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CSIT5600 by M. Hamdi 1 Switching Architectures for Optical Networks.

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Presentation on theme: "CSIT5600 by M. Hamdi 1 Switching Architectures for Optical Networks."— Presentation transcript:

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2 CSIT5600 by M. Hamdi 1 Switching Architectures for Optical Networks

3 CSIT5600 by M. Hamdi 2 SONET Data Center SONET DWD M Access Long HaulAccessMetro Internet Reality

4 CSIT5600 by M. Hamdi 3 Hierarchies of Networks: IP / ATM / SONET / WDM

5 CSIT5600 by M. Hamdi 4 Why Optical? Enormous bandwidth made available –DWDM makes ~160 channels/ possible in a fiber –Each wavelength “potentially” carries about 40 Gbps –Hence Tbps speeds become a reality Low bit error rates –10 -9 as compared to for copper wires Very large distance transmissions with very little amplification.

6 CSIT5600 by M. Hamdi 5 Dense Wave Division Multiplexing (DWDM) Multiple wavelength bands on each fiber  Transmit by combining multiple different frequencies Output fibers Long-haul fiber

7 CSIT5600 by M. Hamdi Anatomy of a DWDM System Terminal A Terminal B Post- Amp Pre- Amp Line Amplifiers MUXMUX DEMUXDEMUX Transponder Interfaces Transponder Interfaces Direct Connections Direct Connections Basic building blocks Optical amplifiers Optical multiplexers Stable optical sources

8 CSIT5600 by M. Hamdi 7 Core Transport Services OC-3 OC-12 STS-1 Provisioned SONET circuits. Aggregated into Lamdbas. Carried over Fiber optic cables. Circuit Origin Circuit Destination

9 CSIT5600 by M. Hamdi 8 WDM Network: Wavelength View WDM link Optical Switch Edge Router Legacy Interfaces Legacy Interfaces Legacy Interfaces (e.g.,PoS, Gigabit Ethernet, IP/ATM) Interfaces

10 CSIT5600 by M. Hamdi 9 Relationship of IP and Optical Optical brings –Bandwidth multiplication –Network simplicity (removal of redundant layers) IP brings –Scalable, mature control plane –Universal OS and application support –Global Internet Collectively IP and Optical (IP+Optical) introduces a set of service-enabling technologies

11 CSIT5600 by M. Hamdi 10 Typical Super POP OXC Core IP router Interconnectio n Network Large Multi-service Aggregation Switch Voice Switch Core ATM Switch SONET Coupler & Opt.amp DWDM + ADM DWDM Metro Ring

12 CSIT5600 by M. Hamdi 11 Typical POP OXC DWDMDWDM Voice Switch SONET-XC DWDMDWDM

13 CSIT5600 by M. Hamdi 12 What are the Challenges with Optical Networks? Processing: Needs to be done with electronics –Network configuration and management –Packet processing and scheduling –Resource allocation, etc. Traffic Buffering –Optics still not mature for this (use Delay Fiber Lines) –1 pkt = Gbps requires 1.2  s of delay => 360 m of fiber) Switch configuration –Relatively slow

14 CSIT5600 by M. Hamdi 13 Wavelength Converters Improve utilization of available wavelengths on links All-optical WCs being developed Greatly reduce blocking probabilities No converters New request 1  New request 1  3 With converters WC

15 CSIT5600 by M. Hamdi 14 Wavelength Cross-Connects (WXCs) A WDM network consists of wavelength cross-connects (WXCs) (OXC) interconnected by fiber links. 2 Types of WXCs –Wavelength selective cross-connect (WSXC) Route a message arriving at an incoming fiber on some wavelength to an outgoing fiber on the same wavelength. Wavelength continuity constraint –Wavelength interchanging cross-connect (WIXC) Wavelength conversion employed Yield better performance Expensive

16 CSIT5600 by M. Hamdi 15 Wavelength Router Control Plane: Wavelength Routing Intelligence Data Plane: Optical Cross Connect Matrix Single Channel Links to IP Routers, SDH Muxes,... Unidirectional DWDM Links to other Wavelength Routers

