Telnet
It is a protocol or set of rules that enables a computer to connect
another computer in network. It is also known as a remote login. The
telnet operates on client-server principle.
- Computer network is an interconnected collection of
autonomous computers. In simple words, computer network is a group of
computers and other devices interconnected by communication channels
that facilitates communication, sharing devices and other resources.
- To create a network you need computers equipped
with network interface cards (NIC), transmission media such as cable,
connection devices such as switches, routers etc and network software
(NOS and communication software).
- Benefits of networking – quick and efficient data
transfer, sharing resources, saving money on software, access to
information in remote computer, high reliability of services, workgroup
computing.
- Drawbacks of networking – network systems are more
sophisticated and complex to operate; when network service become
unstable the productivity fails; proper maintenance of network computer
require considerable time and expertise; file security is more important
if connected to network; spreading of malicious viruses is more
probable in networked environment.
- Computer network consists of hardware components ( servers and/or clients, connectors, network cables, network interface cards, switches, gateway, routers) and Software components (network operating systems, network protocols such as TCP/IP, HTTP, SMTP, POP and so on)
- Network Operating System is a system software that
controls other software and hardware than runs on a network. It provides
services such as printer sharing, common file system and database
sharing, application sharing and other housekeeping tasks of a network.
- Windows Server 2003, Windows Server 2008, Unix, Netware etc are examples of NOS (Network Operating Systems).
- Network Protocol is the set of rules that govern
the transmission of data over network. This is a formal description of
messages formats and the rules that two or more machines must follow to
exchange those messages.
- TCP/IP (Transmission Control Protocol / Internet Protocol) is a basic communication protocol. TCP/IP is a two layer protocol. The higher layer TCP
manages the assembling of a message or file into smaller packets that
can be transmitted over the Internet. It again reassembles the packets
into original message at the receiving end. The lower layer IP handles the address part of each packet so that it gets to the right destination.
- HTTP (Hyper Text Transfer Protocol) is the protocol for transferring files
(text, graphics, images, sound, video and other multimedia files). The
primary function of HTTP is to establish connection with the server and
send HTML pages back to the user’s browser. It is also used to download
other files in browser or other applications.
- SMTP (Simple Mail Transfer Protocol) is the protocol used to send email message across the Internet.
- Post Office Protocol (POP) is the protocol used to
retrieve email messages from server to client’s email applications such
as Eudora, Microsoft Outlook and so on. Most of the modern browser such
as Internet Explorer, Netscape, Firefox, Chrome contains built-in POP in
them.
- 5 Network services – File service, print service, message service, application service and database service.
- File service in network provides file transfer, storage, data migration, file update synchronization etc.
- Print service in network offers printer sharing. It
includes accepting print job request, interpret print job formats,
printer formats, configuration, manage queues and interact with
networkable printers and faxes.
- Message service in network allows the users to pass
on the message from one computer to other computers. Message service
functions are email, voice mail and object orientation applications.
- Application service are the services that run software for network clients and allow computers to share processing power.
- Database service provides centralized data storage and retrieval to network clients.
- 3 Computer Network Models – Centralized computing or hierarchical networking, client/server network, peer-to-peer network.
- Centralized computing network is also called host
based network where there is a central host computer which offer
information, resources, services and applications to the users or other
nodes of network. This network is expensive to implement.
- Client/Server network contains one or more server
computer that provide network services to other computers that are known
as clients. Client/Server network model is the workhorse of the network
world.
- Peer-to-peer network also called workgroup is a
server less network model where each computers are independent and equal
in terms of providing and using network services. This model is
completely decentralized network mode. Though they are easy and
inexpensive to implement, they are suitable only for small
organizations.
- Networks can be classified into 3 types based on geographical spread – LAN, MAN and WAN.
- Local Area Network (LAN) is a small network connecting two to
several hundred computers withing local area such as single building or
company complex. The computers are connected with network cable or
short-range wireless technology.
