COMPUTER NETWORKS

Terminals
Terminal include video display terminals and other end user workstations. Any I/O device that
uses a network to transmit or receive data is a terminal
INTRODUCTION TO TELECOMMNICATION
Telecommunication refers to all types of data transmission, from voice to video. End users needs
to communicate electronically in today’s world. People need to exchange data and information
electronically with one another.
Telecommunications software
It consists of programs that reside in host compute system communications control computer
and end user computer.

Functions of telecommunications software:
Access control: this function establish the connection between terminals and computer in a
network.
Transmission control: this function allows computer snd terminals to send and receive
commands,messages,data and programs.
Network control: this function manage communications in a network.
Error control: it involves detection and correction of transmission errors.
Security error: it protects a communications network from unauthorized access.

Communications processors
Communication processors resemble computer CPUs in the that they have similar
circuitry,have memories, and can be programmed, but their purpose is limiter to enhance data
communication between two points.
Multiplexers,concentrators,and controllers:
A multiplexer allows several terminal to use one line to communicate with a CPU.it allows the
terminals to send their messages simultaneously. A concentrator is essentially a smart
multiplexer it can be programmed has more processing capability and more flexible than
multiplexer. A controllers link groups of terminals or other devices to a communications channel.
Message switchers:
A message switcher is a processor that receives data message from terminal determines their
destination and route them one at a time to the CPU.

Communications media
Channels also called communication lines or links are the which data is transmitted between the
sending and receiving devices in a network. A channel makes use a variety of media.
Twisted-pair wire:
This is the oldest and still most common transmission line and consists of copper wires twisted into
pairs. These lines are used in established communication networks throughout the world for both voice
and data transmission.
Coaxial cable:
It consists of a sturdy copper or aluminum wire wrapped with spacers to insulate and protect it.groups
of coaxial cable may be bundled together in a big cable for ease installation. It can be placed
underground and laid on the floors of lakes. They allows high speed data transmission.
Fiber optic cable:
It use cables consisting of one or more hair thin filaments of glass fiber wrapped in a protective jacket.
They can conduct light pluses by layers at rates as high as two billion bits per second.

Types of networks:
Local area network(LAN):
The computer are geographically close together that is in the same buildings.
Wide area network(WAN):
The computer are farther apart and are connect by telephones lines or radio waves.
Network topology:
Star topology: it is designed with each nodes connected to directly to a central network hub or
concentrator. Data on a star network passes through the hub before continuing to its destination. The hub
manages and controls all functions of the network.
Advantages :
1. Easy to install and wire
2. Easy to detect faults and to remove parts.
Disadvantages:
1. Requires more cables length than a linear topology
2. More expensive than bus topology
with no central host.

Ring topology: it is LAN whose topology is a ring. It can be as simple as a circle or
point to point connection of computer at dispersed locations with no central host.
Advantages:
1. Growth of system has minimal impact on performance
2. All stations have equal access
Disadvantages:
1. Most expensive
2. complex

Bus topology: it consists of a main run of cable with a terminator at each end. All nodes are
connected to the linear cable. Ethernet and localtalk networks use a bus topology.
Advantages:
1. Easy to connect a computer to a bus
2. Requires less cable length than a star topology
Disadvantages:
1. Entire network shuts down if there is a break in the main cable.
2. Difficult to identify the problem if the entire network shuts down.

Tree topology: a tree topology combines characteristics of linear bus and star topologies.
Advantages:
1. Point to point wiring for individual segments
2. Supported by several h/w and s/w vendors.
Disadvantages:
1. Overall length of each segments is limited by the type of cable
2. More difficult to configure and wire than other topologies.

Network protocols:
1. The type of error checking to be used
2. Data compression method, if any
3. How the sending device will indicate that it has finished sending a message
4. How the receiving device will indicate that it has received a message.
5. Some of the popular protocols are TCP/IP, SPX/IPX, APPC, DECnet, APPLETALK, WAP.
Network architecture:
The term architecture refers to either H/W or S/W, or combination of h/w and s/w. the architecture
of a system always defines its board outlines, and may defines precise mechanisms of well.
Peer to peer architecture:
This is a type of network in which each workstation has equivalent and responsibilities. It simpler
and expensive.
Client/server architecture:
This is a network architecture in which each computer or process on the network is either a client
or server .

