Supporting Ethernet in OBS Supporting Ethernet in OBS networksnetworks

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 Lab

Industrial Technology Research Institute, TaiwanIndustrial Technology Research Institute, Taiwan

2002 Journal of Optical Computing 2002 Journal of Optical Computing

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 the

shortcomings 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

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

will play in the development of 10-Gbit will play in the development of 10-Gbit Ethernet MAN.Ethernet MAN.

SONET (Synchronous optical networking) is SONET (Synchronous optical networking) is being proposed for the same but its being proposed for the same but its synchronous time-division multiplexing synchronous time-division multiplexing (TDM) is inefficient for transporting bursty (TDM) is inefficient for transporting bursty traffic of the Ethernet.traffic of the Ethernet.

The author claims that OBS provides a better The author claims that OBS provides a better sharing of network resources and when sharing of network resources and when coupled with generalized multiprotocol label coupled with generalized multiprotocol label switching (GMPLS) provides a robust Ethernet switching (GMPLS) provides a robust Ethernet service.service.

IntroductionIntroduction Recently network providers face new Recently network providers face new

challenges at the MAN level due to the challenges at the MAN level due to the increased user requirementsincreased user requirements..

Tremendous pressure to support Tremendous pressure to support broadband broadband accessaccess and and 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 with proven MAN architecture combined with multi-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 protocol offering good speed, end-to-end protocol consistency for providers and users in a cost consistency for providers and users in a cost effective manner.effective manner.

10GbE can operate over long link spans(40 10GbE can operate over long link spans(40 km) and other transport layers such as km) and other transport layers such as SONET and DWDM.SONET and DWDM.

Intro…Intro…SONETSONET

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

o But it is But it is not optimized for the bursty naturenot optimized for the bursty nature of the present of the present time data traffic and is not able to scale itself to support the time data traffic and is not able to scale itself to support the rapid growth of internet in a cost-effective manner (requires rapid 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 a however, Ethernet by itself cannot be considered to be a carrier class protocol as it does not provide what SONET carrier class protocol as it does not provide what SONET guarantees.guarantees.

o Standards such as Standards such as Ethernet over WDM, resilient packet ring Ethernet over WDM, resilient packet ring (RPR), packet over SONET (PoS)(RPR), packet over SONET (PoS) have been developed have been developed with carrier-grade qualities.with carrier-grade qualities.

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

o This provides a long haul connectivity(40 km) This provides a long haul connectivity(40 km) between two Ethernet switches.between two Ethernet switches.

o Point-point connections are done manually or via Point-point connections are done manually or via multiprotocol lambda switching.multiprotocol lambda switching.

Disadvantage:Disadvantage: Total number of circuits that can be provisioned are Total 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.

Intro…Intro…2. Resilient packet ring (RPR)2. Resilient packet ring (RPR)

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

Has good MAC switching capabilities providing core Has good MAC switching capabilities providing core fiber and ring operation.fiber and ring operation.

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

Though RPR in conjunction with SONET and Though RPR in conjunction with SONET and Ethernet can provide highly efficient MAN, carriers Ethernet can provide highly efficient MAN, carriers have opted to improve SONET transport instead.have opted to improve SONET transport instead.

Intro…Intro…3.Packet over SONET (PoS)3.Packet over SONET (PoS)

PoS is a communication protocol for PoS is a communication protocol for transmitting packets over SONET.transmitting packets over SONET.

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

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

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

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

Intro…Intro…Next-generation SONETNext-generation SONET

Provides better bandwidth granularity than Provides better bandwidth granularity than SONET and POS.SONET and POS.

Virtual Concatenation (VC) technique allows Virtual Concatenation (VC) technique allows a better match between Ethernet data rates and a better match between Ethernet data rates and SONET line rate improving circuit use. SONET line rate improving circuit use.

GFP is proposed to adapt multiservices to the GFP is proposed to adapt multiservices to the SONET by a uniform mapping of Ethernet SONET by a uniform mapping of Ethernet frames and client signals. frames and client signals.

