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Optical Networks 2008 Topics • Optical Links – Light Sources, Detectors and Receivers – Optical Fiber Channel – Optical Amplifiers • Digital Optical Communications – Time and Wavelength Multiplexing – Optical Cross-Connects (OXC) • Optical Networks – First Generation Optical Networks and SONET – Second Generation Optical Networks • Multi Protocol Lambda Switching • DWDM optoelectrical metro network Review of Optics • What is a monochromatic wave • Polarization of light • Interaction between Light and Matter Total Internal Reflection and Absorption • Diffraction • Interference Light Sources • LED -- Light emitter diodes • Laser diodes • Single mode laser diodes Detectors and Receivers • Solid state detectors • PIN diode • Circuit noise and signal to noise ratio in a receiver • Direct detection and bit error rate • Avalanche photodiodes (APD) Detectors and Receivers (cont.) Optical Fiber Channel (1) • Total internal reflection in a optical fiber • Telecommunications industry uses two windows: 1310 & 1550 nm – 1550 window is preferred for long-haul applications (Less attenuation, Wider window, Optical amplifiers) Optical Fiber Channel (2) • Multimode fibers and their limitations Optical Fiber Channel (3) • Single mode fibers and limitations • Non-linearities in fibers • Coupling light in a fiber and connecting two fibers Fiber Amplifiers erbium doped fiber amplifiers (EDFA) Semiconductor Optical Amplifiers (SOA) Topics • Optical Links – Light Sources, Detectors and Receivers – Optical Fiber Channel – Optical Amplifiers • Digital Optical Communications – Time and Wavelength Multiplexing – Optical Cross-Connects (OXC) • Optical Networks – First Generation Optical Networks and SONET – Second Generation Optical Networks • Multi Protocol Lambda Switching • DWDM optoelectrical metro network Digital Optical Communications • Signal Quantization / Coding: from analog to digital signal and vice versa • Digital Modulation: Amplitude, Phase, and Frequency Modulation • Multiplexing to increase the bandwidth of an optical channel – Time Division Multiplexing – Wave Division Multiplexing (WDM) • WDM vs. DWDM Digital Optical Communications (cont) DWDM 2.488 Gbps (1) 1310/1510 nm 2.488 Gbps (16) λ1 λ2 λ3 λ4 λ5 λ16 1530-1565 nm ramge 1310/1510 nm 16 uncorrelated wavelengths 16*2.488 Gbps = 40 Gbps 16 stabilized, correlated wavelengts Fiber Optics Transmission Optical Switch • 1-input 2-outoput illustration with four wavelengths Input & Output fiber array Wavelength Dispersive Element 1-D MEMS Micro-mirror Array Input Fiber Output Fiber 1 1011 Digital Mirror Control Electronics Output Fiber 2 • 1-D MEMS (micro-electromechanical system) with dispersive optics – Dispersive element separates the ’s from inputs – MEMS independently switches each – Dispersive element recombines the switched ’s into outputs All-Optical Switching • Optical Cross-Connects (OXC) – Wavelength Routing Switches (WRS) – route a channel from any I/P port to any O/P port • Natively switch s while they are still multiplexed • Eliminate redundant optical-electronic-optical conversions DWDM Demux DWDM Fibers in DWDM Mux DWDM Fibers out All-optical DWDM Demux OXC DWDM Mux Optical Add-Drop Multiplexor (OADM) 1 2 1 OADM 2 3 ’3 3 ’3 Wavelength () Converters (WC) improve utilization of available wavelengths on links needed at boundaries of different networks all-optical WCs being developed greatly reduce blocking probabilities 3 3 2 2 WC 1 1 New request 1 3 New request 1 3 No Wavelength converters With Wavelength converters Topics • Optical Links – Light Sources, Detectors and Receivers – Optical Fiber Channel – Optical Amplifiers • Digital Optical Communications – Time and Wavelength Multiplexing – Optical Cross-Connects (OXC) • Optical Networks – First Generation Optical Networks and SONET – Second Generation Optical Networks • Multi Protocol Lambda Switching • DWDM optoelectrical metro network Optical Networks • 1 st Generation: optical fibers substitute copper as physical layer – Submarine Systems – SONET (synchronous optical) in TDM – FDDI