Download AN INTRODUCTION TO NETWORK, NETWORK TOPOLOGIES AND

AN INTRODUCTION TO NETWORK, NETWORK TOPOLOGIES AND TYPES
1.1 DATA COMMINICATION
Data communications are the exchange of data between two devices via some form of
transmission medium such as a wire cable. For data communications to occur, the communicating
devices must be part of a communication system made up of a combination of hardware (physical
equipment) and software (programs). The effectiveness of a data communications system depends on
four fundamental characteristics: delivery, accuracy, timeliness, and jitter.
1. Delivery. The system must deliver data to the correct destination. Data must be received by the
intended device or user and only by that device or user.
2. Accuracy. The system must deliver the data accurately. Data that have been altered in transmission
and left uncorrected are unusable.
3. Timeliness. The system must deliver data in a timely manner. Data delivered late are useless. In the
case of video and audio, timely delivery means delivering data as they are produced, in the same order
that they are produced, and without significant delay. This kind of delivery is called real-time
transmission.
4. Jitter. Jitter refers to the variation in the packet arrival time. It is the uneven delay in the delivery of
audio or video packets. For example, let us assume that video packets are sent every 30 ms. If some of
the packets arrive with 30-ms delay and others with 40-ms delay, an uneven quality in the video is the
result.
Components
A data communications system has five components:
1. Message. The message is the information (data) to be communicated. Popular forms of information
include text, numbers, pictures, audio, and video.
2. Sender. The sender is the device that sends the data message. It can be a computer, workstation,
telephone handset, video camera, and so on.
3. Receiver. The receiver is the device that receives the message. It can be a computer, workstation,
telephone handset, television, and so on.
4. Transmission medium. The transmission medium is the physical path by which a message travels
from sender to receiver. Some examples of transmission media include twisted-pair wire, coaxial cable,
fiber-optic cable, and radio waves.
5. Protocol. A protocol is a set of rules that govern data communications. It represents an agreement
between the communicating devices. Without a protocol, two devices may be connected but not
communicating.
Data Representation
Information today comes in different forms such as text, numbers, images, audio, and video.
Modes of data communication/communication channel/Data Flow
Channel means a path, or a line, a link from one station to another station is called data transmission
mode. There are following ways to do communication Communication between two devices can be simplex, half-duplex, or full-duplex as shown in figure.
Simplex
In simplex mode, the communication is unidirectional, as on a one-way street. Only one of the two
devices on a link can transmit; the other can only receive. Keyboards and traditional monitors are
examples of simplex devices. The keyboard can only introduce input; the monitor can only accept
output. The simplex mode can use the entire capacity of the channel to send data in one direction.
Half-Duplex
In half-duplex mode, each station can both transmit and receive, but not at the same time. When one
device is sending, the other can only receive, and vice versa. In a half-duplex transmission, the entire
capacity of a channel is taken over by whichever of the two devices is transmitting at the time. Walkietalkies and CB (citizens band) radios are both half-duplex systems.
The half-duplex mode is used in cases where there is no need for communication in both
directions at the same time; the entire capacity of the channel can be utilized for each direction.
Full-Duplex
In full-duplex made (also, called duplex), both stations can transmit and receive simultaneously. In fullduplex mode, signals going in one direction share the capacity of the link with signals going in the other
direction. This sharing can occur in two ways: Either the link must contain two physically separate
transmission paths, one for sending and the other for receiving; or the capacity of the channel is divided
between signals travelling in both directions.
One common example of full-duplex communication is the telephone network. The full-duplex
mode is used when communication in both directions is required all the time. The capacity of the
channel, however, must be divided between the two directions.
Data Transmission
Data may transfer from one device to another by means of some commincation media. The
electromagnetic or light waves that transfer data from one device to another device in encoded form
are called signals. Data transmission across the network can occur in two forms that is ‘
i)
ii)
Analog signal –
The transfer of data in the form of electrical signals or continuous waves is called analog
signal or analog transmission. An analog signal is measured in volts and its frequency is in
hertz (Hz).
Advantages of analog signaling –
Allows multiple transmission across the cable
Suffer less from attenuation
Disadvantage of analog signaling –
Suffer from EMI
Can only be transmitted in one direction without sophisticated equipment
Digital signalThe transfer of data in the form of digit is called digital signal or digital data transmission.
Digital signal consist of binary digits 0 & 1. Electrical pulses are used to represent binary
digits. Data transmission between computers is in the form of digital signal.
Advantages of digital signaling –
Equipment is cheaper and simpler than analog equipment.
Signal can be transmitted on a cable bidirectional.
Digital signal suffer less from EMI.
Disadvantages of digital signaling –
Only one signal can be sent at a time.
Digital signals suffer from attenuation.
Techniques of Data communication –
There are two possible techniques of sending data from the sender to receiver that is
1) Parallel transmissionIn this, each bit of character/data has a separate channel and all bits of a character are transmitted
simultaneously. Here the transmission is parallel character by character.
2) Serial transmission –
In this, the data is sent as one bit at a time having a signal channel for all bits.
There are two types of serial transmission –
a) Asynchronous serial transmission
Computer communication that occur one bit at a time with start and stop bits at the beginning and
end of each character is called Asynchronous serial transmission. In this type of transmission no fixed
time relationship with one character.
Advantage –
This type of transmission is very simple.
This type of transmission is very cheaper.
Disadvantage –
This type of transmission is very simple.
b) Synchronous serial transmission
In this method a clock signal is used and the sending as well as the receiving devices are synchronized
with this clock signal. It doesn’t use start and stop bits but the character are sent in character as
groups called block.
Advantage –
It is very fast as compared to Asynchronous serial transmission.
Disadvantage It is more expensive and complex equipment.
1.2 Introduction: Networking:
A group of computers and other devices connected together is called a network and the
concept of computer sharing is called networking.
