1. Introduction to Information Technologies Chapter 1 - Introduction
Fall 2004
Computer Networks
Chapter 1 - Introduction
History of Internet

2. Data Communication
Exchange of any type of information (data) via some medium
Its predecessor is telecommunication where human voice was transmitted
Three fundamental characteristics
Delivery
Accuracy
Timeliness
Spring 2006
Computer Networks

3. Bits and Bytes
Computers use binary digits or bits (0s and 1s) to represent data
BIT = BInary digiT
The common code for encoding letters is ASCII (American Standard Code for Information Interchange)
7 bits are used to encode a single character
To accomodate larger number of characters Extended ASCII code with 8 bits per character was introduced
8 bits = 1 byte (a unit for measuring amount of data)
Spring 2006
Computer Networks

4. Data Representation Text – using different codes
Each character is represented by certain number of bits
The number of bits in the code determins the number of different characters
ASCII (7 bits), Extended ASCII (8 bits), Unicode (16 bits), ISO (32 bits)
Numbers – Binary number system
Images – A matrix of pixels represented by bit patterns
Video – A combination of images
Audio – Digitized voice and music
Spring 2006
Computer Networks

5. Bits and electrical signals
Data communication uses corresponding electrical signals to represent bits
Different encodings are possible
The simplest way is to represent 1 with negative and 0 with positive voltage
Spring 2006
Computer Networks

6. Humans vs. Machines Humans can recognized the transformed message
receiver
transmitter
MEDIUM
Transformed message
Original message
Noise + attenuation
Humans can recognized the transformed message
Machines
(Not necessarily)
Therefore, a strict set of rules (protocols) are required.
Spring 2006
Computer Networks

7. Components of Data Communication System
Step 1:
Step 2:
Step 3:
::::::::::
Step 1:
Step 2:
Step 3:
::::::::::
Protocol
Protocol
Message
Medium
Sender
Reciever
Spring 2006
Computer Networks

8. Direction of Data Flow Simplex channel Half-duplex channel
The transmission is only in one direction
Half-duplex channel
The transmission is in both directions, but only one at a time (both directions cannot be used at the same time)
Duplex channel
The transmission is in both directions without limitation
Spring 2006
Computer Networks

9. Different Line Configurations
Point-to-point
Two devices on a single channel (dedicated channel)
Multipoint
Many devices on a single channel (shared channel)
Spring 2006
Computer Networks

10. Topology of Networks
Topology defines the arrangement of links in a network
Topology
Partial Mesh
Full Mesh
Bus
Ring
Star
Spring 2006
Computer Networks

11. Computer Networks Classification
Circuit board
Data flow machine
1 m
System
Multicomputer
Room
10 m
100 m
Building
Local area Network (LAN)
1 km
Campus
10 km
City
Metropolitan Area Network (MAN)
100 km
Country
Wide Area Network (WAN)
Continent
1000 km
10,000 km
Planet
The Internet
Spring 2006
Computer Networks

12. LAN – Local Area Network
Single building LAN
backbone
Multiple building LAN
Spring 2006
Computer Networks

13. MAN - Metropolitan Area Network
Public city network
Spring 2006
Computer Networks

14. WAN – Wide Area Network
Spring 2006
Computer Networks

15. Internetworking Concept and Model
The goal is to build a unified, cooperative interconnection of networks that supports a universal communication service
Detaches the notions of communication from the details of network technologies, and hides low level details from the user
Provides a mechanism that delivers packet from their source to their ultimate destination in real time
Spring 2006
Computer Networks

16. The Internet Today
Communication is possible by using a common Internet protocol that glues different networks.
Internet emerged from the academic community and therefore has no central governance so far.
Spring 2006
Computer Networks

17. The internet versus the Internet
Internetowork or internet (small ”i”) – generic term to mean an interconnection of networks
Internet (Uppercase I) – the specific worldwide network that uses the IP protocol (Internet protocol)
Spring 2006
Computer Networks

18. Protocols
A set of rules or conventions agreed by communicating parties.
Protocols allow one to specify/understand communication without knowing details of a particular vendor’s hardware
Complex data communication systems do not use a single protocol to handle all transmission tasks.
They require a set of cooperative protocols: protocol family or protocol suite
Spring 2006
Computer Networks

19. The Key Elements of a Protocol
Syntax
referes to the structure of data, meaning the order in which they are presented
Semantics
refferes to the meaning of each section of bits, how a particular pattern to be interpreted and which action should be taken based on the interpretation
Timing
refferes to when data should be sent and how fast they can be sent
Spring 2006
Computer Networks

20. Standards
Standards provide guidelines to the manufacturers, vendors, goverment agencies and other service providers to ensure connectivity between different entities
Development of standrds is a very slow process
Two types of standards:
De jure (by law) -legislated by an officially recognized body
De facto (by fact) – that are actually implemented into the products)
propriatory (closed)
nonpropriatory (open)
Spring 2006
Computer Networks