Supporting Ethernet in Obs Networks 3446

8/6/2019 Supporting Ethernet in Obs Networks 3446

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Supporting Ethernet in OBSSupporting Ethernet in OBSnetworksnetworks

Sami Sheeshia and Chunming QiaoSami Sheeshia and Chunming Qiao Department of computer science and engineeringDepartment of computer science and engineering

State University of New York at BuffaloState University of New York at Buffalo

Jeffrey U.J.LiuJeffrey U.J.Liu Computer and Communications Research LabComputer and Communications Research LabIndustrial Technology Research Institute, TaiwanIndustrial Technology Research Institute, Taiwan

2002 Journal of Optical Computing2002 Journal of Optical Computing


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OverviewOverview

AbstractAbstract IntroductionIntroduction

- various standards to enhance Ethernet- various standards to enhance Ethernet 10GbE over SONET10GbE over SONET

- disadvantages and quantifying its inefficiencies- disadvantages and quantifying its inefficiencies Ethernet over OBSEthernet over OBS

- presenting a viable alterative which avoids the- presenting a viable alterative which avoids theshortcomings of SONET.shortcomings of SONET.

Ethernet over OBS specific integration issues-Ethernet over OBS specific integration issues-- such as OBS burst size- such as OBS burst size

- Multiprotocol Label Switching (MPLS) issues- Multiprotocol Label Switching (MPLS) issues


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AbstractAbstract The paper introduces the likely role that OBS willThe paper introduces the likely role that OBS will

play in the development of 10-Gbit Ethernetplay in the development of 10-Gbit EthernetMAN.MAN.

SONET (Synchronous optical networking) isSONET (Synchronous optical networking) is

being proposed for the same but its synchronousbeing proposed for the same but its synchronoustime-division multiplexing (TDM) is inefficienttime-division multiplexing (TDM) is inefficientfor transporting bursty traffic of the Ethernet.for transporting bursty traffic of the Ethernet.

The author claims that OBS provides a betterThe author claims that OBS provides a bettersharing of network resources and when coupledsharing of network resources and when coupledwith generalized multiprotocol label switchingwith generalized multiprotocol label switching(GMPLS) provides a robust Ethernet service.(GMPLS) provides a robust Ethernet service.


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IntroductionIntroduction Recently network providers face newRecently network providers face new

challenges at the MAN level due to thechallenges at the MAN level due to theincreased user requirementsincreased user requirements.. Tremendous pressure to supportTremendous pressure to supportbroadbandbroadband

accessaccess andand high speed WAN at low cost.high speed WAN at low cost. So the above factors demands a flexible,So the above factors demands a flexible,

proven MAN architecture combined withproven MAN architecture combined withmulti-vendor compatible implementations.multi-vendor compatible implementations.

10GbE10GbE promises to play an important role,promises to play an important role,offering good speed, end-to-end protocoloffering good speed, end-to-end protocol

consistency for providers and users in a costconsistency for providers and users in a costeffective manner.effective manner. 10GbE can operate over long link spans(4010GbE can operate over long link spans(40

km) and other transport layers such askm) and other transport layers such asSONET and DWDM.SONET and DWDM.


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IntroIntroSONETSONET

o

Historically, wide-area connectivity is been provided byHistorically, wide-area connectivity is been provided bySONET which were built to carry voice traffic.SONET which were built to carry voice traffic.

o But it isBut it is not optimized for the bursty naturenot optimized for the bursty nature of the presentof the present

time data traffic and is not able to scale itself to support thetime data traffic and is not able to scale itself to support the

rapid growth of internet in a cost-effective manner (requiresrapid growth of internet in a cost-effective manner (requires

ADMs, hubs etc).ADMs, hubs etc).

o Gigabit Ethernet has been popular in LAN and the MAN ,Gigabit Ethernet has been popular in LAN and the MAN ,

however, Ethernet by itself cannot be considered to be ahowever, Ethernet by itself cannot be considered to be a

carrier class protocol as it does not provide what SONETcarrier class protocol as it does not provide what SONET

guarantees.guarantees.

o Standards such asStandards such as Ethernet over WDM, resilient packet ringEthernet over WDM, resilient packet ring

(RPR), packet over SONET (PoS)(RPR), packet over SONET (PoS) have been developed withhave been developed with

carrier-grade qualities.carrier-grade qualities.