A network is a group of two or more computer system linked together.
A computer network is the infrastructure that allows two or more computers (called host) to
communicate with each other. The network achieves this by providing set of rules for communication
which should be followed by all participating host. The computer on a network may be linked through
cables, telephone lines or radio waves or satellite or infrared light beam.
Benefits /Advantage of Network –
1) Sharing Information –
The computer can help you centralize the information and maintain control over it. If you select
one computer to store the sheered information & then all other computer reference this
information over then network.
2) Sharing Hardware resources –
A network allows anyone connected to network to use printers, fax, modem, scanner, tape
backup units or almost any other device that can be affected to a computer.
3) Sharing Software resources –
Administrator can centrally install and configure the software and also restrict access to the
software. it is assign than doing interrelation it on every one of computer in as organization.
4) Preserving informationA network allows information to be back up to a central location it is difficult to maintain regular
backup on a number of standalone computer so important information can last easily by mistake
or by accident
5) Protecting information-
A network provide more secure environment for a computer is important information can last
easily by mistake or by accident
6) EmailThe computer network can help people communicate by email. We can attach electronic
document to mail message like photo sound & video clip
7) Increased cost efficiencyThere are many software available in the market which are courtly & take time for installation
computer network resolve this issue as the s/w can be stored or installed on a sys or a server &
can be used by different workstations
8) Internet accessInternet access sharing small computer network allows multiple access to share a single in that
communication.
9) Internet access sharingThe internet is itself on erroneous network, so whatever you access the internet, you using a
network.
10) Increased storage capacityOne can design a storage sever on the network in order to have a huge storage capacity.
Disadvantage of Network –
1) Security IssueOne of the mayor draw backs of computer network is the security issue. If a computer on a
network, a hacker can get unauthorized access by using different tools. In case of big
organization various network security software are used to prevent the theft of any confidential
and classified data.
2) Rapid spread of virusIf any computer system in a network gets affected by computer virus, there is a possible threat
of other system getting affected too. Viruses get spread on a network easily because of
interconnectivity of workstation of workstations. Such spread can be dangerous if the computer
have important database which get corrupted by the virus.
3) Expensive set upThe initial set up cost of computer network can be high depending on the number of computers
to be connected. Costly devices like routers, switches, hubs etc. can add up cost of a person
trying to install a computer network. Also need to buy NIC card for each of the workstation in
case they are not built.
4) Dependency on the main serverIn case the main file server of a computer network breaks down the system become useless. In
case of big network the file server should be powerful computer which makes it expensive.
Why do we need Network –
1) Better connectivity
2) Better communication
3) Better sharing of information
4) Bring people together
Goal of Computer network
1) Sharing of files
2) Sharing printer and other devices
3) Enables common administrator and security
4) Support network applications such as email and database services
Uses of Network
1) Business application –
Many companies have a substantial numbers of computers. By resource sharing and making all
programs, equipment and especially data available to anyone on the network without regard to
the physical location of the resources and the user. By connecting different departmental
computers in a network to extract and correlate information about the entire company.
In the simplest of terms, one can imagine a company IS as consisting of one or more
databases and some number of employees who need to access them remotely. In this model the
data are stored on powerful computer called server. In contrast the employees have simpler
machine called client. This whole arrangement is called the client server model. It is widely used
and forms the basis of the networking usage.
Communication takes the form of the client process sending a message over the network
to the server process. The client process then waits for a reply message. When the server
process gets the request, it performs the requested work and sends back a reply.
A second goal of setting up a computer network has to do with people rather than information
or even computer.
Virtually every company has two or more computers have email facility which is used for
daily communication. Apart from this, employee can make change online document. Yet another
form of computer assistant communication is video conferencing.
A third goal for many companies is doing business electronically with other companies
especially supplier and customers. Airlines, bookstores and music vendors discovered
convenience of shopping from home. Consequently many companies provide catalogs of their
goods and services online and take order online. it is called E- Commerce.
2) Home application –
Some of the more popular uses of Internet for home users are as follows –
a) Access to remote information
To access to remote information comes in many forms. It can be surfing the www for
information includes the art, business, cooking, health, sports, politics, history, travel and
many more. Many newspapers have gone online. The next step beyond newspaper is the
online digital library.
b) Person to person communication –
E mail is used for daily communication and it is growing rapidly. Worldwide news groups
with discussions on every topic are available.
Other communication oriented application include carrying out telephone call, video call
and internet radio, these are rapidly growing areas. Another application is tele-learning.
c) Interactive Entertainment – Entertainment is huge and growing industry. The killer
application is video on demand. It may be possible to select any television programs or
movie. New films, live TV become interactive medium. Other application like playing games
online.
d) E-Commerce – Home shopping is already popular and allows users to buy product online.
Many people pay their bill, manage their bank account and handle these investments
electronically.
3) Mobile users –
Wireless network and M Commerce are two new technologies. It can support voice and data
network connectivity using wireless via a radio transmission medium.
4) Social issues –
The widespread introduction of networking has introduced new social, ethical and political
problems. A popular feature of many network are news group or bulletin boards whereby
people can exchange messages. As long as subjects are restricted to technical topics, problem
will not arise. The trouble comes when news groups are set up on topics that people actually
care about like politics, religion or sex.
Primary Network components
Today, network consist of three primary components
1) ServerServer comes in many size and shapes. They are core components of the network, providing a
link to the resources necessary to perform any task. The server is the “Leader of the pack”
offering directions to the client computer regarding where to go to get what they need.
It offers network the capabilities of controlling resources and can thus reduce
administrative difficulties. They can be used to distribute processes for balancing the load on the
computer and thus increases speed and performance. They can also offer improved reliability for
files. That’s why if one server goes down then not all of the files are lost.
Server perform several task for example –
Server that provides files to users on the network is called File Server.
Server that provides print services to users on the network is called Print Server.
