P-OTN_Packet Optical Transport Network

7/27/2019 P-OTN_Packet Optical Transport Network

1/20Copyright June 2008 TPACK A/S (www.tpack.com)

Bringing Packet and Optical togetherAt the turn of the century, the world was a differentplace. The vision for telecommunication networksseemed to be clear: an intelligent, all-IP packetnetwork supporting multiple IP-based servicesdelivered directly over fiber.

Fast forward to today and it would appear that thevision has been achieved, at least if you look at corenetworks: IP over WDM is a reality and can be directlydeployed using core router interface modules. Yet inmetro and access networks, the rise of CarrierEthernet and Connection-Oriented Packet Switchinghave challenged that vision, and now dominatenetwork and system architectural debates.

This is not just a technology debate. Carriers havelegitimate concerns with regard to the manageabilityand operation of large packet networks. Theyrecognize that their success to date is based onSONET/SDH transport networks, which also underliethe majority of packet networks. Transport of Ethernetdirectly over SONET/SDH has also proven successful.

What many carriers desire is a continuation of thissuccess in a fully packet-based context making use ofthe latest developments in connection-orientedEthernet and the scalability of OTN and ROADM-based WDM networks.

This is the basis for P-OTN1) or Packet OpticalTransport Networks.

P-OTN:Packet Optical Network Transformation

1) P-OTN (Packet Optical Transport Network) is the integration of packet networking technologies such as Ethernet and MPLSwith optical network technologies such as WDM and ROADM. P-OTN provides the network infrastructure for NGN andsupports multiple services including Carrier Ethernet.

However, with the inexorable growth in traffic,tighter integration of Ethernet with opticalnetworks is desirable, in order to drive costefficiencies and economy of scale. P-OTNpromises to reduce capacity costs and networkcomplexity, while improving scalability andflexibility.

To better understand the driving forces andbenefits of P-OTN, TPACK is providing this whitepaper which addresses the different approaches toP-OTN, including information on how TPACK canassist equipment vendors in capitalizing on theopportunities these technologies provide.

TPACK is focused on providing solutions thatenable the transport of Ethernet data acrosstelecommunication networks with Carrier Class

quality. Ethernet over SONET/SDH and Ethernetover MPLS (including VPLS and PWE3) haveproven to be the most popular methods to date.




Infrastructure Market in TurmoilWhen it comes to telecommunications, the vision forthe future is undisputed: multiple next generationservices based on Internet Protocol (IP) delivered overa fully packet based network. What is in contention ishow to get from here to there.

There are currently a multitude of technology optionsfor carriers and vendors to choose between fromextension of existing SONET/SDH networks withGFP/VCAT/LCAS to MPLS, VPLS, T-MPLS/MPLS-TP,PBB, PBB-TE, OTN etc.

Amidst this turmoil, some points are becoming clear;the preferred interface is Ethernet, as it provides thebest scalability from 10 Mbps to potentially 100 Gbps,while optical transport is the only economical meansof meeting the current and expected growth inbandwidth demand.

Hence the interest in merging packet and opticaltechnology into a converged solution.

Some commentators observe that packet optical is

the hottest trend in optical networking in 2008.

This white paper sets out to examine the packetoptical marketplace, the market drivers and serviceapplications that are placing new requirements oncarrier networks. In turn, these new networkapplications place new requirements on systemsand technology implementations, which are alsodescribed.

In this paper, TPACK addresses the P-OTN orPacket Optical Transport Network market. That is tosay, packet transport networks built upon the ITU-T's

established set of OTN network standards such asG.709. P-OTNs can be built using multiple optical,Ethernet and/or MPLS network elements, includingfully converged elements which Verizon, for example,has termed P-OTP or Packet Optical TransportPlatform.

From this strategic perspective, P-OTN encompassesthe multitude of different system descriptions thathave recently appeared, including PONP2, POTS3,CET4, and others less commonly used such asOPT5. These descriptions and possible distinctionsare explained later in this paper.

As network and system architects work to defineflexible, cost-effective and future-proof designs, it isalready clear that one size of system solution will notfit all network circumstances. Indeed, mainstreamindustry opinion holds that further evolution and

incorporation of new standards from ITU-T, IEEE andIETF will be a defining characteristic of P-OTN overthe coming years.

In chasing such a moving target, the risk for bothnetwork and system implementers is twofold:

Freezing a design too soon means earlyobsolescence, wasted effort and strandedinvestment, since interoperability with forthcomingsolutions is compromised;

Jumping forwards too far by adopting pre-standardised approaches, or approaches that fail tobe adopted by the wider market, carries exactlythe same consequences.

In both scenarios, carriers cannot achieve theeconomy of scale they need for profitability. Whilstfor system suppliers, playing a waiting game iscommercial suicide in today's cut-throat marketregime - thus the tightrope must be walked betweenadvancing too quickly, and being left behind.

