View
220
Download
0
Category
Preview:
Citation preview
8/4/2019 CH02 Basic Concepts of Data Communications
1/75
TJ 2013 Data Communications
Basic Concepts of
Data CommunicationsChapter 2
8/4/2019 CH02 Basic Concepts of Data Communications
2/75
TJ 2013 Data Communications
Objectives
At the end of this chapter, studentsshould: Be able to differentiate between host
and terminal Be able to differentiate between bit and
byte
Be able to explain various types of
character code Be able to explain the different types of
transmission modes.
8/4/2019 CH02 Basic Concepts of Data Communications
3/75
TJ 2013 Data Communications
Contents
Host vs. Terminal
Bits vs. Byte
Character Code Serial vs. Parallel Transmission
Asynchronous vs. Synchronous
Transmission Simplex, Half-Duplex & Full-Duplex
Communications
8/4/2019 CH02 Basic Concepts of Data Communications
4/75
TJ 2013 Data Communications
Host vs. Terminal
8/4/2019 CH02 Basic Concepts of Data Communications
5/75
TJ 2013 Data Communications
Host
A computer on a network thatprovides services to other computerson the network
Accessed by a user working at aremote location.
System that contains data is called
the host, while the computer atwhich the user sits is called theterminal.
8/4/2019 CH02 Basic Concepts of Data Communications
6/75
TJ 2013 Data Communications
Host
Types of host:
(revision of OSK topic)
Super Computer Mainframe
Mini Computer
Micro Computer
8/4/2019 CH02 Basic Concepts of Data Communications
7/75
TJ 2013 Data Communications
Terminal
Some definitions of terminal:
A device that allows users to sendcommands to a computer somewhere
else.
A monitor and keyboard attached to acomputer (usually a mainframe), used
for data entry and display. Unlike a personal computer, a terminal
does not have its own CPU or hard disk
8/4/2019 CH02 Basic Concepts of Data Communications
8/75
TJ 2013 Data Communications
Terminal
Some definitions of terminal:
A computer Workstation linked to aServer or other computer over a
network on which a user may displayinformation
Machine that allows you to send
commands to a remote computer A device that works as a client of a
central computer or host in a network
8/4/2019 CH02 Basic Concepts of Data Communications
9/75
TJ 2013 Data Communications
Terminal
Types of terminal
Dumb
Smart
Intelligent
8/4/2019 CH02 Basic Concepts of Data Communications
10/75
TJ 2013 Data Communications
Terminal
Dumb Terminal A computer terminal with no processing
or programming capabilities, generally
used for simple data entry or retrievaltasks.
Consist of a keyboard and displaymonitor
Keyboard is used to sent data to the CPU Display monitor acts as output device
that accepts data from the CPU.
8/4/2019 CH02 Basic Concepts of Data Communications
11/75
TJ 2013 Data Communications
Terminal
Smart Terminal
A terminal that can do some processing,usually to edit data it receives
Consist of keyboard, display monitorand memory
Has the capability of sending additional
information to host such as terminaladdress, error control etc.
8/4/2019 CH02 Basic Concepts of Data Communications
12/75
TJ 2013 Data Communications
Terminal
Intelligent
A terminal that has both memory anddata processing capabilities
Contains not only a keyboard andscreen, but also has built-in processingcapabilities and storage devices
Programmable terminal to perform newtasks such as, write data to the storagedevices.
8/4/2019 CH02 Basic Concepts of Data Communications
13/75
TJ 2013 Data Communications
Host vs. Terminal
8/4/2019 CH02 Basic Concepts of Data Communications
14/75
TJ 2013 Data Communications
Bits vs. Bytes
8/4/2019 CH02 Basic Concepts of Data Communications
15/75
TJ 2013 Data Communications
Bits
A bitis the smallest unit of informationthat can be stored or manipulated on acomputer
It consists of either zero or one. Depending on meaning, implication, or
even style it could instead be described asfalse/true, off/on, no/yes, and so on.