Server can be multi-purpose or single purpose. If they are multipurpose they can be both
a file server and print server at a time. If they are single purpose server, it is a file server only or
print server.
Another way of categorizing server is whether they are dedicated or non dedicated
server.
Dedicated Server – These are assigned to provide specific applications or services for the
network and nothing else. Because a dedicated server is specializing in only few tasks, it requires
fewer resources from the computer.
In most of the bigger LAN installation the server’s only job is to help workstations access
data, software and hardware resources. Such a server is called a dedicated server.
Non-dedicated server –
These are assigned to provide one or more network services and local access. It is expected
more flexible than dedicated server. They can be used not only to direct traffic and perform
administrative action but often to serve as a front end for the administration to work with other
applications or servers because it act as server as well as workstation.
Many network uses both dedicated and non dedicated server in order to involve the best
of both, offering improved network performance with dedicated server and flexibility with non
dedicated server.
2) Client or workstation –
Clients are the computers that the users on a network do their work on performing
activities such as word processing, database design, graphic design and office or personal work.
They are basically computer except that they are connected to network that offers additional
resources. In network that offer additional resources. In network terms workstation are also
known as client computer. As client, they are allowed to communicate with the servers in the
network to use network resources.
It takes several items to make a workstation into a client. We must install NIC (network
Interface Card) a special expansion card that allow to talk to the server/. We must connect it to a
cabling system that connects to another computer. And we must install some special software
called client software which allows the computer to talk to the server.
To the client, the server may be nothing more than just another drive letter. The client is
able to use the server for more storage/more applications or through which it may communicate
with other computer.
To user, being on a network changes few thingsi. store more information
ii. Share and receive information from other user.
iii. Use program that would be large use by itself.
3) Resources –
A resource is any item that can be used on a network. It can include broad range of items but
most important items are as follows –
Printer and other devices
Files
application and
disk storage
There are generally two resource access model on a network –
1) Client server based network model
2) Peer to Peer (P2P) based network model
What is a Client Server Network?
The type of computing system, in which one powerful workstation serves the requests of other systems,
is an example of client server technology. A computer network is an interconnection of computers
which share various resources.
What is computer server?
A computer server is the powerful computer, or the set of computers connected to each other, which
provide services to other systems. They usually have database integrated in them, and are very
powerful machines with very advanced configuration. They process the requests of client machines.
Their role is to make management of network easy and uniform.
Features of Servers :1) They have large storage capacity.
2) They are able to provide information to many computers simultaneously, therefore have large RAM.
3) Its processor speed is high, as it may have to execute multi-tasking too.
What are clients in client-server model?
Clients are the individual components which are connected in a network. They have a basic
configuration. Client sends a request/query to server and server responds accordingly. Please note that
the client doesn't share any of its resources. They are subordinates to servers, and their access rights
are defined by servers only. They have localized databases.
Client Server Architecture
Components of Client Server Network 1) Clients or Workstations.
2) Servers.
3) Network Devices: - They connect the clients and servers, and at the same time ensure proper
collision free routing of information.
4) Other components like scanner, printer, etc can also be connected to network architecture.
Advantages of Client Server Networks over Peer to Peer Networks
1) Centralization: Unlike P2P, where there is no central administration, here in this architecture there is
a centralized control. Servers help in administering the whole set-up. Access rights and resource
allocation is done by Servers.
2) Proper Management : All the files are stored at the same place. In this way, management of files
becomes easy. Also it becomes easier to find files.
3) Back-up and Recovery possible: As all the data is stored on server its easy to make a back-up of it.
Also, in case of some break-down if data is lost, it can be recovered easily and efficiently. While in peer
computing we have to take back-up at every workstation.
4) Upgradation and Scalability in Client-server set-up : Changes can be made easily by just upgrading
the server. Also new resources and systems can be added by making necessary changes in server.
5) Accessibility: From various platforms in the network, server can be accessed remotely.
6) As new information is uploaded in database, each workstation need not have its own storage
capacities increased (as may be the case in peer-to-peer systems). All the changes are made only in
central computer on which server database exists.
7) Security: Rules defining security and access rights can be defined at the time of set-up of server.
8) Servers can play different roles for different clients.
Disadvantages of Client Server Architecture v/s P-2-P Technology
1) Congestion in Network: Too many requests from the clients may lead to congestion, which rarely
takes place in P2P network. Overload can lead to breaking-down of servers. In peer-to-peer, the total
bandwidth of the network increases as the number of peers increase.
2) Client-Server architecture is not as robust as a P2P and if the server fails, the whole network goes
down. Also, if you are downloading a file from server and it gets abandoned due to some error,
download stops altogether. However, if there would have been peers, they would have provided the
broken parts of file.
3) Cost : It is very expensive to install and manage this type of computing.
4) You need professional IT people to maintain the servers and other technical details of network.
P2P(Peer to Peer Network)In Peer to Peer (or P2P) network each of the participation workstation (computer) has same
(equivalent) privileges, capabilities and responsibilities. This type of network architecture is
completely different from client/server architectures. In Client Server Architectures, some computers
store information and have access to resources, which other computers in network can access
through them. These computers or machines with extra privileges are called Servers and dedicatedly
“serve” clients.
In Peer-to-peer (P2P) networking the need for central servers is eliminated, and all computers interact
and share resources as equals. Thus it can be said P2P architecture is the alternative to server-client
network design. Each communication node has both server and client capabilities.
This peer-2-peer application structure was first popularized by file sharing systems like Napster. P2P is
especially popular in homes where an expensive, dedicated server computer is neither necessary nor
practical. Peer-to-peer networks are generally simpler, but their performance usually decreases when
there is heavy load.
This type of file transfer system is decentralized and allows a user to search through all the linked
computers for desired file. To use P2P, a user should download P2P software on his machine and
configure it. Torrents use this technology effectively.
