TCOM 503 Fiber Optic Networks Spring, 2006 Thomas B. Fowler, Sc.D. Senior Principal Engineer...
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Transcript of TCOM 503 Fiber Optic Networks Spring, 2006 Thomas B. Fowler, Sc.D. Senior Principal Engineer...
TCOM 503Fiber Optic Networks
Spring, 2006
Thomas B. Fowler, Sc.D.
Senior Principal Engineer
Mitretek Systems
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Course overview
This course, together with TCOM 513, presents basic material needed to understand optical communications– Physical principles of optical devices and networks – Components of fiber optic systems and how they
function– Light as a communications medium: modulation, noise,
detection of signals– How these components work together to create useful
fiber optic networks– How fiber optic networks are used to create large-scale
communications networks– How all-optical networks will function, and their
advantages and problems
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Course goal
Impart general background on optical communications Enable students to undertake more detailed study of any
aspect of optical communications Give enough information so that students become informed
consumers and decision makers on many optical communications issues
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Course organization
7 weeks Main text: Understanding Optical Communications, Harry
Dutton, Prentice-Hall, 1998 Supplementary text: Fiber Optic Communications, 4th
Edition, Joseph C. Palais, Prentice-Hall, 1998 Other material to be downloaded from Internet (see
syllabus) Student evaluation
– Homework 40%– Project outline 20%– Final exam 40%
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Topics for TCOM 503
Week 1: Overview of fiber optic communications Week 2: Brief discussion of physics behind fiber optics Week 3: Light sources for fiber optic networks Week 4: Fiber optic components fabrication and use Week 5: Modulation of light, its use to transmit information Week 6: Noise and detection Week 7: Optical fiber fabrication and testing of components
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Week 1: Overview of fiber optic communications
Basics of communications systems Fiber optic networks compared to other networks Advantages of and drivers for optical networks Architecture of typical fiber optic networks Brief history of optical networking Fiber optic network terminology General communications systems background
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What is purpose of communications system?
To transfer information from one location to another
– Voice
– Data
– Video
– Audio Desirable attributes
– Fast
– Accurate
– Secure
– Scalable
– Routable/switchable
– Capable of handling multiple types of information (data)
– Cheap
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Components of a telecommuncations system—physical view
Source EncoderModulator/ transmitter
Receiver/ demodulator Decoder Receiver
Link
Cable
Microwave
Other wireless
Light
Smoke signals
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Components of a telecommuncations system—logical view
Source Interface Interface Receiver
Packet-switched network
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What is optical networking?
Use of optical components in place of electronic components in a network environment– Light waves (including infrared) as a medium for the
transmission or switching of data– Pure optical or all-optical networks use light exclusively
from end to end Most commonly, optical elements (optical fiber, optical
amplifiers) are used in transmission links– Known as opto-electronic networks (OEO)– Switching still done electronically (“in silicon”)– No pure optical networks at present– All-optical switching is a laboratory project at present,
though opto-mechanical systems exist which use flipping mirrors
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What is optical networking? (continued)
Long-term goal is the all-optical network, with all switching, transmission, and routing done optically– Conversion to/from electrical signals occurs only at
boundary– Likely to be commercialized within 5 years
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How are optical networks different?
Optical networks differ from conventional electronic or “wireline” networks– Rely upon light waves to carry data, rather than
electron-based transmission in wires Differ from conventional wireless networks
– Operate at much higher frequencies • Hundreds of terahertz vs. 30 GHz• Wavelength (l) of 1600 nm ~ 188 THz
– Use waveguides (in the form of optical fiber) to carry the data-bearing waves.
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Optical and electronic networks
Modulator
Input signal Connector Optional optical amplifier
Amplifier Decoder
Output signal
Optical fiber Optical fiber
Light Wavelength = 800-1600 nm
Electricity Electricity
Light source
Detector
Modulator
Input signal
Amplifier Decoder
Output signal
Electromagnetic Radiation Frequency = 100 Kz to 30 GHz Electricity Electricity
Trans-mitter
Detector Receiver
CSU/DSU
Input signal Optional repeater amplifier
CSU/DSU
Output signal
T1, T45 cable T1, T45 cable
Electricity
Opt
ical
Ele
ctro
nic
Wire
less
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Why optical networks?
