Fiber Optic Transmission and Wavelength Division Multiplex

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White Paper Nortel Networks WDM for Cable MSOs: Technical Overview

Transcript of Fiber Optic Transmission and Wavelength Division Multiplex

Page 1: Fiber Optic Transmission and Wavelength Division Multiplex

White Paper

Nortel Networks

WDM for Cable MSOs:Technical Overview

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Wavelength DivisionMultiplexing (WDM)Multi-Service Operators (MSOs) haveseveral technology choices available toprepare them for GbE based servicedelivery and the inevitable growth indigital transport bandwidth. This white paper is intended to provide an overview of Wavelength DivisionMultiplexing (WDM) digital transporttechnology choices.

Wavelength Division Multiplexing is atechnology used to expand fiber opticbandwidth by enabling signals from different sources to independently traveltogether on a single optical fiber. Fibercapacity is increased by mapping incom-ing optical signals to specific lightwavelengths or optical channels. WithWDM, optical transmitters are equippedwith ‘wavelength specific’ lasers attachedto filters to enable the passive multiplex-ing of several optical signals onto a singlefiber. Figures 1 and 2 illustrate bothtraditional and WDM fiber optic transport technologies.

In WDM systems, each optical channelremains independent of other opticalchannels as if it were using its own fiberpair. Digital WDM systems enable bitrate and protocol independent access tothe optical transport layer. This is crucialfor metropolitan area network deploy-ments as they eliminate the costs associated with mapping common dataprotocols into traditional network pay-loads. Each optical channel is indepen-dently multiplexed and demultiplexed at the ends of the transmission networkin its original format. Therefore, differ-ent digital optical data formats utilizingdifferent data rates can be transmitted intheir native formats over the same opticalfiber. For example, gigabit Ethernet,Fibre Channel, ITU-R601 optical video,DV6000, SONET, ATM, FDDI,ESCON, FICON, and other optical

Figure 1. Traditional digital fiber optic transport

Figure 2. Fiber optic transport using Wavelength Division Multiplexing (WDM)

Digital transceiver

Single pair of fibers

Digital transceiver

Digital transceiver

Single pair of fibers

Digital transceiver

Digital transceiver

Single pair of fibers

Digital transceiver

Digital transceiver

Single pair of fibers

Digital transceiver

Digital transceiver

Single pair of fibers

Digital transceiver

Digital transceiver

Digital transceiver

Digital transceiver

Digital transceiver

Digital transceiver Digital transceiver

WDM MUX WDM MUX

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data formats can all be traveling at thesame time within a single pair of opticalfibers. Figure 3 displays the bit rate andprotocol independent feature of WDMtechnology.

WDM technology promises to solvefiber exhaust problems and eliminate thecost of converting native data into tradi-tional digital networking formats (e.g.SONET or ATM). It is expected thatWDM will be the central technology inthe “all optical” networks of the future.WDM systems are being deployed todayto complement existing network tech-nologies, such as SONET and ATM,and add new capabilities for high band-width and native data transport.

There exist two types of WDM tech-nologies used in networks today. Theseare defined as Dense WavelengthDivision Multiplexing (DWDM) andCoarse Wavelength Division Multi-plexing (CWDM).

Dense Wavelength DivisionMultiplexing (DWDM)Dense Wavelength Division Multiplex-ing (DWDM), a WDM technology, is characterized by narrower opticalchannel spacing than Coarse WDM(CWDM). DWDM enables largechannel counts within a limited spectralband—specifically the C and/or L opticalbands—as supported by the spectralbandwidth amplification capability oftoday’s optical fiber amplifier technology.

DWDM systems require precise opticalmux/demux filters to provide channelspacing of 200 GHz, 100 GHz, or 50GHz and less (i.e. approx. 1.6 nm spacingfor 200 GHz systems and approximately0.4 nm for 50 GHz spacing). Addition-ally, due to the narrow channel spacingand optical windows used, DWDMsystems require well controlled, cooledlasers to prohibit drift outside of a givenDWDM optical channel.

