Transport alternatives for wavelength services
TRANSPACKET
white paper
Transport alternatives
for wavelength services
A carrier’s guide to wavelength service
deployments
Executivesummary
Datacenterstriggeragrowingneedfordedicatedcapacityacross
fibre-opticalnetworks.Wavelengthservicesareofferedto
datacentersandserviceprovidersrequiringadedicatedhigh
capacitywithstrictlatencyrequirements.However,awavelength
serviceistypicallynotaphysicalopticaltransparentwavelength
throughthecarrier’snetwork.Thiswhitepaperdiscusses
wavelengthservicetransportmethodsandrequirements.Virtual
wavelengthsfulfilltherequirementsofawavelengthservice,
whileavoidingdedicatingwavelengthsorfibersacrossthe
network,thusconsiderablyloweringthecarrier’sproductioncost.
Transport alternatives for wavelength services
Transport alternatives for wavelength services
A carrier’s guide to wavelength service deployments
Steinar Bjørnstad (CTO), Raimena Veisllari (Product Manager), TransPacket AS, 19.02.2016
Introduction
Datacenters are one of today’s most important drivers for bandwidth. Typical needs involve high
capacity low latency connections for inter- and intra- datacenter connectivity. Wavelengths across
fibre-optical networks are often the preferred choice of transport for this purpose because it
enables a dedicated bandwidth with low and fixed latency. Other prominent wavelength service
customers are service providers and large businesses in need of dedicated high-capacity
connectivity. These customers typically rent wavelengths from carriers with both national and
international fibre-networks.
Carrierswithfibre-opticnetworks,especiallytheTier1´s,areofferingwavelengthservicestotheir
customers.ThenameoftheservicestemsfromthewavelengthintheWavelengthDivision
Multiplexing(WDM)technique,enablingphysicalwavelengthstobeputupacrossanoptical
network.However,thereisnotaconsistentdefinitionamongcarriersonwhatthewavelength
serviceactuallyisandwhatitcontains.Typically,theserviceisnotanopticalinputtothecarrier’s
network,butinvolvesanOTN-framingandadedicatedtransport-channelacrossthecarrier’s
network.
Adedicatedtransport-channelfulfillsthecapacityandlatencyrequirementsofwavelengthservices.
Itdoeshoweverhaveahighproductioncostsincevacantcapacitycannotbeutilizedforlower
priorityservices,likefore.g.VPNandEthernet-services.Ontheotherhand,VPNandEthernetservicesdonotfulfillthelatencyandcapacityrequirementsofthewavelengthservice.Virtual
wavelengthservicesarebasedontheTransPacketFUSIONnetworktechnologyenablingEthernetto
fulfillthecapacityandlatencyrequirementsofawavelengthservice.Sincededicatingwavelengthsor
similaristhennolongerneeded,itenablesthecarriertobringdownproductioncosttothelevelof
anEthernetservice.
Wavelength service transport alternatives
Thissectionbringsanoverviewofdifferenttransport-methodsforofferingwavelengthservices.
Whattypeofservicemightbepreciselydefinedasawavelengthserviceornotisalongstoryand
perhapsmoreamatterofdefinition.Whatismoreimportantistheuseroftheserviceandthe
propertiestheuserrequiresfromtheservice.Typically,theapplicationsofsuchservicesareboth
internalbythecarrier,connectingroutersorswitches,andexternalcustomersbuyingwavelength
services.Fromauser-perspective,howtheserviceisactuallyproducedbecomeslessimportant,
whatmattersiswhattypeofserviceactuallyisbeingofferedandthatthisfulfillstheuser
requirements.Inthissectionwediscussthepropertiesofdifferenttypesofwavelengthserviceor
“static-line”typeofofferingsandexplainprosandconsfortheseservicesseenfromboththeone
whoisofferingtheservice(thecarrier)andtheuseroftheservice(customer)perspective.