We can also call a bita binarydigit,especially when working with the 0 or 1values
8/4/2019 CH02 Basic Concepts of Data Communications
16/75
TJ 2013 Data Communications
Bytes
A byte also happens to be how manybits are needed to represent lettersof the alphabet and other characters.
For example, the letter "A" would be0100 0001
8/4/2019 CH02 Basic Concepts of Data Communications
17/75
TJ 2013 Data Communications
Bytes
Revision
Hexadecimal
0100 = ?
1000 = ?
1010 = ?
8/4/2019 CH02 Basic Concepts of Data Communications
18/75
TJ 2013 Data Communications
Bit vs. Byte
The Basic Data Transfer
kilo (k)* = 10 ^ 3 = 1,000 (thousand)
mega (M) = 10 ^ 6 = 1,000,000 (million)
giga (G) = 10 ^ 9 = 1,000,000,000 (billion)
tera (T) = 10 ^ 12 = 1,000,000,000,000 (trillion)
* Note:k = kilobitK = Kilobyte
8/4/2019 CH02 Basic Concepts of Data Communications
19/75
TJ 2013 Data Communications
Bit vs. Byte
Data Storage / Memory Math
1 byte (B) = 8 bits (b)
1 Kilobyte (K / KB) = 2^10 bytes = 1,024 bytes
1 Megabyte (M / MB) = 2^20 bytes = 1,048,576 bytes
1 Gigabyte (G / GB) = 2^30 bytes = 1,073,741,824 bytes
1 Terabyte (T / TB) = 2^40 bytes = 1,099,511,627,776 bytes
8/4/2019 CH02 Basic Concepts of Data Communications
20/75
TJ 2013 Data Communications
Character Code
8/4/2019 CH02 Basic Concepts of Data Communications
21/75
TJ 2013 Data Communications
Data Representation
Information comes in different forms Text, numbers, images ,audio, video, etc.
With few exceptions, digital computerscommunicate through a series of 1s and 0sknown as bits.
This binary representation can also bethought of as being on and off.
8/4/2019 CH02 Basic Concepts of Data Communications
22/75
TJ 2013 Data Communications
Data Representation
Groups of bits are referred to as bytes In most systems, a byte consists of 8 bits
Usually each byte represents a single character
A-Z, a-z, 0-9 punctuation characters (e.g., @, #, %)
special characters (LF, CR, ESC)
Bits and bytes are closely related to
the binary number system.
8/4/2019 CH02 Basic Concepts of Data Communications
23/75
TJ 2013 Data Communications
Character Codes The relationship of bytes to characters is
determined by a character code
Each time a user presses a key on aterminal/PC, a binary code is generated
for the corresponding character.
8/4/2019 CH02 Basic Concepts of Data Communications
24/75
TJ 2013 Data Communications
Character Codes
Various character codes have been used indata communication including:
Morse, Baudot
EBCDIC, ASCII Unicode
Regardless of the character code, both theterminal/ host or sender/receiver must
recognize the same coding scheme
8/4/2019 CH02 Basic Concepts of Data Communications
25/75
TJ 2013 Data Communications
Morse Code
First character code developed
For transmitting data over telegraphwires
telegrams
Used dots (short beep) and dashes(long beeps) instead of 1s and 0s
More frequent the character, thefewer the beeps
8/4/2019 CH02 Basic Concepts of Data Communications
26/75
TJ 2013 Data Communications
8/4/2019 CH02 Basic Concepts of Data Communications
27/75
TJ 2013 Data Communications
Morse Code
Problems:
variable length characterrepresentation
required pauses between letters
no lower case, few punctuation orspecial characters
no error detection mechanism
8/4/2019 CH02 Basic Concepts of Data Communications
28/75
TJ 2013 Data Communications
Baudot Code
One of first codes developed for machineto machine communication
Uses 1s and 0s instead of dots and