Figure 3. Bit rate and protocol independent fiber optic access with WDM

Independentoptical bit rates

and formats

WDM fiber max

Single optical fiber

λ1

λ2

λ3λ4

SONET

ATM

Gigabit Ethernet

Fibre channel

Figure 4. Spectral amplification region of today’s optical fiber amplifiers

Amplified optical spectrum

O - band E - band S - band C - band L - band

DWDM window

λ (nm) 1280 1320 1360 1400 1440 1480 1520 1560 1600 1640 λ (nm)

1310nm

I I I I I I I I I I

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The objective of DWDM systems is to“squeeze” as many channels as possibleinto the amplified portions of opticalspectrum as shown in Figure 5. The frequency grid for DWDM systems isdefined in the ITU-T G.694.1Recommendation.

By sharing the cost of amplifiers acrossmany optical channels, DWDMbecomes a very cost-effective technologyfor high bandwidth, multi-channel digi-tal transport applications that requireamplification to overcome distance asevidenced in long haul, regional, andmetropolitan core networks.

DWDM originally gained its roots inthe long haul and regional transportspace. This was due to the need to max-imize fiber resources as much as possiblein these networks. DWDM technologywas used to pack as many data channelsas possible into the minimum amountof fibers. The intent was to amortize the equipment cost of DWDM systemsacross a very large number of datachannels and maximum amount ofdistance. In fact, long haul DWDMsystems that support up to 160 10-Gbps wavelengths over fiber distancesof thousands of miles are now avail-able. In the metro area, fiber resourceswere not as scarce and it wasn’t untilthe past four or five years that DWDMbecame a cost-effective technology formetropolitan applications.

Introduction to Metro Digital DWDM systemsDigital DWDM systems that arespecifically designed to meet the eco-nomic and technical requirements ofmetropolitan applications are availablefrom several vendors. These systems arecost optimized for metro area networkapplications and are now beingdeployed by several MSOs. These

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Figure 5. DWDM C band and L band wavelength region

O - band E - band S - band C - band L - band

DWDM window

λ (nm) 1280 1320 1360 1400 1440 1480 1520 1560 1600 1640 λ (nm)

1310nm

I I I I I I I I I I

Figure 6. Multiple native optical services over a digital DWDM transport system

Survivable switched DWDM optical ring

Gigabit Ethenet

Fast Ethernet

SONET/SDH (OC-n)

ATM

DV6000

PrismaDT

Fibre channel

Serial digital interface

DVB-ASI

ESCON

FICON

GDPS

FDDI

etc.

TM

TM

systems enable the consolidation of fiberand sharing of network resources. A met-ropolitan digital DWDM system is char-acterized by lower cost per channel andtypically operates over distances of up to100 to 300 kilometers. Metro DWDMsystems today can combine in excess ofmore than 30 separate optical channelson a single optical fiber pair.

The task of metro DWDM equipment is to accept client optical signals of vary-ing bit rates and protocols (i.e. GbE,SONET OC-n, ATM, DV6000,PrismaDT, Fibre Channel, etc.) and provide conversion of these to ITU-TG.694.1-compliant DWDM wavelengthsprior to multiplexing them together viapassive DWDM filters. Most equipmentcan accept the client optical signals in anyformat on any type of fiber (i.e. 850 nmMM fiber, 1310 nm SM fiber, etc.).

Some metro DWDM equipment alsoprovides support for sub 50 msec healingprotection capability that is configurableon a per wavelength basis. Therefore,Layer 1 transport protection capabilitiescan be employed on optical protocols that do not offer them natively (i.e. suchas PoS, Fibre Channel, and GigabitEthernet), resulting in increased networkreliability/availability. DWDM transportelements providing the option for protec-tion switching functionality are commonlyreferred to as “switched DWDM” pho-tonic networking platforms. In addition,some of these systems perform full 3R(Retiming, Reshaping, Regeneration)functions on all client protocols toincrease network resiliency. SwitchedDWDM systems are ideal for MSO digital transport networks that requirenumerous transport network connectiontypes and configurations to satisfy themultiple traffic requirements of the MSOmultiservice menu.

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Switched DWDM networkconnection typesSwitched DWDM transport elementswere designed to complement SONET/ATM networks by providing increasedcapacity per fiber while leaving tradi-tional protection switching functions to existing SONET/ATM network elements. These applications may usethe unprotected connections as illus-trated in Figure 7 and Figure 8.

