Optical Networks Introduction SMU CSE 8344 Why Optical

Optical Networks Introduction SMU CSE 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 SMU CSE 8344

History – 1 st Generation: Copper is transmission medium – 2 nd Generation: Optical Fiber (late 80 s) • 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 SMU CSE 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 SMU CSE 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 SMU CSE 8344

Wavelength Division Multiplexing (WDM) Frequency-registered transmitters l 1 Receivers R All-Optical Amplification Of Multi-Wavelength Signal!!! R l 2 WDM Mux l 3 OA OA WDM De. Mux R 40 - 120 km (80 km typically) l. N Up to 10, 000 km (600 km in 2001 basic commercial products) SMU CSE 8344 R

Regenerators • 3 R – Reshaping – Re-clocking – Amplification • 2 R – Reshaping – Amplification • 1 R (Example – EDFA) – Amplification SMU CSE 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 SMU CSE 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 SMU CSE 8344

Enabling Technologies • • Fiber and laser technology EDFA MEMS (Micro-Electro Mechanical Systems) Opaque vs. all-optical networks SMU CSE 8344

Current Protocol Stack IP ATM SONET WDM SMU CSE 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 SMU CSE 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 SMU CSE 8344

The Roadmap SMU CSE 8344

WDM Network Architecture SMU CSE 8344

Classes of WDM Networks • Broadcast-and-select • Wavelength routed • Linear lightwave SMU CSE 8344

Broadcast-and-Select Passive Coupler SMU CSE 8344 w 0 w 1

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. SMU CSE 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 SMU CSE 8344

A WR Network H I OXC G J F B A K 1 3 SONET 1 2 IP SMU 1 IP E 2 1 D O C N L M SONET CSE 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 SMU CSE 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 subproblems: – Routing – Wavelength assignment • Static vs. dynamic lightpath establishment SMU CSE 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 SMU CSE 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 SMU CSE 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 SMU CSE 8344

Wavelength Assignment • For the network with wavelength conversion capability, wavelength assignment is trivial • For the network with wavelength continuity constraint, use heuristics SMU CSE 8344

Wavelength Assignment under Wavelength Continuity Constraint • • • First-Fit (FF) Least-Used (LU) Most-Used (MU) Max_Sum (MS) Relative Capacity Loss (RCL) SMU CSE 8344

First-Fit • All the wavelength are indexed with consecutive integer numbers • The available wavelength with the lowest index is assigned SMU CSE 8344

Least-Used and Most-Used • Least-Used • Most-Used – Record the usage of each wavelength – Pick up a wavelength, which is least used before, from the available wavelength pool SMU – Record the usage of each wavelength – Pick up a wavelength, which is most used before, from the available wavelength pool CSE 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. SMU CSE 8344