Course Details Optical Networks Jason Jue The University of Texas at Dallas Instructor: Jason Jue E-mail: jjue@utdallas.edu URL: http://www.utdallas.edu/~jjue/optical/ Lectures: Thursday 2-5 pm Course Description: Introduction to optical networks. Topics include: enabling technologies, wavelength-division multiplexing, wavelength-routed optical networks, virtual topology design, routing and wavelength assignment, network control and management, protection and restoration, traffic grooming, optical packet switching, optical burst switching, optical access networks. Course References Grading Textbook: B. Mukherjee, Optical WDM Networks, Springer, 2006 Additional References: R. Ramaswami and K. Sivarajan, Optical Networks: A Practical Perspective, second edition, Morgan Kaufmann 2001 Selected papers from research literature Assignments: 25% Exam: 25% Project: 50% Course Project The project will involve selecting a topic in optical networks and evaluating protocols, architectures, or schemes related to the selected topic. Projects may involve one or more of the following: Implementation of optical network protocols or applications in C, C++, Java, etc. Development of a computer simulation to study optical network characteristics and to evaluate optical network architectures and protocols Development of an analytical model for evaluating network behavior and performance Formulation and solution of network optimization problems Project presentations will be held at the end of the semester. Outline of Course Introduction Overview and motivation Historical evolution Research issues Optical components and technology Wavelength-routed (circuit-switched) optical networks Static network design RWA, logical topology design, traffic grooming Dynamic network design RWA, signaling, blocking probability analysis Protection and restoration Optical burst switching Signaling Contention resolution Scheduling QoS Photonic packet switching Contention resolution buffering, deflection, wavelength conversion QoS Optical metro and access networks 1
The Need for More Bandwidth Optical Networks Growing bandwidth demands driven by Growth of the Internet Number of hosts and users increasing exponentially Higher access rates Emerging high-bandwidth applications Scientific/GRID computing petabytes of information File-sharing composes majority of Internet traffic IPTV killer app for fiber to the home? IP telephony, video conferencing In addition to providing raw bandwidth, network must also provide services to support needs of applications Optical networks are critical for satisfying these growing demands What is an optical network? How can an optical network provide the necessary bandwidth and services? What is the state of technology and deployment? What is an Optical Network? Network in which data is transmitted using optical signals Elements of an optical network Optical transmission system Transmission medium Transmitters (lasers, LEDs) Receivers (photodetector) Switching/interconnection elements Electronic Circuit-based (SONET,SDH) Packet-based (IP, Ethernet) Optical Circuit-based (Optical cross-connect) Packet-based Burst-based Software and protocols Routing, connection establishment, contention resolution, protection, etc. Optical Communications Communication system characterized by: Frequency (wavelength) of signal Propagation medium c 8 Wavelength: λ = f ; c = 3 10 m/s Optical communication systems Frequency range: 10 14 10 15 Hz (3 μm to.3 μm) Medium: Optical fiber, free-space optics Why Optical Communications? Attenuation of Light in Fiber Optical communication systems provide high bandwidth and low attenuation (power loss) Typical copper media bandwidth: Telephone line - 1.1 MHz CAT5 cable (Ethernet) - 100 MHz Coaxial cable - 1 GHz Typical copper media attenuation: CAT5 200 db/km at 100 MHz Coaxial cable 10-20 db/km (90% - 99% loss/km) Potential fiber bandwidth: ~50 THz Fiber attenuation: 0.2 db/km Other benefits of fiber Resistant to electromagnetic interference Resistant to corrosion 14 14 (3.75 10 Hz) (1.67 10 Hz) Amount of attenuation (loss per km) depends on wavelength of light db = 10 log (Pin/Pout) At 1.5 μm: 0.2 db/km ~ 5% loss/km Bandwidth: c Δf = Δλ λ 2 2
Utilizing Fiber Bandwidth Cable and Fiber Deployment (10000 s-km) Problem: Peak electronic transmission rates limited to 40 Gbps Approaches for increasing bandwidth: Increase transmission rates (100 Gbps and beyond) Install more fiber Multiplex signals from different sources onto a single fiber Multiplexing Approaches: Optical Time Division Multiplexing (OTDM) Interleave bits of different electronic signal streams Requires synchronization Wavelength Division Multiplexing (WDM) Signals on different wavelengths multiplexed onto same fiber Each wavelength can operate at peak electronic rates Source: KMI Research Annual Fiber Deployment (Thousands of Miles) Optical TDM Year 2000 2001 2002 IXC 6,076 2,485 932 ILEC 6,184 5,567 2,641 CLEC 5,282 2,889 746 Interleave bits of different electronic signal streams Requires synchronization Dispersion 2003 932 3,355 808 2004 1,243 4,225 932 2005 1,553 5,468 1,025 2006 2,113 6,711 1,305 IXC = Interexchange Carrier (AT&T, Sprint, MCI) ILEC = Incumbent