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A Brief Introduction to Optical Networks

A Brief Introduction to Optical Networks. Gaurav Agarwal gaurav@eecs.berkeley.edu. What I hope you will learn. Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures Circuit, Packet and Burst Protection and Restoration. Outline.

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A Brief Introduction to Optical Networks

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  1. A Brief Introduction to Optical Networks Gaurav Agarwal gaurav@eecs.berkeley.edu

  2. What I hope you will learn • Why Optical? • Intro to Optical Hardware • Three generations of Optical • Various Switching Architectures • Circuit, Packet and Burst • Protection and Restoration EECS - UC Berkeley

  3. Outline • Why Optical? (Any guesses???) • Intro to Optical Hardware • Three generations of Optical • Various Switching Architectures • Circuit, Packet and Burst • Protection and Restoration EECS - UC Berkeley

  4. Bandwidth: Lots of it • Usable band in a fiber • 1.30m - 1.65m  40 THz •  spaced at 100 GHz  400 s per fiber • Link Speeds upto 40 Gbps per  • OC-3  155Mbps • OC-768  40Gbps becoming available • Total link capacity • 400  * 40Gbps = 16 Tbps! • Do we need all this bandwidth? EECS - UC Berkeley

  5. Other advantages • Transparent to bit rates and modulation schemes • Low bit error rates • 10-9 as compared to 10-5 for copper wires • High speed transmission • To make this possible, we need: • All-Optical reconfigurable (within seconds) networks • Definitely a difficult task EECS - UC Berkeley

  6. All-Optical Switch* All-Optical Switch* All-Optical Switch* What a path will look like Lasers generate the signal Optical receivers Optical Amplifier * All-optical Switch with wavelength converters and optical buffers EECS - UC Berkeley

  7. Outline • Why Optical? • Intro to Optical Hardware • Three generations of Optical • Various Switching Architectures • Circuit, Packet and Burst • Protection and Restoration EECS - UC Berkeley

  8. Fiber & Lasers • Fiber • Larger transmission band • Reduced dispersion, non linearity and attenuation loss • Lasers • Up to 40Gbps • Tunability emerging • Reduced noise (both phase and intensity) • Made from semiconductor or fiber EECS - UC Berkeley

  9. Optical Amplifiers • As opposed to regenerators • Make possible long distance transmissions • Transparent to bit rate and signal format • Have large gain bandwidths (useful in WDM systems) • Expensive (~$50K) Now: Optical Amps Then: Regenerators EECS - UC Berkeley

  10. 1 1 2 OADM 2 3 ’3 3 ’3 Optical Add-Drop Multiplexers • Optical Add-Drop Multiplexer (OADM) • Allows transit traffic to bypass node optically • New traffic stream can enter without affecting the existing streams EECS - UC Berkeley

  11. Optical Switches • Route a channel from any I/P port to any O/P port • Can be fixed, rearrangable, or with  converters • MEMS (Micro Electro Mechanical Systems) • Lucent, Optical Micro Machines, Calient, Xros etc. • Thermo-Optic Switches • JDS Uniphase, Nanovation, Lucent • Bubble Switches • Agilent (HP) • LC (Liquid Crystal) Switches • Corning, Chorum Technologies • Non-Linear Switches (still in the labs) EECS - UC Berkeley

  12. MEMS Switches 2-D Optical Switches • Crossbar architecture • Simple Digital Control of mirrors • Complexity O(N²) for full non blocking architecture • Current port count limited to 32 x 32. EECS - UC Berkeley

  13. 3D MEMS Switch Architecture 3-D Optical Switches • Analog Control of Mirrors. • Long beam paths (~1m) require collimators. • Complexity O(N) (Only 2N mirrors required for a full non blocking NxN switch) • Lucent Lambda Router : Port 256 x 256; each channel supports up to 320 Gbps. EECS - UC Berkeley

  14. Wavelength Converters • Improve utilization of available wavelengths on links • All-optical WCs being developed • Greatly reduce blocking probabilities 3 2 3 2 WC No  converters With  converters 1 New request 1 3 1 New request 1 3 EECS - UC Berkeley

  15. Optical Buffers • Fiber delay lines are used • To get a delay of 1msec: • Speed of Light = 3*108 m/sec • Length of Fiber = 3*108 *10-3 m = 300 km EECS - UC Berkeley

  16. Outline • Why Optical? • Intro to Optical Hardware • Three generations of Optical • Various Switching Architectures • Circuit, Packet and Burst • Protection and Restoration EECS - UC Berkeley

  17. E-O Switch O-E-O Switch O-E Switch Generation I • Point-to-point optical links used simply as a transmission medium • Fiber connected by Electronic routers/switches with O-E-O conversion • Regenerators used for long haul Electronic data as the signal Signal received as electronic Regenerators EECS - UC Berkeley

  18. Generation II • Static paths in the core of the network • All-Optical Switches (may not be intelligent) • Circuit-switched • Configurable (but in the order of minutes/hours) • Soft of here EECS - UC Berkeley

