CTE 226

Introduction To Networking

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REVISED EDITION

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Introduction

In its broadest sense, a network consists of two or more entities,or objects, sharing resources and information. Although thishandout is about computer networks, there are networks that don’tinvolve computers, and those networks are everywhere. You havegrown accustomed to working with them, possibly without evenknowing it. It may not matter to you that, in a basic sense,sharing (giving or getting) is a fundamental aspect of networking.You just know that you do it.There is family network in which related people share theirresources and information. This sharing is bi-directional becauseeven the youngest family members share information of some sort. Asthe family grows, so does the network. There is peer network whichis outside the family, (a community) that offers a wider array ofresources than the typical family can provide. There is alsocontact network where friends and associates help in performingsome tasks. The more people you meet the more the chance of gettingthings done quickly and easily. All these are “Human Networks”, andshould help you understand that networking is common between peopleand it’s not just an activity restricted to computers. However, forthe purpose of this course, our studies would be based on ComputerNetworks.

Computer NetworkA computer network is simply two or more computers connectedtogether so they can exchange information. A small network can beas simple as two computers linked together by a single cable. Thiscourse introduces you to the hardware and software needed for anetwork, and explains how a small network is different from largernetworks and the Internet. Most networks use hubs to connectcomputers together. A large network may connect thousands ofcomputers and other devices together. A wireless network connectscomputers without a hub or network cables but use radiocommunications to send data between each other. Networking allowsyou to share resources among a group of computer users. If you havea printer connected to your computer, you can share the printer

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with other computers on the network. Then instead of buying aprinter for every computer, all the computers can print across thenetwork to the printer. If you already have access to the Internetfrom one computer on your network, you can share that Internetconnection with other computers on the network. Then all thecomputers on your network can browse the Web at the same time,using this single Internet connection.

A computer network is basically established by the network layer inthe Open Systems Infrastructure model, popularly known as the OSImodel. Computer networks exist on various scales, from linksbetween machines in the same room up through wiring connecting themachines in a building or campus to regional, national and globalnetworks. Various media are used to carry the communicationssignals: copper wire, fibre-optic cables and wireless or radiotransmissions etc.

The concept of sharing resources over a network is callednetworking. The computers in a network can share data, messages,graphics, printers, fax machines, modems, and other hardware andsoftware resources. The individual systems must be connectedthrough a pathway (called the transmission medium) that is used totransmit the resource or service between the computers. All systemson the pathway must follow a set of common communication rules fordata to arrive at its intended destination and for the sending andreceiving systems to understand each other. The rules governingcomputer communication are called protocols. In summary, allnetworks must have the following:

1. A resource to share (resource) 2. A pathway to transfer data (transmission medium) 3. A set of rules governing how to communicate (protocols)

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Simplest form of a computer network

Having a transmission pathway does not always guaranteecommunication. When two entities communicate, they do not merelyexchange information; rather, they must understand the informationthey receive from each other. The goal of computer networking,therefore, is not simply to exchange data but to understand and usedata received from other entities on the network. An analogy ispeople speaking, just because two people can speak, it does notmean they automatically can understand each other. These two peoplemight speak different languages or interpret words differently. Oneperson might use sign language, while the other uses spokenlanguage. As in human communication, even though you have twoentities who "speak," there is no guarantee they will be able tounderstand each other. Just because two computers are sharingresources, it does not necessarily mean they can communicate.Because computers can be used in different ways and can be locatedat different distances from each other, enabling computers tocommunicate often can be a daunting task that draws on a widevariety of technologies.

Network Elements Servers:- Servers are the computers that provide the shared

resources to network users. There is usually only one server in a small network, but bigger networks may have more than oneserver.

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Clients:- Clients are the computers that can access the sharednetwork resources provided by a server.

Peer:- A peer requests and provides network services. i.e. it performs both functions.

Media:- The computers in a network are connected to each otherby hardware components, such as cables. These components are called the media.

Shared Data:- A server provides shared resources and data overa network. The files that are provided by the server over the network are called shared data. This shared data can be a document, a worksheet or a folder.

Resources:- Files, printers or other items that can be used bynetwork users are known as resources. These resources can be either hardware or software resources.

Benefits of Computer NetworkA network offers benefits, such as data sharing and onlinecommunication that are not provided by a stand-alone computer(Computers that are not connected to each other are called stand-alone computers.). The advantages of a network are:

File and Data Sharing: Networks offer a quick and easy way to share files and data directly. Instead of using a disk or USB key to carry files from one computer or office to another, youcan share files directly using a network.

Security: Specific directories can be password protected tolimit access to authorized users. Also, files and programs ona network can be designated as "copy inhibit" so you don’thave to worry about the illegal copying of programs.

Resource Sharing:- All computers in the network can shareresources such as printers, fax machines, modems, andscanners.

Communication: Even outside of the internet, those on thenetwork can communicate with each other via electronic mail

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over the network system. When connected to the internet,network users can communicate with people around the world viathe network.

Centralized Software Management:- One of the greatest benefitsof installing a network is the fact that all of the softwarecan be loaded on one computer (the file server). Thiseliminates that need to spend time and energy installingupdates and tracking files on independent computers throughoutthe building.

Communication Medium:- A computer network can provide apowerful communication medium among people spread widely atdifferent physical locations. It acts as a powerfulcommunication medium when it comes to sharing information andresources. Even outside of the internet, those on the networkcan communicate with each other via electronic mail over thenetwork system. When connected to the internet, network userscan communicate with people around the world via the network.

Flexible Access: Networks allow their users to access filesfrom computers throughout the network. This means that a usercan begin work on a project on one computer and finish up onanother. Multiple users can also collaborate on the sameproject through the network.

Error reduction and improve consistency: One can reduce errorsand improve consistency by having all staff work from a singlesource of information, so that standard versions of manualsand directories can be made available, and data can be backedup from a single point on a scheduled basis, ensuringconsistency.

Data Management:- In a business environment, a network allowsthe administrators to much better manage the company'scritical data. Instead of having this data spread over dozensor even hundreds of small computers in a haphazard fashion astheir users create it, data can be centralized on shared

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servers. This makes it easy for everyone to find the data,makes it possible for the administrators to ensure that thedata is regularly backed up, and also allows for theimplementation of security measures to control who can read orchange various pieces of critical information.

Speed:- Sharing and transferring files within Networks arevery fast. Networks provide a very rapid method for sharingand transferring files. The sharing of data with the otherusers in a stand-alone environment requires physical transferof data. This can be done by copying the data on a compact orflash disk or taking a printout. This requires more time andis inconvenient as compared to sharing the data over anetwork.

Disadvantages of Computer Network Expensive to Install:- Although a network will generally save

money over time, the initial costs of installation can beprohibitive. Cables, network cards, and software areexpensive, and the installation may require the services of atechnician.

Data Security:- If a network is implemented properly, it ispossible to greatly improve the security of important data. Incontrast, a poorly secured network puts critical data at risk,exposing it to the potential problems associated with hackers,unauthorized access.

Cables May Break:- One broken cable can stop the entirenetwork.

File Server May Fail:- Although a file server is no moresusceptible to failure than any other computer, when the filesserver "goes down," the entire network may come to a halt.When this happens, the entire network users may lose access tonecessary programs and files.

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Virus Infections:- If any computer system in a network getsaffected by computer virus , there is a possible threat ofother systems getting affected too. Viruses get spread on anetwork easily because of the interconnectivity ofworkstations. Such spread can be dangerous if the computershave important database which can get corrupted by the virus.

Network Application Areas There is a long list of application areas, which can be benefitedby establishing Computer Networks. Few of the potentialapplications of Computer Networks are:

1. Information retrieval systems which search for books,technical reports, papers and articles on particular topics

2. News access machines, which can search past news, stories orabstracts with given search criteria.

3. Airline reservation, hotel booking, railway-reservation, car-rental, etc.

4. A writer's aid: a dictionary, thesaurus, phrase generator,indexed dictionary of quotations, and encyclopedia.

5. Stock market information systems which allow searches forstocks that meet certain criteria, performance comparisons,moving averages, and various forecasting techniques.

6. Electronic Financial Transactions (EFT) between banks and viacheque clearing house.

7. Games of the type that grow or change with various enthusiastsadding to the complexity or diversity.

8. Electronic Mail Messages Systems (EMMS). 9. Corporate information systems such as marketing information

system, customer information system, product informationsystem, personnel information system, etc.

10. Corporate systems of different systems such as Order-Entry System, Centralized Purchasing, Distributed InventoryControl, etc.

11. On-line systems for Investment Advice and Management, TaxMinimization, etc.

12. Resources of interest to a home user. 13. Sports results.

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14. Theatre, movies, and community events information. 15. Shopping information, prices, and advertisements. 16. Restaurants; good food guide. 17. Household magazine, recipes, book reviews, film reviews. 18. Holidays, hotels, travel booking. 19. Radio and TV programmes. 20. Medical assistance service. 21. Insurance information. 22. Computer Assisted Instruction (CAI). 23. School homework, quizzes, tests. 24. Message sending service. 25. Directories. 26. Consumer reports. 27. Employment directories and Job opportunities. 28. Tax information and Tax assistance. 29. Journey planning assistance viz. Train, bus, plane etc. 30. Catalogue of Open University and Virtual University courses.

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31. HOW TO CONFIGURE A NETWORK - COMPUTER NETWORKING MODELS

Before configuring a computer network, you have to decide that,which networking model you require. The term computer network modeldefines the category in which a computer network can be groupedinto. Computer can interact with each other on a network indifferent ways and fulfill different roles. There are two maintypes of network models to define these interactions. Peer to peerand client-server network model. The third one is Hybrid which isthe combination of the first two.

Peer-to-Peer NetworksIn the peer to peer network model you simply use the same Workgroupfor all the computers and a unique name for each computer.Additionally, you will have to give a unique IP address of the sameclass A, B, or C for all the computers in your network and itsrelated subnet mask

In a peer-to-peer network, there are no dedicated servers, andthere is no hierarchy among the computers. All the computers areequal and therefore are known as peers. Each computer functions asboth a client and a server because there is not centralized server.Peer to peer network is used where no security is required in thenetwork. If a computer fails to work then all other computers worknormally. There is no administrator responsible for the entirenetwork. Each user determines what data on his/her computer isshared on the network. The figure below shows a peer-to-peernetwork in which each computer functions as both a client and aserver.

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Computers in a peer-to-peer network are called peers. In a peer-to-peer network, all computers are considered equal; they all have thesame abilities to use the resources available on the network.Computers are not dedicated to function as servers. They use thenetwork to share resources among the independent peers. Thecomputer whose applications are required by the other networkedcomputers functions as a server. The other computers function asclients. Therefore, a dedicated administrator is not assigned fornetwork management.