TPACK has built its business by helping systems

houses to walk this line: allowing them to push theirsolutions forwards while building in the flexibilityrequired for inevitable future changes. A partnerwhite paper SOFTSILICON for Flexible PacketTransportexplores TPACK's approach and thebenefits that manufacturers can gain, ensuring thatthey stay afloat in this time of market turmoil andpacket network transition.

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2) PONP: Packet Optical Networking Platform3) POTS: Packet Optical Transport System4) CET: Carrier Ethernet Transport5) OPT: Optical Packet Transport



NGN Context: Carrier Drivers andRequirementsCarriers now operate a much greater variety ofarchitectures, even as network convergence reshapesnetworks from single stovepipes (a separatenetwork per service) to a shared infrastructure. Inmany cases, the transition timescale extends up to adecade. Different and changing service prioritiesmean that each carrier's investment decisions andnetwork design have to be reviewed often.

Underpinning this huge market dynamic is a

fundamental transition towards packet-based servicesand networks. For many carriers, the eventual goal isan IP-transformed network, capable of efficientlysupporting the array of new and future applicationsthat are currently developed.

The following list highlights the key challenges andpriorities that carriers are trying to address and theareas that system vendors can focus on in theirofferings.

Development of a strategy for NGN evolution;

Choice of architecture for future packet servicedevelopment;

Improvement in network efficiency, scalability andmanagement;

Support of legacy services in parallel with newservice roll-out;

Reduction of CapEx and OpEx, despite networktransition costs.

It is obvious that when designing practical networkplatforms, a variety of options for functional andtechnology integration exists and carriers are keen toleverage convergence to lower their TCO.

Converging packet and optical is an attractiveproposition, especially if it can be achieved with aflexible solution that can allow a phased migrationfrom existing transport infrastructure based onSONET/SDH to a fully packet-oriented infrastructure.Two broad integration categories can be identified:Packet Optical Transport Platforms and Converged

Packet Switch/Routers (colloquially, IP-over-WDM).

With IP-over-WDM, a WDM interface or transponderis provided in a router (typically), which allows a WDMlink between routers. The consequence of thisapproach is that packet switching decisions are madeat layer 3 and requires this intelligence at each packetswitching point.

An alternative approach is to provide a layer 2 packetinterface with a separate optical transport interface.Switching can be performed at layer 2, which is often

desirable from a transport perspective. This is thebasis for Packet Optical Transport Network (P-OTN).

In this paper, we will concentrate on P-OTN, but forthose interested in an overview of IP-over-WDM,please see the Cisco whitepaper Converge IP andDWDM Layers in the Core Network.





NGN Development: Easing PacketTransition using P-OTNBefore defining P-OTN in more detail, it is useful toset the context for P-OTN, namely the transportnetwork. For many with a packet background, theneed for a separate transport network has beendifficult to understand, but with the rise of real-timepacket services, such as Voice over IP and IPTV, theneed for greater control and planning of bandwidth isbecoming more important leading to a greaterappreciation for the role that transport networks fill.

As depicted in Fig. 1, P-OTN can be seen as thenatural evolution of advancements in both opticaland packet transport protocols driven by transportnetwork requirements.

The classical definition of transport networks is theprovision and management of network capacity whereplanned changes for each connection are normallyseparated by a long time period - typically of theorder of weeks, or even years. However, transportnetworks must also react quickly in the event offailure, by raising alarms and instigating protection/-

restoration facilities within milliseconds.

Transport has historically referred to Layer 1networks (eg. SONET/SDH or WDM technology),however the shift towards packet services means thatLayer 2 now has an important role to play.Packet transport networks must enable carriers todrive the same economy of scale for NGN as theyhave done for legacy networks:

Price/performance: achieving the lowest cost-per-bit transport;

Service reach: providing the widest geographical

footprint for customers;

Multi-service: so that costs are shared acrossmultiple lines of business;

High availability: with low failure rate, fastprotection and optional restoration schemes;

High QoS: predictable latency, low errors anddeterministic service delivery;

Transparency: to handle any end-user or carrier's

service unaltered;

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Fig. 1: Transport Evolution



Strong security: to support any customer's datawith confidence;

SLAs: delivering on a carrier's promise forperformance and availability.

Some may question why, in a packet world, atransport network is still needed: since everything isgoing to be IP, all that's needed is routers, withintelligence centralised at Layer 3 and with integralIP-over-WDM ports for transport.

However, on a per-bit carried capacity basis, theCapEx for routers is many times more expensive thanalternatives and many carriers believe that their OpExis also considerably higher. This drives a requirementfor a separate, intelligent transport network at Layers0/1/2 independent of Layer 3 switching/routingfunctionality. If L3 sophistication is not needed, thenit should not be paid for.

What is Packet Optical Transport?NG-SONET/SDH platforms have served carriers wellin the early days of packet transition since the turn ofthe new century. However, their limitations arebecoming more noticeable as capacities increase andthe traffic mix changes.