Advantages of Peer-to-peer networking over Client –Server networking are :1) It is easy to install and so is the configuration of computers on this network,
2) All the resources and contents are shared by all the peers, unlike server-client architecture where
Server shares all the contents and resources.
3) P2P is more reliable as central dependency is eliminated. Failure of one peer doesn’t affect the
functioning of other peers. In case of Client –Server network, if server goes down whole network gets
affected.
4) There is no need for full-time System Administrator. Every user is the administrator of his machine.
User can control their shared resources.
5) The over-all cost of building and maintaining this type of network is comparatively very less.
Disadvantages (drawbacks) of Peer to peer architecture over Client Server are:1) In this network, the whole system is decentralized thus it is difficult to administer. That is one person
cannot determine the whole accessibility setting of whole network.
2) Security in this system is very less viruses, spy wares, Trojans, etc malwares can easily transmitted
over this P-2-P architecture.
3) Data recovery or backup is very difficult. Each computer should have its own back-up system
4) Lot of movies, music and other copyrighted files are transferred using this type of file transfer. P2P is
the technology used in torrents.
Peer to peer networks are good to connect small number (around 10) of computer and places where
high level of security is not required. In case of business network where sensitive data can be present
this type of architecture is not advisable or preferred.
Types of server
A server in a network is dedicated to perform specific tasks in support of other computer on the
network. One server may perform all these tasks or a separate server may be dedicated to each task.
1) File server
File server offers services that allow network users to share files. File services are the network
applications that store, retrieve and move data. With the file services, user can exchange, read, write
and manage shared files and data contained in them.
File server designed specially
to support the file services for a network. Several popular file
servers are Win NT, Netware and AppleShare.
Types of services –
a) File Transfer –
Before networking “sneaker net “was the dominant method. By using network, user can
now typically transfer files between client and servers and between multiple servers.
With all this, file transferring takes place, the need of file security arises. Every NOS
(Network operating system) has its own level of file security. Higher levels use password to
control system access, file attribute to limit file usage and encryption scheme to prevent data
from being obtained by unauthorized individuals.
b) File storage and data migration –
As a network administrator, we must find the most affordable and efficient means of
storing huge amount of data. There are three main categories of file storage
Online storage – consist of hard drive storage. It can be called up quickly.
Offline storage –devices includes media such as tape and removable optical disk. This storage
offers high capacity, low price alternative to online storage.
Near line storage –devices offers fairly low and high storage capacity. It provides efficient data
access and faster.
Data Migration – The process by which data is moved from online to offline or near line storage
is called data migration. NOS usually some type of facility available as an option.
c) File update synchronization –
Its goal to ensure that each user has the latest version of file. By using time and date stamping
and user tracking, file synchronization works to ensure that changes made to a file is organized in the
chronological order in which they actually took place and the files are properly updated.
File synchronization is usually third party option of an upgrade package for most NOS.
d)
File archiving It is the process of backing up files on offline storage devices such as tapes or optical disk.
2. Print Server –
Printing on a network can be more efficient way for users to work. The print data is
transfer to the queue at network speed. The user can then continue working in an application
while the network takes care of printing.
Network printing also cut costs by allowing shared access to printing devices. This is
especially important when it comes to the more expensive variety of printers. High quality color
printers, high speed printer and large format printer and plotter to cost a lot.
Another print service is fax services. Fax machine are now a fundamental communication
device around the world. With network print services we can fax straight from your workstation
to a receiving fax machine. This way, we can eliminate the steps of printing a hard copy and
scanning it into a fax machine.
From an application we can send a document to a fax queue which then takes care of
faxing. Further with fax server, we can receive faxes directly on workstation computer. OCR
(Optical character Reader) software can even convert these faxes into editable text thereby
saving a lot of time and efforts.
Print Server allow user to perform the following things
a) To share printer and to share hardware resources.
b) Allow us to place printer where it is convenient.
3. Application server
Application software is a software frame work that provides an environment in which
application can run, no matter what the applications are or what they do. It is used to serve web
based applications because application server contains web server internally.
It allows a client on a network to access and use extra computing power and expensive
software application on a shared computer. They are used when efficiency and security requires
a program to stay close with the data and the data stays in one place. For example if an
organization needs a powerful database, we can add a server to provide this application.
4.
5.
1.
2.
3.
4.
Windows NT 4 and Windows 2000 server make excellent application server.
It can be dedicated computers set up specially for the purpose of providing application
services or they can serve multiple functions. It is kind of software engine that will deliver
various applications to another device.
Application Server Example –
Sun Java AS, Web logic server, Apache, Geronimo, IBM web sphere AS, Glass Fish server
Web server Example –
Apache, IIS, TomCat, Jetty
Database server
The database server is one of application server. It allows a network with powerful database
capabilities. So user of a relatively weak client can enjoy the same power of database server.
Most database systems are client server based. This means that the database applications
run on two separate components –
The client end of the application runs on the client providing an interface and handling less
function.
The server end portion of the application can handle the intensive performance of database
operations. It manages database, process queries and replying a client.
Message serverMessage server allows a wide variety of communications methods that are much
complex than a simple file server can handle. Data can take the form of graphic, digitized video,
audio, text and binary. Message servers must co-ordinate the complex interactions between
users, documents and applications.
Four main types of message services are –
E-mail
Workgroup applications
Object oriented applications
Directory services
NETWORKS
A network is a set of devices (often referred to as nodes) connected by communication links. A node can
be a computer, printer, or any other device capable of sending and/or receiving data generated by
other nodes on the network.
Distributed Processing
Most networks use distributed processing, in which a task is divided among multiple computers. Instead
of one single large machine being responsible for all aspects of process, separate computers (usually a
personal computer or workstation) handle a subset.
Network Criteria
A network must be able to meet a certain number of criteria. The most important of these are
performance, reliability, and security.