for LAN, Gbit Ethernet etc. • 2 nd Generation: optical switching and multiplexing/ WDM – broadcast-and-select networks – WDM rings – wavelength routing networks • 3 th Generation: optical packet switching??? Big Picture Data Center SONET SONET DWD M DWD M SONET SONET Access Metro Long Haul Metro Access SONET • Encode bit streams into optical signals propagated over optical fiber • Uses Time Division Multiplexing (TDM) for carrying many signals of different capacities – A bit-way implementation providing end-to-end transport of bit streams – All clocks in the network are locked to a common master clock – Multiplexing done by byte interleaving Practical SONET Architecture ADM – Add-Drop Multiplexer DCS – Digital Crossconnect Protection Technique Classification • Restoration techniques can protect network against: – Link failures • Fiber-cables cuts and line devices failures – Equipment failures • OXCs, ADMs, electro-optical interface. • Protection can be implemented – In the optical channel sublayer (path protection) – In the optical multiplex sublayer (line protection) • Different protection techniques are used for – Ring networks – Mesh networks Path Protection / Line Protection Normal Operation Path Switching: restoration is handled by the source and the destination. Line Switching: restoration is handled by restoration is handled the nodesby adjacent the nodestoadjacent the failure. to the Span Protection: if failure. additional fiber is available. Line Protection. Shared Protection Normal Operation 1:N Protection • Backup fibers are used for protection of multiple links • Assume independent failure and handle single failure. • The capacity reserved for protection is greatly reduced. In Case of Failure Protection in Ring Network (Unidirectional Path Switched Ring) 1+1 Path Protection Used in access rings for traffic aggregation into central office (Bidirectional Line Switched Ring) 1:1 Span and Line Protection Used in metropolitan or long- haul rings 1:1 Line Protection Used for interoffice rings Protection in Mesh Networks • Network planning and survivability design – Disjoint path idea: service working route and its backup route are topologically diverse. – Lightpaths of a logical topology can withstand physical link failures. Working Path Backup Path Trend: IP over DWDM • • • • IP is good for routing, traffic aggregation, resiliency ATM for multi-service integration, QoS/signaling SONET for traffic grooming, monitoring, protection DWDM for capacity IP over DWDM: Why? • • • • • IP and DWDM => Winning combination – IP for route calculation, traffic aggregation, protection – DWDM => Cheap bandwidth – Avoid the cost of SONET/ATM equipmnt IP routers at OC-192 (10 Gbps) => Don't need SONET multiplexing Optical layer for route provisioning, protection, restoration Coordinated restoration at optical/IP level Coordinated path determination at optical/IP level • MPS MPS = Multi-Protocol Lambda Switching – MPLS + OXC – Combining MPLS traffic eng control with OXC • All packets with one label are sent on one wavelength • Next Hop Forwarding Label Entry (NHFLE) – <Input port, > to <output port, > mapping DWDM Summary • • • • • • DWDM => Switching Bottleneck => O/O/O switches High speed routers => IP directly over DWDM Data and control plane separation => IP Control Plane Data will be circuit switched in the core IP needs to be extended to provide addressing, signaling, routing, and protection for lightpaths High-speed point-to-point Ethernet => LANWAN convergence The Current Home Service System Copper pair telephone line Satellite dish The Optoelectrical Multip-Service System Telepnone To telephone company backbone Satellite dish Internet Router To the Internet for modem connections Satellite dish Satellite dish Copper pair telephone line Copper pair telephone line Coxial cable (50/75 O) To telephone backbone Internet RouterTo the Internet for cable modems Sigle mode Fiber cable Coxial cable (75 O) Cable TV company Multip-Service Company To cable TV network To the Internet To cable TV network Why Optical Networks? DWDM optoelectricl metro network