Advantages Cost-effective bandwidth Noise isolation Security Smaller physical presence Readily upgradable
Drivers Demand for bandwidth Commoditization of optical
networking components Reduced number of
components Shorter service contracts Promise of rapid provisioning
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Advantages
Cost-effective bandwidth– Above a certain threshold price per unit of bandwidth is
lower– For very high bandwidths (~Gbit/second and higher)
and even relatively short distances (~100 m), optical fiber is usually the only practical choice
Noise isolation– Optical fibers are not affected by electrical noise-
producing sources• Can be used in environments where adequate
shielding of electrical cables would be difficult or impossible
– Only in environments with high levels of radioactivity is there a potential problem
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Advantages (continued)
Greater security– Optical fiber does not emit electromagnetic radiation
which can be intercepted• Much more secure than many other types of wiring,
such as category 5 untwisted pair used for Ethernet applications
– Tapping optical fiber is also much more difficult Smaller physical presence
– Single optical fiber cable with a diameter of less than 6 mm can replace a bulky cable with hundreds of wires
– Critical in applications where space is at a premium• Ships and aircraft• Retrofitting buildings and rewiring cities, where
space in conduits may also be very limited
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Advantages (continued)
Ready upgrade path– Constant improvements to fiber optic cable itself– In most cases, increased bandwidth can be had by
installing new optical multiplexing equipment
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Disadvantages
Higher cost per meter Greater difficulty in splicing and maintenance
– Technicians need to be retrained Need to convert optical signals back to electronic signals
for processing
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Supply
Exuberance of late 90s and early 2000s led to huge volumes of fiber put in the ground
New technologies mean more bandwidth even from existing fibers
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Drivers
Huge and insatiable demand for bandwidth—cooled after dot com crash– May have been hyped all along– But developments such as more video on Internet and
anticipated use of Internet for video delivery in future will require optical connections to or close to homes
Commoditization of optical network components enables more powerful and economical networks to be built
Reduced number of components means network simplification and equipment consolidation
Shorter service contracts implies faster depreciation and more rapid replacement of equipment with newer technology
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Relative cost per DS3 (45 mbit/sec) mile
Source:Qtera Networks/NGN99PPN=Purely Photonic Networks
0%
20%
40%
60%
80%
100%
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
Year
Co
st
Re
lati
ve
to
19
80
6 GHz Digital Radio
405 MB/s
565 MB/s
810 MB/s
1.2 GB/s
1.8 GB/s
2.4 GB/s
10 GB/sWDM 10 GB/s
PPN 10 GB/s
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Evolution of optical networks
Source: Sycamore Networks/NGN 99
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Problems with end-end all-optical networks
Physical limitations of devices still limit scalability and performance of optical networks
Multi-vendor environment and rapidly evolving technology limits plug-and-play compatibility
Subnetworks are easier to monitor and manage
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Optical network capacity vs. distance
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Schematic diagram of typical optical network today
Source: Sycamore Networks/NGN 99
Source Encoder Modulator/ transmitter
ReceiverDecoderReceiver/ demodulator
Link
end user services
end userservices
SONET
SONET
DWDM
DWDM
SONET
SONET
end user services
end user services
1
n
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Simplified optical network with ring architecture
Source: Tektronix
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History of optical communications systems
Glass invented, c. 2500 BC Fires have been used for signaling since Biblical times
– Famous opening of Aeschylus’ play Agamemnon (c. 458 BC):
I wait; to read the meaning in that beacon light,a blaze of fire to carry out of Troy the rumorand outcry of its capture….
Smoke signals have also been used for thousands of years, most notably by Native Americans
Lanterns in Boston’s Old North Church used to signal Paul Revere on his famous ride (1775)
Flashing lights used on ships for communication since time of Lord Nelson (1758-1805)
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History of optical communications systems (continued)
Optical telegraph built in France during 1790s by Claude Chappe– Signalmen occupied a series of towers between Paris and Lille,
230 km– Signals relayed using movable signal arms– 15 minutes to send a message
In 1840, Daniel Colladon demonstrated light guiding in jet of water in Geneva – Used in opera Faust, 1853, by Paris Opera
In 1870, John Tyndall demonstrated principle of guiding light through internal reflections, using a jet of pouring water (duplicating Colladon’s work)
In 1880, Alexander Graham Bell patented photophone, which utilizes unguided light bounced off of vibrating mirrors to carry speech– Intended for long distance– Didn’t work in cloudy weather
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History of optical communications systems (continued)
Also in 1880, William Wheeler invented system of light pipes to direct light around homes– Pipes lined with a highly reflective coating– Single electric arc lamp placed in the basement
In 1888, first use of bent glass rods to illuminate body cavities (medical team of Roth and Reuss of Vienna)
In 1895, early attempt at television by French engineer Henry Saint-Rene using a system of bent glass rods for guiding light images
In 1898, American David Smith applied for a patent on a bent glass rod device to be used as a surgical lamp
In 1920's, idea of using arrays of transparent rods for transmission of images for television and facsimiles respectively patented by Englishman John Logie Baird and American Clarence W. Hansell