In addition, switched DWDM trans-port network elements were alsodesigned to replace the SONET/ATMtransport layer where appropriate. In order to be capable of both theseoptions, 50 msec optical layer protec-tion switching functionality can beemployed as illustrated in Figure 9.Therefore, different options can beprovisioned on the same network on aper connection (i.e. wavelength) basis.

Figure 7. Unprotected wavelength connection with unprotected client interface

Survivable switched DWDM optical ring

QAM modulator

GbE Unprotected client interface

Unprotected wavelength connection

Same wavelength on the unused portion of the ring can be used for another connection

VDD server

GbE

Unprotected client interface

Figure 9. Protected wavelength connections with unprotected client interface

Survivable switched DWDM optical ring

Client data is duplicated and transported in both directions

around the switched DWDM ring

Unprotected clientinterface

Protected wavelength connection

Unprotected clientinterface

Aggregation switch

DOCSIS 1.1CMITS

50 msec protection switching is performed by the switched DWDM equipment

GbE or PoS

GbE or PoS

Figure 8. Dual unprotected wavelength connections with protected client interface

SONET Survivable switched DWDM optical ring

Protection switching performed by subtending

optical equipment

Protected clientinterface

SONET W

E

W

E

Protected clientinterface

Dual unprotected wavelength connections

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DWDM passive filtering and equalizationThe passive DWDM filtering componentis also important to consider when imple-menting a metro digital DWDM system.As previously stated, DWDM systemsrequire precise optical mux/demux filtersto provide channel spacings of 200 GHz,100 GHz, or 50 GHz and less. Further-more, metro DWDM systems can combine in excess of 30 wavelengths ontoa single fiber pair. To simplify the passiveportion of the DWDM system, passivefilter designs typically use a “banded”approach to DWDM filtering. Typically,a DWDM band consists of three or fouroptical channels on a single filter andprovides less optical loss than multiple,single channel filters. Banded filters arecreated by combining wideband groupfilters with fine channel filters as dis-played in Figure 10.

By using this approach, 8 to 10 band filters are used in a system instead of 30or more individual channel filters. Bandfilters provide dedicated connectivity ofmultiple channels between end pointswith a single filter. The “banded” filterapproach results in less sparing require-ments, simpler network design, and loweroptical attenuation. Additionally, by uti-lizing bands of optical channels within theDWDM system, equalization of opticalpower levels becomes much simpler. Thisis especially important in ring-basedDWDM designs where amplification isrequired. Equalization involves the adjust-ment of power levels entering an amplifieras shown in Figure 11.

As in RF systems, the input power levelsto an amplifier (of all channels) shouldbe equal or “flat”, and at the properlevel, to maximize amplifier performanceand ensure each channel receives a proportionate degree of amplification. The same applies to optical networks.

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Figure 10. Four channel DWDM band filter

OMX4λ Passive optical mux/demux

4 bi-directional optical channels—each channel up to 10 Gbps

7 bands passed

7 bands passed

1 band added

1 band dropped

4 channel filter

Band pass filter

Band pass filter

4 channel filter

Figure 11. DWDM band equalization

B2

B1

B3

B2B1 B3Equalize

OFA

Band channels arrive at an amplifierat different power levels

For optimal optical reach, theoptical channels should arrive at

the amplifier with the same optical power

Because optical channels can have multi-ple different entry points into a DWDMring, this can result in the optical wave-lengths arriving at different power levels atthe input to an optical amplifier station. If single channel filters are utilized, ring-based DWDM systems with amplificationbecome extremely difficult to equalize.

DWDM network traffic configurationsMetro digital DWDM transport net-works can support multiple traffic configurations such as point-to-point,hubbed, meshed, and drop + continue.These configurations are enabled throughthe strategic placement of the passive filtercomponents and DWDM transport

equipment. Each wavelength connectionis independently configured and can differfrom other wavelength connections.Therefore, metro DWDM systems cansimultaneously support multiple per-wavelength traffic configurations. Theoptimal network configuration will bedictated by the multiservice provider’sservice suite and delivery requirements.

