that do not fit on the ITU 50 GHz or 100GHz grid, but will utilize a flexgrid with a less rigid channel spacing (where some or all of the channelscould use more than the standard 50GHz bandwidth). This allows for variable channel widths and enablesoperators to efficiently use spectrum to maximize fiber capacity. They will also incorporate fast switchingspeeds to decrease latency, and superior optical channel monitoring at the ROADM ports to better regulatesignal power.Photonic Integrated Circuits (PICs) have shown to be very effective in reducing the cost of the DWDMsystems deployed by operators [5]. For example, Infinera’s PIC-based transport system is the #1 mostwidely deployed DWDM system in North America and includes a PIC-based Line Module with more than100 optical components (lasers, modulators, wavelength lockers, etc.) integrated on a single monolithicIndium Pho - sphide chip approximately 5mm square. Next generation PICs are now under development toincorporate more complex modulation schemes such as QPSK and QAM, which are required to achieve100Gbps per wavelength and higher and achieve aggregate capacities of 500Gbps or 1Tbps per PIC, andmore than 10Tbps per fiber over long-haul networks.2) Packet-Optical Transport Systems Figure 3. Packet-Optical Transport Systems (P-Packet-optical transport systems/ platforms (P-OTS or P- OTS): Architectures in use today.OTP) are a new class of networking platforms thatcombine the functions and features of SONET/SDH/OTN ADMs or cross-connects, Ethernet switching andaggregation systems, and WDM/ROADM transport systems into either a single network element or a smallset of network elements. The goal of a Packet-Optical Transport System is to combine the best features of
  4. 4. all of the legacy technologies, such as SONET/SDH, IP, ATM, and Ethernet. As a result, the requirementscan be thought of as drawing upon the features of each technology in the following way:a) From SONET/SDH: Resilience — 50 ms recovery, path provisioning, and OAM.b) From ATM: Sophisticated Traffic Management and QoS as in ATM, including traffic engineering andguaranteed QoS.c) From IP/Ethernet: Very high efficiency from statistical multiplexing of packets/frames, and packet-flowcontrol that are key for multimedia traffic.d) Flexible grooming or the ability to efficiently map a rich service mix onto the underlying transport layerby switching at the wavelength (lambda) level, sub-wavelength (ODU) level, port (TDM or SONET/SDH)level, and sub-port/packet (Ethernet, MPLS) level.P-OTS architectures may be divided into three broad types:a) IP-over-Glass or Layer 3 routers with integrated transponders connected to a DWDM system. These relyon the router to perform switching function and eliminate O-E-O interfaces. Network architecture issimplified by eliminating SONET/SDH, thus reducing Capex and Opex.b) Carrier Ethernet Switch Routers with Connection-Oriented Ethernet (COE) controlled using PBB-TE orMPLS-TP plus a DWDM layer. The goal here is to leverage the low cost points of Ethernet, while gettingthe advantage of its traffic management and traffic engineering capabilities.c) Packet-Optical Devices combining SONET/SDH and IP/Ethernet switching/ aggregation with DWDMtransport. They emphasize a modular architecture, where sub-wavelength multiplexing and packetswitching are done and traffic is groomed onto DWDM transport. These systems permit router bypass ofnon-IP traffic (e.g. L2 traffic, TDM traffic, and transit traffic), and minimize wavelength requirements byintegrating SONET/SDH, MPLS, and OTN switching onto a single system. The best alternative willdepend on the existing and projected traffic mix (TDM to packet balance in the operator’s network),existing capital investment in network assets (SONET/SDH ADMs, ROADMs, switches/routers), need forefficient utilization of optical resources (wavelengths), and the carrier’s operations model (i.e., whetherthe IP/MPLS and transport teams are separate or common).3) Photonic Control-Plane SoftwareThe data plane, comprising flexible ROADMs and packet-optical transport systems, must be complementedby a highly integrated management and control plane that spans the packet, TDM, and optical domains.This control plane software is critical for future agile optical networks. The control plane, which usesrouting and signaling to set up the connections between nodes, coupled with an efficient managementplane, is essential to orchestrate the operations of the data plane. Developments in the control plane areoccurring within the IETF, which has developed the GMPLS control plane that is now being refined toinclude wavelength switched optical network (WSON) requirements. This will allow the control plane tohave simplified knowledge of the optical parameters (such as chromatic dispersion and polarization modedispersion) and simple rules that can be used to decide whether an optical path is adequate or requiressignal regeneration. The ITU-T has developed control plane requirements and architecture, under theumbrella of ASON (Auto - matically Switched Optical Networks).The GMPLS/ASON control plane comprises a common part and a technologyspecific part to includetechnologies such as SONET/SDH, OTN, wavelengths, and MPLS-TP. By combining electrical and opticalswitching and an integrated control plane, the operators will be able to continually optimize their networks,and devolve them to the lowest-cost and most power-efficient solutions. The User-to-Network Interface(UNI) and the External Network-to-Network Interface (E-NNI) implementations, based on the ITU-T, OIFand MEF standards could prove very useful for carriers. The UNI standards should enable operators to havepacket switching devices that can signal the agile optical network, and request wavelength services forcertain duration over a specific path and with a defined level of protection. E-NNI implementations willenable Wavelength Networks to share topology and availability information in a way to facilitate servicedeployment across multi-vendor (and possibly even multi-carrier networks) in an end-to-end manner.Open Issues Even as advancements in packet-optical integration continue to be made, challenges remainbefore a fully agile optical network is a reality. An important consideration is providing the control planewith knowledge of the optical impairments, and enabling routing transparently between vendors. Similarly,
  5. 5. handling increasing customer application rates, say 1, 10 or 40 Gb/s on 100 Gb/s infrastructure, will requirethe use of OTN (G.709) multiplexing and electrical switching, plus control plane support. Finally,modularity of the system makes the challenge of integration for an operator much easier. This modularitycomes in multiple forms, as universal switch fabrics and the ability to mix-andmatch linecards (from allTDM to all packets and everything in between), or as modularity of the associated software with the abilityto selectively turn on or off specific features.This article was written by Vishal Sharma, Principal Technologist & Consultant, Metanoia, Inc. (MountainView, CA), and Mark Allen, Ph.D., Director of Systems Engineering, Infinera Corporation (Sunnyvale,CA). For more information, contact Mr. Sharma at vsharma@metanoia-inc.com, Dr. Allen atmark.allen@infinera.com, or visit http://info.hotims.com/34451-201.
  6. 6. References[1] Michael Kennedy, “Sizing-Up The Approaches,” Presentation, Network Strategy Partners,Fierce Telecom: Packet- Optical Networking Platforms Webinar, July 14, 2010.[2] Steven Gringeri, Bert Basch, Vishnu Shukla et al, “Flexible Architectures for Optical TransportNodes and Networks,” IEEE Comm. Mag., Vol. 48, Issue 9, July 2010, pp. 40-50.[3] Matt Rossi, “Enterprise Bandwidth Consumption,” Presentation, Zayo Enterprise Networks,Fierce Telecom: Making the 100 Gb/s Connection Webinar, July 21, 2010. [4] Internet Engineering TaskForce IETF, “MPLS-TP Standard,” WikiPage, http://wiki.tools.ietf.org/misc/mpls-tp/wiki/drafts,Accessed 12/29/2010. [5] Mark Allen, Chris Lou, Serge Melle, Vijay Vusirikala, “Digital OpticalNetworks Using Photonic Integrated Circuits Address the Challenge of Reconfigurable OpticalNetworks,” IEEE Comm. Mag. Vol. 44, Issue 12, Dec. 2007, pp. 2-11.