17 CSIT5600 by M. Hamdi 16 Optical Network Architecture IP Router Optical Cross Connect (OXC) OXC Control unit Control Path Data Path UNI Mesh Optical Network IP Network

18 CSIT5600 by M. Hamdi 17 OXC Control Unit Each OXC has a control unit Responsible for switch configuration Communicates with adjacent OXCs or the client network through single-hop light paths –These are Control light paths –Use standard signaling protocol like GMPLS for control functions Data light paths carry the data flow –Originate and terminate at client networks/edge routers and transparently traverse the core

19 CSIT5600 by M. Hamdi 18 Optical Cross-connects (No wavelength conversion) Optical Switch Fabric All Optical Cross-connect (OXC) Also known as Photonic Cross-connect (PXC)

20 CSIT5600 by M. Hamdi 19 Optical Cross-Connect with Full Wavelength Conversion M demultiplexers at incoming side M multiplexers at outgoing side Mn x Mn optical switch has wavelength converters at switch outputs 1, 2,..., n 1, 2,..., n 1, 2,..., n 1 2 M Optical CrossBar Switch Wavelength Converters Wavelength Mux Wavelength Demux 1, 2,..., n 1, 2,..., n 1, 2,..., n n 1 2 n 1 2 n 1 2 n 1 2 n n M

21 CSIT5600 by M. Hamdi 20 Wavelength Router with O/E and E/O Cross-Connect 1 3 Outgoing Interface Outgoing Wavelength Incoming Interface Incoming Wavelength

22 CSIT5600 by M. Hamdi 21 Demux 1 Incoming fibers O E O Individual wavelengths Mux Outgoing fibers O-E-O Crossconnect Switch (OXC) O/E N 2 E/O Switches information signal on a particular wavelength on an incoming fiber to (another) wavelength on an outgoing fiber. 1 N 2 WDM (many λs)

23 CSIT5600 by M. Hamdi 22 Optical core network Opaque (O-E-O) and transparent (O-O) sections E/O Client signals O/E to other nodes from other nodes EEO O Transparent optical island OO OO E O O O O E O Opaque optical network

24 CSIT5600 by M. Hamdi 23 OEO vs. All-Optical Switches Capable of status monitoring Optical signal regenerated – improve signal-to-noise ratio Traffic grooming at various levels Less aggregated throughput More expensive More power consumption Unable to monitor the contents of the data stream Only optical amplification – signal-to-noise ratio degraded with distance No traffic grooming in sub- wavelength level Higher aggregated throughput ~10X cost saving ~10X power saving OEOAll-Optical

25 CSIT5600 by M. Hamdi 24 Large customers buy “lightpaths” A lightpath is a series of wavelength links from end to end. cross-connect optical fibers Repeater One fiber

26 CSIT5600 by M. Hamdi 25 Hierarchical switching: Node with switches of different granularities Fibers O A. Entire fibers Fibers O O O B. Wavelength subsets O O “Express trains” O C. Individual wavelengths E O “Local trains”

27 CSIT5600 by M. Hamdi 26 Wide Area Network (WAN) GAN links OXC: Optical Wavelength/Waveband Cross Connect WAN : Up to wavelengths Gbit/s/ wavebands (> 10 )

28 CSIT5600 by M. Hamdi 27 Packet (a) vs. Burst (b) Switching

29 CSIT5600 by M. Hamdi 28 MAN (Country / Region) optical burst formation IP packets

30 CSIT5600 by M. Hamdi 29 Optical Switching Technologies MEMs – MicroElectroMechanical Liquid Crystal Opto-Mechanical Bubble Technology Thermo-optic (Silica, Polymer) Electro-optic (LiNb03, SOA, InP) Acousto-optic Others… Maturity of technology, Switching speed, Scalability, Cost, Relaiability (moving components or not), etc.

31 CSIT5600 by M. Hamdi 30 MEMS Switches for Optical Cross- Connect Proven technology, switching time (10 to 25 msec), moving mirrors is a reliability problem.