The simplest configuration is point-to-point. Passive components and DWDMequipment are placed at each end of asimple point-to-point link. The networkcan be grown in a “just in time” fashionby adding filters at the ends of the fiberpair and modules to the DWM equip-ment only when required.

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The hubbed ring configuration is opti-mized for hubbed traffic flows, such as used in MSO IP/TDM access net-works. East and West DWDM bandfilters are placed at each hub location,with each hub having access to its bandonly. All other optical bands not des-tined for a particular site are seamlesslypassed through the site via the band filters. At the headend, all bands areterminated. Figure 12 displays the traffic flows and configuration of ahubbed ring configuration.

The meshed ring configuration is targetedprimarily at metropolitan interoffice andinter-hub trunking applications. Suchapplications use ring topologies for sur-vivability, and can provide connectionsbetween any two points on the ring. Thewavelength re-use feature of the meshring configuration allows SONET and/or RPR equipment to re-use the samewavelength in each span of the DWDMring while continuing to provide networkprotection switching capability. Themesh connectivity capability is enabledby having the ability to locate any bandfilter at any point on the ring as shownin Figure 13. Ultimately, this enables thetermination of any band at more thantwo places on the ring. When a band is terminated at more than two places on the ring, the ring has the ability toprovide wavelength meshing.

The drop and continue configuration is targeted primarily at metropolitanpoint-to-multipoint applications. Suchapplications use ring topologies for sur-vivability, and can provide connectionsbetween one transmit location and mul-tiple receive locations on the same ring.

The drop and continue feature of theDWDM transport equipment allows asingle location to transmit unidirec-tional signals in one or both directions

Figure 12. DWDM hubbed ring configuration

OMX 83

OMX 83

OMX 85

OMX 85OMX 84

OMX 84

OMX 82

OMX 82

OMX 81

OMX 81

OMX 81

OMX 81

OMX 82

OMX 82

OMX 83

OMX 83

OMX 85

OMX 85

Headend

OMX 84

OMX 84

Each hub has a private, multi-channel, east and west path to the headend

Protected, logical, hubbed connectivity each hub and headend

Figure 13. Meshed ring configuration

Headend

Each hub has a private, multi-channel, multi-band path to other locations in the ring

Wavelength bands can be terminated at more than two places on the ring to provide wavelength meshing

OMX 81

OMX 81

OMX 82

OMX 82

OMX 83

OMX 83

OMX 85

OMX 85

OMX 84

OMX 84

OM

X 8

2

OM

X 8

2

OM

X 8

5

OM

X 8

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OM

X 8

1

OM

X 8

1

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OMX 83

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OMX 81

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OM

X 8

4

OM

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4

OM

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3

OM

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OM

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1

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around the DWDM ring while usingthe same wavelength in each span ofthe ring. East and West band filters, all of the same band, are placed at eachhub site and the headend. This conceptis shown in Figure 14. This feature isparticularly suited to the transport of multiple broadcast video signals (via DV6000, PrismaDT, etc.) from a single headend location to multipleprimary hub locations.

DWDM wavelength monitoringThere are two predominant methods for providing DWDM wavelength andsystem monitoring. These include both“in-band” and “out-of-band”.

In-band monitoring is typically used to provide per wavelength performancemonitoring. In-band monitoring is typically enabled with per-wavelength,transparent optical service channels.These service channels are embedded asoverhead into each installed wavelengthand therefore do not require their ownseparate transmission equipment.

Out-of-band monitoring is used to col-lect system information from several net-work elements located within the ring.Typically, an out-of-band service channel(OSC) is used to communicate betweenDWDM sites. The OSC uses its ownindependent wavelength that is locatedoutside the window used for client wave-length traffic. The OSC is used to collectoverall system information such that itcan be reported to higher-level manage-ment systems.

