Transcript Computer Network Unit-I

UNIT-I
Computer Network
Computer Network
 Computer network - A collection of computing
devices that are connected in various ways in order
to communicate and share resources
 Usually, the connections between computers in a
network are made using physical wires or cables
However, some connections are wireless, using radio
waves or infrared signals
General Terms
 The generic term node or host refers to any device
on a network
 Data transfer rate - The speed with which data is
moved from one place on a network to another
Goals of Computer Network
 Resource and load sharing
 Programs do not need to run on a single machine
 Reduced cost
 Several machines can share printers, tape drives, etc.
 High reliability
 If a machine goes down, another can take over
 Mail and communication
Network components
 Servers
 Clients
 Transmission Media
 Network Interface Card
 Shared printers and other peripherals
 Hub
 Shared data
 Local Operating System
 Network Operating System
 Switch
Network Components (contd)
 Servers - Servers are computers that hold shared
files, programs, and the network operating system.
Servers provide access to network resources to all the
users of the network. For example, there are file
servers, print servers, mail servers, communication
servers, database servers, print servers, fax servers
and web servers, to name a few.
 Clients - Clients are computers that access and use
the network and shared network resources.
Network Components (contd)
 Transmission Media - Transmission media are the
facilities used to interconnect computers in a network,
such as twisted-pair wire, coaxial cable, and optical fiber
cable. Transmission media are sometimes called
channels, links or lines.
 Network Interface Card - Each computer in a
network has a special expansion card called a network
interface card (NIC). The NIC prepares(formats) and
sends data, receives data, and controls data flow between
the computer and the network.
Network Components (contd)
 Shared printers and other peripherals - Shared printers and
peripherals are hardware resources provided to the users of the
network by servers.
 Hub - Hub is a device that splits a network connection into
multiple computers. It is like a distribution center.
 Shared data - Shared data are data that file servers provide to
clients such as data files, printer access programs and e-mail.
 Local Operating System - A local operating system allows
personal computers to access files, print to a local printer, and have
and use one or more disk and CD drives that are located on the
computer. Examples are MS-DOS, Unix, Linux, Windows 2000,
Windows 98, Windows XP etc.
Network Components (contd)
 Network Operating System - The network operating
system is a program that runs on computers and servers,
and allows the computers to communicate over the
network.
 Switch - Switch is a telecommunication device grouped
as one of computer network components. Switch is like a
Hub but built in with advanced features. Like a hub,
switch doesn't broadcast the received message to entire
network, rather before sending it checks to which system
or port should the message be sent.
Types of Networks
 The size of a network can be expressed by the geographic
area they occupy and the number of computers that are
part of the network. Networks can cover anything from a
handful of devices within a single room to millions of
devices spread across the entire globe.
 Different networks based on size are:
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Personal area network, or PAN
Local area network, or LAN
Metropolitan area network, or MAN
Wide area network, or WAN
Types of Networks (contd)
In terms of purpose, many networks can be
considered general purpose, which means they are
used for everything from sending files to a printer to
accessing the Internet. Some types of networks,
however, serve a very particular purpose. Some of the
different networks based on their main purpose are:
 Storage area network, or SAN
 Enterprise private network, or EPN
 Virtual private network, or VPN
Classification of Computer network
Computer networks can be categorized by following
categories:
 By range
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personal area network (PAN)
wireless PAN
local area network (LAN)
wireless LAN
metropolitan area network (MAN)
wide area network (WAN)
Classification of Computer Network (contd)
 By functional relationship
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client-server
multitier architecture
Peer-to-peer
 By network topology
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bus network
star network
ring network
grid network
toroidal networks and hypercubes
tree and hypertree networks
Layered Network Architecture
 According to the ISO standards, networks have been
divided into 7 layers depending on the complexity of the
functionality each of these layers provide.
 Physical Layer
 Data Link Layer
 Network Layer
 Transport Layer
 Session Layer
 Presentation Layer
 Application Layer
Physical Layer
 This layer is the lowest layer in the OSI model.
 It helps in the transmission of data between two machines that are
communicating through a physical medium.
 The following are the main functions of the physical layer:
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Hardware Specification
Encoding and Signaling
Data Transmission and Reception
Topology and Network Design
Coaxial Cable
Hybrid Cable
Wireless Card Network Card
Data Link Layer
 This layer provides reliable transmission of a packet.