32 CSIT5600 by M. Hamdi 31 WDM “transparent” transmission system Wavelengths aggregator multiple λs Fibers (O-O nodes) Wavelengths disaggregator O O O O O O Optical switching fabric (MEMS devices, etc.) Incoming fiber Tiny mirrors Outgoing fibers

33 CSIT5600 by M. Hamdi 32 Upcoming Optical Technologies WDM routing is circuit switched –Resources are wasted if enough data is not sent –Wastage more prominent in optical networks Techniques for eliminating resource wastage –Burst Switching –Packet Switching Optical burst switching (OBS) is a new method to transmit data A burst has an intermediate characteristics compared to the basic switching units in circuit and packet switching, which are a session and a packet, respectively

34 CSIT5600 by M. Hamdi 33 Optical Burst Switching (OBS) Group of packets a grouped in to ‘ bursts ’, which is the transmission unit Before the transmission, a control packet is sent out –The control packet contains the information of burst arrival time, burst duration, and destination address Resources are reserved for this burst along the switches along the way The burst is then transmitted Reservations are torn down after the burst

35 CSIT5600 by M. Hamdi 34 Optical Burst Switching (OBS)

36 CSIT5600 by M. Hamdi 35 Optical Packet Switching Fully utilizes the advantages of statistical multiplexing Optical switching and buffering Packet has Header + Payload –Separated at an optical switch Header sent to the electronic control unit, which configures the switch for packet forwarding Payload remains in optical domain, and is re- combined with the header at output interface

37 CSIT5600 by M. Hamdi 36 Optical Packet Switch Has –Input interface, Switching fabric, Output interface and control unit Input interface separates payload and header Control unit operates in electronic domain and configures the switch fabric Output interface regenerates optical signals and inserts packet headers Issues in optical packet switches –Synchronization –Contention resolution

38 CSIT5600 by M. Hamdi 37 Main operation in a switch: –The header and the payload are separated. –Header is processed electronically. –Payload remains as an optical signal throughout the switch. –Payload and header are re-combined at the output interface. payloadhdr Wavelength i input port j Optical packet hdr CPU Optical switch payload hdr Re-combined Wavelength i output port j

39 CSIT5600 by M. Hamdi 38 Output port contention Assuming a non-blocking switching matrix, more than one packet may arrive at the same output port at the same time. Output ports payloadhdr payloadhdr payloadhdr Optical SwitchInput ports

40 CSIT5600 by M. Hamdi 39 Sync. Fixed packet size Synchronization stages required Slotted networks OPS Architecture: Synchronization Occurs in electronic switches – solved by input buffering

41 CSIT5600 by M. Hamdi 40 Fixed packet size Synchronization stages required Slotted networks Sync. OPS Architecture: Synchronization

42 CSIT5600 by M. Hamdi 41 Fixed packet size Synchronization stages required Slotted networks OPS Architecture: Synchronization Sync.

43 CSIT5600 by M. Hamdi 42 Fixed packet size Synchronization stages required Slotted networks OPS Architecture: Synchronization Sync.

44 CSIT5600 by M. Hamdi 43 Fixed packet size Synchronization stages required Slotted networks OPS Architecture: Synchronization Sync.

45 CSIT5600 by M. Hamdi 44 OPS Architecture: Synchronization Sync.

46 CSIT5600 by M. Hamdi 45 OPS: Contention Resolution More than one packet trying to go out of the same output port at the same time –Occurs in electronic switches too and is resolved by buffering the packets at the output –Optical buffering ? Solutions for contention –Optical Buffering –Wavelength multiplexing –Deflection routing

47 CSIT5600 by M. Hamdi 46 OPS Architecture Contention Resolutions

48 CSIT5600 by M. Hamdi 47 OPS: Contention Resolution Optical Buffering –Should hold an optical signal How? By delaying it using Optical Delay Lines (ODL) –ODLs are acceptable in prototypes, but not commercially viable –Can convert the signal to electronic domain, store, and re- convert the signal back to optical domain Electronic memories too slow for optical networks

49 CSIT5600 by M. Hamdi Optical buffering OPS Architecture Contention Resolutions

50 CSIT5600 by M. Hamdi Optical buffering OPS Architecture Contention Resolutions

51 CSIT5600 by M. Hamdi Optical buffering OPS Architecture Contention Resolutions

52 CSIT5600 by M. Hamdi 51 OPS: Contention Resolution Wavelength multiplexing –Resolve contention by transmitting on different wavelengths –Requires wavelength converters - $$$