For example, Ethernet functionality is typically limitedto cards within a shelf and the number of ports percard is limited. The Ethernet switching capacity maybe limited by available EoSONET/SDH ASICS to amaximum of 20-40 Gbit/s. More complex distributed

L2 switching architectures may be difficult toimplement.

Further, an increase in switching capacity is neededfor increasing data traffic and higher densityEthernet cards are also required. In addition, newconnection-oriented packet services such asPBB/PBB-TE and T-MPLS/MPLS-TP will need to besupported, capable of interoperating with otherpacket platforms.

In other words, a new architectural approach is

needed: P-OTN.





P-OTN: Evolution and ArchitectureInside the BoxIn the late 1990's, a digital wrapper was conceivedby Lucent, which introduced a channel managementmechanism, forward error correction and amultiplexing hierarchy into the WDM technologythat had exploded into the marketplace. Afterstandardisation by more industry players at ITU-T, thisbecame formalised as the OTN and specified inseveral standards, most notably G.709.

OTN concepts, and its associated OTH multiplex,have over time become adopted throughout theindustry. Today, the majority of long-haul and metroWDM systems use OTN framing and management ontheir optical ports. Some vendors have introducedODU switches that are able to cross-connect OTHpayloads between ports without breaking them downinto their constituent parts (eg. an SONET/SDH clientor an Ethernet client).

The evolution of OTN systems can be illustrated inFig. 2 in 3 phases (simplified protocol stack on the

left, example equipment design on the right):

Phase 1 (2000-2003) - SONET/SDH + OTN: OTNserved as the static WDM layer used to multiplyfibre capacity. The principal SONET/SDH clientwas TDM, although Ethernet-over-SONET/SDH wasbeginning to increase in importance.

Phase 2 (2003-2007) - OTN + Ethernet:SONET/SDH was still an important client, but GbEprivate lines developed to become a significantdriver of deployment, together with some 10GbE.Lower capacity EoSONET/SDH private line services

are also a significant new service on a flexible OTNlayer.

Phase 3 (2007 onwards) - P-OTN. With theintroduction of L2 switching capability, packet andTDM services have become of equal importance.Ethernet is no longer bound to SONET/SDH as aclient, but is carried directly by the OTH, afterpacket processing, aggregation, etc. ROADMsenable the OTN to be dynamically re-configured.

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Despite this illustration of a smooth evolution, and alogical progression towards convergence, in factconvergence drives carriers and vendors to differentarchitectural solutions, depending on their startingpoints, their rate of investment, technologicalpreferences, and their customers' requirements.

For example, particular platforms or particularnetwork nodes may not include L2 aggregation/switching functions - whilst others may place TDMsupport as a secondary priority. Unlike the classicalSONET/SDH networks, whose design tended to be

proscribed by standards and homogeneous in nature,today's networks have evolved organically and displaymore variation.

In fact, several system or platform architectures maybe conceived, each optimised for a particular place ina carrier's network, or for a particular position in asystem vendor's product portfolio. Despite the focuson convergence, network and system architects havemuch more choice in their specific deployment andevolution strategy.


Fig. 2: Evolution of OTN protocol stack and equipment architecture (simplified).




Packet Optical Transport Platforms (P-OTP)While Packet Optical Transport Networks can beachieved by combining the functionality provided byseparate devices (e.g. separate Carrier EthernetSwitch, MSPP and WDM nodes), there is a desireto converge this functionality into a single devicecapable of providing seamless SONET/SDH supporton day one, but capable of supporting a fullypacket-based network thereafter. This type of devicehas been referred to as a Packet Optical TransportPlatform (P-OTP) by Verizon networks and this is thedefintion we will adopt here.

From a systems perspective, definitions of P-OTP stillvary, but a consensus has developed on the followingtop-level criteria. A model P-OTP is a standalone,managed, single network element that comprises acombination of:

Reconfigurable WDM transport using OTN andROADM technology, allowing ring and meshtopologies and capacity to be dynamicallyprovisioned;

Integrated SONET/SDH for existing transportinteroperability, multiplexing/switching to supportnative low latency, high availability TDM services;

Connection-oriented Ethernet (including MPLSPWE3, PBB/PBB-TE and T-MPLS/MPLS-TP) packettransport aggregation/switching and clientinterface support;

Carrier-class OAM and management capabilitieswith optional ASON/GMPLS dynamic control plane.

Many see P-OTP as a migration-enabling platform,and a common requirement is the need to supportboth TDM services and packet services with astrategy for smooth migration towards an all-packetinfrastructure. This all-in-one approach couldtheoretically lead to a collapsed network architecturewith fewer elements that could lead to simplifiedoperations, maintenance, and management.

Several of the available P-OTP single platformarchitectures build upon existing MSPPs orMSTPs with added OTN, ROADM and/or

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Fig. 3: Technology convergence options create P-OTP for P-OTN (picture adapted from Verizon)



Connection-Oriented Ethernet module support, whileother platform architectures are based on universalfabrics capable of natively supporting anycombination of TDM and packet traffic.