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Intro..Intro..1.Ethernet over WDM1.Ethernet over WDM

o This provides a long haul connectivity(40 km) betweenThis provides a long haul connectivity(40 km) between

two Ethernet switches.two Ethernet switches.

o Point-point connections are done manually or viaPoint-point connections are done manually or via

multiprotocol lambda switching.multiprotocol lambda switching.

Disadvantage:Disadvantage:

Total number of circuits that can be provisioned areTotal number of circuits that can be provisioned are

limited.limited.

No traffic grooming or aggregation can be done.No traffic grooming or aggregation can be done.


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IntroIntro2. Resilient packet ring (RPR)2. Resilient packet ring (RPR)

Combines the advantages of Ethernet and SONET toCombines the advantages of Ethernet and SONET togive traditional carrier class features.give traditional carrier class features.

Has good MAC switching capabilities providing coreHas good MAC switching capabilities providing corefiber and ring operation.fiber and ring operation.

Controlled bandwidth allocation, 50-ms serviceControlled bandwidth allocation, 50-ms servicerestoration, bounded delay and jitters etc.restoration, bounded delay and jitters etc.

Though RPR in conjunction with SONET and EthernetThough RPR in conjunction with SONET and Ethernetcan provide highly efficient MAN, carriers have optedcan provide highly efficient MAN, carriers have optedto improve SONET transport instead.to improve SONET transport instead.


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IntroIntro3.Packet over SONET (PoS)3.Packet over SONET (PoS)

PoS is a communication protocol for transmittingPoS is a communication protocol for transmittingpackets over SONET.packets over SONET.

PoS supports the sending of IP packets over WAN.PoS supports the sending of IP packets over WAN.

Disadvantage:Disadvantage: It aggregates and encapsulates IP datagrams inIt aggregates and encapsulates IP datagrams in

Point-to-Point protocol (PPP) without anyPoint-to-Point protocol (PPP) without anydifferentiation among different packet flows.differentiation among different packet flows.

So, lacks multicast and QoS capabilities.So, lacks multicast and QoS capabilities.


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IntroIntro

Next-generation SONETNext-generation SONET Provides better bandwidth granularity than SONETProvides better bandwidth granularity than SONET

and POS.and POS. Virtual Concatenation (VC) technique allows aVirtual Concatenation (VC) technique allows a

better match between Ethernet data rates andbetter match between Ethernet data rates andSONET line rate improving circuit use.SONET line rate improving circuit use.

GFP is proposed to adapt multiservices to theGFP is proposed to adapt multiservices to theSONET by a uniform mapping of Ethernet framesSONET by a uniform mapping of Ethernet framesand client signals.and client signals.

LCAS provides bandwidth-on-demand capabilities.LCAS provides bandwidth-on-demand capabilities.

DisadvantageDisadvantage Does not address issues associated with usingDoes not address issues associated with using

circuit-switching technology for data traffic.circuit-switching technology for data traffic.


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A new proposalA new proposal

Since the standards mentioned either lack end-to-Since the standards mentioned either lack end-to-end optical transparency or do not offer efficientend optical transparency or do not offer efficientuse of core resources,use of core resources, OBS technology is takenOBS technology is taken

advantage of to transmit Ethernet frames overadvantage of to transmit Ethernet frames overWDM links.WDM links.

The author explains this provides aThe author explains this provides a scalable andscalable and

data optimized alternativedata optimized alternative to SONET-basedto SONET-basedconnectivity.connectivity.


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Ethernet over SONETEthernet over SONET

(EoS)(EoS) SONET was designed primarily for voiceSONET was designed primarily for voiceapplications and is based on circuit orientedapplications and is based on circuit oriented

technology.technology.

Dual ring and equipment topology enables SONET toDual ring and equipment topology enables SONET toimplement fast protection mechanisms.implement fast protection mechanisms.