A peer-to-peer network is a small group of people using a network.Peer-to-peer networks members usually perform similar tasks, whichnecessitates the sharing of resources. The peer-to-peer networkssupport 10 computers. The users in a peer-to-peer network arelocated in the same geographical area. Operating systems, such asMicrosoft Windows can be used to set up a peer-to-peer network.Additional software is not required because peer-to-peer networkingis built into the systems.

Another important point of peer-to-peer networks is that the usersof each computer plan and control the security of their resources.The users determine the resources on their computers, which can beshared on the network. The shared network resources, such as diskspace, printers or faxes, can be used by anyone who has access tothe network. This is possible only if the shared network resourcesare not password protected. Peer-to-peer networks have weak andintrusive security because a central server is not used toadminister and secure the network. In addition, some users may notimplement security.

A peer-to-peer network does not support a central login process.This implies that a user who logs on to one peer can access anyshared network resource, which is not controlled by a specificpassword. Peer-to-peer networks are relatively simple. Because eachcomputer functions as a client and a server, there is no need for apowerful central server or for the other components required for a

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high-capacity network. Peer-to-peer networks can be less expensivethan server-based networks.

Peer-to-peer networks are simple and inexpensive to install andmaintain. The cost of implementing peer-to-peer networks is lowbecause a central server is not used to administer the network. Inaddition, the components for a high-capacity network are notrequired in a peer-to-peer network.

In a peer-to-peer network, the users handle administration. Thismeans that all the users need to be trained in how to share files,folders, and printers. In a peer-to-peer network, suddenly shuttingdown your computer can cause one of your colleagues to be unable toprint.

Peer-to-peer networks are appropriate for environments where allthe users are located in the same geographical area and the networksecurity is not an important factor. In addition, these networksare useful when the network expansion is limited.

Advantages of a Peer-To-Peer Network:1. They are easy to configure

2. Computers communicate easily.

3. They don’t require additional server hardware or software

4. Users can manage their own resources.

5. They don’t require a network administrator

6. They reduce total cost of network setup.

Disadvantages of a Peer-To-Peer Network:1. They provide a limited number of connections for shared

resources.

2. Computers with shared resources suffer from sluggish performance.

3. They don’t allow for central management

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4. Users are responsible for managing resources. These resources include data in shared directories, printers, fax cards, and so on.

5. They offer very poor security.

Server Based Networks or Client/Server NetworksA dedicated server is one that functions only as a server and isnot used as a client or workstation. In the client/server networkmodel, a computer plays a centralized role and is known as aserver. All other computers in the network are known as clients.All client computers access the server simultaneously for files,database, docs, spreadsheets, web pages and resources like harddrives, printer, fax modem, CD/DVD ROM and others. In other words,all the client computers depend on the server and if server failsto respond or crash, then networking/communication between theserver and the client computes stops. Client computers aregenerally less powerful than server computers. Server basednetworks (see Figure below) have become the standard models fornetworking.

A server-based network using network operating system is that thenetworks are organized into domains. A domain is a collection ofnetworks and clients that share security information. Domainsecurity and logon permissions are controlled by special serverscalled domain controllers. Users cannot access the resources ofservers in a domain until a domain controller has authenticatedthem.

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In server-based networks, a network administrator centrally managesthe resource security. The administrator defines and manages useraccess to network resources.

Another beneficial of server-based networks is central filestorage. Server-based networks provide easy backup of criticaldata. Data backup is another useful characteristic of server basednetworks.

Server based networks can support a larger number of users thanpeer-to-peer networks. To support a large number of users, server-based networks use monitoring and network management tools.

Security is often the primary reason for choosing a server-basedapproach to networking. In a server-based environment, oneadministrator who sets the policy and applies it to every user onthe network can manage security. (See figure below)

 

Advantages of a client/server network1. They are best suited for 10 or more users.2. Security: - All major server based systems provides

sophisticated security.3. Administration: - Servers are centralized making them easier

to manage.4. Stability: - Server based systems are designed to support a

wide range of organization sizes. Additional servers are addedto increase capacity.

5. Client server networks offer centralized backup where data canbe stored in one server.

6. Flexibility - New technology can be easily integrated into thesystem.

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7. Accessibility - Server can be accessed remotely and across multiple platforms.

Disadvantages of a client/server network1. Cost: - More expensive in terms of hardware and network

operating system.2. Complexity: - Experienced system administrators are required

to manage the systems.3. Dependence: - When server goes down, operations will cease

across the network.

Hybrid NetworksA Hybrid network is the combination of client/server and peer-to-peer networks. Typically, hybrid networks are client/servernetworks that also include some peers.

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TYPES OF NETWORKToday when we speak of networks, we are generally referring tothree primary categories: Local Area Networks, Metropolitan AreaNetworks, and Wide Area Networks. A network consists of two or morecomputers that are linked in order to share resources (such asprinters and CD-ROMs), exchange files, or allow electroniccommunications. The computers on a network may be linked throughcables, telephone lines, radio waves, satellites, or infrared lightbeams.

Categories of Networks

A network is characterized by three primary attributes:TopologyThe topology is the pattern used to connect the computers together.With a bus topology, a network cable connects each computer to thenext one, forming a chain. With a star topology, each of thecomputers is connected to a central nexus called a hub/Switch. Aring topology is essentially a bus network with the two ends joinedtogether.

MediumFour basic types of media are used in networks, i.e. coaxial cable,twisted-pair wires, fiber-optic cable, and wireless.

Each medium has its advantages and disadvantages relative to cost,speed, and expandability. Coaxial cables provide high speed and low

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error rates. Twisted-pair wires are cheaper than coaxial cables,can sustain the speeds common to most personal computers, and areeasy to install. Fiber-optic cable is the medium of choice forhigh-speed local-area networks. Wireless local-area networks havethe advantage of expandability. 

ProtocolsThe topology and the medium used on a particular network arespecified by the protocol.

Local Area Network (LAN)A Local Area Network (LAN) is a network with two or more computersconnected to each other in a single location. It is a network thatis confined to a relatively small area. The Local Area Network(LAN) is by far the most common type of data network. As the namesuggests, a LAN serves a local area (typically the area of a floorof a building, but in some cases spanning a distance of severalkilometers). Typical installations are in industrial plants, officebuildings, college or university campuses, or similar locations. Inthese locations, it is feasible for the owning Organization toinstall high quality, high-speed communication linksinterconnecting nodes. Typical data transmission speeds are one to100 megabits per second.

The primary usage of local-area networks (LANs) is the sharing ofhardware, software, or information, such as data files, multimediafiles, or electronic mail. Resource sharing provided by local-areanetworks improves efficiency and reduces overhead.

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Each of the computers on the LAN is also called a node.

This type of network has the lowest cost and least overallcapability of all the types. Because the pieces of equipment in aLAN are in relatively close proximity, LANs are inexpensive toinstall. Their closeness and resultant low costs typically resultin the use of the fastest technology on a LAN. Thus, this networkclassification usually has the highest speed components and fastestcommunications equipment. This is because it takes less overallinvestment to get the smaller network running the faster equipment.LANs, therefore, are commonly considered the building blocks forcreating larger networks.

This type of network cannot be used to connect computers that arein different locations, for example, in buildings across a town orcity. Therefore, a LAN is not suitable for large businesses withoffices in several locations.

Characteristics of LANs Major characteristics of LANs are:

1. The network operates within a building or floor of a building.2. LANs provide multiple connected desktop devices (usually PCs)

with access to high-bandwidth media.3. An enterprise purchases the media and connections used in the

LAN; the enterprise can privately control the LAN as itchooses.

4. LANs rarely shut down or restrict access to connectedworkstations; local services are usually always available.

5. By definition, the LAN connects physically adjacent devices onthe media.

Metropolitan Area Network (MAN)Metropolitan Area Network is a combination of two or moreindividual Local Area Networks but with a small criterion of the

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boundary of the network not exceeding the city limits, thusintegrating the network as a single unit within a city. Wide AreaNetwork is basically an extension of the Local Area Network exceptfor the fact that the size of the network extends to a very largearea.

Metropolitan Area Network (MAN) is a computer network usuallyspanning a campus or a city, which typically connect a few localarea networks using high speed backbone technologies. Itinterconnects users with computer resources in a region larger thanthat covered by even a large Local Area Network (LAN). A MAN oftenprovides efficient connections to a wide area network (WAN).

Much of the same technology, such as the fast networking componentsand communications equipment used in LANs, can be used in MANs, butmore are required. Although, the speeds achieved in a MAN aretypically as high as in a LAN, it requires high-speed connections,such as fiber optics. Increasing the distance and the technologylevels increases the relative installation and operation costs ofMANs.

There are three important features which discriminate MANs fromLANs or WANs:

1. The network size falls intermediate between LANs and WANs. AMAN typically covers an area of between 5 and 50 km diameter.Many MANs cover an area the size of a city, although in somecases MANs may be as small as a group of buildings or as largecity.

2. A MAN (like a WAN) is not generally owned by a singleorganization. The MAN, its communications links and equipmentare generally owned by either a consortium of users or by asingle network provider who sells the service to the users.

3. A MAN often acts as a high speed network to allow sharing ofregional resources (similar to a large LAN). It is alsofrequently used to provide a shared connection to othernetworks using a link to a WAN.

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A wide area network (WAN) is a telecommunications network, usuallyused for connecting computers, that spans a wide geographical area.It is a network that traverses some distance and usually connectsLANs, whether across the city or across the nation. Most WANs arisefrom the simple need to connect one building to another. It is anetwork that traverses some distance and usually connects LANs,whether across the city or across the nation.

An example of a WAN connection would be a company with two officesin distant cities, each with its own LAN and connected by a leasedtelephone line. This type of WAN is illustrated in the figurebelow. Each end of the leased line is connected to a router and therouters are connected to individual LANs. Any computer on either ofthe LANs can communicate with any one of the other computers at theother end of the WAN link or with a computer on its own LAN.

 

Although WANs serve a purpose similar to that of local areanetworks (LANs), WANs are structured and operated quitedifferently. The user of a WAN usually does not own thecommunications lines that connect the remote computer systems;instead, the user subscribes to a service through atelecommunications provider. Unlike LANs, WANs typically do notlink individual computers, but rather are used to link LANs. WANsalso transmit data at slower speeds than LANs.

WANs are either point-to-point, involving a direct connectionbetween two sites, or operate across packet-switched networks, inwhich data is transmitted in packets over shared circuits. Point-to-point WAN service may involve either analog dial-up lines, inwhich a modem is used to connect the computer to the telephoneline, or dedicated leased digital telephone lines, also known as"private lines."

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Point-to-point WAN service providers include both local telephonecompanies and long distance carriers. Packet-switched networkservices are typically chosen by organizations which have lowvolumes of data or numerous sites, for which multiple dedicatedlines would be too expensive.