However, it is also possible to deploy P-OTN usingseparate single-layer network elements, eachoptimised at the Optical and Packet switching layers.In theory this approach could help carriers leveragewhat they already have deployed in their networks,leading to cost savings via investment protection. Inaddition, this approach might also provide advantages

in terms of further scalability and product maturitythat today's single-element solutions might lack.

Benefits of P-OTNEvidence suggests that carriers are indeed interestedin a separate, intelligent transport network optimised

for packets. Firstly, CapEx forecasts for transportnetworks are not set to decline, but do show a shift inspending from SONET/SDH to P-OTN suggesting thatP-OTN is earmarked to replace SONET/SDH.

Secondly, emerging requirements on routers areemphasizing Layer 3 to Layer 7 support, such as DeepPacket Inspection and acceleration of applications.

Analysts such as Infonetics Research track the trendsin equipment investment, and the key evolutionarytrends can be seen in Fig. 4. According to Infonetics,

the market for optical network hardware will growfrom $14bn to $15bn over the next 4 years with WDMgrowing at the expense of SONET/SDH. Note thatthe Packet Optical Transport System portion ofWDM is growing from $1bn in 2007 to $2.5bn in2011, explaining a large part of this growth.

P-OTN1:Packet Optical Network Transformation

Fig. 4: Optical network equipment revenue (source: Infonetics, Feb 2008)




In contrast, analyst company Heavy Reading believesthat the packet-optical transport systems marketsegment will grow from essentially $0 in 2007 to reach$2.8bn by the end of 2012, a CAGR of 110% from2008-2012.

Despite widespread agreement that SONET/SDH isnot the long-term solution, even the most aggressiveforecasts predict that SONET/SDH will remain with usfor the next 10 to 15 years. What's more, it does notappear that SONET/SDH is being replaced by CarrierEthernet Switches and Routers, but by P-OTN.

.An integrated P-OTN approach offers many genericbenefits to carriers:

Supports multiple services: TDM (SDH, PDH),Ethernet, SAN, Video;

Scales from 100% packet to 100% TDM, takingcare of service migration;

Scales from 2Mbit/s to 10/40Gbit/s in a singleplatform architecture;

Any-port to any-port switching, for full nodeflexibility;

Remote management eliminates expensive andslow manual intervention;

Native timing and synchronisation support for userplatforms/applications;

Card commonality with legacy MSPP, easing sparesinventory;

OTN-based transport protection and OAM, forcarrier-class availability;

Connection oriented Ethernet for carriermanagement;

C/DWDM, Mux/Demux, (R)OADM for photonicnetworking;

ASON/GMPLS for dynamic control and serviceprovisioning;

Carriers' drive towards a lower OpEx is supporteddue to native P-OTN interworking with other TDMand packet platforms. Integration of all L1 and L2technologies in a single management system meansthat established operational procedures can beleveraged.

Carriers' drive to lower CapEx is supported due toinvestment protection (eg. full reuse of installed

NG-SONET/SDH base). In addition, if a carrier'sfuture network evolution or demands are unclear, thisapproach avoids buying into a dead-end.

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Fig. 5: Integration of OTN, COE, SONET/SDH into P-OTN engine blocks

Copyright June 2008 TPACK A/S (www.tpack.com)

TPACK: SOFTSYSTEM Modular ApproachSince the precise formulation of P-OTN is still underdefinition - and under standardisation - the questionof how best to ensure flexibility and adaptability for achanging future must be addressed.

In terms of network flexibility, the right mix of TDMand packet functionality must be supported, and thismix will change as time progresses. In terms ofsystem flexibility, the optimum architecture mustaccommodate a wide range of deployment options.

And in terms of chip-level requirements, criticalfunctions must be integrated in various combinationsto fit the various system architecture requirements.TPACK has developed P-OTN building blocks, assummarised in Fig. 5. Specific OTN, COE andSONET/SDH functions have been integrated intooff-the-shelf engine blocks, ready for customisationand system integration.

The configurations shown in Fig. 6 are illustrativebased on current TPACK reference solutions. Forexample, the TPOX3203 Packet Optical Engine com-bines OTN mapping with Connection OrientedEthernet switching and traffic management allowing aP-OTN muxponder solution. The TPOX4214 extendsthis functionality with SONET/SDH client interface,two OTU-2 interfaces and an ODU-1 crossconnect toallow a full P-OTN add-drop multiplexer solution.

However, the strength of these solutions is that they

are open to adaptation and customization by custo-mers to fit their system architecture needs.

Contact TPACK today and find out how we can helpyou with your P-OTN requirements atwww.tpack.com/contact.html





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Fig. 6: Multiple P-OTP implementation options provide P-OTN flexibility



ConclusionTransport networks have historically delivered reliable,deterministic operation that can be interworked, ifnecessary, using systems from a wide variety ofdifferent vendors. Management systems tend to bewell-organized and the network itself can be readilymanaged and maintained by good operational staffwithout requiring exceptional skills.