Local Exchange Carrier (SBC, GTE) CLEC = Competitive Local Exchange Carrier Source: KMI Corp. Wavelength Division Multiplexing Evolution of Optical Fiber Communication Signals on different wavelengths multiplexed onto same fiber Each wavelength can operate at peak electronic rates 40 40 40 1950 s - Fibers used for medical imaging applications Loss of 1 db/m (20% loss/m or 99% loss after 20 m) 1960 - Invention of laser Development of free-space optical communication systems 1966 - Charles Kao proposes optical fiber for communications 1970 - First low-loss fiber developed at Corning by Maurer, Keck, and Schultz Attenuation of 17 db/km 1977 - First commercial system deployed by AT&T Multimode fiber Attenuation of 2 db/km 45 Mbps over 7 km distance limited by modal dispersion 3
Evolution of Optical Fiber Communication Telecommunication Network Overview Early 80 s - Deployment of single-mode systems Attenuation of 0.5 db/km for 1300 nm laser 180 Mbps over 20-40 km distance limited by attenuation Mid 80 s - Deployment of 1550 nm single-mode systems Attenuation of 0.2 db/km 400 Mbps over 40-80 km limited by chromatic dispersion Early 90 s - Development of Erbium-doped fiber amplifiers (EDFA) Enabled all-optical amplification of signals in 1550 nm band 2.5 Gbps over 600 km Mid 90 s - WDM systems deployed 40 wavelengths at 2.5 Gbps per wavelength Emerging systems capable of 100 s wavelengths at 40 Gbps per wavelength Optical Network Architecture Evolution Long-haul, metro, metro access Point-to-point systems Add-drop systems Wavelength-routed networks Optical packet/burst-switched networks Last-mile access Twisted pair Coax Hybrid fiber coax networks Passive optical networks (PONs) for FTTH/FTTP Broadcast-and-select optical networks? Local area networks Ethernet Wireless Ethernet over fiber Point-to-Point Systems Point-to-point systems Fiber replaces copper Switching still done electronically Deployed in most long-haul backbone networks Electronic switching: SONET OC-192 (10 Gb/s), OC-48 (2.5 Gb/s) Can be used for Ethernet connections Design issue how to increase link capacity Multifiber solution best for short distances WDM solution best for longer distances (> 50 km) Higher electronic speed solution, e.g. OC-768 (40 Gb/s) Add-Drop Systems Add-drop systems Typically used in ring or linear network topologies Wavelengths can traverse node all-optically Reduces cost (number of transmitters/receivers at each node) Reduces electronic processing requirements Add-Drop Systems Reconfigurable optical add-drop multiplexers (ROADMS) Allow add-drop function to be reconfigured dynamically Increasingly being deployed in long haul and metro networks Provides greater flexibility to service providers Reconfiguration can be automated Quick activation of new services Partially driven by prospect of IPTV in metro networks 4
Optical Circuit-Switched (OCS) Networks Wavelength-routed systems Optical switching of wavelengths from input fibers to output fibers Optical cross-connects provide switching at wavelength granularity Configuration of optical cross-connect may be either static or dynamic Wavelength-Routed Networks Can establish lightpaths optical end-to-end connections Spatial re-use of wavelengths Switching may be all-optical (transparent) or may involve conversion of the signal to electronics (opaque) In absence of wavelength converters, lightpath must occupy same wavelength on entire route wavelength continuity constraint Optical Cross-Connect (OXC) Configurations Opaque vs. Transparent OXC O/E Electrical core Optical core Optical core Optical core E/O Electrical-core OXC Optical-core OXC (Opaque) Fully-optical OXC (Opaque) All-Optical Network (Transparent) Opaque Allows regeneration of signal Allows conversion from one wavelength to another Must be aware of bit rate and signal format OXC and interfaces more expensive Transparent Bit-rate-independent: can increase bit rate without upgrading equipment Lower-cost interfaces Imposes wavelength-continuity constraint if no all-optical wavelength converters are available Optical signal quality issues: limits to how far a signal can be transmitted all-optically Opaque OXCs have been deployed in long haul networks Design Issues in OCS Networks Design Issues in OCS Networks Static design problems: design a network given traffic demands Dynamic design problems: allocate resources for dynamically arriving and departing requests Network dimensioning: grow existing network to meet expected traffic growth Logical topology design What lightpaths to set up to meet a given traffic demand Routing and wavelength assignment Given one or more lightpath requests, find a route and assign a wavelength to each request Traffic grooming Establish lightpaths and assign traffic to lightpaths Objectives: Efficient allocation of resources - minimize cost, maximize utilization Fast provisioning of resources Guarantees with respect to service 5
