Telecom test 1

height of the wave above or below a given reference point (Measured being high or low)

the number of times a signal makes a complete cycle within a given time frame (Measured in Hertz ((Hz)). Hertz is cycles per second

The position of the waveform relative to a given moment of time (change is in degrees, 0 to 360)

the absolute value of the difference between the lowest and highest frequencies of a signal

the process of converting digital data into an analog signal

an encoding technique that converts analog data to a digital signal. Also known as digitization

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

a device that accepts analog data and converts it into digital signals. This process is known as digitization.

the continuous loss of strength (power) that a signal experiences as it travels through a medium

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

the set of all textual characters or symbols and their corresponding binary patterns

an 8-bit code allowing 256 possible combinations of texutal symbols (2^8=256)

a 7-bit code that is used to represent all the printable characters on a keyboard plus many nonprintable control characters (2^7=128)

a character encoding technique that can represent all the languages on the planet

strength (power) of an analog signal

• One amplitude encodes a 0 while another amplitude encodes a 1 (a form of amplitude
• modulation)

• One frequency encodes a 0 while another frequency encodes a 1 (a form of frequency
• modulation)

intermodulation distortion (frequencies mixing together to create new frequencies)

• One phase change encodes a 0 while another phase change encodes a 1 (a form of
• phase modulation)

amplitude shift keying

human voice, transmission of a voice conversation

analog

digital

digital

analog

transmit analog data, you can modulate the data onto a set of analog signals (broadcast radio and tv)

There are numerous techniques available to convert digital data into digital signals.

• Three
• basic techniques:

Amplitude shift keying

Frequency shift keying

• Phase shift keying
• Combine two or more to make complex modulation

• two
• techniques:

Pulse code modulation (the more common)

Delta modulation

an unwanted coupling between two different signal paths

transmitter and receiver are in visual sight of each other (wireless)

a set of unused frequences between two channels on a frequency division multiplexed system

the noise that occurs when the frequencies of two or more signals mix together and create new frequencies

a checklist used when designing or updating a computer network that includes cost, speed, distance, right-of-way, expandability,environment, and security

Land-based, line-of-sight transmission

Approximately 20-30 miles between towers

• Transmits
• data at hundreds of millions of bits per second

Signals will not pass through solid objects

Popular with telephone companies and business to business transmissions

• Similar to terrestrial microwave except the signal travels from a ground station on
• earth 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, and
• HEO)

• 100 to 1000 miles out
• Used
• for wireless e-mail, special mobile telephones, pagers, spying,
• videoconferencing

1000 to 22,300 miles

Used for GPS (global positioning systems) and government

• 22,300
• miles

• Always
• over the same position on earth (and always over the equator)
• Used
• for weather, television, government operations

• satellite
• follows an elliptical orbit

• Used by the military for spying and by
• scientific organizations for photographing celestial bodies

shielded twisted pair

safer, less noise, faster

carry analog signals wide range of frequencies; good for tv with lots of channels

telephone lines and fiber-optic cables

twisted pair wire

• One or more pairs of single conductor wires that have been twisted around each
• other

• Twisting
• the wires helps to eliminate electromagnetic interference between the two wires

• 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

• uses
• digital signaling in which the cable carries only one channel of digital data]
• uses repeaters

• transmits
• analog signals and is capable of supporting multiple channels

Use amplifiers

• A thin glass cable approximately a little thicker than a human hair surrounded by
• a plastic coating and packaged into an insulated cable

• A photo diode or laser generates pulses of light which travel down the fiber
• optic cable and are received by a photo receptor

• very little reflection, fast
• transmission, typically uses a laser, longer transmission distances; known as
• single mode fiber

• causes more ray collisions, so you have
• to transmit slower

• This
• is step index multimode fiber

• Typically
• use LED for light source, shorter distance transmissions