 This layer is concerned with :
 Framing : Breaking input data into frames (typically a few hundred
bytes) and caring about the frame boundaries and the size of each frame.
 Acknowledgment : Sent by the receiving end to inform the source that
the frame was received without any error.
 Sequence Numbering : To acknowledge which frame was received.
 Error Detection : The frames may be damaged, lost or duplicated
leading to errors. The error control is on link to link basis.
 Retransmission : The packet is retransmitted if the source fails to
receive acknowledgment.
 Flow Control : Necessary for a fast transmitter to keep pace with a
slow receiver.
Network Layer
 Its basic functions are routing and congestion
control.
 Routing
 Static
 Dynamic
 Semi-Dynamic
 Congestion Control
 Internetworking
Transport Layer
 Its functions are :
Multiplexing / Demultiplexing
 Fragmentation and Re-assembly
 Types of service
 Error Control
 Flow Control
 Connection Establishment / Release
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Session Layer
 This layer establishes, manages and terminates
connections between applications.
 The session layer sets up, coordinates, and
terminates conversations, exchanges, and dialogues
between the applications at each end.
 It deals with session and connection coordination.
Presentation Layer
 This layer provides independence from differences in
data representation (e.g., encryption) by translating
from application to network format, and vice versa.
 The presentation layer works to transform data into
the form that the application layer can accept.
 This layer formats and encrypts data to be sent
across a network, providing freedom from
compatibility problems.
Application Layer
 This layer supports application and end-user processes.
 Communication partners are identified, quality of service is
identified, user authentication and privacy are considered, and any
constraints on data syntax are identified.
 Everything at this layer is application-specific.
 This layer provides application services for file transfers, e-mail, and
other network software services.
 Telnet and FTP are applications that exist entirely in the application
level. Tiered application architectures are part of this layer.
Network Topologies
Point to Point Connection
Point to Point Connection
 Two computers are connected directly
 Unlimited usage
 Dedicated
 Fixed-price
 Always-on bandwidth
 Providing efficient, dependable high bandwidth communications
 Cost effective
 More cost effective on multiple point to point circuits or a single
connection
 Annual charges are fixed regardless of usage
 Upgrades are easily arranged and implemented as your needs grow
 Speeds
 Available to interconnect your LANs at speeds including 10Mb, 100Mb
and Gigabit Ethernet.
Pint to Multipoint Connection
 In telecommunications, point-to-multipoint
communication is communication which is
accomplished via a distinct type of one-to-many
connection, providing multiple paths from a single
location to multiple locations.
Types of Communication
 Simplex
 Half Duplex
 Full Duplex
Types of Communication (contd)
 Simplex
 Data in a simplex channel is always one way. Simplex
channels are not often used because it is not possible
to send back error or control signals to the transmit
end.
 It's like a one way street. An example of simplex is
Television, or Radio.
Types of Communication (contd)
 Half Duplex
 A half-duplex channel can send and receive, but not
at the same time.
 It's like a one-lane bridge where two way traffic must
give way in order to cross.
 Example of half-duplex is talk-back radio, and CB
Radio (Citizens Band).
Types of Communication (contd)
 Full Duplex
 Data can travel in both directions simultaneously.
There is no need to switch from transmit to receive
mode like in half duplex. Its like a two lane bridge on
a two-lane highway.
 Example: Phone call
Uses of Computer Network
 Communication
 Sharing Resources
 Sharing Software
 Data Sharing
LAN, MAN & WAN
 A LAN (local area network) is a group of computers and
network devices connected together, usually within the same
building.
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A LAN connection is a high-speed connection varying from 10 Mbps to
1000 Mbps
 A MAN (metropolitan area network) is a larger network that
usually spans several buildings in the same city or town.
 A WAN (wide area network), in comparison to a MAN, is not
restricted to a geographical location, although it might be
confined within the bounds of a state or country.
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A WAN connects several LANs, and may be limited to an enterprise (a
corporation or an organization) or accessible to the public. The
technology is high speed and relatively expensive. The Internet is an
example of a worldwide public WAN.
LAN, MAN & WAN (contd)
Criteria
LAN
MAN
WAN
Cost
Low
High
Higher
Network Size
Small
Larger
Largest
Speed
Fastest
Slower
Slowest
Transmission
Media Type
Twisted-pair
Twisted-pair &
fiber optic cables
Fiber optic, radio
wave and satellite
Number of
Computer
Smallest
Large
Largest
Wireless Network
 A wireless network is any type of computer
network that uses wireless data connections for
connecting network nodes.