Metropolitan DWDM benefitsMetro digital DWDM transport net-works enable data traffic consolidationand simplification in the transport network layer. They provide the following benefits:

• High fiber efficiency

• Modular, “pay as you grow,” scalable bandwidth capacity

• Simplified operations and management

• Allows for rapid service introductionwith minimal field dispatches

• Multiple present day and futurenative optical services carried on a single network

• Operational efficiencies and infra-structure savings by eliminating overlay networks

• Optical layer access adaptable to any bit rate or protocol format

• Protects embedded investment…complements existing transport network equipment

• Simultaneously supports multipleper-wavelength traffic flow con-figurations

• Protection provisionable on a perwavelength basis with SONET-likeswitching capability

• Lower cost optics of subtending optical equipment

• Low latency, wire speed transportnative optical protocols (GbE, Fibre channel)

• High availability and fault tolerancefor mission-critical service delivery

Figure 14. DWDM drop and continue configuration

OMX 81 OMX 81OMX 81 OMX 81

OMX 81 OMX 81 OMX 81 OMX 81

Working transmit

Each hub has a private, multi-

channel path tothe adjacent site

Protection transmit

Logical, drop and continue connectivity in counter-rotating direction around ring

OMX 81

OMX 81

OMX 81

OMX 81

Protection switching performedby subtending client equipment

The same wavelength is used on each fiber between locations

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Coarse Wavelength DivisionMultiplexing (CWDM)The cost of deploying WDM technolo-gies is directly related to the channelspacing utilized. As we have learned,DWDM systems use tight channel spacing such that amplifier cost can beshared across multiple optical channels.The drawback is that DWDM systemsrequire more expensive laser and passivefilter components.

In contrast to DWDM where the goal isto maximize transmission capacity overlonger distances, Coarse WavelengthDivision Multiplexing (CWDM) tech-nology utilizes much larger wavelengthspacing and is aimed at reducing network cost for unamplified, shorterdistance networks. CWDM wavelengthspacing has been standardized at 20 nm,which is wide enough to easily accom-modate the wavelength variation oflower cost, uncooled lasers. In June of2002, the ITU-T G.694.2 CWDMwavelength grid standard was definedand is detailed in Figures 15 and 16.

All of these wavelengths are usable,given appropriate choice of opticalfiber (as will be discussed in the follow-ing section), although the first two(1270 and 1290 nm) are in a region of optical spectrum where Rayleighscattering creates higher loss than else-where. Systems that are developed touse the entire CWDM optical spec-trum, including the E band water peakregion, are said to be employing “fullspectrum CWDM” and offer 16 of the18 defined wavelengths. The higherloss of the first two wavelengths is whyfull spectrum CWDM systems typicallyonly offer 16 wavelengths.

Figure 15. ITU-T G.694.2 CWDM nominal central wavelengths

ITU-T G.694.2—Nominal central wavelengths for spacing of 20 nm

1270 nm 1290 nm 1310 nm

1330 nm 1350 nm 1370 nm

1390 nm 1410 nm 1430 nm

1450 nm 1470 nm 1490 nm

1510 nm 1530 nm 1550 nm

1570 nm 1590 nm 1610 nm

Figure 16. Pictorial view of ITU-T G.694.2 CWDM wavelength grid

O - band E - band S - band C - band L - band

CWDM window

λ (nm) 1280 1320 1360 1400 1440 1480 1520 1560 1600 1640 λ (nm) I I I I I I I I I I

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Standard single mode fiber and CWDM: Be awareBefore any deployment of an ITU-TG.694.2-compliant CWDM system, it is critical the fiber type being used bedetermined. As displayed in Figure 17,standard single mode fiber cannot effectively support all channels in the CWDM window. Specifically, wavelengths in the upper end of the Oband and all of the E band (i.e. 1350,1370, 1390, 1410, and 1430 nm) experience very high loss due to the high attenuation “water peak” perfor-mance of standard single mode fiber.

The high water peak of standard singlemode fiber is associated with thehydroxyl ion, which is a residue frommoisture/water incorporated in the glass during the manufacturing process.Furthermore, this ion has also demon-strated a tendency to creep back intoconventional SMF, that may have hadinitial low water peak loss, during thecourse of its useful lifetime. This loss-aging effect renders using conventionalSMF, selected for low water peak loss,very risky for CWDM systems thatoperate over the full spectrum ofCWDM channels.

