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Universi ty of Mauri t iusUniversi ty of Mauri t iusUniversi ty of Mauri t iusUniversi ty of Mauri t ius
CSE 2247– Network Computing
Semester 2 –Year 2010-2011
Lecture 1 – Introduction to Networks
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What is a Computer Network?
A computer network is a system for communicating
between two or more computers and associated devices.It is an interconnection of computers for the purposes of
sharing information and resources.
popu ar examp e o a computer networ s t e nternet,which allows millions of users to share information.
(c) Mr. Chiniah, Lecturer CSE 20112
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Example of a network
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Uses of Computer Network Resource sharing and communication, are two principal
reasons of building and using Computer Network.
Examples of resources shared: Printer, File sharing, Internet Connection, etc.
Some of most popular network applications include:
E-mail, Web-browsing, Digital libraries, Video-on-demand
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Types of Computer Network Class 1: Function-Based Classification
Data
Voice Multimedia
Class 2: Location-and-Distance-based Classification PAN (Personal Area Network)
LAN (Local Area Network)
MAN (Metropolitan Area Network) WAN (Wide Area Network)
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Types of Computer Network (cont..) Class 3: Forwarding-based Classification
Switched Network
Circuit-switching Network Packet-switching Network
Shared Network
Class 4: Ownership-based Classification
Public Networks
Private Networks
Virtual Private Networks
Leased Networks
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Terminology
Bit Rate
Number of bits per second
Given in bps
Bandwidth Maximum frequency supported by the medium.
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ExerciseAn image is 1024 × 768 pixels with 3 bytes/pixel.
a. How long will it take to transmit it over a 56 kbps
modem channel?b. Over a 1-Mbps cable modem?
c. Over a 10-Mb s cable?
d. Over 100-Mbps cable?
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Transmission Medium Guided Transmission Media
Coaxial Cable
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Transmission Medium (cont..) Twisted Pair
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Transmission Medium (cont..) Fibre-Optics
Monomode Fibre-optics cable
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Transmission Medium (Cont..) Multimode Fibre-optics cable
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Transmission Medium (Cont..) Unguided Transmission Media
Electromagnetic Spectrum
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Transmission Medium (Cont..) Radiowave Transmission
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Transmission Medium (Cont..) Microwave Transmission
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Microwave Tower
Transmission path between
Microwave towers
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Transmission Medium (Cont..) Communication Satellite
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Transmission Medium (Cont..) Infrared
Bluetooth
Piconet Scatternet
Wifi
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Reference Models
• The OSI Reference Model
• The TCP/IP Reference Model
•
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Protocol Hierarchies Protocol are used for communication between computers in different
computer networks. Protocol achieves:
What is communicated between computers?
How it is communicated?
When it is communicated?
What conformance (bit sequence) between computers?
Key elements of a protocol are:
SYNTAC: Data format and signal levels
SEMANTICS: Control information for coordination and error handling
TIMING: Synchronization, speed matching, and sequencing
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Protocol HierarchiesI like
rabbits
Location A
3
2
3
2
Location B
Message Philosopher
TranslatorInformationfor the remotetranslator
L: Dutch
Ik vind
konijnen
J'aimebien leslapins
L: Dutch
Ik vind
konijnen
• The philosopher-translator-secretary architecture.
1 1
Secretary
Informationfor the remotesecretary
Fax #---
L: Dutch
Ik vind
konijnen
leuk
Fax #---
L: Dutch
Ik vind
konijnen
leuk
(c) Mr. Chiniah, Lecturer CSE 201120
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Open System Interconnection
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OSI Reference Model
• Layered model:
7. Application6. Presentation
5. Session
. ransport
3. Network
2. Data Link
1. Physical
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The Physical Layer
• Responsibility:
– transmission of raw bits over a communicationchannel.
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– mechanical and electrical interfaces
– time per bit
– distances
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Responsibility:
provide an error-free communication link
Issues:
The Data Link Layer - Data Link Control
header & trailer bits Addressing (Mac Address)
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10110110101 01100010011 10110000001
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The Network Layer Responsibilities:
path selection between end-systems (routing).
subnet flow control. fragmentation & reassembly
translation between different network types.
Issues: packet headers
virtual circuits
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The Transport Layer Responsibilities:
provides virtual end-to-end links between peer processes.
end-to-end flow control Issues:
headers
error detection reliable communication
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The Session Layer
Responsibilities:
establishes, manages, and terminates sessions betweenapplications.
service location lookup
Many protocol suites do not include a session layer.
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The Presentation Layer
Responsibilities:
data encryption data compression
data conversion
Many protocol suites do not include a Presentation Layer.
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The Application Layer Responsibilities:
anything not provided by any of the other layers
Issues: application level protocols
appropriate selection of “type of service”
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Summary of OSI RM
Presentation
Application
Formatting, Compression,Encryption
Provide services to applications
LAYERS FUNCTIONSCORRESPONDING
PROCOTÏLS
HTTP, SMTP, FTP, NFS, Telnet,SMB
JPEG, MIDI, MPEG etc etc
Network File S stem NFS
30
Physical
Data Link
Network
Transport
ess on
Transmit data on media
Reliable data transfer across media;physical addressing
Path selection,logical addressing, routing
Quality and reliability,
ensures data received, segments
, ,control data exchange
SQL, RPC
TCP, UDP, SPX, NetBEUI
IP, IPX, RIP, ICMP, ARP, RARP,
OSPF, NetBEUI, DLC, DecNET
HDLC, SLIP, PPP
NONE
(c) Mr. Chiniah, Lecturer CSE 2011
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TCP/IP Reference Model
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Protocols in TCP/IP model
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Comparing OSI and TCP/IP Models
Concepts central to the OSI model
- Services
-
- Protocols
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A Critique of the OSI Model and
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A Critique of the OSI Model and
Protocols Why OSI did not take over the world
• Bad timing• Bad technology
• Bad implementations• Bad politics
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Bad TimingThe apocalypse of the two elephants.
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