Eastwoods Professional College of Science and Technology
Data Communication
Data
-
Distinct pieces of information.
Information in raw or unorganized form (such as alphabets, numbers, or symbols) that refer to,
or represent, conditions, ideas, or objects.
- Data is limitless and present everywhere in the universe.
- Computers: Symbols or signals that are input, stored, and processed by a computer, for output
as usable information.
Communication
- Communication is the activity of conveying meaningful information.
-
theimpartingorinterchangeofthoughts,opinions, or informationbyspeech,writing,orsigns.
What is Data Communication?
- Data Communication is the process of communicating information in binary form between two
or more points.
- Data Communication is sometimes called computer communication because a majority of the
information interchange today is between computers.
Early forms of communication
- Puffs of smoke from the Indian’s signal fire
-
Reflecions of sunlight from a hand-held mirror
Eastwoods Professional College of Science and Technology
Data Communication
Early Uses of Electricity
- The discovery and harnessing of electricity introduced many new possibilities for
communications codes beyond the smoke signals, mirrors, signal flags, and lanterns in use in
the 18th and 19th centuries.
- Early proposals, submitted to a Scottish magazine in 1753 was simple but had profound
implications for hardware. This idea was to run 26 parallel wires from town to town.
- In 1833, Carl Friedrich Gauss use a code base on a 5-by-5 matrix of 25 letters (I and J were
combined) to send messages by deflecting a needle from one to five times, right to left.
The Telegraph
- Mark and space
- An American, Samuel F.B. Morse, invented the electric telegraph.
- morse first developed the telegraph in 1832
- The best-know demonstration took place in 1844, when morese transmitted, over a wire from
Washington to Baltimore, the message “What hath God wrought!”
- The telegraph was the first electrically based communications system to connect the east and
west costs of the United States and both sides of the Atlantic.
Eastwoods Professional College of Science and Technology
Data Communication
Bits and Bytes
- Number 0 and 1 are the symbols of the binary system.
Computers are more efficient if their internal paths and registers are some power of two in length (2
bits, 4 bits, 8bits, 16 bits, and so on). A commonly used grouping is 8 bits, and this 8- bit group is called
a byte or an octet.
Power of Two
20
21
22
23
24
25
26
27
28
Table 1.1 The Power of two
Positional Weight
1
2
4
8
16
32
64
128
256
9-Bit Binary Number
000000001
000000010
000000100
000001000
000010000
000100000
001000000
010000000
100000000
Communication Codes
- A common characteristic of data communications systems is the use of an intelligent device to
convert a character or symbol into coded form and vice versa. In the Morse system; the
intelligent “devices” were the telegraph operators who converted the characters into dots and
dashes.
- Codes
o A code is a previously agreed on set of meanings that define a given set of symbols and
characters.
o Standard interpretations between signaling elements and characters.
o The Key is standard
- Characters
o Characters are the letters, signs and symbols on an input device’s keyboard; some are
used to control the system. (Remember that the space character is just as important as
any other, even though we tend to think of it as “nothing” or “blank”)
o Communication Systems also use control characters that do not print, but these
characters also must be coded. (Carriage Return or Tab)
- Signaling Elements
o Signaling Elements are the representations of characters that are transmitted over
transmission lines. It is easier to design and build machines to recognize signaling
elements than to build them to recognize characters.
o Something that is sent over a transmission channel and used to represent a character.
Eastwoods Professional College of Science and Technology
Data Communication
Different Types of Communication Code
- Baudot Code
o Emile Baudot developed one of the more successful codes suited for machine encoding
and decoding.
o
Modern code
o There was a need for new codes that could represent all characters, check for errors,
and leave room for further expansion.
o They devised a six-level code to designate the difference between upper-and-lowercase
letters.
o Format operations, a code support linefeed and carriage-return characters.
o
o
EBCDIC(Extended Binary Coded Decimal Interchange Code)
 EBCDIC is a modern code using eight bits to represent 256 bits characters. It
was developed by IBM to provide a standard code for its own products
ASCII(American Standard Code for Information Interchange)
 The ASCII format is arrange so that lowercase letters can be change to
uppercase by changing only one bit. Bits 4 through 7 of the numeric characters
also are the BCD (Binary-coded-Decimal) value of the number.