A Brief Introduction to Optical Networks Gaurav Agarwal [email protected] What I hope you will learn Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching.
Download ReportTranscript A Brief Introduction to Optical Networks Gaurav Agarwal [email protected] What I hope you will learn Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching.
A Brief Introduction to Optical Networks Gaurav Agarwal [email protected] 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 2 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 3 Bandwidth: Lots of it Usable band in a fiber Link Speeds upto 40 Gbps per OC-3 155Mbps OC-768 40Gbps becoming available Total link capacity 1.30m - 1.65m 40 THz spaced at 100 GHz 400 s per fiber 400 * 40Gbps = 16 Tbps! Do we need all this bandwidth? EECS - UC Berkeley 4 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 5 What a path will look like Lasers generate the signal All-Optical Switch* Optical receivers All-Optical Switch* All-Optical Switch* Optical Amplifier * All-optical Switch with wavelength converters and optical buffers EECS - UC Berkeley 6 Outline Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures Circuit, Packet and Burst Protection and Restoration EECS - UC Berkeley 7 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 8 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 9 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 1 2 3 1 OADM 2 ’3 3 ’3 EECS - UC Berkeley 10 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) Thermo-Optic Switches Agilent (HP) LC (Liquid Crystal) Switches JDS Uniphase, Nanovation, Lucent Bubble Switches Lucent, Optical Micro Machines, Calient, Xros etc. Corning, Chorum Technologies Non-Linear Switches (still in the labs) EECS - UC Berkeley 11 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 12 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 13 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 1 New request 1 3 With converters 1 New request 1 3 EECS - UC Berkeley 14 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 15 Outline Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures Circuit, Packet and Burst Protection and Restoration EECS - UC Berkeley 16 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 E-O Switch Signal received as electronic O-E-O Switch O-E Switch Regenerators EECS - UC Berkeley 17 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 18 Gen II: IP-over-Optical Optical Subnet IP Router Network IP Router Network NNI UNI Optical Subnet Light Path Optical Subnet IP Router Network End-to-end path EECS - UC Berkeley 19 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 20 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 21 Integrated Model Leverages “best-of-both-worlds” by interdomain 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 22 Generation III An All-Optical network Optical switches reconfigurable in milliseconds Intelligent and dynamic wavelength assignment, path calculation, protection built into the network Possibly packet-switched Dream of the Optical World EECS - UC Berkeley 23 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 24 Outline Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures Circuit, Packet and Burst Protection and Restoration EECS - UC Berkeley 25 State of the World Today Electronic Network Electronic Network O/E/O O/E/O E/O E/O O/E/O O/E/O O/E/O O/E/O E/O Electronic Network E/O Optical Core EECS - UC Berkeley Electronic Network 26 View of a E/O node Input Port 1 Optical Link 1 Input Port 2 Input Port 3 Electrical Optical Optical Link 2 Input Port 1 Input Port 2 Input Port 3 OP1 OP2 OP3 OP4 Optical Link 3 Input Port 4 Physical View Input Port 4 Logical View EECS - UC Berkeley O P N-1 OPN 27 Optical Circuit Switching Electronic Network Electronic Network O/E/O OS O/E/O OS E/O E/O O/E/O OS O/E/O OS O/E/O OS O/E/O OS E/O Electronic Network E/O Optical Core EECS - UC Berkeley Electronic Network 28 Optical Circuit Switching Electronic Network Electronic Network O/E/O OS O/E/O OS E/O E/O O/E/O OS O/E/O OS O/E/O OS O/E/O WC OS E/O Electronic Network E/O Optical Core EECS - UC Berkeley Electronic Network 29 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 30 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 31 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 32 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 33 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 34 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 35 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 36 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 37 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 38 QoS using Offset-Times Assume two classes of service Class 1 has higher priority Class 2 has zero offset time to1 i Time ta1 ta2(= ts2) ts1 ta2(= ts2) ts1+ l1 to1 i Time ta2(= ts2) tai = arrival time for class i request tsi = service time for class i request ta1 ts2+ l2 ts1 ts1+ l1 toi = offset time for class i request li = burst length for class i request EECS - UC Berkeley 39 Comparison EECS - UC Berkeley 40 Hierarchical Optical Network E/O E/O E/O E/O Optical MAN E/O Optical MAN All O E/O OS OS All O OS E/O OS OS WC E/O E/O E/O All O E/O All O Optical MAN E/O Optical MAN Optical Core E/O E/O E/O E/O EECS - UC Berkeley 41 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 42 Outline Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures Circuit, Packet and Burst Protection and Restoration EECS - UC Berkeley 43 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 Normal Path Normal Path Path Protection Backup Path Link Protection Backup Path EECS - UC Berkeley 44 Types of Protection 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 EECS - UC Berkeley Link Protection Dedicated (each is also reserved on backup link) Shared (a on backup link is shared between many) 45 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 46 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 47 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 48 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 49 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 MPS www.cs.buffalo.edu/pub/WWW /faculty/qiao/ www.lightreading.com EECS - UC Berkeley 50