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History of optical communications systems (continued)
In 1930, German medical student Heinrich Lamm was first person to assemble a bundle of optical fibers to carry an image
– Objective was to look inside inaccessible parts of the body (fiberscope)
– Images were of poor quality In 1954, Dutch scientist Abraham Van Heel and British scientist
Harold. H. Hopkins separately wrote papers on imaging bundles
– Van Heel had idea of cladding bare fiber with material of lower refractive index
In 1956, Narinder S. Kapany of Imperial College in London invented glass-coated glass rod, coined term fiber optics
– Not suited for communications
– Applications in fiberscopes
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History of optical communications systems (continued)
1960 – ruby lasers In 1961, Elias Snitzer of American Optical published theoretical
description of single mode fibers– Fiber with a core so small it could carry light with only one
wave-guide mode– Worked for a fiberscopes– Light loss too high for communications (one decibel per
meter) 1962 – lasers operating on semiconductor chips 1964 – C. K. Kao identifies that maximum loss of ~20 db/km
needed for communications– Corresponds to 1% of energy left after 1 km– Existing glasses not transparent enough– Speculated that losses of 1000 db/km result of impurities in
glass
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History of optical communications systems (continued)
1970 — Corning Glass researchers Robert Maurer, Donald Keck and Peter Schultz invent fiber optic wire or “Optical Waveguide Fibers”– Fused silica, which has high melting point, low refractive
index– “65,000” times more capacity than copper wire
By 1972, losses down to 4 db/km– Today, ~0.2 db/km
1973 — Navy installs fiber-optic telephone link on a ship In 1975, US Government links computers in the NORAD
headquarters at Cheyenne Mountain using fiber optics to reduce interference
In 1977, first optical telephone communication system installed– 1.5 miles long, under downtown Chicago– Each optical fiber carried the equivalent of 672 voice channels
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History of optical communications systems (continued)
1980 — first long distance fiber optic link (Boston-Richmond)
1984 — First SONET networks 1987 — fiber amplifiers invented by Dave Payne at U of
Southampton, UK 1988 — first transatlantic fiber optic link (AT&T) 1990s — Bragg filters 1997 — Wave division multiplexing (WDM) 2000 — dense wave division multiplexing (DWDM)
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Thrusts of fiber optics technology
As distribution mechanism for light To see in otherwise inaccessible places For high-speed communications
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Speed history
1790 — 5 bits 1977 — 44.7 Megabits 1982 — 400 Megabits 1986 — 1.7 Gigabits 1993 — 10 Gigabits 1996 — 1 Terabit 2002 — 3 Terabits
Comparison: entire world’s telephone traffic ~ 5 Tb/sec
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Optical network bandwidth is exploding
0
0.5
1
1.5
2
2.5
3
3.5
1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
Year
Fib
er
Cap
acit
y (T
bp
s)
1.7 Gbps135 Mbps565 Mbps OC-48
OC-192, 32
OC-192, 80
OC-192, 160
OC-192, 160
SONET ERA WDM ERA
OC-192, 320
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How widespread are optical networks?
Source: Teleglobe
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Fiber optic terminology
Lambda (): a single wavelength of light SONET: Synchronous Optical Network—a transport
technology for reliably sending information over optical fiber
Photonic: having to do with devices using light (photons) instead of electronics; analogous to “electronic”
Decibel (db): a unit of power gain or loss, relative to a source. Calculated as 10 log10 (P/Pref). If reference is 1 mw, expression “dbm” is often used.
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Types of optical networks
Present– Simplest: SONET + 1 wavelength of light ()– SONET + 2 – SONET + Dense wave division multiplexing (DWDM)
(many ’s) Future
– IP over ATM over SONET + DWDM– IP over ATM over SONET, private line + DWDM– IP over other transport layer– All optical networks
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World is changing with migration to data from voice
Data-driven network
• Ingress/egress ~2000 km• 80% long-haul, 20% short haul• Traffic statistics unpredictable• Annual growth rate ~30%
Voice-driven network
• Ingress/egress ~500 km• 80% short-haul, 20% long haul• Traffic statistics predictable• Annual growth rate ~7%
Source: Qtera Networks/NGN99
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General communications system background
Analog and digital signals Information theory Layered communications architectures
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Digital and analog signals
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Analog and digital transmission
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Parts of a pulse
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Information theory background
Sampling Digitizing Pulse code modulation Multiplexing
– Time– Frequency– Wave
Information content
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Sampling
Source: Cisco Systems
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Digitizing (quantizing)
Source: Cisco Systems
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Effect of quantizing
Source: U of Waterloo
8 bits/ sample
4 bits/ sample
3 bits/ sample
2 bits/ sample
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Pulse Code Modulation (PCM)
Prefiltering Sampling Quantizing Transmission or storage of string of numbers
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Multiplexing
Definition: combining multiple signals for transmission over a single line or medium
Types– Frequency division multiplexing (FDM): each signal
assigned a different frequency– Wavelength division multiplexing (WDM): each signal
assigned a particular wavelength () (a type of FDM)– Time division multiplexing (TDM): each signal assigned
a fixed time slot in a fixed rotation– Statistical time division multiplexing (STDM): time slots
assigned dynamically to signals based on characteristics to achieve better utilization
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FDM multiplexing details
Source: Kenneth Williams, NC A&T Univ.