As shown, G.652.C fiber (e.g. CorningLeaf, OFS Labs AllWave), also referredto as “low water peak (LWP)” or “Zerowater peak (ZWP)” fiber, is specificallydesigned to remove the high attenua-tion associated with the traditional‘water’ peak, thereby enabling reliabletransmission of optical signals across the entire ITU-T G.694.2 CWDMwavelength grid.

Therefore, new deployments of fiber in MSO access and small distributionshould take this into account if CWDMis planned for deployment over theseinfrastructures.

Figure 18. Single channel CWDM passive optical mux/demux

1 channel CWDM OMX20 nm optical mux/demux

20 nm of optical spectrum—used for one CWDM channel of up to 10 Gbps

All other CWDM channels passed

1 CWDM channel addedBand

add filter

Band drop filter 1 CWDM channel dropped

All other CWDM channels passed

Figure 17. Attenuation and dispersion performance of S-SMF and G.652.C ZWP fibers

1.2

0.9

0.6

0.3

0

O - band E - band S - band C - band L - band

1.21.2ITU-TG 894.2 CWDM wavelength grid (in nm)

λ (nm) 1280 1320 1360 1400 1440 1480 1520 1560 1600 1640 λ (nm) I I I I I I I I I I

20

10

0

-10

Conventional $Mfiber loss Conventional $M and G.852.C ZWP

fiber dispersion

G.652.C ZWP fiber loss

CWDM passive filtering One of the areas that CWDM tech-nology achieves cost benefits overDWDM is in the area of passive filtering. Because CWDM utilizesrelaxed wavelength tolerances, thepassive filtering component is simpler,

has fewer components, and is ulti-mately less expensive. With CWDM,wideband group filtering is all that is required and there is no need forsecondary, fine channel filtering.Figure 18 displays a single channelCWDM filter.

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CWDM optical mux/demux filters arealso available in 4, 8, and 16 channelgranularity. As an example, Figure 19 displays a 4 channel CWDM passiveoptical mux/demux filter.

Sample CWDM network equipment implementationsMany vendors that offer metro digitalDWDM transport equipment also offersmaller, less expensive single or dualwavelength versions of their equipmentthat support CWDM implementationsand provide many of the same advan-tages. These are designed for lower band-width, unamplified, WDM implementa-tions and allow the DWDM opticaltransport network to be extended to theedge. These devices are attractive for lowcost, small footprint, customer premisesdeployments in order to offer managedwavelength services as well as for smallermetro access and collector rings. Figure20 provides sample implementations ofthis approach.

Figure 19. Four channel CWDM passive optical mux/demux

4 channel CWDM OMX4 channel CWDM passive optical

4 bi-directional CWDM channels

All CWDM channels

All remaining CWDM channels

mux/demux

4 channel demux

All CWDM channels

4 channel mux

1

23

4

3

1

2

4

Figure 20. Sample CWDM access ring implementations

Switched DWDM ring

Switched DWDM ring

CWDM ring

CWDM point-to-point

Interconnected rings with two bridge sitesBusiness CWDM access ring

Hubbed ring or hub and spoke

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Figure 21 provides a more detailed lookat a sample CWDM access ring imple-mentation.

In Figure 21, two 4-channel CWDM fil-ters are deployed at the headend. One isused to terminate the east fiber pair andthe other is used to terminate the westfiber pair. Also at the headend is a highdensity equipment shelf used to termi-nate multiple CWDM wavelengths fromboth sides of the ring. At each customersite, two single channel CWDM filtersare installed along with the small foot-print CWDM equipment. This allowseach customer site to have east and westaccess to its CWDM channel only whileallowing all other CWDM channels toseamlessly pass through. The CWDMequipment is used to accept the clientoptical signal, duplicate it if protectionis required, and convert to CWDM-compliant optical channels beforesending it in both directions aroundthe access ring.

As with DWDM, multiple CWDMfilters can be placed throughout a net-work to achieve several traffic configu-rations such as point-to-point, hubbed,and meshed.