- Wireless LAN or WLAN connects devices and computers
over a short distance with wireless technology that uses radio waves.
NIC cards that support wireless connections have small antenna on it.
Data signals transmitted by these antenna are picked up and routed by a
wireless network switch known asAccess Point.
- A wireless technology known as Wi-Fi (Wireless Fidelity) is used for setting up high speed WLANs over a distance up to 30 meters.
- Metropolitan Are Network (MAN) is a medium sized
network that spans over a metropolitan network. MAN typically use
wireless infrastructure or optical fiber connections. Cable TV network
is a good example of MAN.
- Wireless MAN or WMAN is a type of wireless network that connects several wireless LANs over a city. A wireless technology WiMAX (Wireless Interoperability for Microwave Access) is used for setting up wireless MANs within a radius of 50 km.
- WAN (Wide Area Network) is the largest network that
spans over different countries or whole world. WAN uses different
technologies for connection such as long distaance telephone, wires,
microwaves and satellites. The Internet is an example of WAN.
- Network Topology is network structure that tells
how nodes are connected to form the network. Physical topology is the
actual geometric layout of nodes. The basic typologies are Bus, Star and Ring. You can create other topologies like mesh, hybrid, tree topologies by combining and modifying the basic typologies.
- The choice of topology for a network will depend upon the
choice of transmission media, access method, desired performance,
reliability, size, expandability, cost, availability of communication
lines etc.
- Bus topology is one of the basic topology where
nodes (computers and/or network devices) are connected linearly, with
each node directly connected to the network cable (known as trunk or
bus). A drop cable is connected with the trunk using a T connector. The
bus has terminator at both end which absorb the signal to remove it from
bus if it is not picked by any node.
- Bus topology is easy to implement and extend, easier to identify the cable fault but this topology has disadvantages
like limited cable length and number of stations, the problem in
network cable (trunk or bus) causes the break down of entire network,
and the maintenance cost can be higher in long run.
- Ring topology is a network structure where
arrangement of nodes forms a loop or ring. The data is sent to only one
direction of the ring and each node picks up, checks if it is destined
to it, if not re-transmits down to the next neighbor. So the signal
quality in ring topology is high. Any data packet if returned to the
sender, the sender removes it from ring.
- Ring topology performs better under heavy network load than bus
topology, does not require network server and it is easier to use
optical fibers as transmission media but ring topology has disadvantages
like node failure causes network failure, it is difficult to diagnose
faults in ring topology, network configuration is difficult.
- In Star topology, there is a central computer or
network device like hub, switch etc. with which all other nodes are
connected (all-to-one connection). The central computer is called hub
node and other computers are leaf nodes. All the data passes through the
hub node to reach up to its destination. Hub manages and controls all
the functions as well as acts as a repeater for the data flow.
- Star topology has advantages such as it is easy to
install, detect faults and remove parts, no disruptions to the network
functioning when adding new nodes or removing nodes. However star topology suffers from drawbacks
like heavy dependence on hub node and problem in hub node can cause
whole network failure, the performance and scalibility (extendability)
of network depends on the capability of hub.
- A data packet is a basic unit of communication over a digital network. A packet is also called a datagram, a segment, a block, a cell or a frame
depending on the protocol. When data has to be retransmitted, it is
broken down into similar structure of data packet, which are reassembled
to the oritinal data chunk once they reach their destination.
- Hub, repeater, switch, bridge, access points, router, gateway are the network connection devices.
- Hub is a small simple inexpensive device that connects multiple
computers together. Hub receives the incoming data packet, amplifies it
and broadcasts them to all the LAN cards in a network. The destined
recipient receives the data packet and all others discard it.
- Passive hub simply joins wires from several station and does not provide any processing or regeneration of signals.
- Active hub in a network can regenerate signals on the output side to keep the signal strong.
- Intelligent hub can perform a variety of processing functions
including network management, bridging, routing and switching. Switch,
bridge and router are intelligent hub.