Depending on the service, WANs can be used for almost any datasharing purpose for which LANs can be used. Slower transmissionspeeds, however, may make some applications less practical forWANs. The most basic uses of WANs are for electronic mail and filetransfer.

WAN technologies generally function at the lower three layers ofthe OSI reference model: the physical layer, the data link layer,and the network layer.

Components of LAN1. Network Operating System (NOS):- In order for computers to be

able to communicate with each other, they must first have thenetworking software that tells them how to do so. Without thesoftware, the system will function simply as a “standalone,”unable to utilize any of the resources on the network.

2. Network Interface Card (NIC):- In addition to networkoperating software, each network device must also have anetwork interface card. These cards today are also referred toas adapters, as in “Ethernet adapter card” or “Token Ringadapter card.” The NIC card amplifies electronic signals whichare generally very weak within the computer system itself. TheNIC is also responsible for packaging data for transmission,and for controlling access to the network cable. When the datais packaged properly, and the timing is right, the NIC willpush the data stream onto the cable. The NIC also provides thephysical connection between the computer and the transmissioncable (also called “media”). This connection is made throughthe connector port.

3. Wiring Hub/Switch:- In order to have a network, you must haveat least two devices that communicate with each other. In this

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simple model shown below, it is a computer and a printer. Theprinter also has an NIC installed, which in turn is pluggedinto a wiring hub. The computer system is also plugged intothe hub, which facilitates communication between the twodevices. Additional components (such as a server, a few morePCs) may be connected to the hub.

4. Cables or Transmission Media:- The wires connecting the variousdevices together are referred to as cables. Cable prices rangefrom inexpensive to very costly and can comprise of a significantcost of the network itself. Cables are one example oftransmission media. Media are various physical environmentsthrough which transmission signals pass. Common network mediainclude twisted-pair, coaxial cable, fiber-optic cable, and theatmosphere (through which microwave, laser, and infraredtransmission occurs). Another term for this is “physical media.”Note that not all wiring hubs support all medium types.

Wireless LANsNot all networks are connected with cabling; some networks arewireless. Wireless LANs use high frequency radio signals, infraredlight beams, or lasers to communicate between the workstations,servers, or hubs. Each workstation and file server on a wirelessnetwork has some sort of transceiver/antenna to send and receivethe data. Information is relayed between transceivers as if theywere physically connected. For longer distance, wirelesscommunications can also take place through cellular telephonetechnology, microwave transmission, or by satellite.

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Wireless networks are great for allowing laptop computers, portabledevices, or remote computers to connect to the LAN. Wirelessnetworks are also beneficial in older buildings where it may bedifficult or impossible to install cables.

The two most common types of infrared communications are line-of-sight and scattered broadcast. Line-of-sight communication meansthat there must be an unblocked direct line between the workstationand the transceiver. If a person walks within the line-of-sightwhile there is a transmission, the information would need to besent again. This kind of obstruction can slow down the wirelessnetwork. Scattered infrared communication is a broadcast ofinfrared transmissions sent out in multiple directions that bouncesoff walls and ceilings until it eventually hits the receiver.Networking communications with laser are virtually the same asline-of-sight infrared networks.

Wireless LANs have several disadvantages. They provide poorsecurity, and are susceptible to interference from lights andelectronic devices. They are also slower than LANs using cabling.

Wireless Standards and SpeedsThe Wi-Fi Alliance is a global, non-profit organization that helpsto ensure standards and interoperability for wireless networks, andwireless networks are often referred to as Wi-Fi (WirelessFidelity). The original Wi-Fi standard (IEEE 802.11) was adopted in1997. Wi-Fi networks use the Ethernet protocol.

Standard

MaxSpeed

TypicalRange

802.11a 54 Mbps 150 feet

802.11b 11 Mbps 300 feet

802.11g 54 Mbps 300 feet24

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802.11n 100 Mbps 300+ feet

Wireless Fidelity (Wi-Fi)Wireless communication uses radio frequencies (RF) or infrared (IR)waves to transmit data between devices on a LAN. For wireless LANs,a key component is the wireless hub, or access point, used for signaldistribution.

To receive the signals from the access point, a PC or laptop mustinstall a wireless adapter card (wireless NIC). Wireless signals areelectromagnetic waves that can travel through the vacuum of outerspace and through a medium such as air. Therefore, no physicalmedium is necessary for wireless signals, making them a veryversatile way to build a network. Wireless signals use portions ofthe RF spectrum to transmit voice, video, and data. Wirelessfrequencies 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 theirfrequency. Low-frequency electromagnetic waves have a longwavelength (the distance from one peak to the next on the sinewave), while high-frequency electromagnetic waves have a shortwavelength.

Some common applications of wireless data communication include thefollowing:

Accessing the Internet using a cellular phone Establishing a home or business Internet connection over

satellite Beaming data between two hand-held computing devices Using a wireless keyboard and mouse for the PC

Wireless SecurityWireless networks are much more susceptible to unauthorized usethan cabled networks. Wireless network devices use radio waves tocommunicate with each other. The greatest vulnerability to thenetwork is that rogue machines can "eves-drop" on the radio wavecommunications. Unencrypted information transmitted can be

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monitored by a third-party, which, with the right tools (free todownload), could quickly gain access to your entire network, stealvaluable passwords to local servers and online services, alter ordestroy data, and/or access personal and confidential informationstored in your network servers. To minimize the possibility ofthis, all modern access points and devices have configurationoptions to encrypt transmissions. These encryption methodologiesare still evolving, as are the tools used by malicious hackers, soalways use the strongest encryption available in your access pointand connecting devices.

A Note on Encryption: presently, WEP (Wired Equivalent Privacy)encryption can be easily hacked with readily-available free toolswhich circulate the internet. WPA and WPA2 (WiFi Protected Accessversions 1 and 2) are much better at protecting information, butusing weak passwords or passphrases when enabling these encryptionsmay allow them to be easily hacked. If your network is running WEP,you must be very careful about your use of sensitive passwords orother data.

Three basic techniques are used to protect networks fromunauthorized wireless use. Use any and all of these techniques whensetting up your wireless access points:

EncryptionEnable the strongest encryption supported by the devices you willbe connecting to the network. Use strong passwords (strongpasswords are generally defined as passwords containing symbols,numbers, and mixed case letters, at least 14 characters long).

IsolationUse a wireless router that places all wireless connections on asubnet independent of the primary private network. This protectsyour private network data from pass-through internet traffic.

Hidden SSIDEvery access point has a Service Set IDentifier (SSID) that bydefault is broadcast to client devices so that the access point can

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be found. By disabling this feature, standard client connectionsoftware won't be able to "see" the access point. However, theeves-dropping programs discussed previously can easily find theseaccess points, so this alone does little more than keep the accesspoint name out of sight for casual wireless users.

Wi-Fi Devices

1. Wireless Access Point (WAP)A Wireless Access Point (WAP) connects a group of wireless stations toan adjacent wired local area network (LAN). An access point issimilar to an Ethernet hub or switch, but instead of relaying LANdata only to other LAN stations, an access point can relayswireless data to all other compatible wireless devices as well asto a single (usually) connected LAN device, in most cases anEthernet hub or switch, allowing wireless devices to communicatewith any other device on the LAN.

2. Wireless RoutersA wireless router integrates a wireless access point withan IP router and an ethernet switch. The integrated switch connectsthe integrated access point and the integrated ethernet routerinternally, and allows for external wired ethernet LAN devices tobe connected as well as a (usually) single WAN device such as cablemodem or DSL modem. A wireless router advantageously allows allthree devices (mainly the access point and router) to be configuredthrough one central configuration utility, usually through anintegrated web server.

3. Wireless Ethernet BridgeA wireless Ethernet bridge connects a wired network to a wirelessnetwork. This is different from an access point in the sense thatan access point connects wireless devices to a wired network atthe data-link layer. Two wireless bridges may be used to connecttwo wired networks over a wireless link, useful in situations wherea wired connection may be unavailable, such as between two separatehomes.

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Advantages of Wi-Fi1. Availability - Wi-Fi products are widely available in the

market. Different brands of access points and client networkinterfaces are interoperable at a basic level of service.

2. Mobility - Wi-Fi networks support roaming, in which a mobileclient station such as a laptop computer can move from oneaccess point to another as the user moves around a buildingor area.

3. Fast Setup - If your computer has a wireless adapter, locatinga wireless network can be as simple as clicking "Connect toa Network" -- in some cases, you will connect automaticallyto networks within range.

4. Cost - Setting up a wireless network can be much more costeffective than buying and installing cables.

5. Expandability - Adding new computers to a wireless network isas easy as turning the computer on (as long as you do notexceed the maximum number of devices).

Disadvantages of Wi-Fi

1. Interference - Because wireless networks use radio signals andsimilar techniques for transmission, they are susceptible tointerference from lights and electronic devices.

2. Inconsistent connections - Because of the interference caused byelectrical devices and/or items blocking the path oftransmission, wireless connections are not nearly as stableas those through a dedicated cable.

3. Speed - The transmission speed of wireless networks isimproving; however, faster options (such as gigabitEthernet) are available via cables. If you are only usingwireless for internet access, the actual internet connectionis generally slower than the wireless network devices, sothat connection is the bottleneck.

4. Power consumption is fairly high compared to some otherstandards, making battery life and heat a concern.

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5. Security - The most common wireless encryption standard, WiredEquivalent Privacy or WEP, has been shown to be breakableeven when correctly configured.

6. Wi-Fi networks have limited range.

INTERNETWORKInternetwork can be described as two or more networks or networksegments connected using devices that operate at layer 3 (the'network' layer) of the OSI Basic Reference Model, such as arouter. Any interconnection among or between public, private,commercial, industrial, or governmental networks may also bedefined as an internetwork. The interconnected networks use theInternet Protocol. There are at least three variants ofinternetwork, depending on who administers and who participates inthem:

Intranet Extranet "The" Internet

Intranets and extranets may or may not have connections to the Internet.If connected to the Internet, the intranet or extranet is normallyprotected from being accessed from the Internet without properauthorization. The Internet itself is not considered to be a partof the intranet or extranet, although the Internet may serve as aportal for access to portions of an extranet.

IntranetAn intranet is a computer network that uses InternetProtocol technology to securely share any part of an organization'sinformation within that organization. Sometimes the term refersonly to the organization's internal website. It uses IP-based toolssuch as web browsers that are under the control of a singleadministrative entity. That administrative entity closes theintranet to the rest of the world, and allows only specific users.Most commonly, an intranet is the internal network of a company orother enterprise.

