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Understanding Telecommunications Circuit Media

Explore various circuit media such as twisted-pair copper wire, coaxial cable, and fiber optic cables used in telecommunications systems. Learn about attenuation, impact, characteristics, and technologies driving voice and data systems.

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Understanding Telecommunications Circuit Media

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  1. The Management of Telecommunications Houston H. Carr and Charles A. Snyder What Technologies and Media Do We Use for Voice and Data Systems? Chapter 3

  2. Introduction • All transmission must be carried by some medium, whether it be copper, glass, or radio or light waves in space. • Each medium has a capacity and each has a susceptibility to noise.

  3. Noise • Noise is any unwanted, detectable signal that coexists with the intended signal. • Radio Frequency Interference (RFI) • Electromagnetic Interference (EMI)

  4. Circuit verses Channel • A communications circuit is a path over which a signal can travel. • Circuits are generally thought of as something physical, like wire or radio wave. • A channel is the actual path for the signal and may occupy the total circuit or be a portion of it

  5. Electrical, Electromagnetic and Photonic circuits • Electrical uses direct or alternating current to carry a signal on a conductive medium. • Electromagnetic circuits use rapidly varying (high-frequency) current to carry the signal. • Photonic circuits use light as the data carrier on a transparent media.

  6. Types of Media • Twisted-pair copper • Coaxial cable • Radio • Microwave • Satellite • Omi-directional • Photonic • Fiber optic • infrared

  7. Characteristics of circuit media Wire • 22-26 gauge copper • Low bandwidth • Used for virtually all local loops • Low installation cost • Susceptible to noise

  8. Twisted-pair copper wire • Twisted-pair copper wire is the most used, lowest cost media. • A loop formed with a single wire going from the sender to the receiver and back. • Seen as a pair of wires.

  9. Crosstalk • Crosstalk is the radiation of signals from one circuit to another.

  10. Cable shielding guide

  11. Coaxial cable • Coaxial cable is similar to a pair of copper wires except that one wire is a sheath that encompasses the other wire and shields it from noise.

  12. Characteristics of circuit media Coaxial cable • Ground is shielded (immune to interference) • Bandwidth of 300MHz, 500 MHz, 750 MHz • Up to 10,800 voice conversations • Amplifiers every mile • 50-100 analog TV channels/cable • Cable tapped easily; low to medium security • Any analog channel can be digitized with modems with a bandwidth of 27 Mbps.

  13. Solid verses stranded wires • The two wires above have the same capacity • Both are 14 gauge and are 1.63 mm thick • Stranded wire is composed of a group of smaller solid wires. • Stranding makes the wire more flexible

  14. Impact of Attenuation • As discussed in chapter 2, attenuation is the reduction of signal strength (or voltage) as the signal propagates along the circuit. • This means the voltage level of the signal is lowered as the signal moves down the wire. • To keep the signal at acceptable levels, a repeater or amplifier is placed along the circuit to amplify the signal.

  15. Attenuation

  16. Fiber Optic Cables • Made of glass or plastic • Difficult to splice • Secure • Very high speed • Unidirectional strand • Difficult to split signal • Immune to RFI, EMI , crosstalk • Most expensive, greatest bandwidth = low cost/bit

  17. Fiber optic cables • Fiber optic cables are made up of very small one-way glass stands that have the greatest bandwidth of any media used. • Circuits often begin and end with some other media.

  18. Fiber optic cables

  19. Fiber optic circuits • Fiber optic circuits use a laser or light-emitting diode (LED) as the source and an optical detector at the receiving end. • There must be a light-to-electrical signal conversion at each end until optical switching is available.

  20. Dense Wave Division Multiplexing • Dense Wave Division Multiplexing (DWDM) is a fiber optic transmission technique that employs multiple light wavelengths to transmit data. • Allows for the better use of the full bandwidth of a fiber strand.

  21. Hybrid Fiber/Coax (HFC) • Hybrid Fiber/Coax Service (HFC) makes use of the installed CATV network in the neighborhood and uses fiber for high-speed, high-quality distribution to the neighborhood.

  22. Hybrid Fiber/Coax Service

  23. Fiber to the curb • Fiber to the curb (FTTC) has greater bandwidth and lower noise than HFC, but will be very expensive to run all the way to the premise.