In addition to small footprint, protocol-independent CWDM devices as shownabove, GbE optical drivers that complywith the ITU-T694.2 CWDM wave-length grid are now commercially avail-able. These drivers are available in severalform factors (e.g. GBIC, SFP) and invarying power levels so different trans-mission distances can be achieved.These drivers can be installed directlyinto today’s IP routing/Ethernet

Figure 21. Detailed CWDM access ring implementation

Headend

4 channel CWDM OMλs

CWDM access fiber ring2 ring fibers

4 4 3 3

1 channel CWDM OMλs

CWDM shelf

Client signal(GbE, PC, etc.)

Customer 4Client signal(GbE, PC, etc.)

Customer 3

CWDM shelf

1 channel CWDM OMλs

Client signal(GbE, PC, etc.)

1 1 2 2

1 channel CWDM OMλs

CWDM shelf

Client signal(GbE, PC, etc.)

Customer 1 Customer 2

CWDM shelf 1 channel CWDM OMλs

Figure 22. Sample point-to-point GbE-based, CWDM access network implementation

nx GbE

nx GbE

CWDM

CWDM

CWDMnx GbE

nx GbE

CWDM

Ethernet switch

Ethernet switch

IP router

CWDM GbE GBICoptical drivers

4 channel CWDM filters daisy chain additional

CWDM filters for growth

CWDM GbE GBICoptical drivers

switching devices to nullify the needfor external transport equipment whendriving Ethernet, especially GbE, froman IP router/Ethernet switch to pointsfurther in the access network. Thisapproach is ideal for providing high-density, low-cost, GbE connectivity inthe metro access network. Figure 22displays a point-to-point implementa-tion of this approach.

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CWDM benefitsCWDM systems realize lower costimplementations through a combinationof uncooled lasers, relaxed laser wave-length selection tolerances, and widepass-band filters. In addition to beinglower cost, CWDM lasers consume lesspower and take up less space on circuitboards when compared to their DWDMcounterparts. Furthermore, CWDMpassive mux/demux filters are less com-plex and typically lower cost than theirDWDM equivalents. Therefore, CWDMsystems provide a very cost-effective,WDM-based, solution for metropolitanaccess and shorter distance distributionnetworks that require less bandwidththan regional/metropolitan core net-works and where optical amplification is not required. Figure 23 highlights the advantages and limitations ofCWDM technology.

OPTera Metro 5000Multiservice PlatformNortel Networks offers MSOs a familyof market-leading Dense WavelengthDivision Multiplexing (DWDM) platforms that are an efficient meansof increasing the capacity of fiberoptic data transmission systemsthrough multiplexing of multiplewavelengths of light. The OPTeraMetro 5000 Multiservice Platformseries increases the utilization of a single fiber strand by allowing 32 protected wavelengths of data com-munication traffic to be carried with 10G per wavelength scalability.

Nortel Networks DWDM portfolio of products, the OPTera Metro 5000Multiservice Platform series, enablesMSOs to cost-effectively offer their enterprise customers high-speed data

Figure 23. Advantages and limitations of CWDM technology

O - band E - band S - band C - band L - band

CWDM window

λ (nm) 1280 1320 1360 1400 1440 1480 1520 1560 1600 1640 λ (nm) I I I I I I I I I I

ITU-T G.694.2 CWDM channel plan (approved June 2002) driftλ

1580 nm 1600 nm

CWDM advantages• Uses lower cost, lower power, uncooled lasers due to large wavelength spacing and filter tolerance • Can tolerate 6-8 nm of laser drift• Lower cost passive filters (uses wideband group filtering only —no fine channel filtering required)

CWDM limitations• Cannot achieve distances delivered by amplified DWDM systems• Requires G.652.C low/zero water peak (LWP/ZWP) fiber to utilize all CWDM channels, standard SMF cannot effectively support 1370, 1390, 1410, 1430 nm channels

services with a reduced total cost ofownership through simplified networkmanagement and ease of operation.The OPTera Metro 5000 MultiservicePlatform series also serves as a newsource of revenue and cost reductionfor the MSOs that use the products to offer shared services.

OPTera Metro 5100 MultiservicePlatform—The space-efficient OPTera Metro 5100 is a low poweroptical product for small bandwidthrequirements serving metro primary or secondary rings and customerpremises applications. It quickly andeconomically delivers up to eightprotected wavelengths of DWDM.

