internet, wireless and networking lecture

7/30/2019 Internet, Wireless and Networking LECTURE

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LECTURE 1: INTERNET

Internet- is a collection of computers throughout the world which are mostly connected using telephone lines for

the purpose of sharing.- Historically, the Internet was used mainly by governments and educational institutions.

1993 the graphical browser called Mosaicwas developed by Marc Andreessen and his team at theNational Center for Supercomputing Applications (NCSA) gave the its big boost. Later, Andreessenmoved to become the brains behind Netscape Corp., which produced the most successful graphicaltype of browser and server.

Microsoft declared war and developed its MicroSoft Internet Explorer. Microsofts full scale entryinto the browser, server, and Internet Service Provider market completed the major shift over to acommercially based Internet. Bill Gates shows the determination to capitalize on the enormous growthof Internet.

- Today, the Internet is used by millions of people including individuals, small and large businesses,

associations, schools, universities, and governments.-

The most popular part of the Internet is the World Wide Web.

World Wide Web (WWW)- is one of the protocols that let you link to many sites in the Internet.

- The basic unit is the web page.A page can be one or many screens as it displays in your monitor.

- The Web was invented by Tim Berners-Lee and others at the European Laboratory for Particle

Physics (CERN) in Switzerland.

The Web consists of the following:1. Your personal computer.2. Web Browser Software to access the Web.3. A connection to an Internet Service Provider (ISP).

Internet Service Provider (ISP)- is a company that provides a telecommunication connection to the Internet that allows a

user to "be online".- The connection may be provided in many different forms. It could use existing telephone

lines, existing cable TV lines, new fiber optic cable may be strung or the user has to use amodem and dial a phone number.

- Examples of ISPs are: AOL, Earthlink, MSN, Time Warner Cable, Verizon, etc.

4. Servers to host data.5. Routers and switches to direct the flow of data.

How Does the Web Works?

Uniform Resource Locator (URL)- the global address of documents and other resources on the World Wide Web.

http:// indicates that the browser and web server willcommunicate using Hypertext Transfer Protocol.www indicates a resources coming from the World Wide Web..yahoo.com called the domain, identifies which computer called web server, host the site.

- aebihis

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Domain Name- denotes the name of specific Internet area controlled by a company, school, or organization.

- Typical domain names cosnsist of some form of organizations name and a suffix that describes the

type of organization:.com corporation.edu educational institutions.gov government institution.mil military organization.net network provider.org non profit organization

The end of a domain name can often tell you the country of origin:.ph Philippines.uk United Kingdom.fr France.jp Japan

What can we do on the Internet:1. Electronic-mail (E-mail)

2. Information3. Group Discussion4. Entertainment5. News6. On Line Shopping7. Free Programs (software)

Computer Virus- is a program that invades your computer system, hides there, and makes copies of (replicates) itself.

- Viruses spread when you launch an infected application or start up your computer from a disk that has

infected system files.- Some viruses are programmed specifically to damage the data on your computer by corrupting

programs, deleting files, or erasing your entire hard disk.

- aebihis


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LECTURE 2: CONNECTING TO INTERNET

Modems- are the devices that are used to modulate and demodulate the data.

- They convert analogue signals to digital and digital signals to analogue so that signals can travel on

the telephone lines.

Transmission Control Protocol/Internet Protocol (TCP/IP)- The communications protocol used by the Internet. Basically when you see numbers such as

243.236.2.1 this is called the IP address.

IP address- is associated with a device, usually a network card, and is used in the same way your home

address is used.- It let one device find another device in the Internet network.

Network Interface Card (NIC)- are used to physically connect host devices to the network media.

They use this connection to send e-mails, print reports, scan pictures,

or access databases.- a printed circuit board that fits into the expansion slot of a bus on a

computer motherboard.- sometimes called network adapters

Gateway- is a device or software in the network.

- is responsible for connecting physically two different networks.

- can connect a Local Area Network to a Wide Area Network or a Virtual Private Network over the

internet or it can be also used to connect to the internet itself.- is all the times directly connected to the internet well then it is directly exposed to the security threats

which comes from the internet so a Gateway should be properly configured and secured and the inand out traffic should be monitored.

