# Telecom test 1

 What is amplitude? height of the wave above or below a given reference point (Measured being high or low) what is frequency? the number of times a signal makes a complete cycle within a given time frame (Measured in Hertz ((Hz)). Hertz is cycles per second What is phase? The position of the waveform relative to a given moment of time (change is in degrees, 0 to 360) What is bandwidth? the absolute value of the difference between the lowest and highest frequencies of a signal What is modulation? the process of converting digital data into an analog signal What is pulse code modulation? an encoding technique that converts analog data to a digital signal. Also known as digitization What is delta modulation? A method of converting analog data to digital signal in which the incoming analog signal is tracked and binary 1 or 0, is transmitted, respectively, when the analog signal rises or falls What is CODEC? a device that accepts analog data and converts it into digital signals. This process is known as digitization. What is attenuation? the continuous loss of strength (power) that a signal experiences as it travels through a medium What is a modem used for? a device that modulates digital data on to an analog signal for transmission over a telephone line, then demodulates the analog signal back to digital data What is a data code? the set of all textual characters or symbols and their corresponding binary patterns EBCDIC an 8-bit code allowing 256 possible combinations of texutal symbols (2^8=256) ASCII a 7-bit code that is used to represent all the printable characters on a keyboard plus many nonprintable control characters (2^7=128) Unicode a character encoding technique that can represent all the languages on the planet Amplification leads to a signal gaining what? strength (power) of an analog signal Amplitude Shift Keying One amplitude encodes a 0 while another amplitude encodes a 1 (a form of amplitudemodulation) Frequency Shift Keying One frequency encodes a 0 while another frequency encodes a 1 (a form of frequencymodulation) Frequency Shift Keying is subject to what? intermodulation distortion (frequencies mixing together to create new frequencies) Phase Shift Keying One phase change encodes a 0 while another phase change encodes a 1 (a form ofphase modulation) What is the simplest modulation technique? amplitude shift keying Most common example of an analog signal human voice, transmission of a voice conversation What waveform is continuous? analog Which waveform is noncontinuous digital Which signal is in a fixed number of forms? digital Which signal is harder to separate noise? analog Transmitting Analog Data with Analog Signals transmit analog data, you can modulate the data onto a set of analog signals (broadcast radio and tv) Transmitting Digital Data and Digital Signals There are numerous techniques available to convert digital data into digital signals. Transmitting Digital Data with Discrete Analog Signals Threebasic techniques: Amplitude shift keying Frequency shift keying Phase shift keyingCombine two or more to make complex modulation Transmitting Analog Data with Digital Signals twotechniques: Pulse code modulation (the more common) Delta modulation Crosstalk an unwanted coupling between two different signal paths line-of-sight transmission transmitter and receiver are in visual sight of each other (wireless) guardbands a set of unused frequences between two channels on a frequency division multiplexed system intermodulation distortion the noise that occurs when the frequencies of two or more signals mix together and create new frequencies media selection criteria a checklist used when designing or updating a computer network that includes cost, speed, distance, right-of-way, expandability,environment, and security Terrestrial Microwave Land-based, line-of-sight transmission Approximately 20-30 miles between towers Transmitsdata at hundreds of millions of bits per second Signals will not pass through solid objects Popular with telephone companies and business to business transmissions Satellite Microwave Similar to terrestrial microwave except the signal travels from a ground station onearth to a satellite and back to another ground station Can also transmit signals from one satellite to another Satellites can be classified by how far out into orbit each one is (LEO, MEO, GEO, andHEO) LEO (Low-Earth-Orbit) 100 to 1000 miles out Usedfor wireless e-mail, special mobile telephones, pagers, spying,videoconferencing MEO(Middle-Earth-Orbit) 1000 to 22,300 miles Used for GPS (global positioning systems) and government GEO (Geosynchronous-Earth-Orbit) 22,300miles Alwaysover the same position on earth (and always over the equator)Usedfor weather, television, government operations HEO (Highly Elliptical Earth orbit) satellitefollows an elliptical orbit Used by the military for spying and byscientific organizations for photographing celestial bodies Which type of twisted pair is used to deal with interference? shielded twisted pair Advantage of fiber optic over twisted pair and coaxial cable safer, less noise, faster Uses of coaxial cable carry analog signals wide range of frequencies; good for tv with lots of channels Examples of conducted media telephone lines and fiber-optic cables Which is the simplest and most common type? twisted pair wire Twisted Pair Wire One or more pairs of single conductor wires that have been twisted around eachother Twistingthe wires helps to eliminate electromagnetic interference between the two wires Coaxial Cable A single wire wrapped in a foam insulation surrounded by a braided metal shield,then covered in a plastic jacket. Cable comes in various thicknesses Baseband coaxial technology usesdigital signaling in which the cable carries only one channel of digital data]uses repeaters Broadband coaxial technology transmitsanalog signals and is capable of supporting multiple channels Use amplifiers Fiber-Optic Cable A thin glass cable approximately a little thicker than a human hair surrounded bya plastic coating and packaged into an insulated cable A photo diode or laser generates pulses of light which travel down the fiberoptic cable and are received by a photo receptor Thin Fiber Optic Cable very little reflection, fasttransmission, typically uses a laser, longer transmission distances; known assingle mode fiber Thick Fiber Optic Cable causes more ray collisions, so you haveto transmit slower Thisis step index multimode fiber Typicallyuse LED for light source, shorter distance transmissions AuthorAnonymous ID103356 Card SetTelecom test 1 Descriptiontest Updated2011-09-21T19:42:22Z Show Answers