OPTera Metro 5200 MultiservicePlatform—The flexible OPTera Metro5200 Multiservice Platform delivers32 wavelengths of bandwidth throughthe power of DWDM and offers 10G

per wavelength scalability along with anetwork modeling tool that simplifiesthe deployment and operation of effi-cient DWDM networks.

OPTera Metro Cabinet 5200—Thefree-standing OPTera Metro Cabinet5200 is an easy-to-deploy DWDM cabinet solution that extends theOPTera Metro 5200 functionality andflexibility to metropolitan enterpriseand customer premises environmentapplications. This cabinet delivers thebenefits of the OPTera Metro 5200Multiservice Platform in a pre-testedand pre-configured cabinet. TheOPTera Metro Cabinet 5200 solutioncan help customers considerably reduceinstallation time and speed deployment.

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List of acronymsAM Amplitude ModulationATM Asynchronous Transfer ModeBLSR Bi-directional Line Switched RingBW BandwidthCAP Control Access ProtocolCAPEX Capital ExpenditureCBR Constant Bit RateCMTS Cable Modem Termination SystemCO Central OfficeCRM Customer Relations ManagementDHUB Distribution HubDOCSIS Data Over Cable System

Interface SpecificationDPT Dynamic Packet TransportDVC Digital Video CompressionDVB-ASI Digital Video Broadcast

Asynchronous Serial InterfaceDWDM Dense Wavelength Division

MultiplexingETSI European Telecommunications

Standardization InstituteFR Frame RelayGbE Gigabit EthernetGbps Gigabits per secondGFP Generic Framing ProcedureHDT Host Digital TerminalHE Head-endHFC Hybrid Fiber CoaxialIEEE Institute of Electrical and

Electronic Engineers

INM Integrated Network ManagementISP Internet Service ProviderIPPV Impulse Pay Per viewIP Internet ProtocolJIT Just in TimeLAN Local Area NetworkMAN Metropolitan Area NetworkMbps Mega bits per secondMPLS Multi Protocol Label SwitchingMSO Multiple System OperatorNE Network ElementNEBS Network Equipment Building SystemNSG Network Services Gateway

Ethernet to QAM Converter made by Harmonic Inc.

OAM+P Operations, Administration, Maintenance, and Provisioning

OC Optical CarrierPC Personal ComputerPCM Pulse Code ModulationPOS Packet over SONETPPV Pay Per ViewPSTN Public Switched Telephone NetworkQAM Quadrature Amplitude ModulationQOS Quality of ServiceRF Radio FrequencyRPD Return Plant DemodulatorRPR Resilient Packet RingSAN Storage Area NetworkSDH Synchronous Digital HierarchySLA Service Level Agreement

SNMP Simple Network Management Protocol

SOHO Small Office, Home OfficeSONET Synchronous Optical NetworkSRP Spatial Re-use ProtocolSTB Set Top BoxSTM Synchronous Transfer ModeSTS Synchronous Transport SignalTD Transparent DomainTDI Transparent Domain IdentifierTDM Time Division MultiplexingUNI User to Network InterfaceVLAN Virtual Local Area NetworkVOD Video on DemandVoIP Voice Over Internet ProtocolVPN Virtual Private NetworkWAN Wide Area Network

Nortel Networks is an industry leader and innovator focused on transforming how the world communicates and exchanges information. The company is supplying its service provider and enterprise customers with communications technology and infrastructure to enable value-added IP data, voice and multimedia services spanning Wireless Networks, Wireline Networks, EnterpriseNetworks, and Optical Networks. As a global company, Nortel Networks does business in more than150 countries. More information about Nortel Networks can be found on the Web at:

www.nortelnetworks.comFor more information, contact your Nortel Networks representative, or call 1-800-4 NORTEL or 1-800-466-7835 from anywhere in North America.

*Nortel Networks, the Nortel Networks logo, the globemark design, and OPTera Metro are trademarks of Nortel Networks. All other trademarks are the property of their owners.

Copyright © 2003 Nortel Networks. All rights reserved. Information in this document is subject to change without notice. Nortel Networks assumes no responsibility for any errors that may appear in this document.

GSA Schedule GS-35F-0140L1-888-GSA-NTEL

NN104004-050803

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