- Network repeater is a connection device that amplifies and restores
signals for long distance transmission. Repeaters are often used in
trans-continental and submarine communication cables because the signal
loss over such distances would be unacceptable without them. There are
repeaters for copper wires and fiber optics.
- Network switch is a network connection device that is used to
segment networks into different subnetworks called subnets or LAN
segments. It helps to prevent traffic overloading in a network.
- Network bridge is a network device that establishes an intelligent
connection between two local networks with the same standard. In simpler
words, it is a connection device to connect two or more LANs having
similar systems.
- Wireless access point is a device to connect wireless devices and
can connect to wired networks. They have network interface to connect to
the wired network and an antenna or infrared receiver necessary to
receive the wireless signals.
- Router is a network device that connects multiple networks that use
the same protocol. Routers can detect the best rout to forward data
packet.
- Gateway is a network device that can connect disimilar networks with
different protocols. They can transmit data between different operating
systems, different email formats or between totally different networks.
Gateway are commonly used to transfer data between private network and
the Internet.
- MODEM (Modulator and Demodulator)
is a network connection device that performs the modulation and
demodulation function. It is required to connect a computer with network
through telephone lines.
- Modulation is the process of converting computer generated digital
data into analog signals so that they can be transmitted through
telephone lines.
- Demodulation is the process of converting analog signal from
telephone lines into digital data so that the computer can do further
processing.
- The data transfer rate in MODEM is usually measured in bits per
second (bps). The unit kbps is kilo bits per second. Similarly KBps
represent kilo bytes per second.
- A communication Channel (communication link or line)
forms the path over which data travels as it passes from a sending
device to a receiving device in a telecommunications system. It is
composed of one or more transmission media
- Transmission media refers to the mode of connection
needed for data transmission. There are two types of communication
media – guided (bound) and unguided (unbound) transmission media.
- Guided media are the bound transmission media
in which data/signal is guided by the cable or wire. Because these
media are limited by physical geography, they are also called bound
transmission media. All the transmission cables fall under this
category. Some examples are twisted pair cables, co-axial cables, fiber
optics cable etc.
- Twisted pair cables are the oldest and still most
common medium of transmission. It consists of pairs or wires twisted
with each other. The wires are twisted so as to reduce the EMI
(Electro-Magnetic Interference) effect – the disturbance in signal flow
due to the electronic or magnetic field.
- UTP (Unshielded Twisted Pair) and STP (Shielded Twisted Pair) are the two types of twisted pair cables.
- UTP are the most common transmission media for LAN networking. It
does not include shielding around its conductors. UTP can support the
distance up to 100 meters and data transfer speed of 1 Gbps.
- STP include shielding typically a foil wrapper around its conductors
to improve the resistance against interference and signal noise. It is
more expensive than UTP and supports the distance up to 90 meters.
- Co-axial cable was invented by Oliver Heaviside – an English engineer and mathematician in 1880.
- Co-axial cable consists of a central inner
conductor surrounded by a flexible insulating layer which is again
surrounded by fibers of conductor. The term co-axial comes from the
inner conductor and the outer shield sharing the same geometric axis.
- Co-axial cables are popularly used for cable television signals, computer network connection and connecting radio transmitters and receivers with their antennas.
- Fiber optics is the transmission medium where
photons – the pulses of light – flows rather than electrons as in
twisted pair cable or co-axial cables.
- Fiber optic cable consists of (i) core – the glass
or plastic tube through which the light travels, (ii) cladding – the
covering of the core that reflects light back to the core, and (iii) the
protective coating – which protects the cable from hostile environment.
- Fiber optics can easily carry data at more than billion bps. Fiber
optics is not affected by magnetic fields or electronic fields – so free
from EMI.
- Unguided media are the unbound transmission media in which data or
signal is sent through the air instead of cables. It includes wireless
transmission methods such as radio networking (radio wave), infrared,
microwave and infrared.
- In Radio Networking, signals are sent through radio frequency (RF) waves in the 10 KHz and 1 GHz.