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ExtranetAn extranet is a computer network that allows controlled accessfrom the outside, for specific business or educational purposes. Anextranet can be viewed as an extension of a company's intranet thatis extended to users outside the company, usually partners,vendors, and suppliers. It is limited in scope to a singleorganization or entity but which also has limited connections tothe networks of one or more other usually, but not necessarily,trusted organizations or entities (e.g. a company's customers maybe given access to some part of its intranet creating in this wayan extranet, while at the same time the customers may not beconsidered 'trusted' from a security standpoint). Technically, anextranet may also be categorized as a CAN, MAN, WAN, or other typeof network, although, by definition, an extranet cannot consist ofa single LAN; it must have at least one connection with an externalnetwork.

InternetThe Internet is a global system of interconnected computernetworks that use the standard Internet Protocol Suite (TCP/IP) toserve billions of users worldwide. It is a network of networks thatconsists of millions of private, public, academic, business, andgovernment networks, of local to global scope, that are linked by abroad array of electronic, wireless and optical networkingtechnologies. The Internet carries a vast rangeof information resources and services, such as the inter-linkedhypertext documents of the World Wide Web (WWW) and the infrastructureto support electronic mail.

NETWORK ARCHITECTURE

Network Architecture is the design of a communications network. Itis a framework for the specification of a network's physicalcomponents and their functional organization and configuration, itsoperational principles and procedures, as well as data formats usedin its operation.

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It can also be described as the logical and structural layout ofthe network consisting of transmission equipment, software andcommunication protocols and infrastructure (wired or wireless)transmission of data and connectivity between components. 

EthernetThe physical layer of the network focuses on hardware elements,such as cables, repeaters, and network interface cards. By far themost common protocol used at the physical layer is Ethernet. Forexample, an Ethernet network (such as 10BaseT or 100BaseTX)specifies the type of cables that can be used, the optimal topology(star vs. bus, etc.), the maximum length of cables, etc.

Network architecture combines standards, topologies and protocolsto produce a working network. Currently, the most popular networkarchitecture is Ethernet. A network that follows the Ethernetarchitecture standard is known as an Ethernet network.

The term Ethernet refers to the family of local-area network (LAN)products covered by the IEEE 802.3 standard that defines what iscommonly known as the Carrier Sense Multiple Access with CollisionDetection (CSMA/CD) protocol. This is a system where each computerlistens to the cable before sending anything through the network.If the network is clear, the computer will transmit. If some othernode is already transmitting on the cable, the computer will waitand try again when the line is clear. Sometimes, two computersattempt to transmit at the same instant. When this happens acollision occurs. Each computer then backs off and waits a randomamount of time before attempting to retransmit. With this accessmethod, it is normal to have collisions. However, the delay causedby collisions and retransmitting is very small and does notnormally affect the speed of transmission on the network.

The Ethernet protocol allows for bus or star topologies, dependingon the type of cables used and other factors. This heavy coaxialcabling was expensive to purchase, install, and maintain, and verydifficult to retrofit into existing facilities.

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The current standards are now built around the use of twisted pair cable and optical fiber. Three data rates are currently defined for operation over these cables:

1. 10BaseT - Ethernet2. 100BaseT - Fast Ethernet3. 1000BaseT. - Gigabit Ethernet

The number (10, 100, 1000) stands for the speed of transmission(10/100/1000 megabits per second); the "Base" stands for "baseband"meaning it has full control of the wire on a single frequency; andthe "T" stands for "twisted pair" cable. Fiber cable can also beused at this level in 10BaseFL.

The IEEE 802.3 standard defines ethernet at the physical and datalink layers of the OSI network model. Most ethernet systems use thefollowing:

1. Carrier-Sense Multiple-Access with Collision Detection(CSMA/CD) for controlling access to the network media.

2. Use baseband broadcasts3. A method for packing data into data packets called frames4. Transmit at 10Mbps, 100Mbps, and 1000Gbps or 1Gbps.

Types of Ethernet

1. 10Base5 - Uses Thicknet coaxial cable which requires atransceiver with a vampire tap to connect each computer. There is adrop cable from the transceiver to the Attachment Unit Interface(AIU). The AIU may be a DIX port on the network card. There is atransceiver for each network card on the network. This type ofethernet is subject to the 5-4-3 rule meaning there can be 5network segments with 4 repeaters, and three of the segments can beconnected to computers. It uses bus topology. Maximum segmentlength is 500 Meters with the maximum overall length at 2,500meters. Minimum length between nodes is 2.5 meters. Maximum nodesper segment is 100.

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2. 10Base2 - Uses Thinnet coaxial cable. Uses a BNC connector andbus topology requiring a terminator at each end of the cable. Thecable used is RG-58A/U or RG-58C/U with an impedance of 50 ohms.RG-58U is not acceptable. Uses the 5-4-3 rule meaning there can be5 network segments with 4 repeaters, and three of the segments canbe connected to computers. The maximum length of one segment is 185meters. Barrel connectors can be used to link smaller pieces ofcable on each segment, but each barrel connector reduces signalquality. Minimum length between nodes is 0.5 meters.

3. 10BaseT - Uses Unshielded twisted pair (UTP) cable. Uses startopology. Shielded twisted pair (STP) is not part of the 10BaseTspecification. Not subject to the 5-4-3 rule. They can use category3, 4, or 5 cable, but perform best with category 5 cable. Category3 is the minimum. Require only 2 pairs of wire. Cables in ceilingsand walls must be plenum rated. Maximum segment length is 100meters. Minimum length between nodes is 2.5 meters. Maximum numberof connected segments is 1024 (star topology). Uses RJ-45connectors.

4. 10BaseF - Uses Fiber Optic cable. Can have up to 1024 networknodes. Maximum segment length is 2000 meters. Uses specializedconnectors for fiber optic. Includes three categories:

10BaseFL - Used to link computers in a LAN environment, whichis not commonly done due to high cost.

10BaseFP - Used to link computers with passive hubs to getcable distances up to 500 meters.

10BaseFB - Used as a backbone between hubs.

5. 100BaseT - Also known as Fast Ethernet. Uses RJ-45 connectors.Topology is star. Uses CSMA/CD media access. Minimum length betweennodes is 2.5 meters. Maximum number of connected segments is 1024(star topology). IEEE802.3 specification.

100BaseTX - Requires category 5 two pair cable. Maximumdistance is 100 meters.

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100BaseT4 - Requires category 3 cable with 4 pair. Maximumdistance is 100 meters.

100BaseFX - Can use fiber optic to transmit up to 2000 meters.Requires two strands of fiber optic cable.

6. 100VG-AnyLAN - Requires category 3 cable with 4 pair. Maximumdistance is 100 meters with cat 3 or 4 cable. Can reach 150 meterswith cat 5 cable. Can use fiber optic to transmit up to 2000meters. This ethernet type supports transmission of Token-Ringnetwork packets in addition to ethernet packets. IEEE 802.12specification. Uses demand-priority media access control. Thetopology is star. It uses a series of interlinked cascading hubs.Uses RJ-45 connectors.

7. Gigabit Ethernet - Gigabit Ethernet standard is a protocolthat has a transmission speed of 1 Gbps (1000 Mbps). It can be usedwith both fiber optic cabling and copper.

1000BaseT - 1000 Mbps over 2-pair category 5 or better UTPcable.

1000BaseTX - 1000 Mbps over 2-pair category 6 or better UTPcable.

1000BaseFX - 1000 Mbps over fiber cable. 1000BaseSX -1000 Mbps over multimode fiber cable. 1000BaseBX - 1000 Mbps over single mode fiber cable.

The Ethernet standards continue to evolve with 10 Gigabit Ethernet(10,000 Mbps) and 100 Gigabit Ethernet (100,000 Mbps)

Ethernet Protocol Summary

Protocol Cable Speed

Ethernet Twisted Pair,Coaxial, Fiber 10 Mbps

FastEthernet Twisted Pair, Fiber 100 Mbps

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GigabitEthernet Twisted Pair, Fiber 1000

Mbps

The IEEE naming convention is as follows:1. The transmission speed in Mbps2. Baseband (base) or Broadband data transmission3. The maximum distance a network segment could cover in hundredsof meters.

Ethernet Comparisons

Ethernet Cable Speed Topology

Nodes/Net

MaxSegments

Max SegLength

10Base5 Thicknet 10Mbps Bus 100 5 500 meters

10Base2 Thinnet 10Mbps Bus 5-4-3 5 185 meters

10BaseT4 UTP Cat 3, 4 pair 10Mbps Star 1024 4 hubs in

a row 100 meters

10BaseT5 UTP Cat 3, 5 pair 10Mbps Star 1024 4 hubs in

a row 100 meters

10BaseTX UTP Cat 5, 2 pair 10Mbps Star 1024 4 hubs in

a row 100 meters

10BaseF Fiber 10Mbps 1024 2000 meters

100VG-AnyLAN UTP Cat 3,4 100Mbp

s Star 1024 100 meters

UTP Cat 5 100Mbps Star 1024 150 meters

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Fiber 100Mbps Star 1024 2000 meters

HARDWARE REQUIREMENT FOR NETWORK

Networking hardware includes all computers, peripherals, interfacecards and other equipment needed to perform data-processing andcommunications within the network. This section providesinformation on the following components:

Network Interface Card (NIC) Network Cables Switches Patch Panel Firewall Repeaters Bridges Routers Servers Workstations

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Network Interface Card (NIC)A network card (network adapter, network interface card, NIC,Ethernet adapter etc.) is a piece of computer hardware designed toallow computers to communicate over a computer network. It providesthe physical connection between the network and the computerworkstation. Most NICs are internal, with the card fitting into anexpansion slot inside the computer. Every network card has aunique 48-bit serial number called a MAC address, which is writtento ROM carried on the card. Every computer on a network must have acard with a unique MAC address. The IEEE is responsible forassigning MAC addresses to the vendors of network interface cards,which means that no two cards can share the same MAC address.

Whereas network cards used to be expansion cards to plug into acomputer bus, most new computers have a network interface builtinto the motherboard, so a separate network card is not requiredunless multiple interfaces are needed or some other type of networkis used.

Network Interface Cards

A network card typically has a twisted pair and BNC sockets wherethe network cable is connected, and a few LEDs to inform the userof whether the network is active, and whether or not there is databeing transmitted on it.

Network interface cards are a major factor in determining the speedand performance of a network. It is a good idea to use the fastestnetwork card available for the type of workstation you are using.

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NIC are typically available in 10/100/1000 Mbit/s. This means theycan support a transfer rate of 10 or 100 or 1000 Mbit/s.

Network CablesCable is the medium through which information usually moves fromone network device to another. There are several types of cablewhich are commonly used with LANs. In some cases, a network willutilize only one type of cable, other networks will use a varietyof cable types. The type of cable chosen for a network is relatedto the network's topology, protocol, and size. Understanding thecharacteristics of different types of cable and how they relate toother aspects of a network is necessary for the development of asuccessful network.

