Digital Data Transmission
Digital Transmission of Digital Data
Digital Transmission of Digital Data
Digital Data -- can be represented electronically(by sequences of specified voltage levels) or optically Digital Transmission
-- sending of information over a physical communications media in the form of digital signals.
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Digital Transmission of Digital Data
Computers produce binary data
Standards needed to ensure both sender and receiver understands this data
Codes: digital combinations of bits making up languages that computers use to represent letters, numbers, and symbols in a message Signals: electrical or optical patterns that computers use to represent the coded bits (0 or 1) during transmission across media
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Coding a character is represented by a group of bits
Letters (A, B, ..), numbers (1, 2,..), special symbols (#, $, ..)
1000001
ASCII: American Standard Code for Information Interchange
Originally used a 7-bit code (128 combinations), but an 8-bit version (256 combinations) is now in use Found on PC computers
EBCDIC: Extended Binary Coded Decimal Interchange Code
An 8-bit code developed by IBM Used mostly in mainframe computer environment
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Transmission Modes
• Serial Mode • Parallel Mode
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Signaling of Bits
Digital Transmission
Signals sent as a series of “square waves” of either positive or negative voltage Voltages vary between +3/-3 and +24/-24 depending on the circuit
Signaling (encoding)
Defines how the voltage levels will correspond to the bit values of 0 or 1 Examples: Unipolar, Bipolar RTZ, NRZ, Manchester Data rate: describes how often the sender can transmit data 64 Kbps once every 1/64000 of a second
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Signaling of Bits
•Two-level encoding: the signal can only take on a strictly negative or strictly positive value (-X or +X, where X represents a value of the physical quantity being used to transport the signal)
Digital Transmission of Digital Data
Digital Data -- can be represented electronically(by sequences of specified voltage levels) or optically Digital Transmission
-- sending of information over a physical communications media in the form of digital signals.
Page
2
Digital Transmission of Digital Data
Computers produce binary data
Standards needed to ensure both sender and receiver understands this data
Codes: digital combinations of bits making up languages that computers use to represent letters, numbers, and symbols in a message Signals: electrical or optical patterns that computers use to represent the coded bits (0 or 1) during transmission across media
Page
3
Coding a character is represented by a group of bits
Letters (A, B, ..), numbers (1, 2,..), special symbols (#, $, ..)
1000001
ASCII: American Standard Code for Information Interchange
Originally used a 7-bit code (128 combinations), but an 8-bit version (256 combinations) is now in use Found on PC computers
EBCDIC: Extended Binary Coded Decimal Interchange Code
An 8-bit code developed by IBM Used mostly in mainframe computer environment
Page
4
Transmission Modes
• Serial Mode • Parallel Mode
Page
5
Signaling of Bits
Digital Transmission
Signals sent as a series of “square waves” of either positive or negative voltage Voltages vary between +3/-3 and +24/-24 depending on the circuit
Signaling (encoding)
Defines how the voltage levels will correspond to the bit values of 0 or 1 Examples: Unipolar, Bipolar RTZ, NRZ, Manchester Data rate: describes how often the sender can transmit data 64 Kbps once every 1/64000 of a second
Page
6
Signaling of Bits
•Two-level encoding: the signal can only take on a strictly negative or strictly positive value (-X or +X, where X represents a value of the physical quantity being used to transport the signal)
References: • Modern Data Communications Analog and Digital Signals. B. A. Forouzan. Data Communications and Networking,. McGraw Hill, 4th edition, New York, 2007. • http://en.kioskea.net/contents/703-data-transmissiondigital-data-transmission • http://www.scribd.com/doc/20538034/41/UnipolarEncoding • Business Data Communications and Networking 9th Edition by Jerry Fitzgerald and Alan Dennis Page 26