10GbE physical layer is compatible with SONET.10GbE physical layer is compatible with SONET.

( OC-192 link speed, use of SONET framing).( OC-192 link speed, use of SONET framing). Costly aspects like TDM support, performance andCostly aspects like TDM support, performance and

management functions have been avoided.management functions have been avoided.


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Disadvantages of using SONET rings forDisadvantages of using SONET rings for

data transport:data transport:

Basically SONETs point-to-point design, circuit switchBasically SONETs point-to-point design, circuit switchapplications give rise to its limitations.applications give rise to its limitations.


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1.Fixed circuits1.Fixed circuits

SONET provisions point-to-point circuit betweenSONET provisions point-to-point circuit between

ring nodes => allocated a fixed amount of bandwidth.ring nodes => allocated a fixed amount of bandwidth.

In Fig.1(a) each node in the ring is allocated only oneIn Fig.1(a) each node in the ring is allocated only one

quarter of the total bandwidth.quarter of the total bandwidth. Thus a limit is put on the maximum data burst trafficThus a limit is put on the maximum data burst traffic

rates and increases the queuing delay.rates and increases the queuing delay.

To create a logical mesh as in Fig.1(b) requiresTo create a logical mesh as in Fig.1(b) requiresN*(N-1) circuits which is time consuming and alsoN*(N-1) circuits which is time consuming and also

waste ring bandwidth.waste ring bandwidth.


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2.Muticast Traffic2.Muticast Traffic

Layer 2 muticast requires each source to allocate aLayer 2 muticast requires each source to allocate aseparate circuit for each destination.separate circuit for each destination.

Thus, a mesh has to be created in which separateThus, a mesh has to be created in which separate

copies of the packet are sent to each destination.copies of the packet are sent to each destination.

Obviously, result multiple copies traveling around theObviously, result multiple copies traveling around the

ring, wasting bandwidth.ring, wasting bandwidth.


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3.Wasted Protection Bandwidth3.Wasted Protection Bandwidth

o

50% of ring bandwidth and equipment is reserved for50% of ring bandwidth and equipment is reserved for

protection.protection.

o SONET does not give the provider the choice ofSONET does not give the provider the choice of

when and how much bandwidth to reserve forwhen and how much bandwidth to reserve for

protection.protection.o Thus SONET does not provide protection in a cost-Thus SONET does not provide protection in a cost-

effective manner.effective manner.


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4.Added Overhead4.Added Overhead

SONET overhead (TDM capabilities, physicalSONET overhead (TDM capabilities, physicallayer, management functions) for STS-192c frameslayer, management functions) for STS-192c framesresulting from the transportation of 10GbE framesresulting from the transportation of 10GbE framesover circuits built from SONET links is 3.7%.over circuits built from SONET links is 3.7%.

But , at low traffic loads, efficiency worsens asBut , at low traffic loads, efficiency worsens aslarge bursts of Ethernet frames are delivered in alarge bursts of Ethernet frames are delivered in afraction of SONET time slot.fraction of SONET time slot.

Carrying increasing data traffic over manuallyCarrying increasing data traffic over manuallyprovisioned circuit-switched networks makes itprovisioned circuit-switched networks makes itdifficult to develop new services thus increasingdifficult to develop new services thus increasingcost.cost.


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Ethernet-over-SONET EfficiencyEthernet-over-SONET Efficiency

Due to the burstiness and variable frame size of Ethernet trafficDue to the burstiness and variable frame size of Ethernet trafficthere is inefficiency in SONET framing.there is inefficiency in SONET framing.

Efficiency of EoS is given byEfficiency of EoS is given by

EoSEoS == SONETSONET PE (1)PE (1)

wherewhere PEPEpacking efficiency of Ethernet frames into SONETpacking efficiency of Ethernet frames into SONETpayload (SPE).payload (SPE).


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o g - interarrival gapsg - interarrival gaps

o r - unused remainder (due to low traffic load, size ofr - unused remainder (due to low traffic load, size of

incoming frame >>remainder in time slot)incoming frame >>remainder in time slot)

o Let the Ethernet frame size be modeled with anLet the Ethernet frame size be modeled with anexponential distribution with parameterexponential distribution with parameterframe/Byte.frame/Byte.