The following are the types of cables used in networks1. Twisted Pair Cable

a. Unshielded Twisted Pair (UTP) Cableb. Shielded Twisted Pair (STP) Cable

2. Coaxial Cable 3. Fibre Optic Cable

Twisted Pair CableThis is a thin-diameter wire commonly used for telephone andnetwork cabling. The wires are twisted around each other tominimize interference from other twisted pairs in the cable.Twisted pairs have less bandwidth than coaxial cable or opticalfiber. Twisted pair cabling comes in two varieties: shielded andunshielded. Unshielded twisted pair (UTP) is the most popular andis generally the best option.

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Shielded Twisted Pair (STP) - STP is used in noisy and static fieldinterference environments (factories) where the shield around eachof the wire pairs, plus an overall shield, protects againstexcessive electromagnetic interference. A variation of STP, knownas ScTP for "Screened Twisted Pair" or FTP for "Foil Twisted Pair,"uses only the overall shield and provides more protection than UTP,but not as much as STP. STP cabling includes metal shielding overeach individual pair of copper wires. This type of shieldingprotects cable from external EMI (Electromagnetic Interferences).

Screened Shielded Twisted Pair (S/STP) – S/STP cabling is STPcabling with metal shielding also covering the group ofshielded copper pairs. This type of cabling offers improvedprotection from interference from external sources.

Shielded Twisted Pair Cables

Unshielded Twisted Pair (UTP) – UTP cables are not shielded. Thislack of shielding results in a high degree of flexibility as wellas rugged durability. UTP cables are found inmany ethernet   networks and telephone systems.

Screened Unshielded Twisted Pair (S/UTP) – S/UTP, also known as Fullyshielded (or Foiled) Twisted Pair (FTP) and Screened Fullyshielded Twisted Pair (S/FTP), is a screened UTP cable.

 

Unshielded Twisted Pair Cable

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Twisted pair cabling is standardized into various categories bynumbers, which indicate signal integrity attributes. Category 5cable is commonly used for Ethernet with 10BASE-T or 100BASE-TX.

Categories of Unshielded Twisted Pair

Category Speed Use

1 1 Mbps Voice Only (TelephoneWire)

2 4 Mbps LocalTalk & Telephone(Rarely used)

3 16 Mbps 10BaseT Ethernet

4 20 Mbps Token Ring (Rarely used)

5

100 Mbps (2pair) 100BaseT Ethernet

1000 Mbps (4pair) Gigabit Ethernet

5e 1,000 Mbps Gigabit Ethernet

6 10,000 Mbps Gigabit Ethernet

Unshielded Twisted Pair ConnectorThe standard connector for unshielded twisted pair cabling is anRJ-45 connector. This is a plastic connector that looks like alarge telephone-style connector. A slot allows the RJ-45 to beinserted only one way. RJ stands for Registered Jack, implying thatthe connector follows a standard borrowed from the telephoneindustry. This standard designates which wire goes with each pininside the connector.

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COLOUR-CODE / WIRING STANDARDS

Colour Codes for RJ-45 Ethernet PlugEight-conductor data cable (Cat 3 or Cat 5) contains 4 pairs ofwires. Each pair consists of a solid colour wire and a white andcolour striped wire. Each of the pairs is twisted together. Tomaintain reliability on Ethernet, you should not untwist them anymore than necessary (about 1/4 inch).

The pairs designated for Ethernet are orange and green. The othertwo pairs, brown and blue, are unused. The connections shown beloware specifically for an RJ45 plug. The wall jack may be wired in adifferent sequence because the wires may be crossed inside thejack. The jack should either come with a wiring diagram or at leastdesignate pin numbers that you can match up to the colour codebelow.

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There are two wiring standards for these cables, called T-568A andT-568B. They differ only in pin assignments, not in uses of thevarious colours. The illustration above shows both standards. Withthe T-568B specification, the orange and green pairs are located onpins 1, 2 and 3, 6 respectively. The T-568A specification reversesthe orange and green connections, so that the blue and orange pairsare on the centre 4 pins, which makes it more compatible with theTelco voice connections. T-568A is supposed to be the standard fornew installations, and T-568B is the alternative. However, mostoff-the-shelf data equipment and cables seem to be wired to T568B.

Pin Number DesignationsHere are the pin number designations for both standards:

T-568B

T-568A

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Pin Colour

Pair

Description

1 W/O 2 Tx Data+

2 O 2 Tx Data-

3 W/G 3 Rx Data+

4 B 1 Unused5 W/B 1 Unused6 G 3 Rx Data

-7 W/Br 4 Unused8 Br 4 Unused

Pin Colour

Pair

Description

1 W/G 2 Rx Data+

2 G 2 Rx Data-

3 W/O 3 Tx Data+

4 B 1 Unused5 W/B 1 Unused6 O 3 Tx Data

-7 W/Br 4 Unused8 Br 4 Unused

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Note: Odd pin numbers are always the striped wires.

Straight-Through Vs Cross-OverIn general, the patch cords that you use with your Ethernetconnections are "straight-through", which means that pin 1 of theplug on one end is connected to pin 1 of the plug on the other end(for either standard). The only time you cross connections is whenyou connect two Ethernet devices directly together without a hub orconnect two hubs together. Then you need a "cross-over" patchcable, which crosses the transmit and receive pairs. An easy way toremember how to make a cross-over cable is to wire one end with theT-568A standard and the other with the T-568B standard.

Rolled Cable Although rolled cable is not used to connect any Ethernetconnections together, you can use a rolled Ethernet cable toconnect a host to a router console serial communication (com) port.If you have a Cisco router of switch, you would use this cable toconnect your PC running Hyper Terminal to the Cisco hardware. Eightwires are used in this cable to connect serial devices, althoughnot all eight are used to send information, just as in Ethernetnetworking

Rolled Cable

Termination

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UTP cables are terminated with standard connectors, jacks andpunch-downs. The jack/plug is often referred to as a "RJ-45". Themale connector on the end of a patch cord is called a "plug" andthe receptacle on the wall outlet is a "jack."In LANs, as specified by 568, there are two possible pinouts,called T568A and T568B, that differ only in which colour codedpairs are connected - pair 2 and 3 are reversed. Either worksequally well, as long as you don't mix them! If you always use onlyone version, you're OK, but if you mix A and B in a cable run, youwill get crossed pairs!The cable pairs are colour coded as

Pair 1 is white-blue/blue,Pair 2 white-orange/orange, Pair 3 is white-green/greenPair 4 is white-brown/brown.

BLOG

Jacks usually have punch-downs on the back or can be terminatedwithout punch downs using special manufacturer's tools. Again, youMUST keep the twists as close to the receptacle as possible tominimize crosstalk.

Crossover CablesNormal cables that connect a PC/NIC card to a hub are wiredstraight through. That is pin 1 is connected to pin 1, pin 2 to pin2, etc. However, if you are simply connecting two PCs togetherwithout a hub or switch, you need to use a crossover cable made byreversing pair 2 and 3 in the cable, the two pairs used fortransmission by Ethernet. The easy way to make a crossover cable isto make one end to T568A colour coding and the other end to T568B.Then the pairs will be reversed.

Ethernet Cable Instructions:1. Pull the cable off the reel to the desired length and cut. If

you are pulling cables through holes, it’s easier to attachthe RJ-45 plugs after the cable is pulled. The total length of

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wire segments between a PC and a hub or between two PC'scannot exceed the maximum length (in Meters), depending on thetype of cable.

2. Start on one end and strip the cable jacket off (about 1")using a stripper or a knife. Be extra careful not to nick thewires, otherwise you will need to start over.

3. Spread, untwist the pairs, and arrange the wires in the orderof the desired cable end. Flatten the end between your thumband forefinger. Trim the ends of the wires so they are evenwith one another, leaving only 1/2" in wire length. If it islonger than 1/2" it will be out-of-spec and susceptible tocrosstalk. Flatten and insure there are no spaces betweenwires.

4. Hold the RJ-45 plug with the clip facing down or away fromyou. Push the wires firmly into the plug. Inspect each wire isflat even at the front of the plug. Check the order of thewires. Double check again. Check that the jacket is fittedright against the stop of the plug. Carefully hold the wireand firmly crimp the RJ-45 with the crimper.

5. Check the color orientation, check that the crimped connectionis not about to come apart, and check to see if the wires areflat against the front of the plug. If even one of these isincorrect, you will have to start over. Test the Ethernetcable.

Ethernet Cable Tips: A straight-thru cable has identical ends. A crossover cable has different ends. A straight-thru is used as a patch cord in Ethernet connections. A crossover is used to connect two Ethernet devices without a hub or for connecting

two hubs. A crossover has one end with the Orange set of wires switched with the Green se

(considering Type A and B). Odd numbered pins are always striped, even numbered pins are always solid

colored. Looking at the RJ-45 with the clip facing away from you, Brown is always on the

right, and pin 1 is on the left. No more than 1/2" of the Ethernet cable should be untwisted otherwise it will be

susceptible to crosstalk.

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Do not deform, do not bend, do not stretch, do not staple, do not run parallel withpower cables, and do not run Ethernet cables near noise inducing components.

Coaxial cablesCoaxial cabling has a single copper conductor at its center. Aplastic layer provides insulation between the center conductor anda braided metal shield. The metal shield helps to block any outsideinterference from fluorescent lights, motors, and other computers

Coaxial Cable

Although coaxial cabling is difficult to install, it is highlyresistant to signal interference. In addition, it can supportgreater cable lengths between network devices than twisted paircable. The two types of coaxial cabling are thick coaxial and thincoaxial, based on the thickness of core.

ThinnetThin coaxial cable is also referred to as thinnet. 10Base2 refersto the specifications for thin coaxial cable carrying Ethernetsignals. The 2 refers to the approximate maximum segment lengthbeing 200 meters. In actual fact the maximum segment length is 185meters. 10 comes from the maximum transmission speed of 10 Mbit/s.The BASE stands for baseband signaling. It is a thin and flexible coaxial cable, which has a thickness ofabout one-fourth of an inch. Since this type of coaxial cable isflexible, it is easy to work with. They can be used for any kind ofinstallation. Network nodes were attached to the cable via T-typeBNC connectors in the adapter cards. Another benefit of usingthinnet coaxial cable is the low cable cost. Thinnet cable isinexpensive as compared to thicknet cable.

ThiknetThick coaxial cable is also referred to as thicknet. It is abouthalf an inch in diameter. 10Base5 refers to the specifications for

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thick coaxial cable carrying Ethernet signals. The 5 refers to themaximum segment length being 500 meters. Thick coaxial cable has anextra protective plastic cover that helps keep moisture away fromthe center conductor. This makes thick coaxial a great choice whenrunning longer lengths in a linear bus network. Another benefit ofthe thicknet cable is that it can be used as a backbone to connectseveral smaller thinnet-based networks. This is possible becausethe thicknet cable is capable of supporting data transfer over longdistances. One disadvantage of thick coaxial is that it does notbend easily and is difficult to install.