  19. IP Router Network IP Router Network IP Router Network NNI UNI Light Path Optical Subnet Optical Subnet Optical Subnet End-to-end path Gen II: IP-over-Optical EECS - UC Berkeley

  20. Peer Model • IP and optical networks are treated as a single integrated network • OXCs are treated as IP routers with assigned IP addresses • No distinction between UNI and NNI • Single routing protocol instance runs over both domains • Topology and link state info maintained by both IP and optical routers is identical EECS - UC Berkeley

  21. Overlay Model • IP network routing and signaling protocols are independent of the corresponding optical networking protocols • IP  Client & Optical network  Server • Static/Signaled overlay versions • Similar to IP-over-ATM EECS - UC Berkeley

  22. Integrated Model • Leverages “best-of-both-worlds” by inter-domain separation while still reusing MPLS framework • Separate routing instances in IP and ON domains • Information from one routing instance can be passed through the other routing instance • BGP may be adapted for this information exchange EECS - UC Berkeley

  23. Generation III • An All-Optical network • Optical switches reconfigurable in milli-seconds • Intelligent and dynamic wavelength assignment, path calculation, protection built into the network • Possibly packet-switched • Dream of the Optical World EECS - UC Berkeley

  24. Generation III (contd.) • Optical “routers” perform L3 routing • No differentiation between optical and electrical IP domains • Routing decision for each packet made at each hop • Statistical sharing of link bandwidth • Complete utilization of link resources EECS - UC Berkeley

  25. Outline • Why Optical? • Intro to Optical Hardware • Three generations of Optical • Various Switching Architectures • Circuit, Packet and Burst • Protection and Restoration EECS - UC Berkeley

  26. Electronic Network Electronic Network Electronic Network Electronic Network State of the World Today O/E/O E/O E/O O/E/O O/E/O O/E/O O/E/O O/E/O E/O E/O Optical Core EECS - UC Berkeley

  27. View of a E/O node Input Port 1 Input Port 1 O P 1 Optical Link 1 Electrical Optical Input Port 2 Input Port 2 O P 2 Optical Link 2 Input Port 3 O P 3 Input Port 3 O P 4 Optical Link 3 Input Port 4 Input Port 4 O P N-1 O P N Physical View Logical View EECS - UC Berkeley

  28. Electronic Network Electronic Network Electronic Network Electronic Network O/E/O O/E/O O/E/O O/E/O O/E/O O/E/O Optical Circuit Switching OS O/E/O E/O E/O O/E/O OS OS O/E/O OS O/E/O O/E/O OS O/E/O OS E/O E/O Optical Core EECS - UC Berkeley

  29. Electronic Network Electronic Network Electronic Network Electronic Network Optical Circuit Switching O/E/O OS E/O E/O OS O/E/O O/E/O OS O/E/O OS OS O/E/O OS WC O/E/O E/O E/O Optical Core EECS - UC Berkeley

  30. Optical Circuit Switching • A circuit or ‘lightpath’ is set up through a network of optical switches • Path setup takes at least one RTT • Need not do O/E/O conversion at every node • No optical buffers since path is pre-set • Need to choose path • Need to assign wavelengths to paths • Hope for easy and efficient reconfiguration EECS - UC Berkeley

  31. Problems • Need to set up lightpath from source to destination • Data transmission initiated after reception of acknowledgement (two way reservation) • Poor utilization if subsequent transmission has small duration relative to set-up time. (Not suited for bursty traffic) • Protection / fault recovery cannot be done efficiently Example : Network with N switches, D setup time per switch, T interhop delay. Circuit Setup time = 2.(N-1).T + N.D If N = 10, T = 10ms, D = 5ms, setup time = 230 ms. At 20 Gbps, equivalent to 575 MB (1 CD) worth of data ! EECS - UC Berkeley

  32. Optical Packet Switching • Internet works with packets • Data transmitted as packets (fixed/variable length) • Routing decision for each packet made at each hop by the router/switch • Statistical sharing of link bandwidth leads to better link utilization • Traffic grooming at the edges? Optical header? EECS - UC Berkeley

  33. Problems • Requires intelligence in the optical layer • Or O/E/O conversion of header at each hop • Packets are small  Fast switching (nsec) • Need store-and-forward at nodes or Deflection Routing. Also store packet during header processing • Buffers are extremely hard to implement  • Fiber delay lines • 1 pkt = 12 kbits @ 10 Gbps requires 1.2 s of delay => 360 m of fiber) • Delay is quantized • How about QoS? EECS - UC Berkeley

  34. Multiprotocol Lambda Switching • D. Awduche et. al., “Requirements for Traffic Engineering Over MPLS,” RFC 2702 • Problem decomposition by decoupling the Control plane from the Data plane • Exploit recent advances in MPLS traffic engineering control plane • All optical data plane • Use  as a “label” • The  on incoming port determines the output port and outgoing  EECS - UC Berkeley