dashes For transmitting telex messages (punch
tape)
8/4/2019 CH02 Basic Concepts of Data Communications
29/75
TJ 2013 Data Communications
Baudot Code
Fixed character length (5-bits) 32 different codes
increased capacity by using two codes
for shifting11111 (32) Shift to Lower (letters)
11011 (27) Shift to Upper (digits,punctuation)
4 special codes for SP, CR, LF & blank Total = 26 + 26 + 4 = 56 different
characters
8/4/2019 CH02 Basic Concepts of Data Communications
30/75
TJ 2013 Data Communications
8/4/2019 CH02 Basic Concepts of Data Communications
31/75
TJ 2013 Data Communications
Badout Code
Problems: required shift code to switch between
character sets
no lower case, few special characters no error detection mechanism
characters not ordered by binary value
designed for transmitting data, not fordata processing
8/4/2019 CH02 Basic Concepts of Data Communications
32/75
TJ 2013 Data Communications
Badout Code
International Baudot
Added a 6th bit for parity
Used to detect errors within a single
character
8/4/2019 CH02 Basic Concepts of Data Communications
33/75
TJ 2013 Data Communications
EBCDIC
Extended Binary Coded DecimalInterchange Code
8-bit character code developed by IBM
used for data communication, processing andstorage
extended earlier proprietary 6-bit BCD code
designed for backward compatibility ormarketing?
still in use today on some mainframes andlegacy systems.
8/4/2019 CH02 Basic Concepts of Data Communications
34/75
TJ 2013 Data Communications
EBCDIC
Allows for 256 different characterrepresentations (28)
includes upper and lower case
lots of special characters (non-printable)
lots of blank (non-used codes)
assigned to international characters in
various versions used with/without parity (block
transmissions)
8/4/2019 CH02 Basic Concepts of Data Communications
35/75
TJ 2013 Data Communications
8/4/2019 CH02 Basic Concepts of Data Communications
36/75
TJ 2013 Data Communications
ASCII Code American Standard Code for Information
Interchange 7-bit code developed by the American
National Standards Institute (ANSI) most popular data communication character
code today Allows for 128 different character
representations (27) includes upper and lower case
lots of special characters (non-printable) generally used with an added parity bit better binary ordering of characters than
EBCDIC
8/4/2019 CH02 Basic Concepts of Data Communications
37/75
TJ 2013 Data Communications
ASCII Code
Extended ASCII uses 8 data bitsand no parity
Used for processing and storage of data
Allows for international characters
8th bit stripped of for transmission ofstandard character set
8/4/2019 CH02 Basic Concepts of Data Communications
38/75
TJ 2013 Data Communications
8/4/2019 CH02 Basic Concepts of Data Communications
39/75
TJ 2013 Data Communications
8/4/2019 CH02 Basic Concepts of Data Communications
40/75
TJ 2013 Data Communications
UNICODE Designed to support international
languages:Latin; Greek; Cyrillic; Armenian; Hebrew; Arabic;Syriac; Thaana; Devanagari; Bengali; Gurmukhi;Oriya; Tamil; Telegu; Kannada; Malayalam;Sinhala; Thai; Lao; Tibetan; Myanmar; Georgian;
Hangul; Ethiopic; Cherokee; Canadian-AboriginalSyllabics; Ogham; Runic; Khmer; Mongolian; Han(Japanese, Chinese, Korean ideographs);Hiragana; Katakana; Bopomofo and Yi
8/4/2019 CH02 Basic Concepts of Data Communications
41/75
TJ 2013 Data Communications
UNICODE
Uses a 16-bit code for total of 65,536possible char.
