Data communication refers to the electronic transmission of data between computers or other electronic devices. Standard telephone lines were historically used for data communication by connecting modems to computers on each end. Modems convert digital data to analog signals for transmission over telephone lines and back to digital signals on the receiving end. While telephone lines allowed early long-distance data communication, digital telephone lines and dedicated network cables now provide faster transmission speeds.

1. Data Communication with standard
telephones lines By Muhammad
Ahtsham 1
Muhammad Ahtsham

2. Data Communication with standard
telephones lines By Muhammad
Ahtsham 2
It is an application of telecommunications
technology for the purpose of transmitting data.
It transmit data especially to, from , or between
computers.
It refers to the moving or transferring of data
between two electronic devices.

3. Brief History of Data Communication
 1838: Samuel Morse & Alfred Veil Invent Morse
Code Telegraph System
 1876: Alexander Graham Bell invented
Telephone
 1910: Howard Krum developed Start/Stop
Synchronization.
 1930: Development of ASCII transmission Code
 1945: Allied Governments develop the First Large
Computer
 1950: IBM releases its first computer IBM 710
 1960: IBM releases the First Commercial Computer IBM
360
 Than from IC and microchips till SS7, Data communication is so
easy that today data is transferred in fraction of seconds.
Data Communication with standard
telephones lines By Muhammad
Ahtsham 3

4. Data Communication with standard
telephones lines By Muhammad
Ahtsham 4
 At least Two Devices ready to communicate
 A Transmission Medium
 A set of Rules & Procedure for proper communication
(Protocol)
 Standard Data Representation
 Transmission of bits either Serial or Parallel
 Bit synchronization using Start/stop bits in case of
Asynchronous Transmission
 In Synchronous Transmission the agreed pattern of Flag
 Signal encoding rules viz. NRZ or RZ
 Other higher layer protocol
Requirements of Data Communications

5. Communications Channels
A communications channel is a pathway over
which information can be conveyed.
It may be defined by a physical wire that
connects communicating devices, or by a radio,
laser, or other radiated energy source that has no
obvious physical presence.
Data Communication with standard
telephones lines By Muhammad
Ahtsham 5

6. Types of Communication
Microwave Communications:
• Line-of-sight devices which must be placed in relatively
high locations.
• Information is converted to a microwave signal, sent
through the air to a receiver, and recovered.
Data Communication with standard
telephones lines By Muhammad
Ahtsham 6

7. Satellite transmission:
• Communications satellites are relay stations that
receive signals from one earth station and rebroadcast them
to another.
• They use microwave signals.
Data Communication with standard
telephones lines By Muhammad
Ahtsham 7

8.  Telephone circuits are often used to transfer data.
 Telephone networks use circuit switching. The telephone
network had its beginnings in the late 1800s. The entire
network, which is referred to as the plain old telephone system
(POTS), was originally an analog system using analog signals
to transmit voice.
 Networks commonly use dedicated media to transmit data.
However, the public telephone system can also be used for
data communications.
 Standard phone lines transmit data much more slowly than
network media.
Data Communications over Standard
Telephone Lines
Data Communication with standard
telephones lines By Muhammad
Ahtsham 8

9.  Devices such as modems make phone lines practical for
data transmission over long distances.
 Most telephone lines are analog, not digital.
 Modem converts it from analog format to digital format.
Data Communications over Standard Telephone Lines
- Modems
Data Communication with standard
telephones lines By Muhammad
Ahtsham 9

10. As PCs transmit and receive data in digital format, a
device called a modem is needed to convert digital data to
analog format for transmission over phone lines
(MOdulation).
When receiving data from another computer, the modem
converts it from analog format to digital format
(DEModulation).
Data Communication with standard
telephones lines By Muhammad
Ahtsham 10

11. `
The analog signal
(audible)
is sent through
telephone lines.
MODEM MODEM 011010001011010001
Digital signal
Digital signal
This modem converts
digital to analog.
This modem converts
analog to digital.
Data Communication with standard
telephones lines By Muhammad
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12. When choosing a modem, consider the following
factors:
 Transmission speed: The speed at which the modem
sends data - which is measured in bits per second.
 Data compression: The technology the modem uses
to shrink data so it can be transmitted faster.
 Error correction: The method the modem uses to
ensure data is sent and received without errors.
 Internal versus external: It describes whether or not
the modem fits inside the PC case.
Data Communications over Standard Telephone Lines -
Choosing a Modem
Data Communication with standard
telephones lines By Muhammad
Ahtsham 12

13.  Telephone companies are now installing digital
telephone lines which are dedicated to transmitting data
in digital format.
 Digital phone lines transmit data at much higher speeds
than standard analog phone lines.
 Often, data travels across analog lines and digital lines.
In such cases, data may need to be converted from one
format to another multiple times before reaching its
destination.
Using Digital Telephone Lines
Data Communication with standard
telephones lines By Muhammad
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14. Data Communication with standard
telephones lines By Muhammad
Ahtsham 14

15. Data Communication with standard
telephones lines By Muhammad
Ahtsham 15
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16. Data Communication with standard
telephones lines By Muhammad
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