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The packing efficiency of the Ethernet frames into a SONET TspeThe packing efficiency of the Ethernet frames into a SONET Tspe

is given byis given by

Where M- maximum number of Ethernet frames that SPE can hold.Where M- maximum number of Ethernet frames that SPE can hold.

B size of the burst.B size of the burst.

Y Sum of the first frame to the last frame.Y Sum of the first frame to the last frame.

o Due to the bursty nature, the time intervals (g) >>>TspeDue to the bursty nature, the time intervals (g) >>>Tspe

o Thus as g varies ,Thus as g varies , PE becomes proportional to the offered load.PE becomes proportional to the offered load.

=

+

+==

M

k SPE

kBk

SPE

PE

T

B

k

e

kT

YE

1

1

)!1(1

][ (2)


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Ethernet over OBSEthernet over OBS

MPMPS Lack of statistical multiplexing, leads to poorS Lack of statistical multiplexing, leads to poorflexibility.flexibility.

Recent arrival of optical cross connects (OXC) can be used toRecent arrival of optical cross connects (OXC) can be used toextend 10GbE over long distances- point to point permanentextend 10GbE over long distances- point to point permanentresource reservation-no longer shared among different 10GbE.resource reservation-no longer shared among different 10GbE.

OBS is a new technology that exploits the large bandwidths ofOBS is a new technology that exploits the large bandwidths ofDWDM by avoiding electronic processing of optical packets.DWDM by avoiding electronic processing of optical packets.

No O-E-O conversions in OBS.No O-E-O conversions in OBS.

Burst- basic data block, collection of data frames with sameBurst- basic data block, collection of data frames with samedestination address and QoS parameters.destination address and QoS parameters.


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EoSEoS

Optical burst is switched by a predetermined path by aOptical burst is switched by a predetermined path by acontrol packet.control packet.

Improves backbone efficiency and offers excellentImproves backbone efficiency and offers excellent

scalabilityscalability..


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EOSEOS

The GMPLS labels are used to identify the destinationThe GMPLS labels are used to identify the destinationedge switch and are mapped to available wavelengths atedge switch and are mapped to available wavelengths ateach OBS switch.each OBS switch.

1.Switched paths1.Switched paths::

o LOBS do not reserve the resources permanentlyLOBS do not reserve the resources permanently

o LOBS are set up dynamically to support required QoS andLOBS are set up dynamically to support required QoS andtorn down once burst are transmitted.torn down once burst are transmitted.

o Bandwidth allocated dynamically-burst by burst basis.Bandwidth allocated dynamically-burst by burst basis.


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2. Peer-to-Peer Networking:2. Peer-to-Peer Networking:o GMPLS extends WAN connectivity into the MAN-GMPLS extends WAN connectivity into the MAN-

simplifies interfacesimplifies interfaceo Complex optical UNI interfaces not required.Complex optical UNI interfaces not required.

3. Multicast traffic:3. Multicast traffic:o OBS provides multicast at WDM layer using light-OBS provides multicast at WDM layer using light-

splitting techniques-require additional hardware-splitting techniques-require additional hardware-

complicate switch controlscomplicate switch controlso GMPLS-based multicast provides simplification andGMPLS-based multicast provides simplification and

scalability at no cost.scalability at no cost.


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4.Protection and Restoration:4.Protection and Restoration:

o GMPLS fast reroute mechanism can be used to provideGMPLS fast reroute mechanism can be used to provideprotection and restoration by automatically reroutingprotection and restoration by automatically reroutingtraffic on an alternate LOBS.traffic on an alternate LOBS.

o Accomplishes by precomputing number of LOBS pathsAccomplishes by precomputing number of LOBS pathsat the same time the primary LOBS paths are established.at the same time the primary LOBS paths are established.

o Integrating 10GbE over GMPLS enabled OBS requiresIntegrating 10GbE over GMPLS enabled OBS requiresspecific details to burst size and GMPLS extensions.specific details to burst size and GMPLS extensions.