Coaxial Cable ConnectorsThe most common type of connector used with coaxial cables is theBayone-Neill-Concelman (BNC) connector. Different types of adaptersare available for BNC connectors, including a T-connector, barrelconnector, and terminator. Connectors on the cable are the weakestpoints in any network. To help avoid problems with your network,always use the BNC connectors that crimp, rather screw, onto thecable.

BNC Connectors

Fiber Optic CableFiber optic cabling consists of a center glass core surrounded byseveral layers of protective materials. It transmits light ratherthan electronic signals eliminating the problem of electrical

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interference. This makes it ideal for certain environments thatcontain a large amount of electrical interference. It has also madeit the standard for connecting networks between buildings, due toits immunity to the effects of moisture and lighting.

Fiber optic cable has the ability to transmit signals over muchlonger distances than coaxial and twisted pair. It also has thecapability to carry information at vastly greater speeds. Thiscapacity broadens communication possibilities to include servicessuch as video conferencing and interactive services. The cost offiber optic cabling is comparable to copper cabling; however, it ismore difficult to install and modify. 10BaseF refers to thespecifications for fiber optic cable carrying Ethernet signals.

The center core of fiber cables is made from glass or plasticfibers. A plastic coating then cushions the fiber center, andKevlar fibers help to strengthen the cables and prevent breakage.The outer insulating jacket made of Teflon or PVC.

Fiber Optic Cable

There are two common types of fiber cables -- single mode andmultimode. Multimode cable has a larger diameter; however, bothcables provide high bandwidth at high speeds. Single mode canprovide more distance, but it is more expensive.

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Specification Cable Type

10BaseT UnshieldedTwisted Pair

10Base2 Thin Coaxial

10Base5 Thick Coaxial

100BaseT UnshieldedTwisted Pair

100BaseFX Fiber Optic

100BaseBX Single mode Fiber

100BaseSX Multimode Fiber

1000BaseT UnshieldedTwisted Pair

1000BaseFX Fiber Optic

1000BaseBX Single mode Fiber

1000BaseSX Multimode Fiber

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Media Type Comparison

MediaType

MaximumSegmentLength

Speed Cost Advantages Disadvantages

UTP 100 m 10 Mbps to 1000 Mbps

Least expensive

Easy to install; widely available and widely used

Susceptible to interference; can cover only a limited distance

STP 100 m 10 Mbps to 100 Mbps

More expensive than UTP

Reduced crosstalk; more resistantto EMI than Thinnet or UTP

Difficult to work with; can cover only a limited distance

Coaxial

500 m (Thicknet)

185 m (Thinnet)

10 Mbps to 100 Mbps

Relativelyinexpensive, but more costly than UTP

Less susceptible toEMI interference than other types of copper media

Difficult to work with (Thicknet); limited bandwidth; limited application (Thinnet); damage to cablecan bring down entire network

Fiber-Optic

10 km andfarther (single-mode)

2 km and farther (multimode)

100 Mbps to 100 Gbps (single mode)

100 Mbps to 9.92 Gbps (multimode)

Expensive Cannot be tapped, so security is better; can beused over great distances; is not susceptible toEMI; has a higher data rate than coaxial and twisted-pair cable

Difficult to terminate

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Installing Cable - Some Guidelines

When running cable, it is best to follow a few simple rules: 1. Always use more cable than you need. Leave plenty of slack. 2. Test every part of a network as you install it. Even if it is

brand new, it may have problems that will be difficult toisolate later.

3. Stay at least 3 feet away from fluorescent light boxes andother sources of electrical interference.

4. If it is necessary to run cable across the floor, cover thecable with cable protectors.

5. Label both ends of each cable. 6. Use cable ties (not tape) to keep cables in the same location

together.

Patch PanelsA patch panel or patch bay is a panel, typically rack mounted, thathouses cable connections. It is a panel of network ports containedtogether, usually within a telecommunications closet, whichconnects incoming and outgoing lines of a LAN or othercommunication, electronic or electrical system.

In a LAN, the patch panel connects the network's computers to eachother and to the outside lines that enable the LAN to connect tothe Internet or another WAN. Connections are made with patch cords.The patch panel allows circuits to be arranged and rearranged byplugging and unplugging the patch cords.

Patch Panels

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Ethernet SwitchesAn Ethernet Switch is a LAN interconnection device which operatesat the data link layer (layer 2) of the OSI reference model. Aswitch is fundamentally similar to a bridge, but usually supports alarger number of connected LAN segments and has a richer managementcapability.

It is a computer networking device that connects network segments.it provides a central connection point for cables fromworkstations, servers, and peripherals. In a star topology,twisted-pair wire is run from each workstation to a centralswitch/hub. Most switches are active, that is they electricallyamplify the signal as it moves from one device to another. Switchesno longer broadcast network packets as hubs did in the past, theymemorize addressing of computers and send the information to thecorrect location directly It also allows a physical and logicalstar topology and often used to replace network hubs. A switch isalso often referred to as an intelligent hub or switching hub.

If the destination MAC address is known, the frame is forwardedonly to the corresponding port in the MAC address table. If thedestination port is the same as the originating port, the frame isfiltered out and not forwarded.

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Network Switches

As a frame comes into a switch, the switch saves the originatingMAC address and the originating port in the switch's MAC addresstable. The switch then selectively transmits the frame fromspecific ports based on the frame's destination MAC address andprevious entries in the MAC address table.

If the destination MAC address is unknown a broadcast address or(for simpler switches) a multicast address the switch simplytransmits the frame out of all of the connected interfaces exceptthe incoming port. Switches are:

• Usually configured with 8, 12, or 24 RJ-45 ports • Often used in a star or star-wired ring topology • Sold with specialized software for port management • Also called hubs sometimes• Usually installed in a standardized metal rack that also

may store net-modem, bridges, or routers.

Bridges

A bridge is a device that allows you to segment a large networkinto two smaller, more efficient networks. If you are adding to anolder wiring scheme and want the new network to be up-to-date, abridge can connect the two.

Bridges monitor the information traffic on both sides of thenetwork so that it can pass packets of information to the correctlocation. Most bridges can "listen" to the network andautomatically figure out the address of each computer on both sidesof the bridge. The bridge can inspect each message and, ifnecessary, broadcast it on the other side of the network.

The bridge manages the traffic to maintain optimum performance onboth sides of the network. You might say that the bridge is like atraffic cop at a busy intersection during rush hour. It keepsinformation flowing on both sides of the network, but it does not

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allow unnecessary traffic through. Bridges can be used to connectdifferent types of cabling, or physical topologies. They must,however, be used between networks with the same protocol.

RoutersA router translates information from one network to another; it issimilar to a super-intelligent bridge. Routers select the best pathto route a message, based on the destination address and origin.The router can direct traffic to prevent head-on collisions, and issmart enough to know when to direct traffic along back roads andshortcuts. While bridges know the addresses of all computers oneach side of the network, routers know the addresses of computers,bridges, and other routers on the network. Routers can even"listen" to the entire network to determine which sections arebusiest. They can then redirect data around those sections untilthey clear up. Routers can:

• Direct signal traffic efficiently • Route messages between any two protocols • Route messages between linear bus, star, star-wired ring

topologies • Route messages across fiber optic, coaxial and twisted-

pair cabling

Router

Routers forward data packets along networks by using headers andforwarding tables to determine the best path to forward thepackets. Routers work at the network layer 3 of the OSI model.Routers also provide interconnectivity between like and unlikemedia. A router is connected to at least two networks, commonly two

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LANs or WANs or a LAN and its ISP's network. Some DSL and cablemodems, for home use, have been integrated with routers to allowmultiple home computers to access the Internet.

They can connect networks with different architectures such asToken Ring and Ethernet. Although, they can transform informationat the data link level.

Repeaters Since a signal loses strength as it passes along a cable, it isoften necessary to boost the signal with a device called arepeater. The repeater electrically amplifies the signal itreceives and rebroadcasts it. Repeaters can be separate devices orthey can be incorporated into a concentrator (a concentrator is adevice that acts as an efficient forwarder of data transmissionsignals). They are used when the total length of your network cableexceeds the standards set for the type of cable being used. A goodexample of the use of repeaters would be in a local area networkusing a star topology with unshielded twisted-pair cabling. Thelength limit for unshielded twisted pair cable is 100 meters. Themost common configuration is for each workstation to be connectedby twisted-pair cable to a multiport active concentrator. Theconcentrator amplifies all the signals that pass through itallowing for the total length of cable on the network to exceed the100 meters limit.

FirewallA firewall protects networked computers from intentional hostileintrusion that could compromise confidentiality or result in datacorruption or denial of service. It may be a hardware device or asoftware program running on a secure host computer. In either case,it must have at least two network interfaces, one for the networkit is intended to protect, and one for the network it is exposedto.

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Hardware Firewall: Hardware firewall providing protection to a Local Network

Firewall Software: Computer running firewall software to provide protection

A firewall sits at the junction point or gateway between the twonetworks, usually a private network and a public network such asthe Internet. The earliest firewalls were simply routers. The termfirewall comes from the fact that by segmenting a network intodifferent physical subnetworks, they limit the damage that couldspread from one subnet to another just like firedoors or firewalls.

A firewall examines all traffic routed between the two networks tosee if it meets certain criteria. If it does, it is routed betweenthe networks, otherwise it is stopped.

A firewall filters both inbound and outbound traffic. It can alsomanage public access to private networked resources such as hostapplications. It can be used to log all attempts to enter theprivate network and trigger alarms when hostile or unauthorizedentry is attempted.

Firewalls can filter packets based on their source and destinationaddresses and port numbers. This is known as address filtering.Firewalls can also filter specific types of network traffic. This

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is also known as protocol filtering because the decision to forwardor reject traffic is dependent upon the protocol used, for exampleHTTP, ftp or telnet. Firewalls can also filter traffic by packetattribute or state.

A firewall cannot prevent individual users with modems from dialinginto or out of the network, bypassing the firewall altogether.Employee misconduct or carelessness cannot be controlled byfirewalls. Policies involving the use and misuse of passwords anduser accounts must be strictly enforced. These are managementissues that should be raised during the planning of any securitypolicy but that cannot be solved with firewalls alone.