Performance
Performance can be measured in many ways, including transit time and response time. Transit time is
the amount of time required for a message to travel from one device to another. Response time is the
elapsed time between an inquiry and a response. The performance of a network depends on a number
of factors, including the number of users, the type of transmission medium, the capabilities of the
connected hardware, and the efficiency of the software. Performance is often evaluated by two
networking metrics: throughput and delay.
We often need more throughputs and less delay.
Reliability
In addition to accuracy of delivery, network reliability is measured by the frequency of failure, the time
it takes a link to recover from a failure, and the network's robustness in a catastrophe.
Security
Network security issues include protecting data from unauthorized access, protecting data from damage
and development, and implementing policies and procedures for recovery from breaches and data
losses.
Network Attributes /Physical Structures –
There are two types of network attribute –
1) Types of connection and
2) Physical Topology
Type of Connection
A network is two or more devices connected through links. A link is a communications pathway that
transfers data from one device to another. For communication to occur, two devices must be connected
in some way to the same link at the same time. There are two possible types of connections: point-topoint and multipoint.
Point-to-Point A point-to-point connection provides a dedicated link between two devices. The entire
capacity of the link is reserved for transmission between those two devices. Most point-to-point
connections use an actual length of wire or cable to connect the two ends, but other options, such as
microwave or satellite links, are also possible.
Multipoint A multipoint (also called multidrop) connection is one in which more than two specific
devices share a single link. In a multipoint environment, the capacity of the channel is shared, either
spatially or temporally. If several devices can use the link simultaneously, it is a spatially shared
connection. If users must take turns, it is a timeshared connection.
Physical Topology
The term physical topology refers to the way in which a network is laid out physically. Two or more
devices connect to a link; two or more links form a topology. The topology of a network is the geometric
representation of the relationship of all the links and linking devices (usually called nodes) to one
another. There are four basic topologies possible: mesh, star, bus, and ring.
What is Network Topology?
Topology is the map of computer which allows how to connect the computer with each other.
Computer network topology is the way various components of a network (like nodes, links, peripherals,
etc) are arranged. Network topologies define the layout, virtual shape or structure of network, not only
physically but also logically. The way in which different systems and nodes are connected and
communicate with each other is determined by topology of the network. Topology can be physical or
logical.
Physical Topology is the physical layout of nodes, workstations and cables in the network; while logical
topology is the way information flows between different components.
In general, physical topology relates to a core network whereas logical topology relates to basic
network.
Physical topology describes how the cables are run.
Logical topology describes how the network message travels.
It is important to select right topology for how the network will be used. Each topology has its strength
and weakness.
Factors to be taken into consideration while choosing a Network topology
1)
2)
3)
4)
Scale of your project (in terms of number of components to be connected).
Amount of traffic expected on the network.
Budget allotted for the network i.e. amount of money you are willing to invest.
Required response time
Types of Physical Network Topologies
1)
2)
3)
4)
5)
6)
Bus Topology(Physical Topology)
Star Topology (can be both Physical Topology)
Ring Topology(can be both Physical and logical Topology)
Mesh Topology(can be both Physical and logical Topology)
Tree Topology
Hybrid Topology(usally physical topology)
Mesh Topology In a mesh network topology, each of the network node, computer and other devices, are
interconnected with one another. Every node not only sends its own signals but also relays data from
other nodes. In fact a true mesh topology is the one where every node is connected to every other node
in the network. This type of topology is very expensive as there are many redundant connections, thus it
is not mostly used in computer networks. It is commonly used in wireless networks.
Flooding or routing technique is used in mesh topology.
In a mesh topology, every device has a dedicated point-to-point link to every other device. The term
dedicated means that the link carries traffic only between the two devices it connects. To find the
number of physical links in a fully connected mesh network with n nodes, we need n(n - 1) / 2 cables.
Types of Mesh Network topologies:1) Full Mesh Topology:- In this, like a true mesh, each component is connected to every other
component. Even after considering the redundancy factor and cost of this network, its main advantage
is that the network traffic can be redirected to other nodes if one of the nodes goes down. Full mesh
topology is used only for backbone networks.
2) Partial Mesh Topology:This is far more practical as compared to full mesh topology. Here, some of the systems are connected
in similar fashion as in mesh topology while rests of the systems are only connected to 1 or 2 devices. It
can be said that in partial mesh, the workstations are ‘indirectly’ connected to other devices. This one is
less costly and also reduces redundancy.
Advantages of Mesh topology
1) Data can be transmitted from different devices simultaneously. This topology can withstand high
traffic.
2) Even if one of the components fails there is always an alternative present. So data transfer doesn’t
get affected.
3) Expansion and modification in topology can be done without disrupting other nodes.
4) It is more reliable than other topologies.
5) Easy to detect faulty one.
6) Centralized management is not required as in star topology
7) Entire network does not affected by the one faulty device.
Disadvantages of Mesh topology
1) There are high chances of redundancy in many of the network connections.
2) Overall cost of this network is way too high as compared to other network topologies.
3) Set-up and maintenance of this topology is very difficult. Even administration of the network is tough.
4) More cabling is required as compare to other topologies.
5) Each link from one device to another requires an individual NIC
Star Topology
In a star topology, each device has a dedicated point-to-point link only to a central controller, usually
called a hub or switch. Hub acts as signal booster or repeater. The devices are not directly linked to one
another. Devices are attached to the hub by using copper cable or fiber optic cable. It provides cost
effective method for sharing information between different users. It can be used in Air line reservation
and small business offices where employee wants access to common application and files.
When a computer or other networking component transmit a signal to the network, the signal
travel to the hub. Then the hub forwards the signal simultaneously to all other devices connected to the
hub. Ethernet 10BaseT is a network based on the star topology.