Design Issues in OCS Networks Optical Network Survivability Control and signaling Maintaining and distributing network state information Reserve network resources for a given lightpath GMPLS deployment issues Survivability Reserve spare capacity to protect against network failures Protection Reserve back-up resources in advance Guarantees survivability for any single link failure Costly in terms of resources used Restoration Find spare resources after failure has occurred No need to reserve extra resources in advance No guarantee that resources will be available Partial protection/maximum survivability Consider probability of link failures Reserve resources to maximize probability of survivability Emerging Problems in OCS Networks Optical Packet/Burst Switching Advanced reservation/scheduled lightpaths Cross-layer design Physical impairment-aware network design Multi-layer and cross-layer survivability Service differentiation Differentiated QoS Differentiated reliability/survivability Optical multicast Optical packet/burst switching Data switched all-optically on packet-by-packet or burst-by-burst basis Control/header information may be processed electronically Design issues Contention multiple packets head to same output at same time Problem: lack of optical storage technology Quality of Service meeting delay and loss requirements Goal: Provide services to support requirements of emerging applications Issues in Optical Burst Switching (OBS) OBS Research Directions Burst Assembly Scheduling Benefits Flexible allocation of network bandwidth Reduced control overhead Challenges Compensation for lack of optical buffers Support for different applications and classes of traffic (QoS) Signaling Routing Contention Resolution Suitability of OBS for emerging traffic and applications On-demand bulk data transfer Grid computing Storage area networks Voice over IP Video and multimedia Comparison of OBS with alternative architectures Optical packet switching Electronic packets over optical circuits Hybrid optical burst/circuit switched networks Interaction of OBS with higher-layer protocols TCP/UDP over OBS SONET over OBS Proof of concept Experiments and testbeds 6
Optical Packet Switching (OPS) Challenges for OPS Packet Optical Packet-Switched Network Packet consists of payload (data) and header Packets switched directly in the optical domain Reconfigure switch on packet-by-packet basis based on packet headers Higher degree of multiplexing Fast switching time in order of ns At 10 Gbps, 1500 bytes, 1.2 us At 40 Gbps, 1500 bytes, 0.3 us Technologies MEMs: 10 ms Liquid crystal: 4 ms SOA: 1 ns Electro-Optic: 4-10 ns Synchronization Header processing Lack of optical processing Contention Resolution Lack of optical RAM storage Fiber delay line buffer architectures Switching times Optical Access Networks: Hybrid Fiber Coax Optical Access Networks: PONs Passive optical networks (PONs) for last-mile access Recent deployments: AT&T U-Verse Verizon FiOS (Fiber Optic Service) Diagram: http://www.cabledatacomnews.com/cmic/diagram.html Broadcast-and-Select Optical Networks Passive Star Coupler optical broadcast device Nodes equipped with one or more transmitters and one or more receivers Transmitters and receivers may either be fixed to a single wavelength or tunable to different wavelengths Receiving node must have receiver fixed/tuned to same wavelength as sending node s transmitter Challenges for Access Networks MAC protocols Dynamic bandwidth allocation Scheduling 7
Outline of Course Introduction Overview and motivation Historical evolution Research issues Optical components and technology Wavelength-routed (circuit-switched) optical networks Static network design RWA, logical topology design, traffic grooming Dynamic network design RWA, signaling, blocking probability analysis Protection and restoration Optical burst switching Signaling Contention resolution Scheduling QoS Photonic packet switching Contention resolution buffering, deflection, wavelength conversion QoS Optical metro and access networks Resource Reservation for Distributed Computing Applications over Optical Networks Many emerging distributed computing applications Grid computing Storage area networking Distributed content distribution Distributed computing applications require Network resources for transferring data End-node resources for computation, storage, etc. Distributed Computing Jobs Scheduling/Resource Reservation Problem Jobs can be divided into tasks Task properties Amount of data Starting time constraints Ending time constraints (deadline) Required processing time Independent vs. dependent Parallel vs. sequential Shared data vs. partitioned data Schedule/reserve network resources Immediate reservation Reserve if resources available now, otherwise block Advance reservation Schedule/reserve resources at earliest available time Schedule/reserve computing resources Immediate reservation Reserve if resources available now, otherwise block Advance reservation Schedule/reserve resources at earliest available time Queue tasks Wait in queue for resource to become available Joint vs. independent network/computing resource reservation Network Resource Reservation Computing Resource Reservation Routing problem Fixed routing independent of state of network and computing resources Adaptive routing depends on state of network and/or computing resources Adaptive to network resources Adaptive to computing resources Adaptive to both State information distribution for adaptive Centralized vs. distributed Global vs. local information Accuracy of state information Frequency of updates Destination selection problem Fixed Depends on physical topology, total amount of network resources, total amount of computing resources at each node Closest destination(s) Destination with most resources Adaptive Depends on current state/availability of resources Shortest available paths Most available resources State information update issues Resource selection problem How many resources to request from each destination 8