The challenge in hand is to provide the same carrierbenefits but within a packet-based infrastructure.P-OTN provides Carrier Ethernet/MPLS support,

scalability as well as simplified packet networking, andhence deliver the lowest cost-per-packet-bit as well asthe lowest cost-per-circuit-bit. It has a valuable roleto play in the future NGN.

The vision of an all-packet NGN supporting multipleIP-based services is not in danger. It has ratherbecome more nuanced as the need for a broader setof supporting solutions has been identified.Transport is still important to carriers as a separate,operationally-driven domain of intelligence andexpertise designed to assist and complement efficient

IP-service delivery.

In this regard, one can expect a bright future forP-OTPs in P-OTN, though one can also expect thatevolution will continue in both architecture andnaming. Watch this space!





Appendix A

OTN: Introduction to Optical TransportNetworkHere, the basics of OTN are briefly introduced. OTNis a set of global ITU-T optical transport standard,accepted by both ANSI and ETSI organisations.Originally formulated as the digital wrapper, it isspecified in ITU-T Recommendation G.709 andassociated standards.

OTN provides a high capacity multiplexing

hierarchy - the Optical Transport Hierarchy (OTH) -that can transparently support modern services suchas Ethernet and storage, and also legacy services suchas SONET/SDH. It has a well-defined in-band OAMstructure following the SONET/SDH model and allowsservices and the optical channel to be effectively andremotely managed and monitored. It also providesstandardised FEC to improve the performance of theoptical channel and improve deployment economics.

OTN has typically been combined with SONET/SDHin equipment platforms - and is now including packet

functionality to support the P-OTN. Control andmanagement planes such as ASON/GMPLS can alsobe integrated. OTN has gained wide support for itsstandard frame structure and sub-lambda multiplexingand is commonly used as interfaces on routers, opticalswitches, Metro WDM nodes, etc.)

In Figure 7 the line rates defined as part of theOptical Transport Hierarchy (OTH) are shown inclu-ding the OPU client rate and final OTU transmissionrate once all overhead and FEC is included.

OTN structure, line rates and multiplexingOTN was designed to address some of the scalingand transparent transport issues with SONET/SDH.SONET/SDH was designed with only two levels ofswitching at 1.5/2 Mbps and 50/150 Mbps. It was notenvisaged at the time that higher switching capacitieswould be needed. Transparent transport of lowerrate SONET/SDH clients in higher rate SONET/SDHtransport was also an issue. OTN addresses both ofthese issues and introduces a range of enhancements.

While OTN was primarily designed to transport

SONET/SDH, it also supports a number of otherclients including ATM, Ethernet, FC, IP, MPLS andGFP. A "digital wrapper" based on ITU-Trecommendation G.709 is used to encapsulateclient signals for transmission. A number of layers aredefined in OTN, each with its own task. In Fig. 8 thelayers are shown with an overview of their functions.The first 3 layers are related to the Optical Channelincluding the Optical Channel Payload Unit (OPU),which encapsulates the variousclients and performs rate justification, the OpticalChannel Data Unit (ODU), which both handles path

termination (ODUkP) and 6 layers of TandemConnection Monitoring (ODUkT) and finally, theOptical Channel Transport Unit (OTU), which addsFrame Alignment Overhead and Forward ErrorCorrection (FEC) capabilities based on either the stan-dard FEC (OTUk) or on proprietary, vendor specificenhanced FECs (OTUkV).

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OTH Level OPU client OTU framePayload capacity (Gbit/s) Optical line rate (Gbit/s)

1 2.488 320 2.666 057

2 9.995 277 10.709 225

3 40.150 519 43.018 414

Fig. 7: OTH nominal bit rates (source: ITU-T G.709/Y.1331)



After this point, we leave the digital or electricaldomain and enter the analogue or photonic domainrelated to WDM transmission with the Optical

Channel (OCh) Optical Multiplex Section (OMS) andOptical Transport Section (OTS). As this whitepaperconcentrates on digital issues, these OTN areas willnot be discussed further.

As Fig. 8 shows, client signals - Ethernet, SONET/SDHor other GFP-encapsulated clients - are mapped intoan OTH payload and transportedtransparently and unaltered to its destination. Themapping procedure adds ODU headers that operateas the embedded management channel, performserror checking and correction, and so on.

Fig. 8 illustrates the multiplexing of four ODU1signals into an ODU2. The ODU1 signals includingthe Frame Alignment Overhead and an all-0s patternin the OTUk overhead locations are adapted to theODU2 clock via justification (asynchronous mapping).Four of these adapted ODU1 signals are byteinterleaved into the OPU2 payload area, and their

justification control and opportunity signals (JC, NJO)are frame interleaved into the OPU2 overhead area.ODU2 overhead is added after which the ODU2 ismapped into the OTU2. OTU2 Overhead and FrameAlignment Overhead are added to complete thesignal for transport via an OTc signal.

Transporting 10 Gbps EthernetThe standard OPU2 line rate is slightly less than thatrequired for transparent transmission of a 10G

Ethernet signal, , specifically a 10G LAN PHY signal. InITU-T G.sup43 (2008/02), a description is provided ofthe 5 methods to date for handling this. Three of themethods are standard and two are non-standard.