- aebihis


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LECTURE 3: BROWSING THE WEB

Web Browser

- is a software application for retrieving, presenting, and traversing information resources on the World

Wide Web. An information resource is identified by a Uniform Resource Identifier(URI) and may bea web page, image, video, or other piece of content. Hyperlinks present in resources enable users

easily to navigate their browsers to related resources.- can also be defined as an application software or program designed to enable users to access,

retrieve and view documents and other resources on the Internet.- Examples of web browser are: Internet Explorer, Mozilla Firefox, Google Chrome, etc.

Search Engine- A utility that will search the Internet.

- use software (called a wanderer, crawler, robot, worm, spider) which comb the Internet looking for

documents and their addresses.- assembles a web page that listed the results as hypertext links.

A search engine consist of three components:

Spider program that traverses the Web from link to link, identifying and reading pages.

Index database containing a copy of each Web page gathered by the spider. Search engine mechanism software that enable users to query the index and that usually

return results in relevancy ranked order.

Below are some of the Internet Search Engines you can use to search the Web:

Two types of search engines:1. Individual search engines compile their own searchable databases on the web.2. Meta-searchers

- do not compile databases. Instead, they search the databases of multiple sets of

individual engines simultaneously.- provide a quick way of finding out which engines are retrieving the best results for you in

your search.- Example: http://www.alenka.cz

Alenka it enables you to search through various Internet databases.

In the Philippines, some of the famous Search Engines are:

Yehey.com

pinoycentral.com

Edsaworld.com

Library Gateways- are collectins of reviewd and recommended links that have been created by subject specialists,

usually librarians, to support research needs and to pinpoint high quality sites on the web.

- aebihis


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http://en.wikipedia.org/wiki/Software_applicationhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Uniform_Resource_Identifierhttp://en.wikipedia.org/wiki/Web_pagehttp://en.wikipedia.org/wiki/Hyperlinkshttp://en.wikipedia.org/wiki/Application_softwarehttp://en.wikipedia.org/wiki/Internethttp://en.wikipedia.org/wiki/Software_applicationhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/World_Wide_Webhttp://en.wikipedia.org/wiki/Uniform_Resource_Identifierhttp://en.wikipedia.org/wiki/Web_pagehttp://en.wikipedia.org/wiki/Hyperlinkshttp://en.wikipedia.org/wiki/Application_softwarehttp://en.wikipedia.org/wiki/Internet


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- point to realize databases on the web created by professors, researchers, expert, government

agencies, business interests, or other subject specialists and individuals who have a deep interest in aparticular field and have accumulated and compiled web links to it.

Cache- downloaded files are stored in a cache (pronounced cash) on your hard drive.

Netiquette- its network etiquette that is, the etiquette of cyberspace.

- is a set of rules for behaving properly online.

Etiquette- the forms required by good breeding or prescribed by authority to be required in social or official life.

Golden Rule:1. Remember the human.

Stand up for yourself, but try not to hurt peoples feelings.

2. Adhere to the same standards of behavior online that you follow in real life.Standards of behavior may be different in some areas of cyberspace, but they are not lower than inreal life.

3. Know where you are in cyberspace.When you enter a domain of cyberspace thats new to you, take look around. Spend a while listeningto the chat or reading the archives. Get a sense of how the people who are already there act.

4. Respect other peoples time and bandwidth.Its your responsibility to ensure that the time they spend reading your posting isnt wasted.

5. Make yourself look good online.6. Know how to handle flames.

Be pleasant and polite.

Know what youre talking about and make sense.

Dont post flame-bait.

7. Help keep flame wars under control.

Flaming is what people do when they express a strongly held opinion without holding back anyemotion.

8. Share expert knowledge.Dont afraid to share what you know.

9. Respect other peoples privacy.10. Dont abuse your power.11. Be forgiving of other peoples mistake.

- aebihis


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LECTURE 4: THE WIRELESS REVOLUTION

The Internet is changing the way we work, play, entertain ourselves, and communicate with people all over theworld. The Internet is also creating new opportunities and headaches for businesses everywhere.

Wireless signals

- are electromagnetic waves that can travel through the vacuum of outer space and through a mediumsuch as air. Therefore, no physical medium is necessary for wireless signals, making them a veryversatile way to build a network.

