Analog and Digital Flashcards
What gets sent on a network?
Information.
Voice, pictures (facsimile), data (computer files), video, music.
Information may be analog or digital.
To be transmitted, information must be encoded.
Analog Transmission
an analog waveform (or signal) is characterized by being continuously variable along amplitude and frequency.
voice-grade line
analog circuit
-the human voice for example, can typically generate frequencies from 100Hz to 10,000Hz
Analog Characteristics
- limited bandwidth, which means they can not support high-speed data
- analog is that noise accumulated as the signal traverses the network
Digital Transmission
- signal is much simpler than analog
- rather than being a continuously variable waveform, it is a series of discrete pulses, representing one bits and zero its
Collating sequence
coding scheme
- defines what combinations of ones and zeros constitute all the characters in a character set
- e.g. lowercase letters, uppercase letters, punctuation marks, digits, keyboard control functions
Analog Characteristics
Signal
Continuously variable, in both amplitude and frequency
Analog Characteristics
Capacity measurement
Hz
-e.g., a telephone channel is 4KHz
Analog Characteristics
Bandwidth
Low bandwidth (4KHz), which means low data transmission rates (up to 33.6Kbps) because of limited channel bandwidth
Analog Characteristics
Network capacity
Low; one conversation per telephone channel
Analog Characteristics
Network manageability
Poor; a lot of labor is needed for network maintenance and control because dumb analog devices do not prvide management information streams that allow the devive to be remotely managed
Analog Characteristics
Signal Structure
High; the signal contains a wide range of frequencies and amplitudes
Analog Characteristics
Security
Poor;when you tap into an analog circuit, you hear the voice stream in its native form, and it is difficult to detect an intrusion
Analog Characteristics
Error rates
High; 10-5bits (i.e., 1 in 100,000 bits) is guaranteed to have an error
Digital Characteristics
Signal
Discrete signal, represented as either changes in voltage or changes in light levels
Digital Characteristics
Capacity measurement
Bits per second (e.g., a T-1 line carries 1.544Mbps, and an E-1 line transports 2.048Mbps)
Digital Characteristics
Bandwidth
High bandwidth that can support high-speed data applications that involve video and multimedia
Digital Characteristics
Network capacity
High; multiplexers enable multiple conversations to share a communications channel and hense to achieve greater transmission efficiencies
Digital Characteristics
Network manageability
Good; smart devices produce alterts, alarms, traffic statistics, and performance measurements, and technicians at a network control center (NCC) or network operations center (NOC) can remotely monitor and mangage the varios network elements
Digital Characteristics
Signal Structure
Low; only two discrete signals-the one and the zero-need to be transmitted
Digital Characteristics
Security
Good; encryption can be used
Digital Characteristics
Error rates
Low; with twisted-pair, 10-7 bits (i.e., 1 in 10 million bits) has an error; with satellite, 10-9 bits (i.e., 1 in 1billion bits) has an error, and with fiber, 10-11 bits(i.e., 1 in 100 billion bits) to 10-13 bits (i.e., 1 in 10 trillion bits) has an error
codec
- a contraction of coder-decoder
- converts analog signals into digital signals
- there are different codes for different purposes
