Networking lec1 4

Computer Networking
Unit 1
Dr. V. Dutta

Subject : Computer Networks (IC-701)
Unit 1
Computer Network, Goals and Applications, Reference
models – OSI and TCP/IP. A Comparative study. Network
hardware – LAN, MAN and WAN and topologies,
Network Software –protocol hierarchies, design issues
for the layers, Connection Oriented and connection less
services, Switching Techniques – Circuit Switching,
Message switching, Packet Switching.
MCA VIISec B Computer Networking Class-Notes 2

Computer Network
• A computer network is a group of computers that
use a set of common communication protocols over
digital interconnections for the purpose of sharing
resources located on or provided by the network
nodes.
• A network consists of two or more computers
connected together, and they can communicate and
share resources (e.g. information) The System can be
geographically located anywhere.

Network Goals
• Allow activities on multiple computer systems to
communicate with each other
• Shared memory, files, or data
• Message passing
• Remote Procedure Call
• Integrated applications — distributed across physical
space
• Create abstractions that make these (relatively)
transparent

Computer Network Features
• Communication speed
• File sharing
• Back up and Roll back is easy
• Software and Hardware sharing
• Security
• Scalability
• Reliability

Advantages
• Sharing devices such as printers saves money.
• Site (software) licenses are likely to be cheaper than
buying several standalone licenses.
• Files can easily be shared between users.
• Network users can communicate by email and
instant messenger.

Disadvantages
• Purchasing the network cabling and file servers can be
expensive.
• Managing a large network is complicated, requires training
and a network manager usually needs to be employed.
• If the file server breaks down the files on the file server
become inaccessible. Email might still work if it is on a
separate server. The computers can still be used but are
isolated.
• Viruses can spread to other computers throughout a
computer network.
• There is a danger of hacking, particularly with wide area
networks. Security procedures are needed to prevent such
abuse, eg a firewall.

Types of Networks
Depending on one’s perspective, we can classify
networks in different ways
• Based on transmission media: Wired (UTP, coaxial
cables, fiber-optic cables) and Wireless
• Based on network size: LAN and WAN (and MAN)
• Based on management method: Peer-to-peer and
Client/Server
• Based on topology (connectivity): Bus, Star, Ring
etc

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.

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Peer-to-Peer Networks
•Peer-to-peer network is also called workgroup
•No hierarchy among computers  all are equal
•No administrator responsible for the network
MCA VIISec B Computer Networking Class-Notes

12
•Advantages of peer-to-peer networks:
• Low cost
• Simple to configure
• User has full accessibility of the computer
•Disadvantages of peer-to-peer networks:
• May have duplication in resources
• Difficult to uphold security policy
• Difficult to handle uneven loading
•Where peer-to-peer network is appropriate:
• 10 or less users
• No specialized services required
• Security is not an issue
• Only limited growth in the foreseeable future

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Clients and Servers
1. Network Clients (Workstation)
Computers that request network resources or services
1. Network Servers
Computers that manage and provide network resources and
services to clients
 Usually have more processing power, memory and
hard disk space than clients
 Run Network Operating System that can manage not
only data, but also users, groups, security, and
applications on the network
 Servers often have a more stringent requirement on
its performance and reliability

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Advantages of client/server networks
• Facilitate resource sharing – centrally administrate and
control
• Facilitate system backup and improve fault tolerance
• Enhance security – only administrator can have access to
Server
• Support more users – difficult to achieve with peer-to-peer
networks
Disadvantages of client/server networks
• High cost for Servers
• Need expert to configure the network
• Introduce a single point of failure to the system

P2P topology is where one
device is directly connectedwith
another device.
In PTM, Data transmittedfrom
the centralbase stationis
broadcastingtoall the
subscribersBut datacoming
from a subscriber is only
received by the base station.
PTM topology is typically used in
wireless LAN, and wireless WAN.

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Topology ― 3 basic types
Physical, Logical and Hybrid
Bus Topology(Daisy chain) Ring
Topology
Star Topology
Hub

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Bus Topology & Ring Topology
• Simple and low-cost
• A single cable called a trunk (backbone, segment)
• Only one computer can send messages at a time
• Passive topology - computeronly listen for, not regeneratedata
Both are not secure, not fault tolerantand difficult to trouble shoot.
Star Topology
• Each computerhas a cable connected to a single point
• More cabling, hence higher cost
• All signals transmissionthroughthe hub; if down, entire network down
• Depending on the intelligence of hub, two or more computersmay send
message at the same time.

1.
In star topology, the nodes are
connected to the central hub or router.
In ring topology, every node is
connected to it’s left and right side
nodes.
2.
In star topology, only hub is failure
point.
In ring topology, every nodes are failure
point.
3. The cost of star topology is high. The cost of ring topology is low.
4.
In star topology, the information is
travel from central hub or router to all
the nodes.
In ring topology, the information is
travel from nodes to nodes in ring
manner in one direction.
5.
The cables are required in star topology
more than the ring topology.
The cables are required in ring topology
less than the star topology.
6.
There are n links in Star topology, if
there are n nodes.
There are also n links in ring topology, if
there are n nodes present.
7.
A new cable is added to the central hub
to add a new node.
Whereas to add a new node in ring
topology, the connection must be
broken.