Advantages of Star Topology
1) As compared to Bus topology it gives far much better performance, signals don’t necessarily get
transmitted to all the workstations. A sent signal reaches the intended destination after passing through
no more than 3-4 devices and 2-3 links. Performance of the network is dependent on the capacity of
central hub.
2) Easy to connect new nodes or devices. In star topology new nodes can be added easily without
affecting rest of the network. Similarly components can also be removed easily.
3) Centralized management. It helps in monitoring the network.
4) Failure of one node or link doesn’t affect the rest of network. At the same time it is easy to detect
the failure and troubleshoot it.
5) Large amount of cable it uses.
6) Easy to install, configure, expand and manage
Disadvantages of Star Topology
1) Too much dependency on central device has its own drawbacks. If it fails whole network goes down.
2) The use of hub, a router or a switch as central device increases the overall cost of the network.
3) Performance and as well number of nodes which can be added in such topology is depended on
capacity of central device.
4) Require more cable, more expensive and increased devices cause traffic which makes network slow.
Distributed star Topology –
For a large network, a single hub may not able to support all the nodes even it doesn’t have enough
ports for all other computer on the network or computers are too far away for the cabling.
To connect everyone to the network, we need more than one hub but the idea of having 3/4 separate
network in the same building is not very appealing.
This variation called the connected star or distributed star, daisy chains together the hub on your
network so that hubs can communicate.
Bus Topology
Physical Bus Topology –
In bus topology devices share a common backbone cable to send and receive data. A thick
coaxial cable is used to connect all devices. It uses daisy chain scheme to add more devices in a network.
In this, device 1 is connected to device 2 and device 2 is connected to device 3 and so on. The first and
last device is connected to terminator resistor.
The biggest potential problem with a bus network is that if it not terminated correctly then your
network can’t translate correctly. If we are using the bus physical topology, we must prevent break in
continuity along the cable. Malfunctioning nodes and cable breaks can cause problem for all computers.
The network won’t transmit correctly of even one node on the network is malfunctioning
because system depends on every node. If the node is turned off, the data will pass through the T
connector plugged into the NIC to the next active node. However if the node is active and
malfunctioning then problem will occur. The active node will still attempt to process packet but it will
do inaccurately so it slow down whole network or bring or to halt the network.
Cable breaks will cause problem for the bus topology because proper functioning of the network
is dependent on the cable. It is cable efficient. It can be difficult to implement if the machine in your
network are not neatly lined up in a row.
Bus logical Topology –
Ethernet is the best known example of logical bus topology. It is the most popular LAN type.
In bus topology the server is connected at one end of the backbone cable and other devices are
connected at different position along the backbone cable known as trunk. Terminator is placed at each
end of cable. The data is send to all the devices along the cable. As the message arrive at each device, it
checks the destination address, encoded in the message. If the address matches it accept the data. If
the address does not match the device ignore the data. At a time only one device can send data. Due to
this a number of devices waiting for sending data. This result in slowing down the performance of a
network.
Every device on a network share common cable when two devices transfers data at the same
time the signal collide due to this information is destroyed. This process is called as Collision. Collision
can affect the performance of the network.
There are two most popular Ethernet cables types which are used in this topology. They are
10Base2 and 10BaseT.
The bus topology uses a broadcast technique hence only one station at a time send message and
all other listen to the message. A listening station examines the address of recipient address of the
message if it matches with its own address, it copies the message otherwise it ignores the message.
Advantages (benefits) of Linear Bus Topology
1) It is easy to set-up and extend bus network.
2) Cable length required for this topology is the least compared to other networks.
3) Bus topology costs very less.
4) Linear Bus network is mostly used in small networks. Good for LAN.
5) Easy to connect device in a linear bus.
6) Does not require any specialized devices.
Disadvantages (Drawbacks) of Linear Bus Topology
1) There is a limit on central cable length and number of nodes that can be connected.
2) Dependency on central cable in this topology has its disadvantages. If the main cable (i.e. bus)
encounters some problem, whole network breaks down.
3) Proper termination is required to dump signals. Use of terminators is must.
4) It is difficult to detect and troubleshoot fault at individual station.
5) Maintenance costs can get higher with time.
6) Efficiency of Bus network reduces, as the number of devices connected to it increases.
7) It is not suitable for networks with heavy traffic.
8) Security is very low because all the computers receive the sent signal from the source.
Ring Topology
In a ring topology, each device has a dedicated point-to-point connection with only the two
devices on either side of it. A signal is passed along the ring in one direction, from device to device, until
it reaches its destination. Each device in the ring incorporates a repeater. When a device receives a
signal intended for another device, its repeater regenerates the bits and passes them along.
In a ring topology, each device is connected to each other in the form of closed loop like ring.
Each device has only two neighbors for communication purpose one is upstream and another is
downstream. Data travels through many points before reaching the destination which makes it
inefficient network compared with other topologies. For example consider a ring network having 8
devices, if device 1 wants to transmit the data to the device 4, data must be travel from the device 1 to
device 4 through device 2 & device 3 and then it reaches its destination.
The ring topology is commonly used in FDDI (Fiber Distributed Data Interface), Token ring,
Sonnet network. All messages are travelled in the same direction either clockwise or anticlockwise (data
travels only in unidirectional)
In token ring a special signal or a small message called token is continuously passed from one
device to another. The device which has token is allowed to transmit data over the network. Data is
extracted by the appropriate device and the acknowledgement is sent back to the transmitting device.
This topology also sends the data on priorities basis where message of higher priorities are sent before
message with lower priority.
Given the token’s importance on a network using the ring logical topology one computer is
dedicated to token management. This computer is called token master or active monitor, detects lost
token, monitor frame transmission and creates a new tokens when necessary. The active monitor also
maintains a regular clock trick on the network that keep all other nodes synchronized.
Advantages of Ring Topology
1) This type of network topology is very organized. Each node gets to send the data when it receives
an empty token. This helps to reduces chances of collision. Also in ring topology all the traffic flows in
only one direction at very high speed.