Incorporates ASCII in first 128 codes
Incorporates LATIN in first 256 codes
Support found in newer hardware &software, especially web technologies
(e.g., JAVA, XML, HTML)
For more see www.unicode.org
8/4/2019 CH02 Basic Concepts of Data Communications
42/75
TJ 2013 Data Communications
Summary of Character Codes
Morse = .-
Baudot = 5 bit (no parity)
Int. Baudot = 6 bit (5 data + 1 parity)
ASCII = 8 bit (7 data + 1 parity)
or
= 8 bit (no parity)
EBCDIC = 9 bit (8 data + 1 parity)
or
= 8 bit (no parity)
UNICODE = 16 bits (no parity)
8/4/2019 CH02 Basic Concepts of Data Communications
43/75
TJ 2013 Data Communications
Summary of Character Codes
Normally terminals and hosts mustuse the same code
However, code conversionhardware/software can be used toallow different machines tocommunicate
Bits per character affect storage requirements
throughput of information
8/4/2019 CH02 Basic Concepts of Data Communications
44/75
TJ 2013 Data Communications
Summary of Character Codes
Use of larger codes became feasibledue to
higher transmission speeds
denser storage mediums
Choice of character coding schemeis a trade off between
simplicity & brevity
expressivity
8/4/2019 CH02 Basic Concepts of Data Communications
45/75
TJ 2013 Data Communications
Serial vs. Parallel
Transmission
8/4/2019 CH02 Basic Concepts of Data Communications
46/75
TJ 2013 Data Communications
Data Transmissions
8/4/2019 CH02 Basic Concepts of Data Communications
47/75
TJ 2013 Data Communications
Transmission Mode
8/4/2019 CH02 Basic Concepts of Data Communications
48/75
TJ 2013 Data Communications
Parallel
Multiple bits travel down individualwires in a parallel mode
Faster than serial
Shorter distances than possible withserial
8/4/2019 CH02 Basic Concepts of Data Communications
49/75
TJ 2013 Data Communications
Parallel Transmission
8/4/2019 CH02 Basic Concepts of Data Communications
50/75
TJ 2013 Data Communications
Serial
Bits travel along a single wire, one ata time
Slower than parallel
Longer distances possible than withparallel
Examples
USB (universal serial bus) - high-speed,multipoint serial connection standard
IEEE-1394 (Firewire) - higher speed (thanUSB), multipoint serial connection standard
8/4/2019 CH02 Basic Concepts of Data Communications
51/75
TJ 2013 Data Communications
Serial
Serial transmission can be dividedinto two modes:
Synchronous
Asynchronous
8/4/2019 CH02 Basic Concepts of Data Communications
52/75
TJ 2013 Data Communications
Serial Transmission
8/4/2019 CH02 Basic Concepts of Data Communications
53/75
TJ 2013 Data Communications
Asynchronous
Timing of devices independentlyestablished
Start and stop bits are used to
establish timing for each charactertransmitted
Character-at-a-time transmission
Overhead includes start bit and oneor more stop bits per charactertransmitted
8/4/2019 CH02 Basic Concepts of Data Communications
54/75
TJ 2013 Data Communications
In asynchronous transmission, we
send 1 start bit (0) at the beginningand 1 or more stop bits (1s) at the end
of each byte. There may be a gap
between each byte.
Note:
8/4/2019 CH02 Basic Concepts of Data Communications
55/75
TJ 2013 Data Communications
8/4/2019 CH02 Basic Concepts of Data Communications
56/75
TJ 2013 Data Communications
Asynchronous here means
asynchronous at the byte level, butthe bits are still synchronized; their
durations are the same.
Note:
8/4/2019 CH02 Basic Concepts of Data Communications
57/75
TJ 2013 Data Communications
Synchronous
Timing is established by theexchange of a clocking signalsupplied by a device or embedded in
the carrier Block-at-a-time transmission
Synchronization characters precedeand follow the data block
Overhead includes bits insynchronization characters
8/4/2019 CH02 Basic Concepts of Data Communications
58/75
TJ 2013 Data Communications
In synchronous transmission,
we send bits one after another withoutstart/stop bits or gaps.
It is the responsibility of the receiver to
group the bits.