- Radio wave is affected by electrical interference from power lines, buildings, hills and atmospheric conditions.
- Baseband and broadband are teh two types of radio used in
networking. Baseband uses carrier’s entire bandwidth to send a single
data stream while broadband sends multiple signals on the carrier at the
same time.
- Radio transmission was invented by Nikola Tesla in 1893.
- Bueetooth is an open wireless technology standard for exchanging
data over short distance using short wavelength radio transmission.
Bluetooth can be used to create PAN (Personal Area Network).
- Bluetooth was invented by Ericsson company in 1994.
- Infrared is an unbound transmission media in which signals are sent
via pulses of infrared light. Infrared communication is possible only on
LOS (Line of Sight).
- Microwave transmission involves the sending and receiving data using
microwave signals over a microwave link. This link is made up of
microwave radio antennas located at the top of towers. Because there
should not be any obstruction between the microwave antennas and
microwave is transmitted in straight line, the towers are often built on
the top of building or hills.
- Microwave is commonly used for communication system on the surface,
in satellite communication and in deep space radio communication.
- There are 3 different transmission mode – simplex, half-duplex and full duplex.
- Simplex is one way communication mode where one device only sends
the data or signals and other devices only receive. Radio, television
are the examples of simplex transmission mode.
- Half-duplex is two way communication mode but only one at a time. Walki-talkie operates in half duplex mode.
- Full duplex is the transmission mode where data is transmitted in
both the directions simultaneously on the same channel. Telephone is an
example of full duplex mode.
- Bandwidth is the term used to describe how much information can be
transmitted over a connection in certain time. It is the measurement of
the capacity of a communication signal. For digital signals, the
bandwidth is the data speed or rate which is measured in bps (bits per
second) or some larger denominations such as kbps (kilo bits per
second), mbps (mega bits per second) and so on. For analog signals,
bandwidth is the difference between the highest and lowest frequency
components which is measured in hertz (Hz).
- There are 3 bandwidths for communication channels – narrow-band, voice-band and broadband channel.
- Narrowband transmit data at a rate between 40 to 100 bps. It is used
where the data volume is relatively low. Telegraph lines are example of
narrowband channel.
- Voiceband channel transmit data at a rate between 110 to 9600 bps.
It is used to handle moderate data. Standard telephone lines are the
examples of voiceband channel.
- Broadband is high speed, high capacity transmission medium that can
carry signals from multiple independent network carriers. Broadband
channel is established using co-axial or fiber optics cable. Broadband
technology can be used to transmit data, voice and video over long
distances simultaneously.
- Data travels in 2 ways over transmission medium – serial data transmission and parallel data transmission
- In serial data transmission, bits flow in a series or continuous
stream. The cost of communication hardware is considerably reduced
because only a single wire or channel is required for teh serial bit
transmission. Telephone lines use serial transmission.
- In parallel data transmission, bits flow through separate lines
simultaneously. It is a standard method of sending data from computer
CPU to printer. Parallel transmission is suitable only for short
distance and not used over telephone lines.
- Data transmission mode can be Asynchronous or Synchronous
- In asynchronous transmission data is sent and received one byte at a
time. It is often used with microcomputers for terminals with slow
speeds.
- In synchronous transmission greater quantities of information is
sent by sending several bytes or a block at a time. For synchronous
transmission, blocks of bytes must occur at carefully timed intervals.
- The Internet is a global, public wide area network (WAN) that provides internet services such as WWW, email,FTP, IRC, Usenet, Newsgroup, video conferences, e-commerce, e-learning and so on.
- The Internet originated from an experimental network called ARPANET created in 1969 by the U.S. Department of defence’s Advanced Research Projects Agency.
- ARPANET was later replaced by NSFnet which was run
by National Science Foundation which permitted universities and research
agencies to link up with its supercomputers.
- Ultimately, many private networks get connected with ARPANET and NSFnet to form the Internet. The Internet became publicly opened since 1990.
- To set up internet you need a computer, a modem and telephone line.
