ALLAH
1
Introduction to Computer Networks
INTRODUCTION TO COMPUTER
NETWORKS
Introduction to Computer Networks
Computer Networks
Computer network connects
two or more autonomous
computers.
The computers
geographically
anywhere.
can be
located
Introduction to Computer Networks
LAN, MAN & WAN
Network in small geographical Area (Room, Building or a
Campus) is called LAN (Local Area Network)
Network in a City is call MAN (Metropolitan Area Network)
Network spread geographically (Country or across Globe) is
called WAN (Wide Area Network)
Introduction to Computer Networks
Applications of Networks
Resource Sharing
Hardware (computing resources, disks, printers)
Software (application software)
Information Sharing
Easy accessibility from anywhere (files, databases)
Search Capability (WWW)
Communication
Email
Message broadcast
Remote computing
Distributed processing (GRID Computing)
Introduction to Computer Networks
Network Topology
The network topology
defines the way in which
computers, printers, and
other
devices
are
connected. A network
topology describes the
layout of the wire and
devices as well as the
paths used by data
transmissions.
Introduction to Computer Networks
Bus Topology
Commonly referred to as a
linear bus, all the devices
on a bus topology are
connected by one single
cable.
Introduction to Computer Networks
Star & Tree Topology
The star topology is the most
commonly used architecture in
Ethernet LANs.
When installed, the star topology
resembles spokes in a bicycle
wheel.
Larger networks use the extended
star topology also called tree
topology. When used with network
devices that filter frames or packets,
like bridges, switches, and routers,
this topology significantly reduces
the traffic on the wires by sending
packets only to the wires of the
destination host.
Introduction to Computer Networks
Ring Topology
A frame travels around the ring,
stopping at each node. If a node wants
to transmit data, it adds the data as
well as the destination address to the
frame.
The frame then continues around the
ring until it finds the destination node,
which takes the data out of the frame.
Single ring – All the devices on the
network share a single cable
Dual ring – The dual ring topology
allows data to be sent in both
directions.
Introduction to Computer Networks
Mesh Topology
The
mesh
topology
connects
all
devices
(nodes) to each other for
redundancy and fault
tolerance.
It is used in WANs to
interconnect LANs and for
mission critical networks
like those used by banks
and financial institutions.
Implementing the mesh
topology is expensive and
difficult.
Introduction to Computer Networks
Network Components
Physical Media
Interconnecting Devices
Computers
Networking Software
Applications
Introduction to Computer Networks
Networking Media
Networking media can be
defined simply as the
means by which signals
(data) are sent from one
computer
to
another
(either by cable or wireless
means).
Introduction to Computer Networks
Networking Devices
HUB,
Switches,
Wireless
Access
Modems etc.
Routers,
Points,
Introduction to Computer Networks
Computers: Clients and Servers
In a client/server network
arrangement,
network
services are located in a
dedicated computer whose
only function is to respond
to the requests of clients.
The server contains the
file, print, application,
security, and other services
in a central computer that
is continuously available to
respond to client requests.
Introduction to Computer Networks
Networking Protocol: TCP/IP
Models of the Internet
OSI/ISO Reference Model
Application
Presentation
Session
Transport
Network
Data Link
Physical
TCP/IP Reference Model
Application
Model Layers
Open Systems Interconnection
(International Standards Office)
Transport
Internet
Host-to-network
Transmission Control
Protocol/
Internet Protocol
1) Physical layer
• Purpose: Necessary infrastructure.
• Think "wires in the ground and switches
connecting them".
• This is the physical hardware of the internet.
• Wires/optical cables/wireless links and other
technologies provide a way for transmission of
raw bits (0s and 1s).
• Routers and switches connect these cables
and direct the traffic.
2) Data link layer
• Purpose: Provides basic connection between
two logically connected machines.
• Think: “I stuff packets down a wire to my
neighbour”
• Send raw packets between hosts.
• Basic error checking for lost data.
• In TCP/IP the "Physical layer" and the "Data
Link" layer are grouped together and called
the host-to-network layer.
3) Network Layer/Internet Layer
• Purpose: Provide end-to-end communication
between any two machines.
• Think: “I try to get a packet to its destination”
• Tells data which link to travel down.
• Addresses the problem known as routing.
• Deals with the question "where do I go next to
get to my destination?"
• Ensures packets get from source A to
destination B.
4) Transport Layer
• Purpose: Ensure that data gets between A and B.
• Think: “From the source and destination, I make
sure that the data gets there”.
• Ensures a data gets between source and
destination.
• If necessary ensure that connection is lossless
(resend missing data).
• Provides flow control if necessary (send data
faster or slower depending on the network
conditions).
5) Session Layer (not TCP/IP)
• Purpose: Provides a single connection for one
application.
• Think: “I am in charge of the entire message.”
• This connection may be two way or may be
synchronised.
• Not discussed much as it is never implemented.
6) Presentation Layer (Not TCP/IP)
• Purpose: Provides commonly used functions
for applications.
• Think: “I meet internationalisation standards”.
• The main job of the presentation layer is to
ensure that character sets match – e.g. that
Chinese characters are correctly received by
the sends.
• Again not discussed much as it is never
implemented.
7) Application layer
• Purpose: The computer programs which actually do
things with the network.
• Think: “I deliver the mail, browse the web etc.”
• For example, your email client program which will talk
to the email server at the other end.
• At this layer, we have many protocols (http, snmp,
smtp, ftp, telnet) which different bits of software use.
• We often talk in terms of client and server architecture
for the software.
TCP/IP model in summary
Internet (IP) addresses
richard@manor.york.ac.uk (email)
http://www.apoptygma.eu.org (www)
ftp://ftp.uk.debian.org (file transfer)
telnet://towel.blinkenlights.nl (telnet)
144.32.100.24
These are the “real” IP addresses
148.122.211.110 of the above sites. IP addresses
are 32 bits grouped into 4 octets.
195.224.53.39
(Octet = 8 bits – a number from
62.250.7.101
0-255)
IP Networks(1)
• IP addresses use less significant bits first to
indicate sub-networks.
• IP address: 123.45.67.89
• Netmask:255.255.255.0 (no holes allowed)
• If two IP addresses are the same when bitwise
AND’d against the netmask then they are on
the same subnet.
• 123.45.67.?? is always on the same subnet in
the above example.
IP Networks(2)
• IP networks were originally subdivided into
class A, B, C, D and E networks.
Start
End
Networks
Hosts/network
A
1.0.0.0
127.255.255.255
126
16 million
B
128.0.0.0
191.255.255.255
16,382
64K
C
192.0.0.0
223.255.255.255
2 million
254
D
224.0.0.0
239.255.255.255
Multicast
E
240.0.0.0
247.255.255.255
Reserved
Hub
Switch
Switch? Router?
Basic Definitions: Host, Router, Switch,
Source, Destination
• Host: A machine which is a point on a network
which packets travel through – a node in a graph.
• Router: A host which finds a route for packets to
travel down – an intermediate point in a journey.
• Switch: Often used interchangeably with router
but implies that the routes are “fixed”.
• Source: Where data is coming from.
• Destination: (or sink) Where data is going to.
Introduction to Computer Networks
Applications
E-mail
Searchable Data (Web Sites)
E-Commerce
News Groups
Internet Telephony (VoIP)
Video Conferencing
Chat Groups
Instant Messengers
Internet Radio