Transcript Basic Network Information Rate

Basic Network Information Rate
• The demand for higher data rate is driven by
data traffic, widespread of Internet, video, etc
• Optical fibers are used as dominant
transmission system
• Network providers combine signals from many
different users and send aggregate over
transmission medium. This is known as timedivision multiplexing (TDM)
internet is short for internetwork which is a collection of interconnected networks.
Internet refers to the world's largest internetwork which consists of hundreds of thousands of interconnected networks worldwide.
TDM
• In TDM, N independent data sources, each
running a data rate of R b/s are interleaved
electrically into a single information stream of
NxR b/s
• Example:
TDM: T1 system
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The T1 system is used for wireline long-distance service in North America. Speech from a telephone
conversation is sampled once every 125 msec and each sample is converted into eight bits of digital
data. Using this technique, a transmission speed of 64,000 bits/sec is required to transmit the
speech. A T1 line is essentially a channel capable of transmitting at a speed of 1.544 Mbit/sec. This
is a much higher transmission speed than a single telephone conversation needs, so TDM is used to
allow a single T1 line to carry 24 different speech signals between, say, two different telephone
substations (called central offices) within a city. The 1.544 Mbit/sec bit stream is divided into 193bit frames. The duration of each frame is
193 bits per frame/1.544 Mbps = 125 micro seconds
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corresponding to the period between samples of the speech. Each frame is divided into 24 slots,
which are each eight bits wide (corresponding to the number of bits needed to digitize a speech
sample). One additional bit at the end of the frame is used for signaling. The eight bits of data
corresponding to a sample of the speech are placed into one of the 24 slots in the frame.
Digital Transmission hierarchy in
NA telephone line network
• Early applications of fiber optic transmission
link were largely used for trunking of
telephone lines
• T2 (6.312 Mbps) multiplexing of 4 T1
• T3 (44.736 Mbps) multiplexing of seven 6.312
Mbps
• T4 (274.176 Mbps) multiplexing of 6 44.736
Mbps
• With the advent of high-capacity fiber optic,
service providers established a standard signal
format called synchronous optical network
(SONET) in North America and synchronous digital
hierarchy (SDH) in other parts of world.
• The basic building block is called synchronous
transport signal-level 1 (STS-1) with bit rate of
51.84 Mbps
• Higher rate are obtained by interleaving N STS-1
frames.
• OC-N signal will have a line rate of N x OC1 i.e.
OC-192 has line rate of 9953.28 Mbps
Elements of An optical fiber transmission link
• An optical fiber transmission link comprises of
– Transmitter:
• Light source with drive circuit
– Cable offering protection to fiber
– Receiver
• Photo detector plus amplification and signal restoring
circuit
– Amplifiers, connectors, splices, couplers and
regenerators
• Optical fiber can be installed aerially, in ducts,
undersea, or buried in ground.
Elements of An optical fiber
transmission link
Elements of An optical fiber
transmission link
Elements of An optical fiber transmission link
• One of the principle characteristics of an optical fiber is its
attenuation as function of wavelength
• Early technology made use of 800-900 nm (first window)
• By reducing concentration of hydroxyl ions and metallic
impurities , in 1980s manufacturers were able to manufacture
fibers with low loss in 1100-1600nm. Second window
centered at 1310 nm and 3rd window around 1550nm.
Elements of An optical fiber transmission link
• AllWave fiber: In 1998, using ultra purifying process, Lucent eliminated all
water molecules from glass fiber. By reducing wafer-attenuation peak
around 1400nm, this process opens the transmission region between
second and third window.
Elements of An optical fiber transmission link
• A light source is used to launch optical power
into fiber. Semiconductor and LEDs and laser
diodes are used since light output can be
modulated by simply varying bias current
• At the receiver, a photodetector detects the
weakened optical signal and convert it to
electric current
• The principle figure of merit for a receiver is
minimum optical power necessary at desired
data rate to attain either given error
probability for digital systems or specified SNR
for analog system
Elements of An optical fiber transmission link
• Many different wavelength can be send along fiber
simultaneously in 1300-1600nm. Wavelength-division
multiplexing or WDM
• Repeaters are added when path loss exceed the
available power margin. Conventional repeaters do
photon-to-electron conversion, electrical amplification,
retiming, pulse shaping and then electron to phone
conversion. For high speed, multi wavelength, all
optical amplifiers are developed
SONET/SDH optical transport
network
Silica Glass Fiber Communications
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Advantages
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Extreme wide bandwidth
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Low loss, long transmit distance
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Not affected by RF noise and broadcasted signals. Because glass is a good insulator, no conduction electrical current can
flow through an optical fiber, fiber cable are immune to both optical and electrical interference
Rich in global resources
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Optic fiber has 125 micron cladding thickness, core is 8-9 micron in diameter. The final diameter after plastic wrapping layer
is less than 1mm. A 18 core optic cable weights 150 kg/km which 18 core copper cable weights 11 ton/km
Immunity to electromagnetic interference, high signal security
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Continuing development of optical fiber has resulted in fiber cable with extremely low transmission losses compared to best
copper conductors. It is possible to conduct transmission systems with hundreds of kilometers. Single mode fiber at 1550
nm have loss < 0.2 dB/km, the transmission distance without repeaters is larger than 100km
Small volume, light weight
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For wavelength = 1550 nm, the carrier frequency v = c/λ = 2x1014Hz. Assuming usuable bandwith of 1% of the carrier
frequency, yield Δv ~2x1012Hz=2 THz
Raw materials for making optical fiber is silica SiO2 is very rich in global resource and it low cost
Challenges
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Components cost is high such as connectors, light sources, detectors
Specialized skill and tools are required to splice and test systems
Taps in is rather difficult and required preplanning
High cost for right of way, legal renting fees