- use portions of the RF spectrum to transmit voice, video, and data.

- Wireless frequencies range from 3 kilohertz (kHz) to 300 gigahertz (GHz).

- The data-transmission rates range from 9 kilobits per second (kbps) to as high as 54 Mbps.

The primary difference between electromagnetic waves is their frequency.

Low-frequency electromagnetic waves have a long wavelength (the distance from one peak to the

next on the sine wave)

High-frequency electromagnetic waves have a short wavelength.

Wireless Transmission Media and Devices

Cellular Network Standards and Generations

Interestingly enough, the United States is not among the most "wired wireless" countries in the world; thathonor goes to South Korea, Japan, and many European countries. Unfortunately each world region hasadopted separate standards for wireless networks and very often the standards don't allow for crosstransmissions.

Two major standards used in the world are:

Global System for Mobile Communication (GSM): bandwidth is based on time division multiple

access and is used in Europe, China, and Asia, and some regions of the United States.

Code Division Multiple Access (CDMA): transmits over several radio frequencies and randomlyassigns users to a range of frequencies over time. It is used mostly in the United States.

Just as we've experienced generations of computers and computer languages, we allocate generational labelsto wireless phone systems. A short review of their characteristics may help you distinguish among them:

First generation (1G): first appeared in the 1980s and were analog based. Mostly supported only

voice transmissions.

Second generation (2G): appeared in the 1990s and supported better voice quality and short

message services.

Interim generation (2.5G): appeared in the late 1990s and early 2000s and provides increased data

transmissions based on the 2G technology. It's an interim fix until 3G technology is more fully refined.

Third generation (3G): appeared in the early 2000s and are based on packet-switch technology that

allows large amounts of data transmission. Supports voice, video, and graphics.

Mobile Wireless Standards for Web Access

Wireless Application Protocol (WAP) - is the set of rules that controls how wireless devices access Webapplications.

The Wireless Markup Language (WML) combines HTML and XML languages with the requirements forproperly displaying information on the small screen. It's most important characteristic is that it describes datarather than just how the data are displayed. The microbrowser included on wireless devices is similar to a

- aebihis


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regular Web browser you would use on a PC but is optimized for the limitations imposed on the smallerdevices.

Wireless Computer Networks and Internet Access

In order for wireless networks to work in tandem with each other it is necessary to create standards such aswe have with the Internet and other network technologies.

Radio- 10 Khz to 1 Ghz.

- It is broken into many bands including AM, FM, and VHF bands. The Federal communications

Commission (FCC) regulates the assignment of these frequencies. Frequencies for unregulated useare:o 902-928Mhz- Cordless phones, remote controls.

o 2.4 Ghz

o 5.72-5.85 Ghz

Microwave

Terrestrial - Used to link networks over long distances but the two microwave towers must have a line

of sight between them. The frequency is usually 4-6GHz or 21-23GHz. Speed is often 1-10Mbps. The

signal is normally encrypted for privacy. Satellite - A satellite orbits at 22,300 miles above the earth which is an altitude that will cause it to stay

in a fixed position relative to the rotation of the earth. This is called a geosynchronous orbit. A stationon the ground will send and receive signals from the satellite. The signal can have propagation delaysbetween 0.5 and 5 seconds due to the distances involved. The transmission frequency is normally 11-14GHz with a transmission speed in the range of 1-10Mbps.

Infared- is just below the visible range of light between 100Ghz and 1000Thz. A light emitting diode (LED) or

laser is used to transmit the signal. The signal cannot travel through objects. Light may interfere withthe signal.

- The types of infared are:

o Point to point Transmission frequencies are 100GHz-1,000THz . Transmission is between two

points and is limited to line of sight range. It is difficult to eavesdrop on the transmission.o broadcast The signal is dispersed so several units may receive the signal. The unit used to

disperse the signal may be reflective material or a transmitter that amplifies and retransmits thesignal. Normally the speed is limited to 1Mbps. The transmission frequency is normally 100GHz-1,000THz with transmission distance in 10's of meters. Installation is easy and cost is relativelyinexpensive for wireless.