INTERNET
The internet is a global system of interconnected computer networks that interchange data by
packet switching using the standardized internet protocol suite.
What is special about the internet?
Getting information on the internet
Providing information on the internet
Compiling information from the internet
Internet protocols:
Transmission control protocol/internet protocol:
TCP/IP is actually a collection of protocols or rules that govern the way data travels from one
machine to another across network.

• Envelopes and addresses the data
• Enables the network to read the envelope and forward the data to its destination.
• Defines how much data can fit in a single envelope.
The TCP components :
• Breaks data up into packets that the network can handle efficiently
• Verifies whether all the packets have arrived at their destination
• Reassembles the data.
File transfer protocol(FTP)
It is the protocol or set of rules which enables files to be transferred b/w computers. FTP is a
powerful tool which allows files to be transferred from computer A to B.

The basic steps to use FTP are:
1. Connect to the FTP server
2. Navigate the file structure to find the file you want
3. Transfer the file
Hypertext transfer protocol(HTTP)
It is the set of rules or protocol that governs the transfer of hypertext b/w two or more
components. The world wide web encompasses the universe of information that is available
via HTTP. Hypertext is text that is specially coded using a standard system called hypertext
markup language. The html codes are used to create a links.

TELNET:
It is a protocol or set of rules that enables one computer to connect to another computer.
This process is also referred to a remote log in.
 the users computer which initiates the connection is referred to as the local computer and the
machine being connected to which accepts the connection is referred to as the remote, host,
computer.
The remote computer can be physically connected to the next room, the next town, or in another
country
Once connected the user computer emulates the remote computer.
When the user types in commands they are executed on the remote computer.

GOPHER
Gopher is a protocol designed to search,retrieve,display documents from remote sites on the
internet.
It is possible to initiate online connections with other system via gopher.
It accomplishes this using the client/server model of users running client software on their local
machines that provides an interface that interacts with remote servers or computers that have
information of interest.
Gopher was created as a piece of software to utilize some of the services that were becoming
available on the internet

WAIS
It stands for wide area information service.
WAIS is an internet search tool that is based on the Z39.50 standard.
The Z39.50 standard describe a protocol or set of rules for computer to computer
information retrieval.WAIS also works on the clients/server principle.
A WAIS client program enables the users computer to contact a WAIS server submit a
search query and receive a response to that query.
The capability of simultaneously searching in more than one database

Internet addressing
Internet addressing is a systematic way to identify people computer and internet resources. On the internet
the term address is used loosely. Address can mean many different things from an electronic mail address to
a URL.
IP address:
An IP address is an identifier for a particular machine on a particular network , it is part of a scheme to
identify computer on the internet.
 IP addresses are unique
 No two machines can have the same IP number
 IP addresses are also global and standardized
Domain names:
A domain name is a way to identify and locate computers connected to the internet.
 Aero- air transport industry
 Biz- business
 Coop- cooperatives
 educational institutions
 Info- infromation

Electronic mail addresses:
Electronic mail or e-mail allows information to be sent b/w computer and people on the
internet.
The basic structure: username@host.subdomain.second-level-domain.first-level-domain
Uniform resource locator(URL):
A URL identifies a particular internet resource.
Example: http://www.alexisleon.com
Web directory:
A web directory or link directory is a directory on the world wide web. It specializes in
linking to other websites and categorizing those links.
Some of the popular web indexes :
• Aboutus.org(www.aboutus.org)
.