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Ethernet-over-OBS efficiencyEthernet-over-OBS efficiency

OBS efficiency depends on the fraction of time the reservedOBS efficiency depends on the fraction of time the reserved

bandwidth along a LOBS path is used by the burst .bandwidth along a LOBS path is used by the burst .

ts- time at which the bandwidth reservation startsts- time at which the bandwidth reservation starts

T- burst time (burst size L/output data rate bo)T- burst time (burst size L/output data rate bo)

To - offset timeTo - offset time

)( 0 sEoB

tTT

T

+

= (3)


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End-to-end queuing delay depends whether fixed or variableEnd-to-end queuing delay depends whether fixed or variablesize bursts are used.size bursts are used.

Fixed sizeFixed size burst allows paths to be set up as the burst is beingburst allows paths to be set up as the burst is beingassembled.assembled.

In the fixed size the data burst encounters no edge delay asIn the fixed size the data burst encounters no edge delay aslong as the offset time = time taken to assemble the burst.long as the offset time = time taken to assemble the burst.

In theIn the variable-sizevariable-size, control packet can only be sent after entire, control packet can only be sent after entireburst is assembled minimum edge delay is To.burst is assembled minimum edge delay is To.


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Ethernet-over-OBS Burst SizeEthernet-over-OBS Burst Size For better efficiency, the OBS burst must be >>To-ts but not so largeFor better efficiency, the OBS burst must be >>To-ts but not so large

to cause significant queuing delays.to cause significant queuing delays.

High bandwidth, full-duplex operation requires a flow controlHigh bandwidth, full-duplex operation requires a flow control

mechanism: 10GbE source and destination exchange flow controlmechanism: 10GbE source and destination exchange flow control

packets- to prevent data loss, throttle frame transmission rate.packets- to prevent data loss, throttle frame transmission rate.

Flow-control packets are typically 64 bytes, not assembled into burstsFlow-control packets are typically 64 bytes, not assembled into bursts

since it affects efficiency.since it affects efficiency.

Elasticity of OBS burst unlike SONET fixed frame slot size allows itElasticity of OBS burst unlike SONET fixed frame slot size allows it

to adapt to the bursty nature of Ethernet.to adapt to the bursty nature of Ethernet.

Ethernet adaptor requires a minimum IFG between 2 successiveEthernet adaptor requires a minimum IFG between 2 successive

frames; at 10GbE IFG ~9.6ns or 12 Bytes.frames; at 10GbE IFG ~9.6ns or 12 Bytes.

IFG provides receiving station time to update counters, check CRC ofIFG provides receiving station time to update counters, check CRC of

previous frame, mange the buffers.previous frame, mange the buffers.

Two ways to implement IFG:Two ways to implement IFG:


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Two ways to implement IFG:-Two ways to implement IFG:-

o Insert the 12 Byte spacing at the 10GbE receivingInsert the 12 Byte spacing at the 10GbE receivinginterfaceinterface

- places new requirements on the processing at the- places new requirements on the processing at thedestination switch to seek the start of each frame.destination switch to seek the start of each frame.

o Incorporate the IFG within the burstIncorporate the IFG within the burst

- maintains the integrity of Ethernet transmission at the- maintains the integrity of Ethernet transmission at the

expense of wasted bandwidth within each burst.expense of wasted bandwidth within each burst. Since the IFG, preamble, frame check sequence (FCS)Since the IFG, preamble, frame check sequence (FCS)

constitute a large overhead for the 1500 Byte Ethernetconstitute a large overhead for the 1500 Byte Ethernetframe,frame, 9000 Byte frames can be used to improve9000 Byte frames can be used to improveefficiencyefficiency..

For e.g.. 155,520-Byte(SONET slot) carrying 1500 ByteFor e.g.. 155,520-Byte(SONET slot) carrying 1500 Byteframes incurs 1% overhead whereas 9000-Byte frameframes incurs 1% overhead whereas 9000-Byte framerequires fewer IFG, preamble resulting in 0.1%, arequires fewer IFG, preamble resulting in 0.1%, areduction of ten fold.reduction of ten fold.