Bluetooth- wireless technology standard comes installed on some computers and is used to create small

personal area networks.- it's more appropriate to use in battery-powered devices that are within close proximity to each other.

- eliminates cabling between electronic products and accessories, such as between computers and

printers or between phones and headsets.

- is more oriented toward user mobility and eliminating short-distance cabling

Wi-Fi- The recent proliferation of wireless technology is technically known as the 802.11 networking

standard.- It's more commonly, and easily, called Wi-Fifor wireless fidelity.

- can help save money by negating the need for additional phone lines for Internet access or to use a

single peripheral device such as a printer among several different computers. Each computer requiresa wireless network interface card (NIC) containing a built-in radio and antenna. These cards arerelatively inexpensive and you can avoid duplicating more expensive equipment by using a wirelessnetwork.

- aebihis


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WiMax and EV-DO

Because of limitations in frequency ranges associated with Wi-Fi, Bluetooth and other technologies, many

users are left out of the Internet evolution. Therefore a new technology called WiMax is being developed tohelp fill the gaps all across the country.

WiMax - increases the range of transmissions up to approximately 30 miles and increases the transmissionspeeds significantly over that available on regular telephone lines and dial-up modems.

EV-DO and Wireless Cellular Access

Cellular telephone companies are continuing the march towards total convergence of all things digital with itsEvolution Data Optimized (EV-DO) technology.

EV-DO - allow even more ways for users to access digital content from the Internet and other networkswhether that data is voice, videos, graphics, documents, text messaging, or photographs. It won't be longbefore the same connectivity people enjoy in their homes and offices will be available anywhere, anytime, inany form.

M-Commerce and Mobile Computing

As mobile computing devices such as Internet-enabled cell phones, PDAs, and laptop computers, becomemore popular; people want to be able to connect easily to the Internet wherever they are. Because the displaysize and bandwidth of these devices are much smaller than a full size PC, Web pages are resized and mostgraphics are eliminated.

M-Commerce Services and Applications for Mobile Computing

- aebihis


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LECTURE 5: NETWORKING

Networking is the practice of linking two or more computing devices together for the purpose of sharingdata. Networks are built with a mix of computer hardware and computer software.

Key Digital Networking Technologies

Key technologies necessary for network computing:

1. Client/Server Computing

- facilitates computing on all kinds of networks including the Internet. Instead of one huge

mainframe with individual nodes, smaller computers called servers connect to many clients. Thistype of network is ideal for companies that are continually expanding their networks or replacinghardware components.

2. Packet Switching

- is a method of breaking large blocks of text into smaller chunks of data and routing them in the

most economical way through whichever communication channel is available.- The data were broken into small packets on their way out of the server computer and then sent to

and reassembled on the client computer. It happens so quickly and so efficiently that you don'teven notice.

- also checks for transmission errors when data travel from one location to another.

3. TCP/IP and Connectivity

Transmission Control Protocol/Internet Protocol (TCP/IP)- the most popular model for connecting networks. Even though this protocol was originally

created for what we now call the Internet, it is easily transferred to networks of all sizes.

- It provides the easiest methodology for communicating between computers throughstandardized protocols that ignore the hardware and software platforms of the individualpieces of equipment.

- The most important benefit of the TCP/IP model is that it allows two computers to

communicate even if they are based on different hardware and software platforms.

Computer users often lament the fact that it's difficult to share data between different platforms. Most of thisproblem is resolved through open systems:

1. nonproprietary operating systems2. user interfaces3. networking protocols

Open systems allow users to exchange data and information easily and efficiently without worrying about

the type of hardware used on the individual computers.

Networking Models

When dealing with networking, you may hear the terms "network model" and "network layer" used often.

Network models define a set of network layers and how they interact.

There are several different network models depending on what organization or company started them. Themost important two are:

- aebihis


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The TCP/IP Model

- sometimes called the DOD modelsince it was designed for the department of defense.

- it is also called the internet model because TCP/IP is the protocol used on the internet.

OSI Network Model

- the International Standards Organization (ISO) has defined a standard called the Open

Systems Interconnection (OSI) reference model.

- this is a seven layer architecture

Open Systems Interconnect (OSI)

- defines a networking framework for

implementing protocols in seven layers.Control is passed from one layer to the next,starting at the application layer in one station,and proceeding to the bottom layer, over thechannel to the next station and back up thehierarchy.

