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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