The first method (described in clause 6.1) is based onuse of the 10G Base-W (10G WAN PHY). This wasdefined in IEEE 802.3 to allow compatibility withSONET/SDH standards. In other words, the data rateis slightly less than 10G. However, this is typically amore expensive interface than the more common 10GLAN PHY. It is used for interworking as a Network-to-Network Interface (NNI), where 10G LAN PHY is

preferred as a User Network Interface (UNI).

For transport of 10G Base-R (10G LAN PHY) data, thestandard solution (described in clause 6.2) is toterminate the Ethernet line code, preamble, Start ofFrame Delimiter (SFD) and Inter-Packet Gap (IPG),extract the payload, frame using GFP-F and encodeinto an OPU2. This allows transparent payloadtransport, but removes header information. Thiscan be an issue, as there are circumstances wheretransparent transport of the entire 10G LAN PHYincluding preamble, SFD and IPG is necessary (e.g.


Fig. 8: OTN layers (source: ITU-T G.709/Y.1331).




Link Fault Signalling (LFS) and proprietary use of IPGand preamble bits in the Ethernet header).

Two non-standard techniques are described assolutions commonly used to resolve this. In clause 7.1,the solution is to use Constant Bit Rate for 10G(CBR10G) mapping of the signal into OPU2 and to

increase the transmission clock rate to accommodatethe extra bits that need to be transmitted. This allowsthe full 10G LAN PHY frame to be transparentlytransmitted. However, since the clock rate is differentto standard OTN and to avoid confusion, the variouslayers are designated as OPU2e, ODU2e and OTU2erespectively.

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In clause 7.2, a similar technique is used for mappingto an OPU1 instead of an OPU2. It uses the 2.5G

(CBR2G5) mapping described in G.709, which differsfrom CBR10G mapping in that it does not use FrameStuffing (FS) bits. Overclocking is again used wherethe overclocked OTU1 (OTU1e) data rate is slightlyless than that specified for OTU2e (11.0491 Gbpsrather than 11.0957 Gbps). The various layers aredesignated as OPU1e, ODU1e and OTU1e.

The final standard method of transmission describedin clause 7.3 is designed to provide the same level oftransparency for 10G Ethernet as is achieved using

GFP-T in SONET/SDH for Gigabit Ethernet (GE).However, since 10G Ethernet uses a 64B/66B block

code rather than the 8B/10B code used by GE, idlecharacters need to be removed in order to fit into anOPU2. This is equivalent to asynchronous GFP-Ttransparent mapping in SONET/SDH. Since GFP-T isnot suitable for 10G transmission, a modified versionof GFP-F is used.

Discussions are ongoing as to the evolution of thesetransmission methods, especially in the context ofOTU3 and 40G transmission. There is a desire tomake sure that standard methods will allow

Fig. 9: OTN overlapping and cascaded OAM layers



transparent transport of, for example, 4 10G EthernetLAN PHY clients in an OTU3. The concern is that ifthis is not accommodated that proprietary solutionswill again surface hampering interoperability.

At the time of writing, definition of other ODUpayloads is in progress at ITU-T. The ODU0 frame isintended to directly support GbE services, whilst theODU4 frame is intended to support 100GbE services.So, even though OTN is a relatively old standard,there is a lot of activity right now to improve OTN'sability to accommodate various Ethernet clients.


OTN references

Document Description

ITU-T G.872 Architecture for the Optical Transport Network (OTN)ITU-T G.709 Interfaces for the Optical Transport Network (OTN)

ITU-T G.sup43: Transport of IEEE 10G Base-R in Optical Transport Networks (OTN)

ITU-T G.975.1: Forward error correction for high bit-rate DWDM submarine systems

ITU-T G.870: Terms and definitions for Optical Transport Networks (OTN)

See also ITU-Ts Study Group 15 (SG15) webpage for tutorials on OTN:http://www.itu.int/ITU-T/studygroups/com15/index.asp

OTN OAMOne of the significant OTN improvements on

SONET/SDH is Tandem Connection Monitoring(TCM). In OTN 8 levels of monitoring are definedincluding Section Monitoring (SM) for point-to-pointconnections, Path Monitoring (PM) for end-to-endmonitoring and 6 levels of TCM where the start andendpoints can be freely defined. TCM provides thepossibility to nest and overlap monitoring layers tobetter fit real-life situations.

In Fig. 9 an example is shown where a service isprovided by a service provider across two otheroperator's networks.In this example, PM is used to monitor the end-to-end

service. TCM1 is used to monitor transmission in theService Provider Network. TCM2 and TCM3 are usedfor overlapped monitoring of Operator As network.TCM4 monitors Operator Bs network while TCM5monitors the working and protected paths inOperator Bs network. Individual links between nodescan also be monitored using SM.

As can be seen, the various layers can be cascadedor overlap depending on the need.

