Chapter 3 Flashcards
Modem
At the senders computer, translates the computers digital data into analog data that can be transmitted through the voice communication circuits. A second modem at the receivers end translates the analog transmission back into digital data for use by the receivers computer
Codec
Translates analog voice data into digital form for transmission over digital computer circuits
5 key benefits of digital transmission over analog transmission
- digital transmission produces fewer errors, easier to detect and correct errors
- digital transmission permits higher maximum transmission rates
- digital transmission is more efficient
- digital transmissions is more secure because it is easier to encrypt
- integrating voice, video, and data on the same circuit is far simpler with digital transmission
Simplex transmission
Data flows in one direction (TV, radio’s)
Half-duplex transmission
Data flows both directions, but only one at a time
Full duplex transmission
Data flows simultaneously in both directions
Multiplexing
Divide a high-speed circuit into several slower (logical) circuits
Frequency division multiplexing (FDM)
Dividing the circuit “horizontally” so that many signals can travel a single communication circuit simultaneously
Time division multiplexing (TDM)
Shares a communication circuit among two or more computers by having them take turns, dividing the circuit vertically
Statistical time division multiplexing (STDM)
Allows more terminals or computers to be connected to a circuit than does FDM or TDM.
Selection of transmission for the multiplexed circuit is based on a statistical analysis of the usage requirements of the circuits to be multiplexed.
Wavelength division multiplexing (WDM)
A version of FDM used in fiber-optic cables
Digital Subscriber Line (DSL)
Allows for simultaneous transmission of voice (phone calls), data going to the internet (upstream data), and data coming to your house from the internet (downstream data)
Inverse multiplexing
Combines many low-speed circuits into one high-speed circuit
Guided media
Transmission flows along physical medium
Wireless (radiates) media
Transmission flows through the air
Coax cable
Has a single copper core, plus outer insulation, shielding, and inner insulation
- less prone to interference
characteristics:
Price - inexpensive (but more costly than TP)
Distance- up to 2km (1.2mi)
Use- cable tv/internet
Twisted Pair cable
Insulated pair of wires bundled together
Characteristics:
Price- inexpensive
Distance- typically up to 100m
Use- telephones/LAN
Fiber optic cable
- Data transmitted using light from lasers or LEDs
- Resistant to interference or corrosion
- extremely fast data rates
Characteristics:
Price- expensive
Distance- 500m-100km
Use- trunk line/backbone, long distance circuits, undersea cables
Radio transmission
Wireless transmission of electrical waves through air
Characteristics:
Distance- depends on frequency and power
Use- wireless LANs, cellular and cordless phones, baby monitors
Microwave transmission
- High-frequency radio communication
- requires line of sight which may require large antennas and towers
Characteristics:
Distance- 60km
Use- trunk line/backbone, long distance
Serial transmission
- Sends but by bit over a single wire sequentially
- slower than parallel mode
Parallel transmission
- uses several wires, each wire sending one bit at the same time as the others
- multiple bits transmitted simultaneously
Unipolar signal
Voltage is 0 or positive representing binary bits
Bipolar Nonreturn to zero (NRZ)
Voltage is positive or negative but not zero
Bipolar return to zero (RZ)
Voltage is positive or negative, returning to zero between each bit
Manchester signal
Voltage is positive or negative and bits are indicated by a mid-bit transition (used by Ethernet)
Plain old telephone service (POTS)
Enables voice communications between two telephones.
-human voice (sound waves) concerted into electrical signals by the sending telephone and converted back to sound waves at the far end
Modulation
Technical term used to describe the “shape changes” of waves when transmitting
Amplitude Modulation (AM)
The amplitude or height of the wave is changed
-more susceptible to noise (more errors) during transmission than FM
Frequency Modulation
Modulation technique where each 0 or 1 is represented by a number of waves per second (different frequency)
Phase Modulation (PM)
Phase refers to the direction in which the waves begin
Local loop
The wires that run from your home or business to the telephone switch that connects your local loop into the telephone network (sometimes called the last mile)