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
• Centralized Control
• Distributed processing (GRID Computing)
• Security is good - users cannot see other users' files unlike on stand-alone
machines.
• Data is easy to backup as all the data is stored on the file server.

*All People Seems to Need DataProcessing

TCP/IP that is Transmission Control Protocol and Internet Protocol
was developed by Department of Defense's Project Research
Agency (ARPA, later DARPA) as a part of a research project of
network interconnection to connect remote machines.
The features that stood out during the research, which led to
making the TCP/IP reference model were:
Support for a flexible architecture. Adding more machines to a
network was easy.
The network was robust, and connections remained intact until
the source and destination machines were functioning.
The overall idea was to allow one application on one computer to
talk to(send data packets) another application running on
different computer, using multiple paths.

Network issues
• Addressing
• Routing
• Name Resolution (By DNS)
• Flow & Control
• Interoperability

TCP/IP Reference Model is a four-layered suite of communication protocols. ... TCP stands for
Transmission Control Protocol and IP stands for Internet Protocol. The four layers in
the TCP/IP protocol suite are − Host-to- Network Layer −It is the lowest layer that is
concerned with the physical transmissionof data.
The Link layer is sometimes referred to as the Network access layer. The Transport layer is
sometimes called the Host-to-Hostlayer.
data
segments
packets
Frames
bits

Q. Find the Network ID , SubnetMask and Class for the given IP?
Q. Convert Network ID/IP into Binary.

Convert into Binary : IP 192.168.37.200
27 26 25 24 23 22 21 20
128 64 32 16 8 4 2 1
1 1 0 0 0 0 0 0 192
1 0 1 0 1 0 0 0 168
0 0 1 0 0 1 0 1 37
1 1 0 0 1 0 0 0 200
200 128+64+8
192 putting‘1’ for 128and 64 rest ‘0’
168 putting‘1’ for 128+32 +8
37  32+4+1
As Shown above, we can take ‘1’for the numbers whose sum is 192 i.e 128+64,
similarly for 168  128+32+8 so on ..
Therefore binary form is: 11000000.10101001.00100101.10010001

To find Network ID, usablehost and broadcastID?
e.g. 1) 160.10.20.30
Network ID : 160.10.0.0
Broadcast ID: 160.10.255.255
In class B
2) 17.210.201.210
Network ID : 17.0.0.0
Broadcast ID: 17.255.255.255
Usable ID : . 28*3 -2 = 224 -1 in Class A
As the number of usable host in this (ClassB) IP is
8bits + 8 bits = 16 therefore its 216 (Total IPs) minus 2.
216 – 2 = 65534 usable IPs can be given to computer.
As 1st (networkIP) and last (Broadcast)oneis Reserved.

Switching Techniques
• In large networks, there can be multiple paths from
sender to receiver. The switching technique will
decide the best route for data transmission.
• Switching technique is used to connect the systems
for making one-to-one communication.

Message Switching

Packet switching method uses two routing
1. Datagram Packet Switching
2. Virtual Circuit Packet Switching
A virtual circuit network uses a fixed path for a particular
session, after which it breaks the connection and another path
has to be set up for the next the next session. A Datagram based
network is a true packet switched network. There is no fixed
path for transmitting data

1. Virtual Circuit Packet Switching 1. DatagramPacket Switching
Virtual circuits are connection-oriented,whichmeans
that there is a reservationof resources like buffers,
bandwidth, etc. for the time during whichthe newly
setup VC is going to be used by a data transfer session.
It is connectionless service.There is no needfor
reservationof resources as there is no dedicatedpathfor
a connectionsession.
A virtual circuit network uses a fixedpathfora particular
session,afterwhichit breaks the connectionandanother
path has to be set up for the next the next session.
A Datagrambasednetwork is a true packet switched
network. There is no fixedpathfortransmittingdata.
All the packets follow the same pathandhence a global
header is required only for the first packet of connection
and other packets will not require it.
Every packet is free to choose any path,andhence all the
packets must be associatedwitha header containing
informationabout the source andthe upper layer data.
Packets reachinorder to the destinationas data follows
the same path.
Data packets reachthe destinationinrandomorder,
whichmeans they need not reachin the order in which
they were sent out.
Virtual Circuits are highly reliable. Datagramnetworks are not as reliable as Virtual Circuits.
Implementationof virtual circuits is costly as eachtime a
new connectionhas to be set up withreservationof
resources andextra informationhandlingat routers.
It is always easy andcost-efficient toimplement
datagramnetworks as there is no need of reserving
resources andmakinga dedicatedpatheachtime an
applicationhas to communicate.

Assignment 1-2.
• LAN, WAN, PAN, HAN, CAN, MAN, SAN, WLAN, BAN,
NAN etc.
• Make ppt of : Router, Switch, Hub, Repeater,
Gateway, Connectors, Cables types. Write 3
sentences on each.
• Take any three IP address of Each Class A, B and C :
1. convert it into binary
2. Find the network ID
3. Find the usable ID

Networking lec1 4

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