 Types of wireless networks
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Wireless PAN
Wireless LAN
Wireless mesh network
Wireless MAN
Wireless WAN
Cellular network
Wireless Network (contd)
 Properties
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General
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Wireless networks offer a vast variety of uses by both business and
home users.
Performance
The performance of wireless networks satisfies a variety of
applications such as voice and video.
 The use of this technology also gives room for expansions, such as
from 2G to 3G and, most recently, 4G technology, which stands for
fourth generation of cell phone mobile communications standards.
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Space / Range
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Wireless networks allow for users to designate a certain space which
the network will be able to communicate with other devices through
that network.
Wireless Network (contd)
 Difficulties
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Interference
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Absorption and reflection
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In multipath fading two or more different routes taken by the signal, due to
reflections, can cause the signal to cancel out at certain locations, and to be
stronger in other places
Hidden node problem
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Some materials cause absorption of electromagnetic waves, preventing it
from reaching the receiver, in other cases, particularly with metallic or
conductive materials reflection occurs.
Multipath fading
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Compared to wired systems, wireless networks are frequently subject
to electromagnetic interference.
The hidden node problem occurs in some types of network when a node is
visible from a wireless access point (AP), but not from other nodes
communicating with that AP.
Shared resource problem

Bandwidth allocation becomes complex with multiple participating users.
Peer to Peer Network
 The "peers" are computer systems which are
connected to each other via the Internet.
 Files can be shared directly between systems on the
network without the need of a central server.
 In other words, each
computer on a P2P
network becomes a
file server as well as
a client.
Client Server Network
 A computer network is referred to as client/server if
(at least) one of the computers is used to "serve"
other computers referred to as "clients". Besides the
computers, other types of devices can be part of the
network.
Client Server Network (contd)
 Advantages
 Centralization
 Proper Management
 Back-up and Recovery possible
 Upgradation and Scalability
 Each workstation need not have its own storage capacities
 Security
 Disadvantages
 Congestion in Network
 Not as robust
 Cost
Connection Oriented Services
 There is a sequence of operation to be followed by the users of
connection oriented service. These are :
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Connection is established
Information is sent
Connection is released
 In connection oriented service we have to establish a connection
before starting the communication.
 Connection oriented service is more reliable than connectionless
service. We can resend the message in connection oriented service if
there is an error at the receivers end.
 Example of connection oriented is TCP (Transmission Control
Protocol) protocol.
Connection Less Services
 It is similar to the postal services, as it carries the full address
where the message (letter) is to be carried.
 Each message is routed independently from source to
destination. The order of message sent can be different from
the order received.
 In connectionless the data is transferred in one direction from
source to destination without checking that destination is still
there or not or if it prepared to accept the message.
 Authentication is not needed in this. Example of
Connectionless service is UDP (User Datagram Protocol)
protocol.
Connection Oriented Services & Connection Less
Services
Features
How is data sent?
Connectionless
Connectionless
one packet at a time
as continuous stream of packets
Do packets follow same route?
no
Are resources reserved in network?
no
Are resources reserved in
communicating hosts?
Can data sent can experience variable
latency?
virtual circuit: yes
without virtual circuit: no
virtual circuit: yes
without virtual circuit: no
no
yes
yes
yes
Is connection establishment done?
no
yes
Is state information stored at network
nodes?
no
virtual circuit: yes
without virtual circuit: no
What is impact of node/switch crash?
only packets at node are lost
all virtual circuits through node fail
What addressing information is
needed on each packet?
Is it possible to adapt sending rate to
network congestion?
full source and destination address
hard to do
virtual circuit: a virtual circuit
number
without virtual circuit: full source
and destination address
virtual circuit: easy if sufficient
buffers allocated
without virtual circuit: harder to do
Network Interface
 Interfaces are networking communication points for your computer.
Each interface is associated with a physical or virtual networking
device.
 Typically, your server will have one configurable network interface
for each Ethernet or wireless internet card you have.
 In addition, it will define a virtual network interface called the
"loopback" or localhost interface. This is used as an interface to
connect applications and processes on a single computer to other
applications and processes.
 Many times, administrators configure one interface to service traffic
to the internet and another interface for a LAN or private network.
Prepared by - ROHIT KOSHTA