  24. Basic HFC for Video and Voice

  25. Bandwidth and speed of telecommunications media

  26. Broadband • Broadband is high speed or wide bandwidth. • Generally meaning an analog path that is frequency division multiplexed to create several channels.

  27. Baseband • Baseband uses all bandwidth of a circuit as one channel. • A narrow band, generally not subdivided into channels • Often describing a digital circuit.

  28. Wireless technology

  29. Microwave Radio Terminal • 4-28 GHz voice circuits in a 30-MHz-wide channel • Line of sight – 20 to 30 miles between towers • Mostly used for analog • Subject to interference by rain • Must have an FCC license, regulated • No right-of-permit required; great for building-to-building within a city

  30. Satellite Radio • Uplink and downlink each 22,300 miles (geosynchronous orbit) • Footprint is one-third of earth • Propagation delay = 44,600 miles/186 mps = .2398 seconds • Most common carriers have left satellite for terrestrial • Only security is encryption

  31. Omni-directional Radio • Wireless – replaces wires and cables • Passes thru walls • Very localized • Easy to install; easy to move

  32. Infrared (Photonic) • Limited to within a set of walls (room) • Omni-directional • Low speed • Easy to install; easy to move • Not secure • Very localized

  33. Wireless • Wireless is the driving technology of the 21st century. • Wireless is the absence of physical channels. • A wired circuit means the user is tethered to the point of connection.

  34. Wireless • Fixed wireless is designed to be a point-to-point like and is not designed to be movable. • Offers the potential of bypassing the expense for new providers of having to install the last mile. • Potentially faster to install. • Fixed wireless is a direct replacement for a wired circuit.

  35. Wireless • Forms of wireless connectivity • Fixed node (desktop machines and servers) • Moveable node (laptops that are carried from point-to-point) • Moving node (wireless PDAs and palmtop computers)

  36. Radio (Air Medium) • Radio is a medium that has become more valuable for new wireless applications. • Use omnidirectional transmitters and receivers.

  37. Radio frequency bands are limited and have high value. • Knowing this, governments now auction off radio bandwidth/spectrum.

  38. NTSC • National Television Standards Committee • NTSC is the standard for television sets from 1927 – 2006. • Replaced by HDTV.

  39. High Definition Television • High Definition Television (HDTV) increases the information-carrying capacity of the TV channel but required greater bandwidth. • HDTV can be in the analog or digital environment. • Japan uses analog version. • United States uses digital version.

  40. Internet TV • Internet TV means user can see any station’s programming anywhere on the globe. • As bandwidth of the Internet increases and delays decrease, this generally “free” resource continues to evolve • Can make a local provider a global competitor.

  41. Cellular phone

  42. Cellular phone • Cellular telephone is one of the fastest growing areas in telecommunications. • An air-medium technology. • It is the replacement for mobile radio-telephones and the precursor of PCS. • PCS (Personal Communications System) is digital telephone plus paging. • All cellular phones use analog carrier signals; the voice may be digital, as in the case of PCS. • Call phones do not have dial tones, they send a data packet to request the desired party.

  43. Mobile Cellular Telephone System

  44. Mobile Communications Network

  45. Cellular Technology • In a typical urban cellular network, a single cell may range from a few blocks to a few square miles, with even smaller cells installed to cover things like tunnels, subways and other hard-to-reach areas. • In rural areas, a cell can cover as much as 30 square miles.

  46. Mobile Communications Network

  47. Cellular Technology • Technically, PCS refers to cellular service that uses the 1,900 MHz band. • Those same technologies are called “digital cellular” if they are transmitting at 800 MHz.

  48. Cellular Technology • PCS offers a number of advantages over analog cellular technologies, • greater data throughput, • greater reliability • better clarity. • Analog systems provide more extensive coverage

  49. Timeline of Cellular

  50. Cellular Radio (Telephone) Protocols • Advanced Mobile Phone Service (AMPS) • Analog • 800 Mhz frequency band • Time Division Multiple Access (TDMA) • Single channel divided into several timeslots • Global System for Mobile Communications (GSM) • Digital implementation of TDMA • Operational in Europe, growing in US and other countries. • Code Division Multiple Access (CDMA) • Spread spectrum technology • Improved talk time and bandwidth on demand.

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