smucse 8344 optical networks introduction. smucse 8344 why optical? bandwidth low cost ($0.30/yard)...
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SMU CSE 8344
Optical Networks
Introduction
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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
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History
– 1st Generation: Copper is transmission medium
– 2nd 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
– 3rd Generation: Intelligent optical networking (1999)
• Routing and signaling for optical paths
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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
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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
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Wavelength Division Multiplexing(WDM)
40 - 120 km(80 km typically)
Up to 10,000 km(600 km in 2001 basic commercial products)
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WDMMux
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Frequency-registeredtransmitters
Receivers
All-Optical AmplificationOf Multi-Wavelength Signal!!!
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Regenerators
• 3R– Reshaping– Re-clocking– Amplification
• 2R– Reshaping– Amplification
• 1R (Example – EDFA)– Amplification
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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
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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
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Enabling Technologies
• Fiber and laser technology• EDFA• MEMS (Micro-Electro Mechanical
Systems)• Opaque vs. all-optical networks
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Current Protocol Stack
IP
ATM
SONET
WDM
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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
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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
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The Roadmap
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WDM
Network Architecture
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Classes of WDM Networks
• Broadcast-and-select• Wavelength routed• Linear lightwave
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Broadcast-and-Select
Passive
Couplerw1
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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.
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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
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A WR Network
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OXC
IP SONET
SONET
IP
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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
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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
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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
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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
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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
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Wavelength Assignment
• For the network with wavelength conversion capability, wavelength assignment is trivial
• For the network with wavelength continuity constraint, use heuristics
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Wavelength Assignment under Wavelength Continuity Constraint
• First-Fit (FF)• Least-Used (LU)• Most-Used (MU)• Max_Sum (MS)• Relative Capacity Loss (RCL)
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First-Fit
• All the wavelength are indexed with consecutive integer numbers
• The available wavelength with the lowest index is assigned
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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
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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.
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