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Transport alternatives for wavelength services
Alien-wavelength
Anativewavelengthservicehasanopticalinputtotheopticalnetwork,andisaphysicalwavelength
withoutframing.ItistypicallyfeddirectlyintotheopticalmultiplexerofaCoarseWDM(CWDM)or
DenseWDM(DWDM)system,asillustratedinfigure1.Ifavariableopticalattenuatorandpowermonitoringdeviceisinsertedbetweenthecustomerandthemultiplexer,themaximumpowerofthe
wavelengthcanbecontrolled.Thewavelengthissetupend-to-endthroughthenetwork,passing
onlyopticalnetworkelements,likee.g.opticalmultiplexers,opticalamplifiersandopticalswitches.
Inacarrier’sperspectivethistypeofserviceisoftencalledan“alien-wavelengthservice”sincethe
carrierhasnotfullcontrolofparameterslikeprotocol,bitrate,customer’swavelength,spectral
width,qualityandpowerofthewavelengthbeingtransportedinthenetwork.Thecarrieristhen
unabletoguaranteethequalityandperformanceoftheservice.Therefore,largecarrierstypicallydo
notofferthisservicetoexternalcustomers.Thismayhoweverbeaviablemethodforinternaluseby
thecarrier,ife.g.thewavelengthoccursatanoutputinterfaceofoneofthecarrier’sswitcheswhere
thecarrierhasfullcontrolonwavelengthandoutputpoweratitsinterface.
Figure1:Feedinganalien-wavelengthall-opticallyintoaWDMsystem.
Multi-format Transponder-based wavelengths
If the carrier has transponders at the ingress and egress of the network, as illustrated in figure 2, it
enables the carrier to have control of parameters like power, quality, spectral width and
wavelength. This is because a transponder does full regeneration of the signal (3R) and offers
remote monitoring capability. The wavelength may then be routed end-to-end through the network
all-optically. The content of the wavelength (i.e. protocol format of the signal) is however
transparent, and not monitored. Hence, the carrier offering the service is not able to give full
quality guarantees, e.g. the link may be running with bit-errors. Comparing with the alien
wavelength approach, there will be a limitation on both minimum and maximum bitrate supported.
This is partly given by the transponders ability to regenerate signals of different bitrates, but
chromatic dispersion and other physical impairments in the optical path also play a key-role for
distance limitations on bitrates of 2.5 Gb/s and beyond. Carriers do, however, typically not see
this as a major drawback since it is desirable to offer capacity services rather than the “raw
material” like a fibre or wavelength.
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Transport alternatives for wavelength services
Figure2,WavelengthservicefedthrougharegenerativetransponderintoaWDMsystem.
OTN-transport
Sincecarriersareconcernedaboutsecurity,reliabilityandQualityofService(QoS)oftheirservice
offerings,offeringfulltransparencyisoftennotpreferred.Byusingmulti-formattransponders,the
carriercontrolsphysicalparameterslikewavelengthandpower,avoidinginterferencewithother
wavelengths,butisnotabletodetectbit-errorsandsupervisionofthecontentofthesignals.
However,ifthetransponderisperformingOTN-framing,likeillustratedinfigure3,itenablesthe
carrierwithfullOperationAdministrationandMonitoring(OAM)functionality,ensuringtheQoSof
theserviceandissuingalarmsiftheexpectedQoSisnotmet.Evenifthistypeofserviceactuallyisa
typeofTDMserviceandnotprotocolandbitratetransparent,likethealien-wavelengthinprinciple
is,thisiswhatmajorT1-carrierstypicallycallawavelengthservice.
Figure3,WavelengthservicefedthroughatransponderperformingOTNframing,enablingOAM
capability.TheOTNwavelengthmaybeswitchedwithinthenetworkusingall-opticalswitchingor
usinganelectronicOTNcross-connect.