53 CSIT5600 by M. Hamdi 52 Wavelength conversion OPS Architecture Contention Resolutions

54 CSIT5600 by M. Hamdi Wavelength conversion OPS Architecture Contention Resolutions

55 CSIT5600 by M. Hamdi Wavelength conversion OPS Architecture Contention Resolutions

56 CSIT5600 by M. Hamdi Wavelength conversion OPS Architecture Contention Resolutions

57 CSIT5600 by M. Hamdi Wavelength conversion OPS Architecture Contention Resolutions

58 CSIT5600 by M. Hamdi 57 Deflection routing When there is a conflict between two optical packets, one will be routed to the correct output port, and the other will be routed to any other available output port. A deflected optical packet may follow a longer path to its destination. In view of this: –T he end-to-end delay for an optical packet may be unacceptably high. –Optical p ackets may have to be re-ordered at the destination

59 CSIT5600 by M. Hamdi 58 Electronic Switches Using Optical Crossbars

60 CSIT5600 by M. Hamdi 59 Scalable Multi-Rack Switch Architecture Switch Core Optical links Line card rack Number of linecards is limited in a single rack –Limited power supplement, i.e. 10KW –Physical consideration, i.e. temperature, humidity Scaling to multiple racks –Fiber links and central fabrics

61 CSIT5600 by M. Hamdi 60 Logical Architecture of Multi-rack Switches Optical I/O interfaces connected to WDM fibers Electronic packet processing and buffering –Optical buffering, i.e. fiber delay lines, is costly and not mature Optical interconnect –Higher bandwidth, lower latency and extended link length than copper twisted lines Switch fabric: electronic? Optical? Crossbar Scheduler Switch Fabric System Framer Line Card Laser Local Buffers Framer Line Card Laser Local Buffers Framer Line Card Laser Local Buffers Framer Line Card Laser Local Buffers Fiber I/O

62 CSIT5600 by M. Hamdi 61 Optical Switch Fabric Less optical-to-electrical conversion inside switch –Cheaper, physically smaller Compare to electronic fabric, optical fabric brings advantages in –Low power requirement, Scalability, Port density, High capacity Technologies that can be used –2D/3D MEMS, liquid crystal, bubbles, thermo-optic, etc. Hybrid architecture takes advantage of the strengths of both electronics and optics Crossbar Scheduler Switch Fabric System Framer Line Card Laser Local Buffers Framer Line Card Laser Local Buffers Framer Line Card Laser Local Buffers Framer Line Card Laser Local Buffers Fiber I/O

63 CSIT5600 by M. Hamdi 62 Electronic Vs. Optical Fabric Trans. Line Buffer Switching Fabric Inter- connection Trans. Line BufferInter- connection Electronic Trans. Line Buffer Switching Fabric Inter- connection Trans. Line BufferInter- connection Optical Electronic E/O or O/E Conversion favorred

64 CSIT5600 by M. Hamdi 63 Multi-rack Hybrid Packet Switch

65 CSIT5600 by M. Hamdi 64 Features of Optical Fabric Less E/O or O/E conversion High capacity Low power consumption Less cost However, Reconfiguration overhead (50-100ns) –Tuning of lasers (20-30ns) –System clock synchronization (10-20ns or higher)

66 CSIT5600 by M. Hamdi 65 Scheduling Under Reconfiguration Overhead Traditional slot-by-slot approach Low bandwidth usage Scheduler Time Line ScheduleReconfigureTransfer

67 CSIT5600 by M. Hamdi 66 Reduced Rate Scheduling Challenge: fabric reconfiguration delay –Traditional slot-by-slot scheduling brings lots of overhead Solution: slow down the scheduling frequency to compensate –Each schedule will be held for some time Scheduling task 1.Find out the matching 2.Determine the holding time Fabric setup (reconfigure) Traffic transfer Time slot Slot-by-slot Scheduling, zero fabric setup time Reduced rate Scheduling, each schedule is held for some time Slot-by-slot Scheduling with reconfigure delay