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

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

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

A new proposalA new proposal

Since the standards mentioned either lack end-Since the standards mentioned either lack end-to-end optical transparency or do not offer to-end optical transparency or do not offer efficient use of core resources, efficient use of core resources, OBS OBS technology is taken advantage of to transmit technology is taken advantage of to transmit Ethernet frames over WDM links.Ethernet frames over WDM links.

The author explains this provides a The author explains this provides a scalable scalable and data optimized alternativeand data optimized alternative to SONET- to SONET-based connectivity.based connectivity.

Ethernet over SONETEthernet over SONET(EoS)(EoS)

SONET was designed primarily for voice SONET was designed primarily for voice applications and is based on circuit oriented applications and is based on circuit oriented technology.technology.

Dual ring and equipment topology enables SONET to Dual ring and equipment topology enables SONET to implement 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 and Costly aspects like TDM support, performance and

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

Disadvantages of using SONET rings for Disadvantages of using SONET rings for data transport:data transport:

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

1.Fixed circuits1.Fixed circuits

• SONET provisions point-to-point circuit between SONET 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 one In 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 traffic Thus 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) requires To create a logical mesh as in Fig.1(b) requires N*(N-1) circuits which is time consuming and also N*(N-1) circuits which is time consuming and also waste ring bandwidth.waste ring bandwidth.

2.Muticast Traffic2.Muticast Traffic Layer 2 muticast requires each source to allocate a Layer 2 muticast requires each source to allocate a

separate circuit for each destination.separate circuit for each destination. Thus, a mesh has to be created in which separate Thus, 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 the Obviously, result multiple copies traveling around the

ring, wasting bandwidth.ring, wasting bandwidth.

3.Wasted Protection Bandwidth3.Wasted Protection Bandwidth

o 50% of ring bandwidth and equipment is reserved for 50% of ring bandwidth and equipment is reserved for protection.protection.

o SONET does not give the provider the choice of SONET does not give the provider the choice of when and how much bandwidth to reserve for when 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.

4.Added Overhead4.Added Overhead SONET overhead (TDM capabilities, physical SONET overhead (TDM capabilities, physical

layer, management functions) for STS-192c layer, management functions) for STS-192c frames resulting from the transportation of 10GbE frames resulting from the transportation of 10GbE frames over circuits built from SONET links is frames over circuits built from SONET links is 3.7%.3.7%.

But , at low traffic loads, efficiency worsens as But , at low traffic loads, efficiency worsens as large bursts of Ethernet frames are delivered in a large bursts of Ethernet frames are delivered in a fraction of SONET time slot.fraction of SONET time slot.

Carrying increasing data traffic over manually Carrying increasing data traffic over manually provisioned circuit-switched networks makes it provisioned circuit-switched networks makes it difficult to develop new services thus increasing difficult to develop new services thus increasing cost. cost.

Ethernet-over-SONET EfficiencyEthernet-over-SONET Efficiency

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

Efficiency of EoS is given by Efficiency of EoS is given by ηηEoSEoS = = ηηSONET SONET ∙ ∙ ηηPE (1)PE (1)

where where ηηPEPE packing efficiency of Ethernet frames into packing efficiency of Ethernet frames into

SONET payload (SPE).SONET payload (SPE).

o g - interarrival gapsg - interarrival gaps

o r - unused remainder (due to low traffic load, size of r - 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 an Let the Ethernet frame size be modeled with an exponential distribution with parameter exponential distribution with parameter λλ frame/Byte. frame/Byte.

The packing efficiency of the Ethernet frames into a SONET Tspe The 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 , ηηPE becomes proportional to the offered load.PE becomes proportional to the offered load.

M

k SPE

kBk

SPEPE T

B

k

e

kT

YE

1

1

)!1(1

][ (2)

Ethernet over OBSEthernet over OBS

MPMPλλS – Lack of statistical multiplexing, leads to poor S – Lack of statistical multiplexing, leads to poor flexibility.flexibility.