OTN sub-wavelengths
However,sincetherearealimitednumberofwavelengthsinthenetwork,occupyingawavelength
throughacarrier’snetworkisresourcedemandingandcomesatacorrespondingexpense.This
expensebecomestoohighforlowbitratewavelengths.Thenextstepforthecarrieristhereforeto
offerasub-rateofthewavelength,alsocalledsub-wavelengths.OTNenablesdividingcapacityinto
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Transport alternatives for wavelength services
chunksofgranularity1Gb/susingamuxponder,asillustratedinfigure4.Lowestbitratesupportedis
1Gb/sandtheODU-flexformatallowsframingofsignalswithanybitratebetween1Gb/sand100
Gb/s.Hence,ahigherutilizationofthephysicalwavelengthcanbeachievedbymultiplexingseveral
OTNchannelsintoawavelengthchannel.Sincethecharacteristicsofthesesub-wavelengthservices
aresimilartothecharacteristicoftheOTNbasedtransponderwavelengthservice,carriersmayalso
offerthesub-wavelengthsaswavelengthservices.
TheOTNapproachishoweverstillTimeDivisionMultiplexed(TDM)-based,notofferingthe
throughputefficiencyofpacketswitchednetworks;packetswitchednetworksofferstatistical
multiplexing,enablingoversubscriptionandhighlycost-efficientnetworks.
Figure4,Wavelengthservicebasedon“sub-wavelengths”fedthroughamuxponderperformingOTN
framing,multiplexingofchannelswith1Gb/sgranularity,andOAM.Atintermediatenodesinthe
network,wavelengthsandsub-wavelengthsmaybeswitchedelectronicallyinOTNcross-connects.
Reserved bandwidth across packet switched networks
(VPN services)
Packetnetworkshavetheabilityofhandlingoversubscription,enablinghigherthroughputefficiency
thannetworksofferinganytypeofwavelengthservice.ByreservingbandwidthacrossanIP/Ethernet
basednetwork,loss-freeconnectionswithaguaranteedbandwidthcanbeachievedacrossthe
packetnetwork.However,thepacketnetworkdoesnotofferthesamecharacteristicsasthe
wavelengthorTDMbasednetworks.Thelatencyisnotfixed,andtypicallythelatencymaybe
significantlyhigher.Furthermore,therearedependenciesbetweentheservices;latencyandlatency
(packetdelay)variation(PDV)inthepacketnetworkdependsontheloadofthenetwork.Hence,
carriersdonormallynotofferthistypeofserviceasawavelengthservicebutasaVPNservice.The
drawbackofthistypeofserviceis,asmentioned,thatitdoesnotallowfullisolationbetweenthe
servicesandanadditionallackoftiming-transparencyduetothePDV.I.e.theservicemaynotbe
suitablefortransparenttransportofcustomertrafficcontainingtiming-criticaltrafficlikee.g.IEEE
1588synchronizationpackets.
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Transport alternatives for wavelength services
Virtual wavelengths
Whiletheservice-offeringsdiscussedsofarshowatradeoffbetweenthroughputefficiency,service
transparencyandisolation,virtualwavelengthsavoidsthistradeoff.Virtualwavelengthsareenabled
bytheTransPacketFUSIONtechnology.ItallowstransportacrossEthernetnetworkswithfixed,low
latency,i.e.timingtransparency,andwithoutpacketloss.Hence,transportcharacteristicsaresimilar
toTDMbasednetworks,whilethroughputefficiencyissimilartothepacketnetwork.Asillustratedin
figure5,carriersmayoffervirtualEthernetbasedwavelengthsofanycapacityupto100Gb/s,similar
totheOTN-basedapproachinfigure3.
Figure5,Wavelengthservicebasedonavirtualwavelengthinterfacewiththesamebitrateasthe
physicalinterface.Additionaltrafficmaybestatisticallymultiplexedintothewavelengththrough
additionalEthernetinterfaces.ThevirtualwavelengthapproachalsooffersOAMcapabilities.
Furthermore,asillustratedinfigure6,virtualwavelengthsmayalsobeofferedforsub-ratesofthe
physicalwavelength,similartotheOTNsub-wavelengthapproachillustratedinfigure4.However,in
differencefromOTN,FUSIONincommonwithpacketnetworks,allowsefficientutilizationofthe
networkthroughstatisticalmultiplexingandifdesirablealsooversubscription.Asforconventional
Ethernetnetworks,additionallowerprioritytrafficmaybeaddedthroughinterfacesofanyrate,e.g.