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Performance comparison of EoS and EoBPerformance comparison of EoS and EoB

under different traffic conditions.under different traffic conditions.

Ti : burst aggregation time

EoS

EoB, Tg=1%

EoB, Tg=1%

EoB, Tg=5%

EoS


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Ethernet-overEthernet-overMPLS issuesMPLS issues

What is Multi-protocol Label Switching (MPLS) ?What is Multi-protocol Label Switching (MPLS) ?

A data mechanism to provide a unified service for both circuit-basedA data mechanism to provide a unified service for both circuit-basedclients and packet-switching clients.clients and packet-switching clients.

Supports various network technologies like ATM, IP etc.Supports various network technologies like ATM, IP etc. MPLS sets up label-switched paths (LSP) for packets , thus savingMPLS sets up label-switched paths (LSP) for packets , thus saving

time for a LSR (router) to look up the next node for forwarding thetime for a LSR (router) to look up the next node for forwarding thepacket to.packet to.

Does not have common control and traffic engineering forDoes not have common control and traffic engineering forwavelength , TDM and fiber switching.wavelength , TDM and fiber switching.

Forwarding Equivalence class (FEC)Forwarding Equivalence class (FEC)Set of packets with similar characteristics is forwarded the same way.Set of packets with similar characteristics is forwarded the same way.


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Working of a Label Switched PathWorking of a Label Switched Path

MPLS network

: LSR (Label Switch Router)

: LER (Label Edge Router)

IP 1

IP 1

IP 2

IP 3

IP 2

IP 2 5

IP 1 5

3

3

IP 1 9

IP 2 9

IP 3 9

IP 3 2

IP 3 7

IP 2

IP 3A

B

C


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Generalized Multi-protocol LabelGeneralized Multi-protocol Label

Switching (GMPLS)Switching (GMPLS) Extends the MPLS functionality for TDM (labels-time slots) andExtends the MPLS functionality for TDM (labels-time slots) and

FDM (labels= electromagnetic frequency of light waves).FDM (labels= electromagnetic frequency of light waves).

Ethernet tunnels provisioned dynamically to create wide-area-Ethernet tunnels provisioned dynamically to create wide-area-VLANs.VLANs.

Peer-to-peer networking where CPE is part of the MPLS cloud.Peer-to-peer networking where CPE is part of the MPLS cloud.

Establishes space division multiplexed paths where labels indicateEstablishes space division multiplexed paths where labels indicatethe position of the data.the position of the data.

Establishes common control plane between IP service managementEstablishes common control plane between IP service managementand optical layers.and optical layers.


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VLL : Virtual Leased Linesor Ethernet tunnels.

CPE : Customer PremiseEquipment.

PE : Providers Edge

switch. VLAN (Virtual LAN) :a group of end-stations onmultiple LAN segments andcan communicate as if theywere on a single LAN.


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CPE exchanges tables with the providers edge (PE) switches using GMPLS signaling.CPE exchanges tables with the providers edge (PE) switches using GMPLS signaling.

Ethernet frame arriving at the CPE from local LANS carry the original Ethernet fields andEthernet frame arriving at the CPE from local LANS carry the original Ethernet fields and

802.1p/q headers (p-802.1p/q headers (p- covers traffic class expediting and dynamic multicast filtering part ofcovers traffic class expediting and dynamic multicast filtering part of

MAC bridges, q-defines services provided in Virtual LANs).MAC bridges, q-defines services provided in Virtual LANs).

Frame is mapped to a FEC. FEC lookup yields the outgoing port and virtual circuit (VC)Frame is mapped to a FEC. FEC lookup yields the outgoing port and virtual circuit (VC)

label, which is added to the frame and forwarded on the outgoing port toward PE switch.label, which is added to the frame and forwarded on the outgoing port toward PE switch.


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The PE switch maps the Ethernet frame into an OBS burstThe PE switch maps the Ethernet frame into an OBS burst

and provides the required signaling by GMPLS labeland provides the required signaling by GMPLS label

assignment in one of the following two addressingassignment in one of the following two addressing

schemes,schemes,

1.1. Flat assignment schemeFlat assignment scheme::

PE constructs a label forwarding base as shown below.PE constructs a label forwarding base as shown below.