68 CSIT5600 by M. Hamdi 67 Scheduling Under Reconfiguration Overhead Reduce the scheduling rate –Bandwidth Usage = Transfer/(Reconfigure+Transfer) Approaches –Batch scheduling: TSA-based –Single scheduling: Schedule + Hold Constant

69 CSIT5600 by M. Hamdi 68 Single Scheduling Schedule + Hold –One schedule is generated each time –Each schedule is held for some time (holding time) –Holding time can be fixed or variable –Example: LQF+Hold

70 CSIT5600 by M. Hamdi 69 Routing and Wavelength Assignment

71 CSIT5600 by M. Hamdi 70 Optical Circuit Switching An optical path established between two nodes Created by allocation of a wavelength throughout the path. Provides a ‘ circuit switched ’ interconnection between two nodes. –Path setup takes at least one RTT –No optical buffers since path is pre-set Desirable to establish light paths between every pair of nodes. Limitations in WDM routing networks, –Number of wavelengths is limited. –Physical constraints: limited number of optical transceivers limit the number of channels.

72 CSIT5600 by M. Hamdi 71 Routing and Wavelength Assignment (RWA) Light path establishment involves –Selecting a physical path between source and destination edge nodes –Assigning a wavelength for the light path RWA is more complex than normal routing because –Wavelength continuity constraint A light path must have same wavelength along all the links in the path –Distinct Wavelength Constraint Light paths using the same link must have different wavelengths

73 CSIT5600 by M. Hamdi 72 No Wavelength Converters POP Access Fiber Wavelength 1 Wavelength 2 Wavelength 3 WSXC

74 CSIT5600 by M. Hamdi 73 With Wavelength Converters POP Access Fiber Wavelength 1 Wavelength 2 Wavelength 3 WIXC

75 CSIT5600 by M. Hamdi 74 Routing and Wavelength Assignment (RWA) RWA algorithms based on traffic assumptions: Static Traffic –Set of connections for source and destination pairs are given Dynamic Traffic –Connection requests arrive to and depart from network one by one in a random manner. –Performance metrics used fall under one of the following three categories: Number of wavelengths required Connection blocking probability: Ratio between number of blocked connections and total number of connections arrived

76 CSIT5600 by M. Hamdi 75 Static and Dynamic RWA Static RWA –Light path assignment when traffic is known well in advance –Arises in capacity planning and design of optical networks Dynamic RWA –Light path assignment to be done when requests arrive in random fashion –Encountered during real-time network operation

77 CSIT5600 by M. Hamdi 76 Static RWA RWA is usually solved as an optimization problem with Integer Programming (IP) formulations Objective functions –Minimize average weighted number of hops –Minimize average packet delay –Minimize the maximum congestion level –Minimize number of Wavelenghts

78 CSIT5600 by M. Hamdi 77 Static RWA Methodologies for solving Static RWA –Heuristics for solving the overall ILP sub-optimally –Algorithms that decompose the static RWA problem into a set of individual sub-problems, and solve a sub-set –http://www.tct.hut.fi/~esa/java/wdm/http://www.tct.hut.fi/~esa/java/wdm/ Methodologies for solving Static RWA –Heuristics for solving the overall ILP sub-optimally –Algorithms that decompose the static RWA problem into a set of individual sub-problems, and solve a sub-set –http://www.tct.hut.fi/~esa/java/wdm/http://www.tct.hut.fi/~esa/java/wdm/ Methodologies for solving Static RWA –Heuristics for solving the overall ILP sub-optimally –Algorithms that decompose the static RWA problem into a set of individual sub-problems, and solve a sub-set –http://www.tct.hut.fi/~esa/java/wdm/http://www.tct.hut.fi/~esa/java/wdm/

79 CSIT5600 by M. Hamdi 78 Solving Dynamic RWA During network operation, requests for new light- paths come randomly These requests will have to be serviced based on the network state at that instant As the problem is in real-time, dynamic RWA algorithms should be simple The problem is broken down into two sub-problems –Routing problem –Wavelength assignment problem


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