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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

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Basic Network Information Rate

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  1. 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 time-division 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.

  2. 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:

  3. TDM: T1 system • 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 193-bit frames. The duration of each frame is 193 bits per frame/1.544 Mbps = 125 micro seconds • 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.

  4. Digital Transmission hierarchy in NA telephone line network

  5. 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

  6. 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

  7. 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.

  8. Elements of An optical fiber transmission link

  9. Elements of An optical fiber transmission link

  10. 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.

  11. 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.

  12. 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

  13. 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

  14. SONET/SDH optical transport network

  15. Silica Glass Fiber Communications • Advantages • Extreme wide bandwidth • For wavelength = 1550 nm, the carrier frequency v = c/λ = 2x1014Hz. Assuming usuablebandwith of 1% of the carrier frequency, yield Δv ~2x1012Hz=2 THz • Low loss, long transmit distance • 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 • 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 • 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 • Raw materials for making optical fiber is silica SiO2 is very rich in global resource and it low cost • Challenges • 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

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