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Wave division multiplexing details
Source: Los Alamos National Laboratory
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WDM demultiplexing
Source: Los Alamos National Laboratory
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Time division multiplexing details
Source: Kenneth Williams, NC A&T Univ.
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Time division multiplexing details (cont)
Source: Kenneth Williams, NC A&T Univ.
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Information content
Shannon showed that the capacity in bits/second of an additive white Gaussian noise channel is given by the famous Tuller-Shannon formula:
C = BW log2 (1 + S/N)
BW = transmission bandwidth S/N = signal-to-noise ratio
This capacity only available with optimal encoding Note that bandwidth cannot be larger than transmission
frequency, and typically is much smaller– Optical systems typically operate at frequencies of ~200
THz, so even a bandwidth of 1% of that is 2 THz, and with S/N of 100 gives capacity ~ 20 x 1012 bits/second
– Electronic systems, operating at 30 GHz or so are limited to about 3 x 109 bits/second
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Layered communications architecture
What it is How it works Why it is needed What it looks like
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Communications systems architecture
An architecture is the highest-level organization and dynamics of a system
What a layered communications architecture is– Hierarchically organized set of operations– Corresponding set of methods of encoding information– Permits the reliable transmission and reconstruction of
complex messages across multiple network segments Types of data communications systems
– Packetized– Non-packetized
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The five functions of a communications system
Put information into a form suitable for transmission Send information through a physical medium, utilizing
some type of channel– Due to physical constraints is always characterized by
degradation, including noise and distortion. At receiving end, extract or reconstruct the original
message, which is the lowest level logical entity which has meaning to the end systems. – May involve reassembly, decoding/decripting, and error
detection and correction. Route message to place where it needs to be used. Perform control and sequencing functions
– Ensure correct action taken for multiple messages
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Necessity of these functions
Functions (1) and (2) are necessary because transmission of information through a noisy channel requires special coding to minimize errors and maximize the transmission speed (Shannon’s Theorem)– Invariably means that information as transmitted is in
form completely different than that required for its ultimate use
Other three functions each require different processing capability– Usually translates to different physical hardware and
different software or its equivalent
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Necessity of these functions (continued)
Isolation of one function from another desirable because it permits changes to be made internally in the processing of each function which are invisible to other functions– Facilitates incremental optimization of the overall
system– Allows addition of new, higher-level functions by adding
new layer(s) to code
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Characteristics of layered architectures
Different parts of the requisite coding and processing are performed by separate layers
Output from each layer in a standard form Each layer contains a logical grouping of functions which
together provide a set of specific services. Services of layer N are available to layer N+1, and layer N in
turn utilizes the services of layer N-1 Break exists between the physical layers (those concerned
with information as coded for transmission through a physical channel) and the logical layers (those concerned with information as an abstract or symbolic entity)– Latter set of layers is concerned with symbolic
manipulation of the information with reference to the meaning it will ultimately have for end system or user
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Layering in communications systems
Component Component Component ComponentHeader Trailer
Processing at level N
Higher levelcomponent
…
Processing at level N-1 Processing at level N-1 Processing at level N-1… …
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Virtual Session
End-to-End Messages
Physical
Presentation Presentation
Session Session
Network Network
Data Link Control
Data Link Control
PhysicalPhysical
Physical Link, e.g. electrical signals
Physical portion of code
Logical portion of
code
Virtual Network ServiceApplicationApplication
End-to-End PacketsTransport Transport
DLC DLC DLC DLC
NetworkNetwork
Bits
Packets
Frames
Physical Physical Physical
Originating site
Terminating site
Subnet node
Subnet node
Seven layer OSI network architecture
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OSI and TCP/IP Comparison
Application
Presentation
Session
Transport
Network
Data Link
Physical
TCP
IP
Applications:TelnetFTP
SMTPHTTP
Ethernet (802.3)
LLC SublayerMAC Sublayer
Physical signalingMedia attachment
TCP/IP
ApplicationProtocols
OSI Reference ModelTCP/IP Implementation
Using Ethernet
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Traffic Routing Across TCP/IP Network
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All-optical network protocol stack
Source: Richard Barry, Optical Networking Technologies, NGN99