Like CPE label assignment , each label designates aLike CPE label assignment , each label designates aunique LAN-MAC-FEC, one for each frame.unique LAN-MAC-FEC, one for each frame.

Only provides simple point to point connection.Only provides simple point to point connection.

Increases amount of labels and signaling.Increases amount of labels and signaling.


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2.2. Hierarchical assignment scheme:Hierarchical assignment scheme:

Here each VLAN is assigned one VLL or LOBS label asHere each VLAN is assigned one VLL or LOBS label as

shown in below.shown in below.

So labels with same LOBS label aggregated in to the sameSo labels with same LOBS label aggregated in to the same

burst.burst.

Allows easy rerouting of VLAN traffic in event of failure.Allows easy rerouting of VLAN traffic in event of failure.

Additional processing overhead.Additional processing overhead.


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PE looks up the incoming label, determines the VLAN, adds a LOBS label as shown below.PE looks up the incoming label, determines the VLAN, adds a LOBS label as shown below.

Frames with same LOBS label are aggregated into the same burst.Frames with same LOBS label are aggregated into the same burst.


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EoB path protection and restorationEoB path protection and restoration

1.1. At WDM level:At WDM level:

At optical layer, schemes match that of SONET but inflexible,At optical layer, schemes match that of SONET but inflexible,subjects of current research.subjects of current research.

2.2. At Ethernet level:At Ethernet level:

Spanning Tree Protocol (STP ) is used to provide redundant paths.Spanning Tree Protocol (STP ) is used to provide redundant paths. Long convergence time not suitable =>LOBS constantly setup andLong convergence time not suitable =>LOBS constantly setup and

torn down.torn down.

3.3. At GMPLS levelAt GMPLS level:: Head end - when path fails, OBS switch signals head-end switch toHead end - when path fails, OBS switch signals head-end switch to

use a backup LOBS path.use a backup LOBS path. Local reroute makes a local decision to redirect the burst.Local reroute makes a local decision to redirect the burst.


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Timely detour path is needed.Timely detour path is needed.

So, preestablished paths is essential in burst traffic.So, preestablished paths is essential in burst traffic.

Shortest reroute time =>decision made as close to the failure point.Shortest reroute time =>decision made as close to the failure point.

Since it takes time to inform the head node, local reroute mechanismSince it takes time to inform the head node, local reroute mechanism

is preferred.is preferred. Impossible to predict where failure may occur.Impossible to predict where failure may occur.

Every switch and link along the path is protected, detour paths setupEvery switch and link along the path is protected, detour paths setup

dynamically at the same time primary paths are set up.dynamically at the same time primary paths are set up.


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Local reroute requires establishing (N-1) detour paths asLocal reroute requires establishing (N-1) detour paths as

shown.shown.

where N- number of OBS switches that the LOBS traverses.where N- number of OBS switches that the LOBS traverses.

C l iC l i


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ConclusionConclusion Extending Ethernet services over OBS provides betterExtending Ethernet services over OBS provides better

scalability and bandwidth efficiency than with SONET.scalability and bandwidth efficiency than with SONET. SONET is limited by its TDM nature and bySONET is limited by its TDM nature and by MPMPSS

which does not provide statistical multiplexing.which does not provide statistical multiplexing. As DWDM evolves more and more wavelength will beAs DWDM evolves more and more wavelength will be

supported on each fiber.supported on each fiber.

Ethernet is best for LAN-MAN connectivity.Ethernet is best for LAN-MAN connectivity. OBS provides efficient sharing of backbone resources.OBS provides efficient sharing of backbone resources. GMPLS provides standard control mechanism to bridgeGMPLS provides standard control mechanism to bridge

distant MANs, provides protection with no permanentdistant MANs, provides protection with no permanentreservation of resources.reservation of resources.

Providers improve their revenue stream and consumersProviders improve their revenue stream and consumersreduce their network operational cost.reduce their network operational cost.


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Supporting Ethernet in Obs Networks 3446