- is similar to TCP/IP in that it supports any

hardware and software connected to the

network.- was developed as an international reference

model.

Application (Layer 7)- This layer supports application and end-user processes. Communication partners are

identified, quality of service is identified, user authentication and privacy are considered, andany constraints on data syntax are identified. Everything at this layer is application-specific.

- This layer provides application services for fi le transfers, e-mail, and

othernetwork software services. Telnet and FTP are applications that exist entirely in theapplication level. Tiered application architectures are part of this layer.

Presentation (Layer 6)- This layer provides independence from differences in data representation (e.g., encryption) by

translating from application to network format, and vice versa. The presentation layer works totransform data into the form that the application layer can accept.

- This layer formats and encrypts data to be sent across a network, providing freedom from

compatibility problems.- It is sometimes called the syntax layer.

Session (Layer 5)- This layer establishes, manages and terminates connections between applications.

- The session layer sets up, coordinates, and terminates conversations, exchanges, and

dialogues between the applications at each end.-

It deals with session and connection coordination.

Transport (Layer 4)- This layer provides transparent transfer of data between end systems, orhosts, and is

responsible for end-to-end error recovery and flow control.- It ensures complete data transfer.

Network (Layer 3)- This layer provides switching and routing technologies, creating logical paths, known as virtual

circuits, for transmitting data from node to node.

- aebihis


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- Routing and forwarding are functions of this layer, as well as addressing,internetworking,

error handling,congestion control and packet sequencing.

Data Link (Layer 2)- Data packets are encoded and decoded into bits.

- It furnishes transmission protocol knowledge and management and handles errors in the

physical layer, flow control and frame synchronization.- The data link layer is divided into two sub layers:

o The Media Access Control (MAC) layer

- controls how a computer on the network gains access to the data and

permission to transmit it.o Logical Link Control (LLC) layer

- controls frame synchronization, flow control and error checking.

Physical (Layer 1)- This layer conveys the bit stream - electrical impulse, light or radio signal -- through

the network at the electrical and mechanical level.- It provides the hardware means of sending and receiving data on a carrier, including defining

cables, cards and physical aspects.

- Fast Ethernet, RS232, andATM are protocols with physical layer components.

Networking Media

Cables have different specifications and expectations. Important considerations related to performance are asfollows:

What speeds for data transmission can be achieved? The speed of bit transmission through the cable

is extremely important. The speed of transmission is affected by the kind of conduit used.

Will the transmissions be digital or analog? Digital or baseband transmission and analog or broadband

transmission require different types of cable.

How far can a signal travel before attenuation becomes a concern? If the signal is degraded, network

devices might not be able to receive and interpret the signal. The distance the signal travels throughthe cable affects attenuation of the signal. Degradation is directly related to the distance the signaltravels and the type of cable used.

The following Ethernet specifications relate to cable type:

10BASE-T

- refers to the speed of transmission at 10 Mbps.

- The type of transmission is baseband, or digitally interpreted.

- The T stands fortwisted pair.

10BASE5

- refers to the speed of transmission at 10 Mbps.- The type of transmission is baseband, or digitally interpreted.

- The 5 indicates that a signal can travel for approximately 500 meters before attenuation could

disrupt the ability of the receiver to interpret the signal.- is often referred to as Thicknet. Thicknet is a type of network and 10BASE5 is the Ethernet

specification used in that network.

10BASE2

- refers to the speed of transmission at 10 Mbps.

- The type of transmission is baseband, or digitally interpreted.

- aebihis


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- The 2, in 10BASE2, refers to the approximate maximum segment length being 200 meters

before attenuation could disrupt the ability of the receiver to appropriately interpret the signalbeing received. The maximum segment length is actually 185 meters.

- is often referred to as Thinnet. Thinnet is a type of network and 10BASE2 is the Ethernet

specification used in that network.

Physical Media:

1. Twisted pair- Wire is twisted to minimize crosstalk interference. It may be shielded or unshielded.

Unshielded Twisted Pair (UTP). Normally UTP

contains 8 wires or 4 pair. 100 meter maximum length.4-100 Mbps speed.