Recent arrival of optical cross connects (OXC) can be used to Recent arrival of optical cross connects (OXC) can be used to extend 10GbE over long distances- point to point permanent extend 10GbE over long distances- point to point permanent resource 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 of OBS is a new technology that exploits the large bandwidths of DWDM 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 same Burst- basic data block, collection of data frames with same destination address and QoS parameters.destination address and QoS parameters.

EoS…EoS…

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

Improves backbone efficiency and offers excellent Improves backbone efficiency and offers excellent

scalabilityscalability..

EOS…EOS…

The GMPLS labels are used to identify the The GMPLS labels are used to identify the destination edge switch and are mapped to available destination edge switch and are mapped to available wavelengths at each OBS switch.wavelengths at each OBS switch.

1.Switched paths1.Switched paths::o LOBS – do not reserve the resources permanentlyLOBS – do not reserve the resources permanentlyo LOBS are set up dynamically to support required LOBS are set up dynamically to support required

QoS and torn down once burst are transmitted.QoS and torn down once burst are transmitted.o Bandwidth allocated dynamically-burst by burst Bandwidth allocated dynamically-burst by burst

basis.basis.

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 controls

o GMPLS-based multicast provides simplification GMPLS-based multicast provides simplification and scalability at no cost.and scalability at no cost.

4.Protection and Restoration:4.Protection and Restoration:o GMPLS fast reroute mechanism can be used to GMPLS fast reroute mechanism can be used to

provide protection and restoration by automatically provide protection and restoration by automatically rerouting traffic on an alternate LOBS.rerouting traffic on an alternate LOBS.

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

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

Ethernet-over-OBS efficiencyEthernet-over-OBS efficiency OBS efficiency depends on the fraction of time the reserved OBS 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 time To - offset time

)( 0 sEoB tTT

T

(3)

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

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

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

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

Ethernet-over-OBS Burst SizeEthernet-over-OBS Burst Size For better efficiency, the OBS burst must be >>To-ts but For better efficiency, the OBS burst must be >>To-ts but

not so large to cause significant queuing delays.not so large to cause significant queuing delays. High bandwidth, full-duplex operation requires a flow High bandwidth, full-duplex operation requires a flow

control mechanism: 10GbE source and destination control mechanism: 10GbE source and destination exchange flow control packets- to prevent data loss, exchange flow control packets- to prevent data loss, throttle frame transmission rate.throttle frame transmission rate.

Flow-control packets are typically 64 bytes, not Flow-control packets are typically 64 bytes, not assembled into bursts since it affects efficiency.assembled into bursts since it affects efficiency.

Elasticity of OBS burst unlike SONET fixed frame slot Elasticity of OBS burst unlike SONET fixed frame slot size allows it to adapt to the bursty nature of Ethernet.size allows it to adapt to the bursty nature of Ethernet.

Ethernet adaptor requires a minimum IFG between 2 Ethernet adaptor requires a minimum IFG between 2 successive frames; at 10GbE IFG ~9.6ns or 12 Bytes.successive frames; at 10GbE IFG ~9.6ns or 12 Bytes.

IFG provides receiving station time to update counters, IFG provides receiving station time to update counters, check CRC of previous frame, mange the buffers.check CRC of previous frame, mange the buffers.

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

o Insert the 12 Byte spacing at the 10GbE receiving Insert the 12 Byte spacing at the 10GbE receiving interfaceinterface

- places new requirements on the processing at the - places new requirements on the processing at the destination 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 - maintains the integrity of Ethernet transmission at

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

(FCS) constitute a large overhead for the 1500 Byte (FCS) constitute a large overhead for the 1500 Byte Ethernet frame, Ethernet frame, 9000 Byte frames can be used to 9000 Byte frames can be used to improve efficiencyimprove efficiency..

For e.g.. 155,520-Byte(SONET slot) carrying 1500 For e.g.. 155,520-Byte(SONET slot) carrying 1500 Byte frames incurs 1% overhead whereas 9000-Byte Byte frames incurs 1% overhead whereas 9000-Byte frame requires fewer IFG, preamble resulting in frame requires fewer IFG, preamble resulting in 0.1%, a reduction of ten fold.0.1%, a reduction of ten fold.

