Optical Packet Switching - University of California, Berkeleyee233/sp06/student... · Optical...

Optical Packet Switching

Yu Ben, Qian Ying TangMay 2, 2006

Outline

Packet Switching Overview Optical Packet SwitchingSJ Yoo (UC Davis)

ArchitectureBenefitsSocial and Economic Impacts

Conclusion

What is Packet Switching

A set of rulesGoverns how messages should be transmitted between two pointsDivides long message into pieces-PACKETS.Transmission is connectionlessRequires routers and routing algorithms

Open Systems Interconnection Model

Packet switchingFits in Here

Packet Switching-DemoWant to transmit a file between host A and D

Host A

Host BHost E

Host D

Host C

Node 1 Node 2

Node 3

Node 4

Node 5

Node 6 Node 7

Packet Switching-DemoFile is split into packets

Host A

Host BHost E

Host D

Host C

Node 1 Node 2

Node 3

Node 4

Node 5

Node 6 Node 7

Packet Switching-DemoHeaders contain destination/order info is appended

Host A

Host BHost E

Host D

Host C

Node 1 Node 2

Node 3

Node 4

Node 5

Node 6 Node 7

Packet Switching-DemoTransmitted through network

Host A

Host BHost E

Host D

Host C

Node 1 Node 2

Node 3

Node 4

Node 5

Node 6 Node 7

Forwarding Table

Dest. Next Node

CDBE

2245

Why Packet SwitchingDynamic bandwidth allocation

Links will be occupied on demandAlternative routes when congestion occurred

Packets from different sources can coexist on the same customer-to-network physical link without interference. Allows terminals operating at different bit rates to internet-work with each other

Routers will buffer the packets from a higher bit rate hosts

Yet, Problems….

Network Topology

Optical Transmission MediaIn MAN, The link between nodes are optical fibersPackets are optical signalsO-E-O conversion required at the interfaceLarge Overhead

Electrical Electrical

Optical Optical

Optical

Solution: Optical label SwitchingPlace optical label at subcarrier frequencyRouting information can be extracted by converting header onlyConversion will leave payload untouched

Architecture of OLS

Elements of OLS networksEdge Router

Transmitting Node: Append optical label @ subcarrier frequencyConversion to Optical Signal

Receiving Node Remove optical LabelConversion back to Electrical Signal

Core RouterPerform the Switching

Transmitting Node

DFB Laser SourceModulation Signal

Data @higher Bit RateHeader @lower Bit Rate

OutputModulated Optical Signal

Header ElectricalData

OpticalSignal

Core RouterSwitching node ArchitectureSenders/Receivers can be on different wavelength

From Sender1

From SenderN

SwitchNode

Controller

NxMOpticalSwitch

N by M switching Node

Optical Header Receiver

ControlLine

Fiber Delay Loop

Fiber Delay Loop

To Receiver1

To Receiver M

Switch Node ControllerNetwork Control Units

Communicate with other nodes / update Forwarding TableForwarding units

Header Buffer: One per wavelengthForwarding table Interface: Obtain Address InfoPriority Control and Decision

Network Control Unit

Header Buffer

Header Buffer

Input 1

Input 2

ForwardingTable

Interface

ForwardingTable

PriorityControl andDecisions

To Optical switch

To Wavelength converter

To New headerGenerator

ControlSignals

New headerGeneration

Label SwappingIn Electrical Packet switching, headers may be modified as passing a switch

The TTL (time to live) bits in the IP header to prevent a packet looping in the network foreverInterfacing between one type of network to another

Require the optical label to be writable/rewritableModify the switching nodeAdd a label writer

IP network

ATM networkInterface Router

Label Rewriter Details

Data payload ReceiverPhoto detectorAmplifier & LPF

Subcarrier/header ReceiverHomodyne Detection

Receiving Node

BER test of cascaded OLS Router

Network Features of OLSAll-optical between end stations

Once a packet leaves a host computer, it sees one long fiberHeader is decoupled from the data payload

They can be in different bit ratePayload may not be digitally encoded

Packet on a given path experiences the same delayWhen a packet is blocked at a given node, it can be routed at a different path or dropped

Timing consideration

Contention control by wavelength deflectionWhen packets from multiple users arrive at a switch node at the same time, contention happensCan route a packet to a different, less loaded wavelength

Social/Economic Impacts of OLSBridging the Gap between the IP protocol and WDM at the edge of the network

Replace the existing ring topology in MAN with optical switching

Foundation for next-generation service providerAll optical networkFastSimple to manage

SummaryElectrical packet switching is not compatible with optical transmissionOptical label packet switching

Avoid OEO conversionCompatible with various network layer protocols

Optical label swapping

Compatible with WDMMulti-dimensional contention solutionIncreased complexity

Optical single side band (OSSB)Double Side band labels

Harder to Erase by Fiber Fabry-Perot FilterRequires matching FSR ANDRequires the notch filter to have a sharp and narrow notch

Single Side band Labels

Spectra in optical label swapping

Spectra (a) before and (b) after the OSSBsubcarrier label is suppressed.

Extension to Multi wavelength/protocol