Shielded Twisted Pair (STP). 100 meter maximum length. 16-

155 Mbps speed. Lower electrical interference than UTP.

2. Coaxial - Two conductors separated by insulation such as TV 75 ohm cable. Maximum length of 185to 500 meters.

Thinnet. Thinnet uses a British Naval Connector (BNC) on each end. Thinnet is part of the RG-58

family of cable*. Maximum cable length is 185 meters. Transmission speed is 10Mbps. Thinnetcable should have 50 ohms impedance and its terminator has 50 ohms impedance. A T or barrelconnector has no impedance.

Thicknet. Half inch rigid cable. Maximum cable length is 500 meters. Transmission speed is

10Mbps. Expensive and is not commonly used. (RG-11 or RG-8). A vampire tap or piercing tap isused with a transceiver attached to connect computers to the cable. 100 connections may bemade. The computer has an attachment unit interface (AUI) on its network card which is a 15 pinDB-15 connector. The computer is connected to the transceiver at the cable from its AUI on itsnetwork card using a drop cable.

3. Fiber-optic - Data is transmitted using light rather than electrons. This is the most expensive and mostdifficult to install, but is not subject to interference. Two types of cables are:

Single mode cables for use with lasers.

Multimode cables for use with Light Emitting Diode (LED) drivers.

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Network Topologies

Network topology defines the structure of the network. One part of the topology definition is the physicaltopology, which is the actual layout of the wire or media. The other part is the logical topology, which defineshow the hosts access the media to send data.

A bus topology uses a single backbone cable that is

terminated at both ends. All the hosts connect directlyto this backbone.

A ring topology connects one host to the next and

the last host to the first. This creates a physical ring ofcable.

A star topology connects all cables to a central

point. An extended star topology links individual stars

together by connecting the hubs or switches.

A hierarchical topology is similar to an extended

star. However, instead of linking the hubs or switchestogether, the system is linked to a computer that controls the traffic on the topology.

A mesh topology is implemented to provide as much protection as possible from interruption of

service. For example, a nuclear power plant might use a mesh topology in the networked controlsystems. As seen in the graphic, each host has its own connections to all other hosts. Although theInternet has multiple paths to any one location, it does not adopt the full mesh topology.

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Considerations When Choosing a Topology:

Money. A linear bus network may be the least expensive way to install a network; you do not have to

purchase concentrators.

Length of cable needed. The linear bus network uses shorter lengths of cable.

Future growth. With a star topology, expanding a network is easily done by adding another

concentrator. Cable type. The most common cable in schools is unshielded twisted pair, which is most often used

with star topologies.

Networks and Corporate Infrastructure

Basic Networking Devices:

1. Routers- are bigger devices than the hubs, bridges or the switches and are used on bigger networks.

- They route the data along with connecting many nodes to different networks.

- control the network traffic and send and receive data accordingly.

- has the list of IP addresses using which it controls the data flow to the nodes.

Small networks usually do not require routers and the server can handle. However biggernetworks have to use routers.

2. Bridges- reads the outermost section of data on the data packet, to tell where the message is going.

- It reduces the traffic on other network segments, since it does not send all packets.

- can be programmed to reject packets from particular networks.

- Bridging occurs at the data link layer of the OSI model, which means the bridge cannot read IP

addresses, but only the outermost hardware address of the packet. In our case the bridge canread the ethernet data which gives the hardware address of the destination address, not the IPaddress.

- forward all broadcast messages. Only a special bridge called a translation bridge will allow twonetworks of different architectures to be connected.

- do not normally allow connection of networks with different architectures. The hardware address is

also called the media access control (MAC) address.

To determine the network segment a MAC address belongs to, bridges use one of:

o Transparent Bridging They build a table of addresses (bridging table) as they receive

packets. If the address is not in the bridging table, the packet is forwarded to all segments

other than the one it came from. This type of bridge is used on ethernet networks.o Source route bridging The source computer provides path information inside the

packet. This is used on Token Ring networks.

3. Hubs

- is a device that is used to connect multiple nodes to a single point and the hub is used to connect

these nodes to the network.

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- The signal passes through the hub first and then reaches the nodes so it basically functions like a

connector in many networks.

