5Digital Encoding and Data Transmission
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Objectives
Give examples of digital signals. Identify the two modes of transmitting data
between two points. Explain data integrity inspection using a parity
check. Explain data integrity inspection using a Cyclic
Redundancy Check (CRC). Explain the complete data packaging process. Compare connection-oriented transmission with
connectionless data transmission.
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Objectives
Compare packet switching with circuit switching. Identify the characteristics of the various data
codes. Interpret the structure and contents of a UDP
frame. Compare an Ethernet II frame with an IEEE
802.3 frame. Recall the function of each layers of the OSI
model.
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Digital Signals
Measured in volts After digital encoding, data placed on network
media Encoding marked by voltage level and time
period, which represents expected digital wave shape
Unipolar digital signal Bipolar digital signal
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Non-Return to Zero (NRZ)
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Manchester Encoding
Binary zero is represented by transition from zero to five volts in the midpoint of time period
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Data Transmission Modes
Synchronous transmission—Timing of digital signal important for decoding digital patterns
Asynchronous transmission—Beginning and end of data stream might be determined by: Series of ones or zeros Long period of no digital transmission Various other methods
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Data Packaging and Transmission
A segment gets packaged with extra information to ensure its delivery
Encapsulation process A packet travels across LANs only A frame is encapsulated and can travel across the
Internet
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Parity Check
Protects against corruption such as crosstalk, loose connections, interference
A Cyclic Redundancy Check (CRC) is more sophisticated error detector than parity check
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Data Packaging Process
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Protocols
Connection-oriented communication—Connection is terminated after data is transferred Every frame must be verified Results in slower data transfer speed
Connectionless communication—No need to terminate connection Results in faster transfer speed
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Connection-Oriented and Connectionless Communication
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Circuit and Packet Switching
Two main categories describing the way data are routed between two points
Circuit switching—Permanent Internet connection Packet switching— Data broken down into
packets with a source and destination address
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Packet Switching
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Data Codes
Represent the written word Communicating systems must use the same data
code Data code conversion must occur for data
exchange to take place
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ASCII
Earliest attempt to standardize data codes Sometimes referred to as plain text files Used by word processing programs
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BCD
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EBCDIC
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Unicode
Similar to ASCII Over 65,000 possible characters Used in bar codes for scanning merchandise Used in Braille
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Hypertext Markup Language (HTML)
On web page, color code is translated into color the code represents
Web browsers interpret code and create shade of color indicated
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Protocol Frame Structures
The exact structure used is determined by the: Purpose of communication Type of network architecture Use of specialized equipment and media during
transfer
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UDP Frame Structure
Simple and compact protocol First 16 bits of packet identify source port Second 16 bits identify destination port Checksum uses one’s compliment to check for
errors or corruption Last block of information contains actual data
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UDP Frame
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Ethernet Frame Structure
Most common types are Ethernet II and IEEE 802.3
Generally compatible, but not guaranteed
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Ethernet Destination Address
When filled with all ones, the frame becomes a broadcast frame
Multicast frame is intended for a select number of computers
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OSI Model and Data Encoding
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Application Layer
Where user interfaces with network operating system
Start and final destination of data communication
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Presentation Layer
Raw data is packaged into a universally agreed on form
Data byte order is also agreed on Data encryption occurs
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Session Layer
Establishes a dialog between source and destination
Negotiates decisions about how data flow is controlled and how session ends
Decides on whether confirmation of arrival is needed
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Transport Layer
Responsible for flow of data to and from destination computer
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Network Layer
Provides the means of routing data packets across a WAN or MAN
Uses TCP/IP protocol standards Encapsulates packets with source and destination
IP addresses Responsible for virtual networks
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Data Link Layer
Converts data package into electrical pulses and places pulses on network media
Subdivided into logical link control (LLC) and MAC sublayer
Parity and CRC checks performed
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Physical Layer
Concerned with media, hardware, and network topology
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You are installing a new network that adheres to the IEEE 10GBaseT standard. To which layers of the OSI model do the following aspects of the IEEE 10GBaseT standard relate?
A. 10GBaseT network card
B. Cat 6a or 6 cable
C. CSMA/CD media access method
D.10GBaseT switch
A. data link C. data link
B. physical D. data link
Applied Networking
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The signal shown is an example of a _____ digital signal.
A. bipolar
B. unipolar
B. unipolar
Review
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The signal shown is an example of a _____ digital signal.
A. bipolar
B. unipolar
A. bipolar
Review
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The mode of data transmission in which the digital signal synchronized with a reference signal is referred to as _____.
synchronous
Review
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The mode of data transmission in which the digital signal is not synchronized with a reference signal is referred to as _____.
asynchronous
Review
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To perform a(n) _____, the last bit position in an 8-bit data transmission can be used for the parity code.
parity check
Review
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Place data packaging process stages in sequential order starting with “segments.”