Performance comparison of EoS and EoB Performance 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

Ethernet-overEthernet-over MPLS 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-A data mechanism to provide a unified service for both circuit-based clients and packet-switching clients.based 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 MPLS sets up label-switched paths (LSP) for packets , thus

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

Does not have common control and traffic engineering for Does not have common control and traffic engineering for wavelength , 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.

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

Generalized Multi-protocol Label Generalized Multi-protocol Label Switching (GMPLS)Switching (GMPLS)

Extends the MPLS functionality for TDM (labels-time slots) Extends the MPLS functionality for TDM (labels-time slots) and FDM (labels= electromagnetic frequency of light waves).and 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 Peer-to-peer networking where CPE is part of the MPLS cloud.cloud.

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

Establishes common control plane between IP service Establishes common control plane between IP service management and optical layers.management and optical layers.

VLL : Virtual Leased Lines or Ethernet tunnels.∙ CPE : Customer Premise Equipment.∙ PE : Provider’s Edge switch.∙ VLAN (Virtual LAN) :a group of end-stations on multiple LAN segments and can communicate as if they were on a single LAN.

CPE exchanges tables with the provider’s edge (PE) switches CPE exchanges tables with the provider’s edge (PE) switches using GMPLS signaling.using GMPLS signaling.

Ethernet frame arriving at the CPE from local LANS carry the Ethernet frame arriving at the CPE from local LANS carry the original Ethernet fields and 802.1p/q headers (p- original Ethernet fields and 802.1p/q headers (p- covers traffic covers traffic class expediting and dynamic multicast filtering part of MAC class expediting and dynamic multicast filtering part of MAC

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

Frame is mapped to a FEC. FEC lookup yields the outgoing Frame is mapped to a FEC. FEC lookup yields the outgoing port and virtual circuit (VC) label, which is added to the frame port and virtual circuit (VC) label, which is added to the frame and forwarded on the outgoing port toward PE switch.and forwarded on the outgoing port toward PE switch.

The PE switch maps the Ethernet frame into an OBS burst The PE switch maps the Ethernet frame into an OBS burst and provides the required signaling by GMPLS label and provides the required signaling by GMPLS label assignment in one of the following two addressing assignment 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 a Like CPE label assignment , each label designates a

unique 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.

2. 2. Hierarchical assignment scheme:Hierarchical assignment scheme:• Here each VLAN is assigned one VLL or LOBS label as Here 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 same So 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.

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

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

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 Spanning Tree Protocol (STP ) is used to provide redundant

paths.paths.• Long convergence time not suitable =>LOBS constantly setup Long convergence time not suitable =>LOBS constantly setup

and torn down.and torn down.

3. 3. At GMPLS levelAt GMPLS level::• Head end - when path fails, OBS switch signals head-end switch Head end - when path fails, OBS switch signals head-end switch

to use a backup LOBS path.to 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.

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

point.point. Since it takes time to inform the head node, local reroute Since it takes time to inform the head node, local reroute

mechanism is preferred.mechanism 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 Every switch and link along the path is protected, detour

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

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

ConclusionConclusion Extending Ethernet services over OBS provides Extending Ethernet services over OBS provides

better scalability and bandwidth efficiency than with better scalability and bandwidth efficiency than with SONET.SONET.

SONET is limited by its TDM nature and by SONET is limited by its TDM nature and by MPMPλλS S which does not provide statistical multiplexing.which does not provide statistical multiplexing.

As DWDM evolves more and more wavelength will As DWDM evolves more and more wavelength will be supported on each fiber.be supported on each fiber.

Ethernet is best for LAN-MAN connectivity.Ethernet is best for LAN-MAN connectivity. OBS provides efficient sharing of backbone OBS provides efficient sharing of backbone

resources.resources. GMPLS provides standard control mechanism to GMPLS provides standard control mechanism to

bridge distant MANs, provides protection with no bridge distant MANs, provides protection with no permanent reservation of resources.permanent reservation of resources.

Providers improve their revenue stream and Providers improve their revenue stream and consumers reduce their network operational cost.consumers reduce their network operational cost.

Questions?Questions?