Search engines:
A web search engine is an interactive tool to help people locate information available via the
world wide web. Web search engines are actually databases that contains references to
thousand of resources.
Some of the most popular search engine:
• Google(www.google.com)
• Ask.com(www.ask.com)
Meta search engine:
It is a tool that helps users to locates information available via the world wide web. It provide a
single interface that enables users to search many different search engines, indexes, databases.
Example:
• Dogpile(www.dogpile.com)
• Kartoo(www.kartoo.com)

Mailing basics:
• To –enter the e-mail address of the person to whom the message is sent.
• Cc – enter the e-mail address of the person to whom the copy of the message is sent.
• Subject – enter a brief description as to what the message is about
• Body- enter the actual message here
Address book: An address book is a place where you can store information about the
people with whom you correspond. You just have to select the person’s name, email
id will automatically get inserted.
File attachments: you can attach the any file to mail. The icon with the picture of
a paper clip.
Signature: are you tired of typing in your name and address at the end of
each message that you send. Then you can make use of the signature option
provide.

Setting priority: set priority to a mail message that you are sending. The usual values
are ‘low’,’normal’and ‘high’. When you set the priority of a mail as high, you are
indicating that the message requires immediate attention. The default priority is
normal.
Spamming: sometimes having an email account can be very frustrating. A few third
party products can also help. Some of the spam filter products are:
• Spam Eater pro (www.spameater.com)
• CA anti-spam(www.quirb.com)
Tips for effective email use:
• If the mail is automatically delivered to your mailbox, shutoff the computer beep that
alerts you when you have an incoming messages.
• Compose your message offline. This will save on line time and you will get a change to
review the mail.

• It handles multimedia data effortlessly.
• HTML documents facilitate higher level of documents exchanging scheme
• Ready to access the information worldwide
• Low administration and maintenance costs
Business benefits of intranet:
• People use and get accustomed to the same kinds of approaches and system for internal
company, working externally with other groups, private use for work or leisure purpose
• The skills needed to develop maintain and enhance application are converging and
companies will be able to obtain technical skills from a wider pool.
• A common approach to internal information and published information enables significant
savings.

Web design:
Web page design requires conceptualizing, planning, modeling, and executing
electronic media content and its delivery via the internet using technologies suitable
for rendering and presentation by web browsers or other web based graphical user
interfaces
Web site
A website is a collection of information about a particular topic or subject. Designing
a website is a defined as the arrangements and creation of web pages that it turn
make up a website.

The commercial websites, the basic aspects of design :
• Content
• Usability
• Appearance
• Visibility
 creating a website:
 Choose a domain name
• Register with a registrar
• Choosing a hosting services
• Tell register the ip address
• Create web content
• Store onto hosting server
• Submit new site to search engines.

Website promotion:
• Announcing your website with internet search engines and directories
• Issuing a press release
• Announcing in newsgroup
• Participating in email lists
• Obtaining links from other websites
• Purchasing ad banners on other websites
• Running on site events
• Issuing an e-newsletter
• Conducting a direct e-marketing campaign
• Using your letterheads, brochures, annual reports, visiting cards etc.
HTML:
HTML stands for hypertext markup language. HTML consists of standardized codes or tags that are used
to define the structure of information on web page. These codes enables web pages to have many features
including bold, italic, headings, paragraph break and numbered or bulleted lists.

HTML tags: it is standardized and portable. A documents that has been prepared using HTML
tags can be viewed using a variety of web browsers such as IE and Lynx.
Example: <br> - break , <h1> heading tag.
XHTML tags: the extensible hypertext markup language. XHTML documents allows automated
processing to be performed using standard XML tool – unlike HTML which requires a relatively
complex. Lenient, generally custom parser.
XML: the extensible markup language is a general purpose specification for creating custom
markup language. Its classified as an extensible language, because it allows the user to define
the markup elements. Its purpose is to aid information system in sharing structured data via the
internet.
Advantage:
• XML simplifies data sharing
• XML simplifies data transport
• XML simplifies platform changes
• XML makes your data more available

JAVASCRIPT:
It is a scripting language widely used for client side web development. It was the
originating dialect of the ECMA script standard. It is scripting language which means
it is a lightweight programming language. It is usually embedded language directly into
HTML page and it is an interpreted language so the scripts execute without
preliminary compilation.
PHP:
Hypertext processor is a scripting language originally designed for producing dynamic
web page. It has evolved to include a command line interface capability and can be used
in standalone graphical application.

COMPUTER NETWORKS

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