1,10or100Gb/sEthernet.
Figure6,WavelengthservicebasedonofferingmultipleEthernetvirtualwavelengthsoflowerrate
thanthephysicalwavelength.Additionaltrafficmaybestatisticallymultiplexedintothewavelength
throughadditionalEthernetinterfacesofanyratesimilarorlowerthantherateofthephysical
wavelength.ThevirtualwavelengthapproachoffersstrongOAMcapabilities.
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Transport alternatives for wavelength services
FUSION H1 virtual wavelength service network example
Figure7,VirtualwavelengthservicesenabledbynetworkapplyingTransPacketsFUSIONH1product.
TheTransPacketFUSIONH1nodeenables10GE(10Gb/sEthernet)virtualwavelengthservicesor
sub-rateGE(1Gb/sEthernet)VirtualWavelengthServicesoveranEthernetbased10GEphysical
wavelengthorwavelengthservice.Ontopofthevirtualwavelengthservices,GEEthernetServices
arestatisticallymultiplexedonthesamephysicalwavelength,transparenttothewavelengthservice.
Thisenablesthroughputasforpacketnetworkswhileofferingwavelengthservices.Figure7
illustratesanexampleapplicationdeployingFusionH1inaring-networkofferingsub-rateGEvirtual
wavelengthservices.Add/dropofthevirtualwavelengthsenablesmeshconnectivityinthenetwork,
i.e.foranytypeoflogicaltopology.AllotherGEportsintheH1nodescanbethenusedforoffering
additionalEthernetServices,whicharestatisticallymultiplexedontothesame10GEwavelength
service.Furthermore,theFUSIONringprotectionswitchingmechanismenablesrecord-lowsub-ms
convergencetime,protectingthevirtualwavelengthsinthering.Thesameultra-fastschemeisalso
offeredforprotectionoftheEthernetServices.
Summary
Wavelength services offered by carriers are usually not all-optical physical connections into the
optical network. Transponders or muxponders are applied at the edge of the network for enabling
control and monitoring of the signal entering and exiting the network. This type of transport
typically applies OTN framing and offers fully dedicated and isolated connections with zero
packet loss and a low fixed latency. However, the throughput efficiency is low because the
multiplexing is static and not statistical, as in packet networks. Packet networks on the other hand
have so far not been able to offer strict latency characteristics as in TDM and wavelength based
networks. TransPacket’s FUSION technology allows services with TDM characteristics in Ethernet
networks. Virtual wavelength services perform as wavelength and TDM services. However, in
difference from the wavelength and TDM networks, FUSION allows the throughput efficiency of the
packet networks through full utilization of each of the wavelengths using statistical multiplexing.
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Transport alternatives for wavelength services
Hence, using FUSION technology, the carrier’s production cost of a wavelength can be brought
down to the level of a VPN connection. The characteristics of the different wavelength transport
methods has been outlined in this white-paper and is summarized in table 1.
Property
Bitrate
Transparency
Alien
Yes/distance
(e.g.10Gmight
needdispersion
compensation)
Transponder
Muxponder
Fusion
No/weak
No/weak
No
Dependson
product
Product
dependent
Protocol
Yes
Dependson
product
Timing
Yes
Typical
Loss
detection
No
Dependson
product
Yes
Yes
No
Product
dependent
Product
dependent
Yes,ringor
1+1,(ultrafast,sub-ms)
Reliability& Protection
Performance
Monitoring
capability
(OAM)
Cost
Weak(e.g.
power
monitoring)
High
(dedicated)
Medium,high Medium,high
forOTN-based forOTN-based
High
(dedicated)
Medium
(dedicated)
Ethernet
Yes
High
Low(shared)
Table1.ComparisonofWavelengthservicesolutionsbasedon1)transparencyintermsofbitrate,
protocolformatandtiming;2)reliabilityandperformanceintermsofbiterrorsandpacketloss,
redundancyandprotectionswitching,monitoringofservice;3)Thecarriersproduction-costofthe
service.
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