Significance of OTNOTN is more than just an improvement to

SONET/SDH. OTN also provides manageability to agrowing part of carrier's networks, namely WDM.While WDM to date has traditionally been used as ahigh capacity link between nodes, the introduction ofROADMs has introduced the concept of switchedWDM networks based on ring, meshed or partialmeshed architectures. Managing such networks iscritical to assure effective use of resources andcustomer satisfaction. With TCM, FEC and the abilityto map various clients, both TDM and Packet, OTNprovides manageability, ease of provisioning andgreater efficiency.

For example, by using FEC, it is possible to extendthe distance of fibre transmission or reduce the powerrequired to reach an equivalent distance, whichcould enable more DWDM wavelengths to beaccommodated. SONET/SDH did include in-band FECcapabilities, but based on a less effective scheme thanthe Reed Solomon based methods used in OTN. Oneof the major advantages of FEC in relation to ROADMnetworks, it that it increases the number of nodes thatcan be crossed without suffering packet loss due tocumulative attenuation.




The TPACK AdvantageTPACKs SMARTPACKTM P-OTN family ofSOFTSYSTEM customizable chip solutions is designedspecifically for Packet-Optical Transport Network(P-OTN) applications. SMARTPACKTM P-OTNintegrates Packet, SONET/SDH and OTN switchingand transport in a series of chip solutions designedto fit a variety of platform architectures.

Since P-OTN is an emerging market, where evenagreement on naming is difficult, flexibility to adaptto new requirements or configurations is paramount.

Each carrier and system vendor will have their ownapproach and understanding of P-OTN leading to avariety of system architectures and solutions.Thus TPACKs SMARTPACKTM P-OTN solutions do notseek to dictate system design, but to adapt to it!

The SMARTPACKTM P-OTN family provides a numberof integration options to choose between, but alsothe ability to accommodate customer-specificcombinations. Connection Oriented Ethernet (PBB-TE,T-MPLS and PWE3/VPLS), SONET/SDH and OTNmodules are supported, allowing a flexible mix of

packet switching, TDM and optical transportfunctionality.

For example, The TPOX3203 20 Gbps Packet OpticalEngine provides a Connection Oriented Ethernetswitching and traffic management chip solutionwith an integrated OTU-2 OTN interface. TheTPOX4214 40 Gbps Packet Optical Engine providesthe same functionality as TPOX3203 but with 2xOTU-2 interfaces, transparent transport ofSONET/SDH and an integrated ODU-1 cross-connect.

Both of these chip solutions are open to adaptationand customization as well as acting as inspiration forcustomer defined chip solutions designed to fit agiven system architecture.

SMARTPACKTM P-OTN chip solutions are based onreprogrammable FPGA technology, which allowscustomers to adapt and customize the solution tomeet specific requirements. Future unforeseendevelopments can also be accommodated quickly,which will be critical in P-OTN applications, since theyare still under definition in many cases.

System houses can minimize risks and shortendevelopment cycles by considering a solution fromTPACK. In a new and dynamic market such as this,the stakes are high and mistakes can be costly. TheTPACK approach mitigates against these risks byoffering a P-OTN solution that can be adapted quicklyand easily. This provides system houses with avaluable tool in exploiting the opportunities thatP-OTN provides.

Contact TPACK for more information on the

SMARTPACK

TM

P-OTN solution and on how TPACKcan assist you in your P-OTN development projects.

8



TPACK in briefTPACK is one of the world's leading providers ofembedded software solutions for packet transport.TPACK's solutions are based on Field ProgrammableArrays (FPGAs) with pre-integrated and pre-testeddriver, application and management software. Formedin 2001, TPACK has helped Multi-Service ProvisioningPlatform (MSPP) providers to rapidly develop NextGeneration SONET/SDH (NG-SONET/SDH) linecardand microMSPP solutions for transport of Ethernet,IP/MPLS and VPLS packet data across the existingtelecommunications network. Now TPACK is helping

these and other equipment providers to addressP-OTN, T-MPLS and PBT applications for reliable,carrier grade Ethernet transport using TPACKSMARTPACKTM P-OTN, PBT and T-MPLSSOFTSYSTEM and SOFTSILICON solutions.

- SOFTSILICON can best be described as a FlexibleASSP: it is a standard chip solution similar tocommercial off-the-shelf chips, but has theadvantage that is based on programmabletechnology, namely FPGAs. With the latest advan-ces in FPGA logic density and power consumption,

it is now possible to offer a standard chip solutionwith performance similar to ASSPs. The advantageis that it takes less time to develop and upgradethese chip solutions in response to changingmarket conditions. SOFTSILICON thus provides acost effective solution for Telecom EquipmentManufacturers who need the ability to react quicklyto unforeseen market demands.

- SOFTSYSTEM provides a tailored solution that caninclude SOFTSILICON products, but also software.SOFTSYSTEM supports adaptations andcustomizations based on specific customer

requirements quickly and right-first timeaccelerating Time-to-Market with new systemsolutions.