File Servers A file server stands at the heart of most networks. It is a veryfast computer with a large amount of RAM and storage space, alongwith a fast network interface card. The network operating systemsoftware resides on this computer, along with any softwareapplications and data files that need to be shared. The file servercontrols the communication of information between the nodes on anetwork. For example, it may be asked to send a word processorprogram to one workstation, receive a database file from anotherworkstation, and store an e-mail message during the same timeperiod. This requires a computer that can store a lot ofinformation and share it very quickly. File servers should have atleast the following characteristics:

• 800 megahertz or faster microprocessor (Pentium 3 or 4,G4 or G5)

• A fast hard drive with at least 120 gigabytes of storage • A RAID (Redundant Array of Inexpensive Disks) to preserve

data after a disk casualty • A tape back-up unit (i.e. DAT, JAZ, Zip, or CD-RW drive) • Numerous expansion slots • Fast network interface card • At least 512 MB of RAM

Workstations

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All the user computers connected to a network are calledworkstations. A typical workstation is a computer that isconfigured with a network interface card, networking software, andthe appropriate cables. Workstations do not necessarily need floppydisk drives because files can be saved on the file server. Almostany computer can serve as a network workstation.

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NETWORK TOPOLOGIES

The term topology refers to the way a network is laid out, eitherphysically or logically. The physical topology of a network refersto the configuration of cables, computers, and other peripheralswhile the logical topology is the method used to pass informationbetween workstations. Two or more devices connect to a link; two ormore links form a topology. The topology of a network is thegeometric representation of the relationship of all the links andlinking devices (usually called nodes) to each other. There arefive basic topologies possible: Bus, Ring, Star, Mesh, and Tree.

Bus TopologyBus topology uses a common backbone to connect all the networkdevices in a network in a linear shape. A single cable functions asthe shared communication medium for all the devices attached withthis cable with an interface connector. The device, which wants tocommunicate send the broadcast message to all the devices attachedwith the shared cable but only the intended recipient actuallyaccepts and process that message. The bus topology is oftenreferred to as a "linear bus" because the computers are connected in astraight line. A linear bus topology consists of a main run ofcable with a terminator at each end. All nodes (file server,workstations, and peripherals) are connected to the linear cable.This is the simplest and most common method of networkingcomputers.

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The figure below shows a typical bus topology. It consists of asingle cable called a trunk (also called a backbone or segment)that connects all of the computers in the network in a single line.

 

Computers on a bus topology network communicate by addressing datato a particular computer and sending out that data on the cable aselectronic signals. Network data in the form of electronic signalsis sent to all the computers on the network. Only the computerwhose address matches the address encoded in the original signalaccepts the information. All other computers reject the data. Thefigure below shows a message being sent from 0020af151d8b to02608c133456.

 

Only one computer at a time can send messages. Because only onecomputer at a time can send data on a bus network, the number ofcomputers attached to the bus will affect network performance. Themore computers there are on a bus, the more computers will be

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waiting to put data on the bus and, consequently, the slower thenetwork will be.

There is no standard way to measure the impact of a given number ofcomputers on the speed of any given network. The effect onperformance is not related solely to the number of computers. Thefollowing is a list of factors that in addition to the number ofnetworked computers will affect the performance of a network:

Hardware capabilities of computers on the network Total number of queued commands waiting to be executed Types of applications (client-server or file system sharing,

for example) being run on the network Types of cable used on the network Distances between computers on the network

Computers on a bus either transmit data to other computers on thenetwork or listen for data from other computers on the network.They are not responsible for moving data from one computer to thenext. Consequently, if one computer fails, it does not affect therest of the network. Because the data, or electronic signal, issent to the entire network, it travels from one end of the cable tothe other.

If the signal is allowed to continue uninterrupted, it will keepbouncing back and forth along the cable and prevent other computersfrom sending signals. Therefore, the signal must be stopped afterit has had a chance to reach the proper destination address. Tostop the signal from bouncing, a component called a terminator isplaced at each end of the cable to absorb free signals. Absorbingthe signal clears the cable so that other computers can send data.Both ends of each cable segment on the network must be plugged intosomething. For example, a cable end can be plugged into a computeror a connector to extend the cable length. Any open cable ends notplugged into something must be terminated to prevent signal bounce.

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The diagram below shows a properly terminated bus topology network.

 Advantages1. Easy to implement and extend2. Well suited for temporary networks (quick setup)3. Typically the cheapest topology to implement4. Faster than a ring network.5. If any node on the bus network fails, the bus itself is not

affected.6. Requires less cable than a Star network.

Disadvantages1. Difficult to administer/troubleshoot2. Limited cable length and number of stations3. A cable break can disable the entire network4. Maintenance costs may be higher in the long run5. Performance degrades as additional computers are added or on

heavy traffic6. Low security (all computers on the bus can see all data

transmissions)7. One virus in the network will affect all of them (but not as

badly as a star or ring network)8. Proper termination is required.(loop must be in closed path)

Ring topology

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A ring network is a topology of computer networks where each nodeis connected to two other nodes, so as to create a ring. The ringtopology connects computers on a single circle of cable. Unlike thebus topology, there are no terminated ends. The signals travelaround the loop in one direction and pass through each computer,which can act as a repeater to boost the signal and send it on tothe next computer. The figure below shows a typical ring topologywith one server and four workstations. The failure of one computercan have an impact on the entire network.

One method of transmitting data around a ring is called tokenpassing. (A token is a special series of bits that travels around atoken-ring network. Each network has only one token.) The token ispassed from computer to computer until it gets to a computer thathas data to send. Below figure shows a token ring topology with thetoken. The sending computer modifies the token, puts an electronicaddress on the data, and sends it around the ring.

 

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The data passes by each computer until it finds the one with anaddress that matches the address on the data. The receivingcomputer returns a message to the sending computer indicating thatthe data has been received. After verification, the sendingcomputer creates a new token and releases it on the network. Thetoken circulates within the ring until a workstation needs it tosend data. It might seem that token passing would take a long time,but the token actually travels at roughly the speed of light. Atoken can circle a ring 200 meters (656 feet) in diameter about477,376 times per second.

Ring networks tend to be inefficient when compared to Starnetworks because data must travel through more points beforereaching its destination. For example, if a given ring network haseight computers on it, to get from computer one to computer four,data must travel from computer one, through computers two andthree, and to its destination at computer four. It could also gofrom computer one through eight, seven, six, and five untilreaching four, but this method is slower because it travels throughmore computers.

Ring networks also carry the disadvantage that if one of the nodesin the network breaks down then the entire network will break downwith it as it requires a full circle in order to function.

Advantage1. The transmission of data is relatively simple as packets

travel in one direction only.2. An orderly network where every device has access to the token

and the opportunity to transmit.

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3. Under heavy network load performs better than a starttopology.

4. To manage the connectivity between the computers it doesn’tneed network server.

Disadvantages1. Data packets must pass through every computer between the

sender and recipient; therefore, this makes it slower.2. If any of the nodes fail then the ring is broken and data

cannot be transmitted successfully.3. It is difficult to troubleshoot the ring.4. Moves, adds and changes of devices can affect the entire

network. 5. It is slower than an Ethernet network.

Star topologyIn the computer networking world the most commonly used topology inLAN is the star topology. Star topologies can be implemented inhome, offices or even in a building. All the computers in the startopologies are connected to central devices like hub, switch orrouter. The functionality of all these devices is different. Ascompared to the bus topology, a star network requires more devices& cables to complete a network. The failure of each node or cablein a star network, won’t take down the entire network as comparedto the Bus topology. Signals are transmitted from the sendingcomputer through the hub to all computers on the network. However,if the central connecting device such as hub, switch or routerfails due to any reason, then ultimately, the entire network cancome down or collapse.

 

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The star network offers the advantage of centralized resources andmanagement. However, because each computer is connected to acentral point, this topology requires a great deal of cable in alarge network installation. Also, if the central point fails, theentire network goes down. If one computer or the cable thatconnects it to the hub fails on a star network, only the failedcomputer will not be able to send or receive network data. The restof the network continues to function normally.

Another characteristic of the star topology is that it is easy tomodify. Computers can be added or removed from the network withoutdisturbing the functioning of the network. The star topologysupports the expansion of networks. This is done by placing anotherhub where a computer can be located. This enables several morecomputers or hubs to be connected to the main hub.

A disadvantage of the star topology is that the cost of cabling ishigher in a network based on this topology because all the networkcables need to be extended to one central point.

Advantages1. Easy to implement and extend, even in large networks2. Well suited for temporary networks (quick setup)3. The failure of a non-central node will not have major effects

on the functionality of the network.4. Reliable market proven system5. No problems with collisions of Data since each station have

its own cable to the server/hub.6. Security can be implemented in the hub/switch.7. The centre of a star i.e. the hub or switch is best place to

find network faults.8. It is easy to modify and add new computers to a star network

without disturbing the rest of the network.

Disadvantages1. Depending on the transmission media, length limitations may be

imposed from the central location used

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2. Failure of the central node can disable the entire network3. Limited cable length and number of stations4. Maintenance costs may be higher in the long run

Mesh topologyA mesh topology network offers superior redundancy and reliability.In a mesh topology, each computer is connected to every othercomputer by separate cabling. This configuration provides redundantpaths throughout the network so that if one cable fails, anotherwill take over the traffic. While ease of troubleshooting andincreased reliability is definite pluses, these networks areexpensive to install because they use a lot of cabling. Often, amesh topology will be used in conjunction with other topologies toform a hybrid topology.

Mesh Topology

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Mesh networks are self-healing: the network can still operate evenwhen a node breaks down or a connection goes bad. As a result, avery reliable network is formed. This concept is applicable towireless networks, wired networks, and software interaction. SomeWANs, like the Internet, employ mesh routing. In fact the Internetwas deliberately designed like this to allow sites to communicateeven during a nuclear war.

Mesh topology work on the concept of routes. In Mesh topology,message sent to the destination can take any possible shortest,easiest route to reach its destination. In bus topology, messagesare usually broadcasted to every computer.. Similarly in the Ringtopology message can travel in only one direction i.e clockwise oranticlockwise. Internet employs the Mesh topology and the messagefinds its route for its destination. Router works in finding theroutes for the messages and in reaching them to their destinations.The topology in which every device connects to every other deviceis called a full Mesh topology unlike in the partial mesh in whichevery device is indirectly connected to the other devices.

Advantages1. Provides redundant paths between devices.2. The network can be expanded without disruption to current

users.

Disadvantages1. Requires more cable than the other LAN topologies.2. Complicated implementation.

Tree Topology Tree topologies are comprised of the multiple star topologies on abus. Tree topologies integrate multiple star topologies together ontoa bus. Only the hub devices can connect directly with the tree bus andeach Hub functions as a root of a tree of the network devices. Thisbus/star/hybrid combination supports future expandability of thecomputer networks, much better than a bus or star

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Tree TopologyAdvantages of a Tree Topology

1. Point-to-point wiring for individual segments. 2. Supported by several hardware and software venders.

Disadvantages of a Tree Topology 1. Overall length of each segment is limited by the type of

cabling used. 2. If the backbone line breaks, the entire segment goes down. 3. More difficult to configure and wire than other topologies.

