Data Comm

Topics: OSI model, Data transmission, ASCII Pages: 21 (3181 words) Published: June 22, 2013
(Basics of data communication, OSI layers.)
ALTTC/NP/KKD/Data Communication 1

Data Communications History
• 1838: Samuel Morse & Alfred Veil Invent Morse Code Telegraph System • 1876: Alexander Graham Bell invented Telephone • 1910:Howard Krum developed Start/Stop Synchronisation ALTTC/NP/KKD/Data Communication 2

History of Computing
• 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 ALTTC/NP/KKD/Data Communication 3

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

– 1976: ISO releases HDLC & CCITT releases X.25 (PSPDN)
ALTTC/NP/KKD/Data Communication 4

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

ALTTC/NP/KKD/Data Communication


Voice & Data
• In 70’s & 80’s main thrust in Wide Area Networking (WAN) was to put Data on Voice Circuits using Modem & on ISDN lines • In 90’s the trend is reverse. Major Efforts were on putting Voice Over Data using: – Voice Over Frame Relay – Voice Over Internet – Voice Over ATM etc ALTTC/NP/KKD/Data Communication 6

What is Data Communications? •Exchange of digital information between two digital devices is data communication

ALTTC/NP/KKD/Data Communication


• Networking is the convenient way of making information accessible to anyone, 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
ALTTC/NP/KKD/Data Communication 8

What is Interoperability ?
• The Capability of two or more computers of different vendors to transmit & receive data and to carry out processes as expected by the user is called Interoperability.

IBM Computer
ALTTC/NP/KKD/Data Communication

AT &T Computer

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 ALTTC/NP/KKD/Data Communication 10

Data Representations
• A group of bits are used to represent a character/number/ special symbol/Control Characters • 5-bit code can represent 32 symbols (25=32) • 7-bit code can represent 128 symbols (27=128) & • 8-bit code can represent 256 symbols (28=256) ALTTC/NP/KKD/Data Communication 11

Code Set
• A code set is the set of codes representing the symbols • Very common code sets are : – ASCII : this is ANSI’s 7-bit American Standard Code for Information Interchange • ASCII code(7-bit) is often used with an 8th bit known as parity bit used for detecting errors during Data Transmission • Parity bit is added to the Most Significant bit (MSB)

– EBCDIC : this is IBM’s 8-bit Extended Binary Coded Decimal Interchange Code ALTTC/NP/KKD/Data Communication 12

• ASCII is defined in ANSI X3.4
– 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...
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