You need to install necessary software such as TCP/IP, browser and email
client. Finally you should get a connection to ISP who provide you the
username and password to connect to the Internet.
- A dial-up connection is a temporary connection set up between your computer and ISP server through telephone lines.
- Broadband internet connection is a high bandwidth
connection to the Internet which is easier and faster to use than the
traditional dial-up networking. Broadband can be provided through
telephone line (ADSL), via cable or via satellite or via other wireless
technologies such as Wi-Fi, WiMAX.
- Email is one of the most important service of Internet. It is used
to exchange messages like in traditional mails. Email uses popular
protocols SMTP for sending emails and POP to receive emails.
- WWW (World Wide Web) is the most popular service of
Internet which provides webpages. It was created by Tim Berners Lee in
1991. The web gives users access to a vast array of documents that are
connected to each other by means of hyperlinks.
- Search Engines are very useful Internet service
that helps you to find web pages, people and other resources in the
Internet. Google, Yahoo, Bing are some of the popular search engines.
- FTP (File Transfer Protocol) is another service in
the Internet that lets you send and receive files over the Internet. The
process of transferring a file from remote computer (servers) to your
local computer is known as downloading and the reverse is uploading.
- IRC (Internet Relay Chat) or web chat is a service in the Internet
that lets you exchange instant messages. It is popularly called
chatting.
- Video conference or video teleconference is a set
of interactive telecommunication technologies which allow two or more
locations to interact via two-way video and audio transmission
simultaneously. People on those locations can talk to each other as in
conference. For video conference you need a computer equipped with
microphone, webcam, broadband internet connection.
- Usenet Newsgroups are worldwide discussion groups
in which people share information and ideas on a particular topic.
Discussion takes place in electronic bulletin board and the topic can
range from personal problems to anything that can be discussed.
- Remote Login is one of the earliest Internet service that lets you to log in to a remote computer and use its service and resources.
- eCommerce refers to the buying and selling of goods
and services on the Internet, especially the WWW. Companies set up
their websites through which customers can buy the products and pay
through online payment methods such as credit cards, PayPal and so on.
- E-Learning is the use of technology to enable
people to learn anything at anytime and from anywhere. Because of the
development of the Internet, the distance learning has become possible
and virtual classes help students to attend class from different part of
world.
- Web servers are the server computers and software
in the Internet that offers different internet services. It receives the
requests from clients, fetches the resource and sends it to the client
computers. Apache, IIS are some examples of web server applications.
- Web browsers are the client applications in users’
computers that send request to the web servers and display the web pages
when server returns the request. Mozilla Firefox, Google Chrome,
Internet Explorer are some examples of web browsers.
- Web Page is a HTML document or resource of
information that is suitable for the WWW and can be accessed through a
web browser and displayed on a monitor or mobile device. Web pages are
requested by browsers and sent by servers using HTTP protocol.
- Website is a collection of web pages containing text, images, audio and video files.
- Homepage is the opening page or main page of a
website intended to greet the user, provide information and offer
navigation to other pages in website. The filename of homepage is
usually ‘default’ or ‘index’.
- Uniform Resource Locator (URL) is the address of
web page, images or any other content resource. You can open any content
of Internet by typing its URL on address bar of browser. For example
http://icttrends.com/ecourse/session-13.htm is a URL to open Session 13
page of eCourse in ICT Trends.
- Domain Name System (DNS) is a technology in the Internet to convert Domain Names into IP address and vice versa.
- A domain name is a name chosen for a website in internet or a computer in network.
- HTTP (Hyper Text Transfer Protocol) is a protocol used by world wide
web to establish client and server interaction. HTTP protocol is used
to transfer webpages over internet.
- Intranet is a private network within an
organization that uses the standards and protocols of Internet. It is
used to provide interaction, communication and information to their
employees.
- Extranet is a private network that uses the
internet technology and the public telecommunication system to connect
more than one organization. Many organizations use Internet technologies
to allow suppliers and other limited access to their networks.