2) Even when the load on the network increases, its performance is better than that of Bus topology.
3) There is no need for network server to control the connectivity between workstations.
4) Additional components do not affect the performance of network.
5) Each computer has equal access to resources.
Disadvantages of Ring Topology
1) Each packet of data must pass through all the computers between source and destination. This
makes it slower than Star topology.
2) If one workstation or port goes down, the entire network gets affected.
3) Network is highly dependent on the wire which connects different components.
4) MAU’s and network cards are expensive as compared to Ethernet cards and hubs.
Dual Ring Topology –
In ring topology, single ring is used whereas dual ring network topology consists of two or more
concentric rings that are primary and secondary to connect each device on a network.
Primary ring carries data in one direction whereas secondary ring carries data in opposite direction.
Secondary ring is used if primary ring stops working. This secondary ring is redundant.
In dual ring it is difficult to add new devices. For each station must have two transmitting ports
and two receiver ports.
Basic structure of dual ring is as follows-
Tree Topology/hierarchical TopologyTree Topology integrates the characteristics of Star and linear Bus Topology. Physical Star network
Topology, computers (nodes) are connected by each other through central hub. And in Bus Topology,
work station devices are connected by the common cable called Bus. In Tree Topology, the number of
Star networks is connected using Bus. This main cable seems like a main stem of a tree, and other star
networks as the branches. It is also called Expanded Star Topology. Ethernet protocol is commonly used
in this type of topology. The diagram below will make it clear.
Advantages of Tree Topology
1. It is an extension of Star and bus Topologies, so in networks where these topologies can't be
implemented individually for reasons related to scalability, tree topology is the best alternative.
2. Expansion of Network is possible and easy.
3. Here, we divide the whole network into segments (star networks), which can be easily managed and
maintained.
4. Error detection and correction is easy.
5. Each segment is provided with dedicated point-to-point wiring to the central hub.
6. If one segment is damaged, other segments are not affected.
Disadvantages of Tree Topology
1. Because of its basic structure, tree topology, relies heavily on the main bus cable, if it breaks whole
network is crippled.
2. As more and more nodes and segments are added, the maintenance becomes difficult.
3. Scalability of the network depends on the type of cable used.
Hybrid Topology
It is a combination of different topologies. It is also known as special topology. This topology is useful for
corporate offices to link their internal LAN’s together while adding external network through WAN. A
network can be hybrid. The commonly used topologies are Star Bus or Star Ring. When different types
of topologies are involved their total strength improves the performance of the network.
Advantages of Hybrid Network Topology
1) Reliable : Unlike other networks, fault detection and troubleshooting is easy in this type of topology.
The part in which fault is detected can be isolated from the rest of network and required corrective
measures can be taken, WITHOUT affecting the functioning of rest of the network.
2) Scalable: Its easy to increase the size of network by adding new components, without disturbing
existing architecture.
3) Flexible: Hybrid Network can be designed according to the requirements of the organization and by
optimizing the available resources. Special care can be given to nodes where traffic is high as well as
where chances of fault are high.
4) Effective: Hybrid topology is the combination of two or more topologies, so we can design it in such a
way that strengths of constituent topologies are maximized while there weaknesses are neutralized. For
example Ring Topology has good data reliability (achieved by use of tokens) and Star topology has high
tolerance capability (as each node is not directly connected to other but through central device), so
these two can be used effectively in hybrid star-ring topology.
5) Useful for implanting large network and handles large volume of data.
6) Easy to detect and remove faulty device
Disadvantages of Hybrid Topology
1) Complexity of Design: One of the biggest drawback of hybrid topology is its design. Its not easy to
design this type of architecture and its a tough job for designers. Configuration and installation process
needs to be very efficient.
2) Costly Hub: The hubs used to connect two distinct networks, are very expensive. These hubs are
different from usual hubs as they need to be intelligent enough to work with different architectures and
should be function even if a part of network is down.
3) Costly Infrastructure: As hybrid architectures are usually larger in scale, they require a lot of cables;
cooling systems, sophisticate network devices, etc.
Network Models
Computer networks are created by different entities. Standards are needed so that these
heterogeneous networks can communicate with one another. The two best-known standards are the
OSI model and the Internet model. The OSI (Open Systems Interconnection) model defines a seven-layer
network; the Internet model defines a five-layer network.
Categories of Networks/CLASSIFICATION OF NETWORKS
Networks are classified upon the geographical area they span into the following categories:
Local Area Network
A private network within a range of 10 kilometers owned and controlled by a single organization.
LAN has three main characteristics:
1. A diameter of not more than three kilometers.
2. A total data rate at least several Mbps (Mega Bytes / Sec.)
3. Complete ownership by a single organization.
A local area network (LAN) is usually privately owned and links the devices in a single office,
building, or campus. Depending on the needs of an organization and the type of technology used, a LAN
can be as simple as two PCs and a printer in someone's home office; or it can extend throughout a
company and include audio and video peripherals. Currently, LAN size is limited to a few kilometers.
LANs are designed to allow resources to be shared between personal computers or workstations.
The resources to be shared can include hardware (e.g., a printer), software (e.g., an application
program), or data. A common example of a LAN, found in many business environments, links a
workgroup of task-related computers, for example, engineering workstations or accounting PCs. One of
the computers may be given a large capacity disk drive and may become a server to clients. Software
can be stored on this central server and used as needed by the whole group.
In addition to size, LANs are distinguished from other types of networks by their transmission
media and topology. In general, a given LAN will use only one type of transmission medium. The most
common LAN topologies are bus, ring, and star.
Metropolitan Area Networks
A metropolitan area network (MAN) is a network with a size between a LAN and a WAN. It normally
covers the area inside a town or a city. It is designed for customers who need a high-speed connectivity,
normally to the Internet, and have endpoints spread over a city or part of city. A good example of a
MAN is the part of the telephone company network that can provide a high-speed DSL line to the
customer.
