SMUCSE 8344 Why Optical? Bandwidth Low cost ($0.30/yard) Extremely low error rate (10 -12 vs. 10 -6 for copper Low signal attenuation Low power requirement More secure
SMUCSE 8344 History –1st Generation: Copper is transmission medium –2 nd Generation: Optical Fiber (late 80s) Higher data rates; longer link lengths –Dense Wavelength-Division Multiplexing (DWDM, 1994) Fiber exhaust forces DWDM Erbium-doped fiber amplifiers (EDFAs) lower DWDM transmission cost –3 rd Generation: Intelligent optical networking (1999) Routing and signaling for optical paths
SMUCSE 8344 Medium Characteristics Attenuation: –Wavelength dependent –0.85, 1.3, 1.55 micron windows –Attenuation caused by impurities as well as scattering Dispersion –Inter-modal –Chromatic
SMUCSE 8344 Wavelength Division Multiplexing (WDM) All the bandwidth could not be used due to the electronic bottleneck Two breakthroughs –WDM –Erbium-doped fiber amplifier (EDFA) WDM vs. FDM –WDM is passive and hence reliable –WDM carrier frequency orders of magnitude higher
SMUCSE 8344 Wavelength Division Multiplexing (WDM) 40 - 120 km (80 km typically) Up to 10,000 km (600 km in 2001 basic commercial products) OA 1 2 3 N WDM Mux R R R R WDM DeMux Frequency-registered transmitters Receivers All-Optical Amplification Of Multi-Wavelength Signal!!!
SMUCSE 8344 DWDM Evolution –Faster (higher speed per wave), 40 Gb/s on the horizon –Thicker (more waves), 160 waves possible today –Longer (link lengths before regeneration) A few thousand km possible today –160 waves at 10 Gb/s = 1.6 Tb/s 25 million simultaneous phone calls 5 million books per minute
SMUCSE 8344 WADMs & WXC WADM (Wave Add-Drop Mux) –Evolution from p-t-p –Can add and drop traffic at various locations WXC (Wave crossconnect) –Similar to ADM except that multiple fibers on the input side with the capability to switch colors between fibers
SMUCSE 8344 Enabling Technologies Fiber and laser technology EDFA MEMS (Micro-Electro Mechanical Systems) Opaque vs. all-optical networks
SMUCSE 8344 Current Protocol Stack IP ATM SONET WDM
SMUCSE 8344 How Did We Get Here? SONET over WDM –Conventional WDM deployment is using SONET as standard interface to higher layers IP over ATM –IP packets need to be mapped into ATM cells before transporting over WDM using SONET frame OEO conversions at every node is easier to build than all optical switch
SMUCSE 8344 Problems with Multilayer Inefficient –In IP over ATM over SONET over WDM network, 22% bandwidth used for protocol overhead Layers often do not work in concert –Every layer now runs at its own speed. So, low speed devices cannot fill the wavelength bandwidth. –Under failure, different layers compete for protection
SMUCSE 8344 Wavelength Routed An OXC is placed at each node End users communicate with one another through lightpaths, which may contain several fiber links and wavelengths Two lightpaths are not allowed to have the same wavelength on the same link.
SMUCSE 8344 WRN (cont’d) Wavelength converter can be used to convert a wavelength to another at OXC Wavelength-convertible network. –Wavelength converters configured in the network –A lightpath can occupy different wavelengths Wavelength-continuous network –A lightpath must occupy the same wavelength
SMUCSE 8344 A WR Network B A C D E F G H I J K L M N O 1 2 3 2 1 1 1 OXC IP SONET IP
SMUCSE 8344 Linear Lightwave Networks Granularity of switching in wave bands Complexity reduction in switches Inseparability –Channels belonging to the same waveband when combined on a single fiber cannot be separated within the network
SMUCSE 8344 Routing and Wavelength Assignment (RWA) To establish a lightpath, need to determine: –A route –Corresponding wavelengths on the route RWA problem can be divided into two sub- problems: –Routing –Wavelength assignment Static vs. dynamic lightpath establishment
SMUCSE 8344 Static Lightpath Establishment (SLE) Suitable for static traffic Traffic matrix and network topology are known in advance Objective is to minimize the network capacity needed for the traffic when setting up the network Compute a route and assign wavelengths for each connection in an off-line manner
SMUCSE 8344 Dynamic Lightpath Establishment (DLE) Suitable for dynamic traffic Traffic matrix is not known in advance while network topology is known Objective is to maximize the network capacity at any time when a connection request arrives at the network
SMUCSE 8344 Routing Fixed routing: predefine a route for each lightpath connection Alternative routing: predefine several routes for each lightpath connection and choose one of them Exhaust routing: use all the possible paths
SMUCSE 8344 Wavelength Assignment For the network with wavelength conversion capability, wavelength assignment is trivial For the network with wavelength continuity constraint, use heuristics
SMUCSE 8344 First-Fit All the wavelength are indexed with consecutive integer numbers The available wavelength with the lowest index is assigned
SMUCSE 8344 Least-Used and Most-Used Least-Used –Record the usage of each wavelength –Pick up a wavelength, which is least used before, from the available wavelength pool Most-Used –Record the usage of each wavelength –Pick up a wavelength, which is most used before, from the available wavelength pool
SMUCSE 8344 Max-Sum and RCL Fixed routing MAX_SUM Chooses the wavelength, such that the decision will minimize the capacity loss or maximize the possibility of future connections. RCL will choose the wavelength which minimize the relative capacity loss.