  35. OXCs and LSRs • Electrical Network – Label Switched Routers (LSR) • Optical Network – Optical Cross Connects • Both electrical and optical nodes are IP addressable • Distinctions • No  merging • No  push and pop • No packet-level processing in data plane EECS - UC Berkeley

  36. Optical Burst Switching • Lies in-between Circuit and Packet Switching • One-way notification of burst (not reservation) – can have collisions and lost packets • Header (control packet) is transmitted on a wavelength different from that of the payload • The control packet is processed at each node electronically for resource allocation • Variable length packets (bursts) do not undergo O/E/O conversions • The burst is not buffered within the ON EECS - UC Berkeley

  37. Various OBSs • The schemes differ in the way bandwidth release is triggered. • In-band-terminator (IBT) – header carries the routing information, then the payload followed by silence (needs to be done optically). • Tell-and-go (TAG) – a control packet is sent out to reserve resources and then the burst is sent without waiting for acknowledgement. Refresh packets are sent to keep the path alive. EECS - UC Berkeley

  38. Offset-time schemes • Reserve-a-fixed-duration (RFD) • Just Enough Time (JET) • Bandwidth is reserved for a fixed duration (specified by the control packet) at each switch • Control packet asks for a delayed reservation that is activated at the time of burst arrival • OBS can provide a convenient way for QoS by providing extra offset time EECS - UC Berkeley

  39. ta2(= ts2) ta2(= ts2) to1 ta1 ts1 ts1+ l1 QoS using Offset-Times Assume two classes of service Class 1 has higher priority Class 2 has zero offset time to1 i Time ta1 ts1 ts1+ l1 i Time ta2(= ts2) ts2+ l2 tai = arrival time for class i request tsi = service time for class i request toi = offset time for class i request li = burst length for class i request EECS - UC Berkeley

  40. Comparison EECS - UC Berkeley

  41. Optical MAN Optical MAN Optical MAN Optical MAN Hierarchical Optical Network E/O E/O E/O E/O E/O OS All O All O OS E/O E/O E/O OS OS OS WC E/O E/O E/O E/O All O All O Optical Core E/O E/O E/O E/O EECS - UC Berkeley

  42. Hierarchical Optical Network • Optical MAN may be • Packet Switched (feasible since lower speeds) • Burst Switched • Sub- circuit switching by wavelength merging • Interfaces boxes are All-Optical and merge multiple MAN streams into destination-specific core stream • Relatively static Optical Core • Control distributed to intelligent edge boxes EECS - UC Berkeley

  43. Outline • Why Optical? • Intro to Optical Hardware • Three generations of Optical • Various Switching Architectures • Circuit, Packet and Burst • Protection and Restoration EECS - UC Berkeley

  44. Link vs Path Protection • For failure times, need to keep available s on backup path • Link: Need to engineer network to provide backup • Path: need to do end-to-end choice of backup path EECS - UC Berkeley

  45. Path protection Dedicated (1+1) – send traffic on both paths Dedicated (1:1) – use backup only at failure Shared (N:1) – many normal paths share common backup Link Protection Dedicated (each  is also reserved on backup link) Shared (a  on backup link is shared between many) Types of Protection EECS - UC Berkeley

  46. Restoration • Do not calculate protection path ahead of time • Upon failure, use signalling protocol to generate new backup path • Time of failover is more • But much more efficient usage of s • Need also to worry about steps to take when the fault is restored EECS - UC Berkeley

  47. Protection and Restoration • Time of action • Path calculation (before or after failure ?) • Channel Assignments (before or after failure ?) • OXC Reconfiguration • AT&T proposal • Calculate Path before failure • Try channel assignment after failure • Simulations show 50% gain over channel allocation before failure EECS - UC Berkeley

  48. Protection Algorithms • Various flavors • Shortest path type • Flow type • ILP (centralized) • Genetic programming • In general, centralized algos are too inefficient • Need distributed algos, and quick signalling • Have seen few algos that take into account the different node types (LWC/FWC) EECS - UC Berkeley

  49. Conclusion • Optical is here to stay • Enormous gains in going optical • O/E/O will soon be the bottleneck • Looking for ingenious solutions • Optical Packet Switching • Flavors of Circuit Switching EECS - UC Berkeley

  50. Collective References • “Optical Networks: A practical perspective” by Rajiv Ramaswami and Kumar Sivarajan, Morgan Kaufman. • IEEE JSAC • September 1998 issue • October 2000 issue • IEEE Communications Magazine • March 2000 issue • September 2000 issue • February 2001 issue • March 2001 issue • INFOCOM 2001 • ‘Optical Networking’ Session • ‘WDM and Survivable Routing’ Session • INFOCOM 200 • ‘Optical Networks I’ Session • ‘Optical Networks II’ Session • RFC 2702 for MPS • www.cs.buffalo.edu/pub/WWW/faculty/qiao/ • www.lightreading.com EECS - UC Berkeley

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