A public or private network used to connect various locations including suburbs in metropolitan cities.
The MAN is in between a LAN and WAN. A MAN is a network that covers an entire city, but uses LAN
technology.
Wide Area Network
A public network connecting different cities and towns mostly through telephone links or microwave
links through a satellite.
The features of WAN are:
1. It typically spans entire countries.
2. It has data rates below 1 Mbps.
3. It is owned by multiple organizations (the carrier owns the communication subnet and
numerous clients own the hosts).
A wide area network (WAN) provides long-distance transmission of data, image, audio, and video
information over large geographic areas that may comprise a country, a continent, or even the whole
world.
A WAN can be as complex as the backbones that connect the Internet or as simple as a dial-up line that
connects a home computer to the Internet. We normally refer to the first as a switched WAN and to the
second as a point-to-point WAN. The switched WAN connects the end systems, which usually comprise
a router (internet-working connecting device) that connects to another LAN or WAN. The point-to-point
WAN is normally a line leased from a telephone or cable TV provider that connects a home computer or
a small LAN to an Internet service provider (ISP). This type of WAN is often used to provide Internet
access.
Difference between LAN and WAN
1) The range of LAN is limited (ie. 1 km) and it may be increased by using repeater while the range of
WAN is unlimited (ie. World wide)
2) The communication medium in LAN is private (ie. Owned by the user) while WAN is a public
system(hired by the user)
3) In LAN, the data transmission cost is negligible but in WAN it is very much expensive because medium
is hired.
4) LAN is faster than WAN in reference to data transmission speed.
5) In LAN, transmission accuracy is much higher(because distance is very less and medium is private) but
in WAN, the accuracy is not so much because in space so many waves travels so due to this interference
possibility of distortion is there.
Protocol –
A set of rules that govern communication. Network communication uses protocol. Protocol details what
language the computer are speaking when they talk over a network. If two computers are going to
communicate, they must be using the same protocol.
Networks are full of protocol. A computer needs to know exactly how message will arrive from the
network so it can make sure that the message gets to the right place.
Hardware Protocol –
It defines how the how the hardware devices operate and work together. The 10BaseT Ethernet
protocol is a hardware protocol specifies exactly how two 10BaseT Ethernet devices will exchange
information and what they will do if it is improperly transmitted or interrupted. It determines such
things as voltage levels and which pairs of cables will be used for transmission and reception. There is
no program involves, it is all done with circuit.
Software Protocol Programs communicate with each other via software protocol. Network client and network server both
have protocol packages that must be loaded to allow them to talk to other computer.
These computers contain the protocols the computer needs to access a certain network devices or
service. There are different protocol package for different network and even for different kind of
services on the same network.
Microsoft Win 2000 Server and Novell Netware come with a large number of network protocol so we
can make the best use of our network.
To communicate with the internet, computer must have the TCP/IP set of protocol.
UNICAST
Unicast is the term used to describe communication where a piece of information is sent from
one point to another point. In this case there is just one sender, and one receiver.
How It Work
MULTICAST
Multicast is the term used to describe communication where a piece of information is sent from one or
more points to a set of other points. In this case there is may be one or more senders, and the
information is distributed to a set of receivers (there may be no receivers, or any other number of
receivers).
One example of an application which may use multicast is a video server sending out networked TV
channels. Simultaneous delivery of high quality video to each of a large number of delivery platforms
will exhaust the capability of even a high bandwidth network with a powerful video clip server.
BROADCAST
•
Broadcast is the term used to describe communication where a piece of information is sent from
one point to all other points. In this case there is just one sender, but the information is sent to
all connected receivers.
• Broadcast transmission is supported on most LANs (e.g. Ethernet), and may be used to send the
same message to all computers on the LAN.
Anycast :
Network addressing and routing technique datagram from a single sender are routed to the
topological nearest node in group of the potential receiver all identified by the same destination
address.
Geocast :
Refers to delivery of information to a group of destination in a network identified by their
geographical locations. Multi addressing used by same routing protocol for mobile network.
PROTOCOLS AND STANDARDS
Protocols
In computer networks, communication occurs between entities in different systems. An entity is
anything capable of sending or receiving information. However, two entities cannot simply send bit
streams to each other and expect to be understood. For communication to occur, the entities must
agree on a protocol. A protocol is a set of rules that govern data communications. A protocol defines
what is communicated, how k is communicated, and when it is communicated. The key elements of a
protocol are syntax, semantics, and timing.
1) Syntax. The term syntax refers to the structure or format of the data, meaning the order in
which they are presented. For example, a simple protocol might expect the first 8 bits of data to
be the address of the sender, the second 8 bits to be the address of the receiver, and the rest of
the stream to be the message itself.
2) Semantics. The word semantics refers to the meaning of each section of bits. How is a particular
pattern to be interpreted, and what action is to be taken based on that interpretation?
3) Timing. The term timing refers to two characteristics: when data should be sent and how fast
they can be sent. For example, if a sender produces data at 100 Mbps but the receiver can
process data at only 1 Mbps, the transmission will overload the receiver and some data will be
lost.
Standards Creation Committees
While many organizations are dedicated to the establishment of standards, data telecommunications in
North America rely primarily on those published by the following:
International Organization for Standardization (ISO).
International Telecommunication Elion Telecommunication Standards Sector (ITEl-T).
American National Standards Institute (ANSI).
Institute of Electrical and Electronics Engineers (IEEE).
The Institute of Electrical and Electronics Engineers is the largest professional engineering
society in the world. International in scope, it aims to advance theory, creativity, and product
quality in the fields of electrical engineering, electronics, and radio as well as in all related
branches of engineering. As one of its goals, the IEEE oversees the development and adoption of
international standards for computing and communications.
Electronic Industries Association (EIA).