Objectives Unicast and Multicast Minimize resources consumed Minimize completion time Unicast Given Network Source node Destination node Find Route from source to destination Multicast Given Network Source node Set of destination nodes Find Routes (spanning tree) from source to destinations Anycast and Manycast Optical multicast Anycast Given Network Source node Set of candidate destinations Find One destination out of candidate destinations Route from source to selected destinaiton Manycast Given Network Source node Set of candidate destinations Number of required destinations, k Find Selection of k destinations out of set of candidate destinations Routes from source to selected k destinations Optical multicasting through optical splitters From one input to multiple outputs Fixed or adjustable optical splitters Optical multicast vs. IP multicast No expensive conversion No expensive electronic switches Higher degree of data transparency More efficient in data replication Optical splitter Multicast capable OXCs Manycasting over OBS networks Problem definition Given: a WDM OBS network and bursty dynamic manycast requests Find: a subset of the destinations and a route for the requests Objective: minimize data loss probability Related work The manycast problem is proven to be NP-hard Routing algorithms to minimize the cost of the tree No work has been done on supporting manycasting over OBS networks 9
Our solution New schemes Challenges Finding an optimal solution is NP-hard Real time demand on routing Data loss due to burst contention Our focus Not on optimal routing for each manycast request Instead on the data loss issue of OBS networks Our solution A shortest-path tree based routing algorithm Two new schemes to reduce data loss Static over-provisioning (SOP) Instead of selecting K destinations, we select k + k destinations Even the burst to some destinations are lost, the total number of destinations which actually receive the burst may still be K or more Dynamic membership (DM) K destinations are not decided at the source node If some destinations are blocked along the route tree, we will try to send the burst to some other destinations. Static over-provisioning Dynamic membership with SOP DM Plain manycast SOP & DM Multi-Resource Manycast over Optical Burst Switched Networks 10
Distributed Computing Architecture Optical network Links and switching nodes Circuit-switched, packet-switched, or burst-switched Destination-node resources Computing or storage devices With or without queueing Different destination nodes may have identical resources Multi-Resource Manycast (MRM) Given A network The number of available resources at each destination node A multi-resource manycast request (s, Dc, r ) s - the source node Dc - the set of destination nodes which have available computing resources r - the number of computing resources required by the request Find A selected set of destination nodes The number of resources requested from each selected destination The routes from the source to each selected destination node Objective Minimize resource blocking rate Blocking due to contention in the OBS network Blocking due to contention for resources at destination nodes Destination Selection Heuristics Destination Selection Heuristics Cont. Closest Destination First (CDF) Source node first selects nearest destination which has available resources (0) (2) B D Request (A, {C, D, E}, 6) Most Available First (MAF) Random Selection (RS) A (0) C E (3) (4) Closest Destination First (CDF) Most Available First (MAF) Source node first selects destination nodes that have greatest number of available resources Request (A, {C, D, E}, 6) Random Selection (RS) A (0) (0) B (2) D C E (3) (4) Destination Selection Heuristics Cont. Resource Selection Policy Closest Destination First (CDF) Most Available First (MAF) Random Selection (RS) Randomly chooses a destination with uniform probability among the destinations with available resources Greedy Reserve maximum possible number of resources from each destination Limit per Destination (LpD) Sets a limit on the maximum number of allocated resources per destination Td = maximum fraction of destination s resources that can be requested by a job Request (A, {C, D, E}, 4), Td= 50% (0) B (2) (1) D A (0) C E (6) (3) (4) (2) 11
Produced Bursts per Request (with Greedy Resource Selection) Resource Blocking Rate (with Greedy Resource Selection) Request Arrival Rate 1 request/ms 3 request/ms 5 request/ms 7 request/ms CDF 1.86456 1.97905 2.0884 2.21874 MAF 1.81392 1.78001 1.8078 1.81355 RS 1.8352 1.92495 2.0719 2.13229 Resource Blocking Rate with Limit per Destination 12