Note:
8/4/2019 CH02 Basic Concepts of Data Communications
59/75
TJ 2013 Data Communications
8/4/2019 CH02 Basic Concepts of Data Communications
60/75
TJ 2013 Data Communications
Transmissions Efficiency
Transmissions Efficiency
efficiency=data transmitted X 100
total bits sent
8/4/2019 CH02 Basic Concepts of Data Communications
61/75
TJ 2013 Data Communications
Transmissions Efficiency
Example
Compare a 10K Byte data transmission
usingi. Asynchronous (1 start & 1 stop bit)
ii. Synchronous (10 bytes for wholetransmission)
Determine the efficiency (10 kBytes = 80kbits).
8/4/2019 CH02 Basic Concepts of Data Communications
62/75
TJ 2013 Data Communications
Transmissions Efficiency
Solution
Asynchronous:Add 2 bits (1 Start and 1 Stop bits) for every byte transmitted.
80 kbits + 20 kbits = total of 100 kbits transmitted
efficiency= data transmitted X 100total bits sent
= 80 X 100100
= 80 %
8/4/2019 CH02 Basic Concepts of Data Communications
63/75
TJ 2013 Data Communications
Transmissions Efficiency
SolutionSynchronous
Add 10 bytes (80 bits) for the complete 10K bytedata packet.
80 kbits + 80 bits = total of transmitted
efficiency = data transmitted x 100
= 80 000 X 10080 080
= 99.9%
8/4/2019 CH02 Basic Concepts of Data Communications
64/75
TJ 2013 Data Communications
8/4/2019 CH02 Basic Concepts of Data Communications
65/75
TJ 2013 Data Communications
Simplex, Half-Duplex&Full-Duplex Transmission
Directions
8/4/2019 CH02 Basic Concepts of Data Communications
66/75
TJ 2013 Data Communications
Transmission Characteristics
A character code determines what bits we willsend between a terminal and host
But how will those bits be sent:
Direction of Transmission Path
Parallel vs. Serial Transmission
Serial Transmission Timing
Line Topology
Others which well look at later speed
organization of data (protocol)
transmission media
8/4/2019 CH02 Basic Concepts of Data Communications
67/75
TJ 2013 Data Communications
Flow of Transmission Path
Simplex
Half duplex
Full duplex
8/4/2019 CH02 Basic Concepts of Data Communications
68/75
TJ 2013 Data Communications
Simplex
Data in a simplex channel is alwaysone way.
Simplex channels are not often used
because it is not possible to sendback error or control signals to thetransmit end.
It's like a one way street.
An example of simplex is Television,or Radio
8/4/2019 CH02 Basic Concepts of Data Communications
69/75
TJ 2013 Data Communications
Simplex
8/4/2019 CH02 Basic Concepts of Data Communications
70/75
TJ 2013 Data Communications
Half-Duplex
A half-duplex channel can send andreceive, but not at the same time.
It's like a one-lane bridge where two waytraffic must give way in order to cross.Only one end transmits at a time, theother end receives.
In addition, it is possible to perform errordetection and request the sender toretransmit information that arrivedcorrupted.
8/4/2019 CH02 Basic Concepts of Data Communications
71/75
TJ 2013 Data Communications
Half-Duplex
In some aspects, you can think ofInternet surfing as being half-duplex,as a user issues a request for a web
document, then that document isdownloaded and displayed before theuser issues another request.
Another example of half-duplex istalk-back radio
8/4/2019 CH02 Basic Concepts of Data Communications
72/75
TJ 2013 Data Communications
Half Duplex
8/4/2019 CH02 Basic Concepts of Data Communications
73/75
8/4/2019 CH02 Basic Concepts of Data Communications
74/75
TJ 2013 Data Communications
Full-Duplex
An example can be a consumerwhich uses a cable connection to notonly receive TV channels, but also
the same cable to support theirphone and Internet surfing. All theseactivities can occur simultaneously.
8/4/2019 CH02 Basic Concepts of Data Communications
75/75
Full Duplex
Recommended