4. Switches

- are very similar in functionality to the bridges. However the switches use more ports of

connectivity than a bridge.

- are now taking over all other devices including the hubs and the bridges.

5. Repeater

- connects two segments of your network cable.

- It retimes and regenerates the signals to proper amplitudes and sends them to the other

segments. When talking about, ethernet topology, you are probably talking about using a hub as arepeater.

- Repeaters require a small amount of time to regenerate the signal. This can cause a propagation

delay which can affect network communication when there are several repeaters in a row. Many

network architectures limit the number of repeaters that can be used in a row.- Repeaters work only at the physical layer of the OSI network model.

Types of Networks:

1. Local Area Networks (LANs)- allow businesses to locally share computer

files and printers efficiently and make internalcommunications possible.

- Example of this technology is e-mail. The

LANs manage data, local communications, and

computing equipment.

LANs consist of the following components:

Computers

Network interface cards

Peripheral devices

Networking media

Network devices

2. Wide Area Networks (WANs)- access to computers or file servers in other

locations. Because WANs connect user networksover a large geographical area, they make it

possible for businesses to communicate acrossgreat distances.

- allow computers, printers, and other devices on a

LAN to be shared with distant locations.- provide instant communications across large

geographic areas.

Collaboration software provides access to real-timeinformation and resources and allows meetings to beheld remotely. WANs have created a new class ofworkers called telecommuters. These people never have to leave their homes to go to work.

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WANs are designed to do the following:

Operate over a large and geographically separated area

Allow users to have real-time communication capabilities with other users

Provide full-time remote resources connected to local services

Provide e-mail, Internet, file transfer, and e-commerce services

3. Metropolitan Area Networks (MANs)- areas can also be used to create a MAN.

- usually consists of two or more LANs in a common

geographic area.- Example, a bank with multiple branches may utilize a MAN.

Typically, a service provider is used to connect two or moreLAN sites using private communication lines or opticalservices.

- can also be created using wireless bridge technology by

beaming signals across public areas.

4. Storage Area Networks (SANs)

- used to move data between servers and storage resources. Because it is a separate, dedicatednetwork, it avoids any traffic conflict between clients and servers.

- allows high-speed server-to-storage, storage-to-storage, or server-to-server connectivity.

- This method uses a separate network infrastructure that relieves any problems associated with

existing network connectivity.

SANs offer the following features:

Performance SANs allow concurrent access of disk or tape arrays by

two or more servers at high speeds. This provides enhanced systemperformance.

Availability SANs have built-in disaster tolerance. Data can be

duplicated on a SAN up to 10 km (6.2 miles) away.

Scalability A SAN can use a variety of technologies. This allows easy

relocation of backup data, operations, file migration, and data replicationbetween systems.

5. Virtual Private Networks (VPNs)- is a private network that is constructed within a public

network infrastructure such as the global Internet.- Using VPN, a telecommuter can remotely access the

network of the company headquarters. Through theInternet, a secure tunnel can be built between the PCof the telecommuter and a VPN router at the companyheadquarters.

- is the most cost-effective way to establish a point-to-

point connection between remote users and an

enterprise network.

Intranet and Extranet

Intranet- one common configuration of a LAN

- Intranet Web servers differ from public Web servers in that the

public must have the proper permissions and passwords toaccess the intranet of an organization.

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- are designed to permit users who have access privileges to the internal LAN of the organization.

- Within an intranet, Web servers are installed in the network. Browser technology is used as the

common front end to access information on servers such as financial, graphical, or text-based data.

Extranets- refer to applications and services that are Intranet based, and use extended, secure access to external

users or enterprises.- This access is usually accomplished through passwords, user IDs, and other application-level security.

- is the extension of two or more intranet strategies with a secure interaction between participant

enterprises and their respective intranets.

Components of a simple network structure.

The term serveris used to refer to one of the following:

a computer program running to serve the needs or requests of other programs (referred to in this

context as "clients") which may or may not be running on the same computer.

a physical computer dedicated to running one or more such services, to serve the needs of programs

running on other computers on the same network.

a software/hardware system (i.e. a software service running on a dedicated computer) such as

a database server, file server, mail server, orprint server.

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internet, wireless and networking lecture

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