A. segments
B. binary code
C. packets
D. digital signals
E. Frames
A, B, C, D, E
Review
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A(n) _____ uses complicated mathematical algorithms to determine if one if more bits are corrupt.
Cyclic Redundancy Check (CRC)
Review
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Which mode of communication terminates the session when all data has been transferred?
A. Connection-oriented
B. Connectionless
A. Connection-oriented
Review
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Which mode of communication does not establish a connection before transmitting data?
A. Connection-orientated
B. Connectionless
B. Connectionless
Review
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Two main categories describing the way data are routed between two points are _____ switching and _____ switching.
packet, circuit (any order)
Review
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Which of the following establishes a permanent connection between the source and destination for the duration of the transfer?
A. Circuit switching
B. Packet switching
A. Circuit switching
Review
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Which of the following allows packets to travel different routes to arrive at the destination?
A. Circuit switching
B. Packet switching
B. Packet switching
Review
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The following is an example of the _____ data code representing decimal numbers 2, 5, and 14.
BCD
Review
0010 0101 1110
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The _____ character code uses eight bits to represent alphanumeric characters.
A. ASCII
B. BCD
C. EBCDIC
D. Unicode
A. ASCII
Review
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The _____ character code uses 16 bits to represent individual characters.
A. ASCII
B. BCD
C. EBCDIC
D. Unicode
D. Unicode
Review
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A(n) _____ is a logical connection that matches a service with a computer.
port
Review
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The _____ of a UDP frame uses the one’s compliment to check for errors or corruption.
A. checksum
B. destination port
C. length
D. source port
A. checksum
Review
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The _____ frame type includes a Start Frame Delimiter (SFD).
A. Ethernet II
B. IEEE 802.3
B. IEEE 802.3
Review
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The _____ indicates the start of the frame with a one-byte binary pattern.
A. preamble
B. length
C. SFD
D. frame check sequence
C. SFD
Review
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The _____ frame type was developed before the release of the IEEE 802.3 CSMA/CD standard.
Ethernet II
Review
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Which layer of the OSI model is responsible for the flow of data to and from destination computer?
Transport
Review
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Which layer of the OSI model is concerned with media, hardware, and network topology?
Physical
Review
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Which layer of the OSI mode provides the means of routing data packets across a WAN or MAN?
Network
Review
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Which layer of the OSI model negotiates decisions about how data flow is controlled and how session ends?
Session
Review
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American Standard Code for Information Interchange (ASCII) A character code that uses eight bits to represent
alphanumeric characters. Asynchronous transmission
A type of transmission in which a digital signal is not synchronized with a reference signal.
Binary Coded Decimal (BCD) A binary number format in which each number is
represented as a four-digit binary code.
Glossary
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Bipolar digital signal A digital signal that fluctuates between a positive
five-volt level and a negative five-volt level. Broadcast frame
A frame intended for every computer on the network. Circuit switching
A type of transmission which establishes a permanent connection between two points for the duration of the data transfer period.
Glossary
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Connectionless communication A type of communication in which data is transmitted
to the destination without first establishing a connection.
Connection-oriented communication A type of communication in which a connection is
first established between the source and destination computers before data is transmitted.
Glossary
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Cyclic Redundancy Check (CRC) A sophisticated data integrity check that uses
complicated mathematical algorithms to determine if one or more bits are corrupt.
Data encryption The encoding of data based on a mathematical
formula, which converts the original data symbol into another symbol.
Digital encoding The conversion of data into a digital pattern
acceptable to the network media.
Glossary
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Encapsulation The process of adding information to the segment
that identifies such things as the source address, the destination address, the end of the segment, and the size of the segment.
Extended Binary Coded Decimal Interchange Code (EBCDIC) An IBM character code similar to ASCII.
Frame A packet that is encapsulated with information
needed to travel the Internet.
Glossary
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Hypertext Markup Language (HTML) A programming language used to create Web pages.
Manchester encoding An encoding scheme characterized by a digital pulse
transitioning during the midpoint of the time period. Multicast frame
A frame intended for a preselected number of computers, such as a specific workgroup.
Glossary
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Non-Return to Zero (NRZ) A digital signal that fluctuates between a high
(positive) voltage level and a low (negative) voltage level and never returns to zero for any measurable period of time.
One’s compliment A digital-based mathematical calculation used to
check for errors or corruption.
Glossary
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Packet switching A type of transmission which does not use a
permanent connection between two points for the duration of the data transfer period. Packets may travel different routes to the same destination.
Parity check A method of verifying the integrity of transmitted
data. Port
A number that represents a logical connection and matches a service with a computer.
Glossary
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Segment Raw data that is divided into smaller units.
Synchronous transmission A type of transmission in which a digital signal is
synchronized with a reference signal to ensure proper timing.
Time period The rate of recurrence of an expected signal level
change.
Glossary
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Unicode A character code that uses 16 bits to represent
individual characters. Unipolar digital signal
A digital signal that fluctuates between a positive five-volt and zero-volt level.
Virtual network A logical network within a LAN.
Glossary