Data Communication: Basics, OSI Layers, and History, Lecture notes of Computer Networks

Download Data Communication: Basics, OSI Layers, and History and more Lecture notes Computer Networks in PDF only on Docsity!

K.K.DHUPARSDE (NP-II)

ALTTC

DATA COMMUNICATION

(Basics of data communication,

OSI layers.)

Data Communications History^ • 1838: Samuel Morse & Alfred

Veil Invent Morse CodeTelegraph System

• 1876: Alexander Graham Bell

invented Telephone

• 1910:Howard Krum developed

Start/Stop Synchronisation

Main Contributors of Data Comm.^ • Transmission Technology• Packet Switching Technology• Internet

• 1967: ARPANET

by Advanced Research

Project Agency (ARPA) of U.S.

• 1975: TCP/IP protocol
  • LAN Technology
    • DIX-Ethernet & IEEE 802 Networks
      • WAN
        • 1976: ISO releases HDLC & CCITT releases

X.25 (PSPDN)

Various Networks^ • Home Area Network (HAN)• Local Area Network (LAN)• Metropolitan Area Network (MAN)• Wide Area Network (WAN)• Global Area Network (GAN)

What is Data Communications?^ •Exchange of digital

information between twodigital devices is datacommunication

Networking

• Networking is the convenient way of

making information accessible toanyone, anytime & anywhere.

• Evolution of Networking
  • Computers handling Large Data were

developed

• viz. text, graphics,animation, sound & video
  • Improvements in Personal Computers
    • Small, powerful & cheap user friendly systems.
      • Emergence of Computer Networks
        • Distributed, Intelligent, High-speed LAN/WAN

Requirements of Data Communications^ • 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 synchronisation using Start/stop bits in

case of Asynchronous Transmission

• In Synchronous Transmission the agreed

pattern of Flag

• Signal encoding rules viz. NRZ or RZ• And other higher layer protocol

Data Representations^ • A group of bits are used to

represent a character/number/special symbol/Control Characters

• 5-bit code can represent 32

symbols (

5

• 7-bit code can represent 128

symbols (

7

• 8-bit code can represent 256

symbols (

8

ASCII Code^ • ASCII is defined in ANSI X3.

• Corresponding CCITT recommendation

is

IA5 (International Alphabet No.5)

• ISO specification is ISO 646
  • Total 128 codes
    • 96 codes are graphic symbols (in Col. 2~7).
      • 94 codes are printable• And

2 codes viz. SPACE & DEL characters are

non printable

• 32 codes control symbols (Col. 0 & 1)
  • All are non printable

EBCDIC Code^ • It is an 8-bit code with 256

symbols

• No parity bit for error checking• The graphic symbols are almost

same as ASCII

• Several differences in Control

characters as compared to ASCII

Data Transmission^ • Data Transmission means

movement of the bits over atransmission medium connectingtwo devices

• Two types of Data Transmission

are:– Parallel Transmission– Serial Transmission

17

Parallel Transmission^ •^

In this all the bits of a

byte

are transmitted simultaneously on

separate wires.

-^

Practicable

if^

two

devices

are

close

to

each

other

e.g.

Computer to Printer, Communication within the Computer

(^0) Transmitter

0

1

1

2

0

3

0

4

1

5

0

6

1

7

1

0

0

Receiver

0

0 1

1 0

0

0

0

1

1

1

1

1

1

What is a Bit Rate?^ • Number of bits that can be

transmitted in 1 second

• If t

p^

is the duration of the bit then

the Bit rate R= 1/t

p

• Bit duration need not be same as

the pulse duration

Receiving Data bits^ •^

Received Signal is never same as transmitted

-^

Clock signal samples & regenerates the original bits as it wastransmitted

-^

Received Signal should be sampled at right instant. Otherwiseit will cause bit error

Transmitted SignalReceived SignalClock SignalSampled SignalRecovered Signal

1

1

0

0

0

0

1

1

1

1

0

0

0

0

1

1