- SMARTPACKTM is TPACK's family of SOFTSILICONproducts and solutions targeting Carrier Ethernet

and Packet Transport applications. TPACK'sSMARTPACK products include NG-SONET/SDHpacket mappers and Ethernet/MPLS Carrier PacketEngines (which combine packet processing andtraffic management in a single device). TPACK alsoprovides Carrier Packet Mapper Engine products,which combine the functionality of NG-SONET/SDH packet mappers and Carrier PacketEngines in a single FPGA device. This is madepossible through the use of Stratix III Altera devi-ces, which are based on 65-nm manufacturing pro-cesses. Stratix III FPGAs provide up to 50% power

reduction compared to Stratix II devices allowingmore compact, lower cost and lower powerconsuming MSPP and microMSPP solutions.

- TPACK Carrier Packet Engines provide multi-protocol support of various packet protocols, suchas PBB-TE/PBT, T-MPLS, MPLS, VPLS, PWE3 as wellas standard 802.1ad VLAN/MAC switching. Theseprotocols can be supported simultaneously with fullOAM support and multiple parallel operations perpacket without affecting throughput performance.

- SONET/SDH line rates from 155 Mbps to 10 Gbps

are supported. Together with NG-SONET/SDHstandards (GFP-F, VCAT and LCAS), this allowspacket data rates from 1.5 Mbps to 10 Gbps to betransported with high efficiency including full,transparent transport of 10 Gbps LAN Ethernetpayloads.

- TPACK's customers include Alcatel-Lucent, NEC,Tellabs, Xtera/Meriton Networks and TurinNetworks. TPACK has over 130 design-wins with 8of the top 10 optical transport equipment vendorswho account for over 60% of the market.

- TPACK is headquartered in Copenhagen, Denmarkwith a sales office in Palo Alto, CA, USA.



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P-OTN:Packet Optical Network TransformationBox Summary

Glossary

10GbE 10Gbit/s EthernetANSI American National Standards InstituteASTN Automatic Switched Transport NetworkCapEx Capital ExpenditureCET Carrier Ethernet TransportCOE Connection-Oriented EthernetCWDM Coarse WDMCY Calendar YearDemux DemultiplexerDWDM Dense WDM

E-LAN Ethernet-LANE-LINE Ethernet-LINEEoSDH/-SONET Ethernet over SONET/SDHETH EthernetETSI European Telecommunications StandardsInstituteFEC Forward Error CorrectionFPGA Field Programmable Gate ArrayGbE Gigabit EthernetGFP Generic Framing ProcedureGMPLS Generalized MPLS

HDTV High Definition TV IEEE Institute of Electrical and ElectronicEngineersIETF Internet Engineering Task ForceIMS IP Multimedia SubsystemIP Internet ProtocolIPTV IP TelevisionIP-VPN IP Virtual Private NetworkITU-T International Telecommunication

Union - Telecommunication SectorL2 Layer 2L3 Layer 3LAN Local Area Network

LCAS Link Capacity Adjustment SchemeMPLS Multi-Protocol Label SwitchingMPLS-TP MPLS-Transport ProfileMSPP Multi-Service Provisioning PlatformMSTP Multi-Service Transport PlatformMux MultiplexerNASS Network Attachment SubsystemNG-ADM Next-generation Add-Drop MuxNGN Next-Generation NetworkNG-SDH Next-Generation SDHNPU Network Processing Unit

OADM Optical Add-Drop MuxOAM Operations, Administration

and MaintenanceODUk Optical Channel Data Unit, level kOpEx Operating ExpenditureOPT Optical Packet TransportOPUk Optical Channel Payload Unit, level kOTH Optical Transport HierarchyOTM Optical Transport ModuleOTN Optical Transport Network

OTUk Optical Channel Transport Unit, level kPBB Provider Backbone BridgePBB-TE PBB - Traffic EngineeringPBT Provider Backbone TransportPDH Plesiochronous Digital HierarchyPON Passive Optical NetworkPONP Packet Optical Networking PlatformPOS Packet over SONET/SDHP-OTN Packet-OTNP-OTP Packet-Optical Transport PlatformPOTS Plain Old Telephony SystemPOTS Packet Optical Transport System

PWE3 Pseudo-Wire Emulation Edge-to-EdgeQoS Quality of ServiceRACS Resource and Admission

Control SubsystemROADM Reconfigurable OADMSAN Storage Area NetworkSDH Synchronous Digital HierarchySLA Service Level AgreementSONET Synchronous Optical NetworkSTM-n Synchronous Transport Module, level nTCO Total Cost of OwnershipTDM Time Division MultiplexingT-MPLS Transport-MPLS

TSS Transport Service SwitchVCAT Virtual ConcatenationVLAN Virtual LANVoIP Voice over IPVPLS Virtual Private LAN ServiceVPN Virtual Private NetworkWDM Wavelength Division Multiplexing

XC Cross-connect

P-OTN_Packet Optical Transport Network

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