2. Subject : Computer Networks (IC-701)
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.
3. 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
• 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.
4. 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
• Create abstractions that make these (relatively)
5. Computer Network Features
• Communication speed
• File sharing
• Back up and Roll back is easy
• Software and Hardware sharing
• 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
• Purchasing the network cabling and file servers can be
• 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
• Viruses can spread to other computers throughout a
• There is a danger of hacking, particularly with wide area
networks. Security procedures are needed to prevent such
abuse, eg a firewall.
8. 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
• Based on topology (connectivity): Bus, Star, Ring
9. 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
•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
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
Advantages of client/server networks
• Facilitate resource sharing – centrally administrate and
• Facilitate system backup and improve fault tolerance
• Enhance security – only administrator can have access to
• Support more users – difficult to achieve with peer-to-peer
Disadvantages of client/server networks
• High cost for Servers
• Need expert to configure the network
• Introduce a single point of failure to the system
14. P2P topology is where one
device is directly connected with
In PTM , Data transmitted from
the central base station is
broadcasting to all the
subscribers But data coming
from a subscriber is only
received by the base station.
PTM topology is typically used in
wireless LAN, and wireless WAN.
Topology ― 3 basic types
Physical, Logical and Hybrid
Bus Topology(Daisy chain) Ring
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 - computer only listen for, not regenerate data
Both are not secure, not fault tolerant and difficult to trouble shoot.
• Each computer has a cable connected to a single point
• More cabling, hence higher cost
• All signals transmission through the hub; if down, entire network down
• Depending on the intelligence of hub, two or more computers may send
message at the same time.
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
In star topology, only hub is failure
In ring topology, every nodes are failure
3. The cost of star topology is high. The cost of ring topology is low.
In star topology, the information is
travel from central hub or router to all
In ring topology, the information is
travel from nodes to nodes in ring
manner in one direction.
The cables are required in star topology
more than the ring topology.
The cables are required in ring topology
less than the star topology.
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.
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
20. Applications of Networks
• Resource Sharing
• Hardware (computing resources, disks, printers)
• Software (application software)
• Information Sharing
• Easy accessibility from anywhere (files, databases)
• Search Capability (WWW)
• Message broadcast
• Remote computing
• Centralized Control
• Distributed processing (GRID Computing)
• Security is good - users cannot see other users' files unlike on stand-alone
• Data is easy to backup as all the data is stored on the file server.
36. 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.
38. 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 transmission of data.
The Link layer is sometimes referred to as the Network access layer. The Transport layer is
sometimes called the Host-to-Host layer.
42. Q. Find the Network ID , Subnet Mask and Class for the given IP?
Q. Convert Network ID/IP into Binary.
45. 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
192 putting ‘1’ for 128 and 64 rest ‘0’
168 putting ‘1’ for 128 +32 +8
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
48. To find Network ID, usable host and broadcast ID?
e.g. 1) 220.127.116.11
Network ID : 18.104.22.168
Broadcast ID: 22.214.171.124
In class B
Network ID : 126.96.36.199
Broadcast ID: 188.8.131.52
Usable ID : . 28*3 -2 = 224 -1 in Class A
As the number of usable host in this (Class B) 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 (network IP) and last (Broadcast)one is Reserved.
49. Assignment 1.
• 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
50. 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.