5-4-3 Rule A consideration in setting up a tree topology using Ethernetprotocol is the 5-4-3 rule. One aspect of the Ethernet protocolrequires that a signal sent out on the network cable reach everypart of the network within a specified length of time. Eachconcentrator or repeater that a signal goes through adds a smallamount of time. This leads to the rule that between any two nodeson the network there can only be a maximum of 5 segments, connectedthrough 4 repeaters/concentrators. In addition, only 3 of thesegments may be populated (trunk) segments if they are made ofcoaxial cable. A populated segment is one which has one or morenodes attached to it.

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Selecting a TopologyIt is important to choose the right topology for how the networkwill be used. Each topology has its own characteristic. To choosethe right topology we must see the factors that influenced it. Thefactors are:

Length of cable needed. The linear bus network uses shorterlengths of cable.

Future growth. With a star topology, expanding a network iseasily done by adding another concentrator.

Cable type. The most common cable in schools is unshieldedtwisted pair, which is most often used with star topologies.

The table below also provides some guidelines for selecting atopology.

Topology Advantages Disadvantages

Bus

Use of cable is economical.

Media is inexpensive and easy to work with.

System is simple and reliable.

Bus is easy to extend.

Network can slow down in heavy traffic.

Problems are difficult to isolate.

Cable break can affect many users.

Ring

System provides equal access for all computers.

Performance is even despite many users.

Failure of one computer can impactthe rest of the network.

Problems are hard to isolate.

Network reconfiguration disrupts operation.

Star Modifying system and adding new computers iseasy.

If the centralized point fails, the network fails.

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Centralized monitoring and management are possible.

Failure of one computerdoes not affect the rest of the network.

Mesh

System provides increased redundancy and reliability as wellas ease of troubleshooting.

System is expensiveto install because it uses a lot of cabling.

OPEN SYSTEMS INTERCONNECTION (OSI) LAYER

OSI (Open Systems Interconnection) is a standard description or"reference model" for how messages should be transmitted betweenany two points in a telecommunication network. Its purpose is toguide product implementers so that their products will consistentlywork with other products.

The reference model defines seven layers of functions that takeplace at each end of a communication. Although OSI is not alwaysstrictly adhered to in terms of keeping related functions togetherin a well-defined layer, many if not most products involved intelecommunication make an attempt to describe them in relation tothe OSI model. It is also valuable as a single reference view ofcommunication that furnishes everyone a common ground for educationand discussion

The main idea in OSI is that the process of communication betweentwo end points in a telecommunication network can be divided intolayers, with each layer adding its own set of special, relatedfunctions. Each communicating user or program is at a computerequipped with these seven layers of function. So, in a given

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message between users, there will be a flow of data through eachlayer at one end down through the layers in that computer and, atthe other end, when the message arrives, another flow of data upthrough the layers in the receiving computer and ultimately to theend user or program.

The actual programming and hardware that furnishes these sevenlayers of function is usually a combination of thecomputer operating system , applications (such as your Webbrowser), TCP/IP or alternative transport and network protocols,and the software and hardware that enable you to put a signal onone of the lines attached to your computer.

OSI divides telecommunication into seven layers. The layers are intwo groups. The upper four layers are used whenever a messagepasses from or to a user. The lower three layers (up to the networklayer) are used when any message passes through the host computer.Messages intended for this computer pass to the upper layers.Messages destined for some other host are not passed up to theupper layers but are forwarded to another host.

The seven layers are:1. Layer 7: The application layer2. Layer 6: The presentation layer3. Layer 5: The session layer4. Layer 4: The transport layer5. Layer 3: The network layer6. Layer 2: The data-link layer7. Layer 1: The physical layer

Physical Layer - (Defines the Physical Characteristics of theNetwork)It ensures a safe and efficient travel of data; consists ofelectronic circuits for data transmission etc. It performs servicesrequested by the data link layer. This level refers to networkhardware, physical cabling or a

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wireless electromagnetic connection . It also deals with electricalspecifications, collision control and other low-level functions.

The physical layer is the most basic network layer, providing onlythe means of transmitting raw bits. The shapes of the electricalconnectors, which frequencies to broadcast on, and similar low-level things are specified here. An analogy of this layer in aphysical mail network would be a specification for various kinds ofpaper and ink.

Data-Link Layer - (Provides Safe Communication of Data over thePhysical Network)Data link layer is in charge of data encapsulation under the formof packets and their interpretation at the physical layer. Itresponds to service requests from the network layer and issuesservice requests to the physical layer. This is the layer whichtransfers data between adjacent network nodes in a wide areanetwork or between nodes on the same local area network segment.The data link layer provides the functional and procedural meansto transfer data between network entities and might provide themeans to detect and possibly correct errors that may occur in thePhysical layer.

Network Layer - (Handles Connection to the Network by the HigherLayers)Network layer is in charge of packets transmission from a source Ato a destination B. It responds to service requests fromthe transport layer and issues service requests to the data linklayer.

The network layer addresses messages and translates logicaladdresses and names into physical addresses. It also determines theroute from the source to the destination computer and managestraffic problems, such as switching, routing, and controlling thecongestion of data packets. In essence, the network layer isresponsible for end to end (source to destination) packet delivery,

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whereas the data link layer is responsible for node to node (hop tohop) packet delivery.

The network layer provides the functional and procedural means oftransferring variable length data sequences from a source to adestination via one or more networks while maintaining the qualityof service requested by the transport layer. The Network layerperforms network routing, flow control, networksegmentation /desegmentation, and error functions. The networklayer deals with transmitting information all the way from itssource to its destination - transmitting from anywhere, toanywhere.

Transport Layer - (Provides End-To-End Errors Detection andCorrection)Transport layer is in charge of the delivery of packets from asource A to a destination B. It responds to service requests fromthe session layer and issues service requests to the network layer.

The transport layer provides transparent transfer of data betweenhosts. It is usually responsible for end-to-end error recovery andflow control, and ensuring complete data transfer. In the Internetprotocol suite this function is most commonly achieved by theconnection oriented Transmission Control Protocol (TCP).The datagram -type transport, User (UDP), provides neither errorrecovery, nor flow control, leaving these to the application.

The purpose of the Transport layer is to providetransparent transfer of data between end users, thus relieving theupper layers from any concern with providing reliable and cost-effective data transfer.

Session Layer - (Manages Sessions among Applications)Session layer is in charge of the management of network access. Itresponds to service requests from the presentation layer and issuesservice requests to the transport layer.

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The Session layer provides the mechanism for managing the dialoguebetween end-user application processes. It provides for either fullduplex or half-duplex operation and establishes check pointing,adjournment, termination, and restart procedures.

Presentation Layer - (Provides Standard Data Representations forApplications)Presentation layer determines the format of the data transmitted toapplications, data compressing/decompressing, encrypting etc. Itresponds to service requests from the application layer and issuesservice requests to the session layer.

The presentation layer concerns itself not only with the format andrepresentation of actual user data, but also with data structureused by programs. Therefore, the presentation layer negotiates datatransfer syntax for the application layer.

The presentation layer is responsible for the delivery andformatting of information to the application layer for furtherprocessing or display. It relieves the application layer of concernregarding syntactical differences in data representation within theend- user systems.

Application Layer - (Applications Connected to the Network)Application layer contains the applications which are used by theend-user, such as Java, Word etc. It interfaces directly to andperforms common application services for the application processes;it also issues requests to the presentation layer. Applicationlayer services communicate between software programs and lower-layer network services so that the network can properly interpretan application’s request and, in turn, the application caninterpret data sent from the network. For example, when you chooseto open a Web page in Mozilla Firefox, an Application layerprotocol called HTTP (Hypertext Transfer Protocol) formats andsends your request, then formats and sends the Web server’sresponse. 

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NETWORK SECURITYIn the field of networking, the area of network security consists ofthe provisions and policies adopted by the network administrator toprevent and monitor unauthorized access, misuse, modification, ordenial of the computer network and network-accessible resources.Network security involves the authorization of access to data in anetwork, which is controlled by the network administrator. Userschoose or are assigned an ID and password or other authenticatinginformation that allows them access to information and programswithin their authority. Network security covers a variety ofcomputer networks, both public and private, that are used ineveryday jobs conducting transactions and communications amongbusinesses, government agencies and individuals. Networks can beprivate, such as within a company, and others which might be opento public access. Network security is involved in organizations,enterprises, and other types of institutions. It does as its titleexplains: It secures the network, as well as protecting and overseeing operations beingdone. The most common and simple way of protecting a networkresource is by assigning it a unique name and a correspondingpassword.

Every organization should monitor its systems for possibleunauthorized intrusion and other attacks. This needs to be part ofthe daily routine of every organization's IT unit, as it isessential to safeguarding a company's information assets.

Network security starts with authenticating the user, commonly witha username and a password. Since this requires just one detailauthenticating the user name —i.e. the password, which is somethingthe user 'knows'.

Once authenticated, a firewall enforces access policies such aswhat services are allowed to be accessed by the networkusers. Though effective to prevent unauthorized access, thiscomponent may fail to check potentially harmful content suchas computer worms or Trojans being transmitted over thenetwork. Anti-virus software or an intrusion prevention system(IPS) helps detect and inhibit the action of such malware.

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An anomaly-based intrusion detection system may also monitor thenetwork and traffic for unexpected (i.e. suspicious) content orbehavior and other anomalies to protect resources, e.g. from denialof service attacks or an employee accessing files at strange times.Individual events occurring on the network may be logged for auditpurposes and for later high-level analysis.

Security management for networks is different for all kinds ofsituations. A home or small office may only require basic securitywhile large businesses may require high-maintenance and advancedsoftware and hardware to prevent malicious attacksfrom hacking and spamming.

The three legs of the "Security Trinity," prevention, detection,and response, comprise the basis for network security. The securitytrinity should be the foundation for all security policies andmeasures that an organization develops and deploys.

The Security Trinity.PreventionThe foundation of the security trinity is prevention. To providesome level of security, it is necessary to implement measures toprevent the exploitation of vulnerabilities. In developing network

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security schemes, organizations should emphasize preventativemeasures over detection and response: It is easier, more efficient,and much more cost-effective to prevent a security breach than todetect or respond to one. Remember that it is impossible to devisea security scheme that will prevent all vulnerabilities from beingexploited, but companies should ensure that their preventativemeasures are strong enough to discourage potential criminals-sothey go to an easier target.

DetectionOnce preventative measures are implemented, procedures need to beput in place to detect potential problems or security breaches, inthe event preventative measures fail. It is very important thatproblems be detected immediately. The sooner a problem is detectedthe easier it is to correct and cleanup.

ResponseOrganizations need to develop a plan that identifies theappropriate response to a security breach. The plan should be inwriting and should identify who is responsible for what actions andthe varying responses and levels of escalation.

The following highlights the security measures that should be putin place in an organisation:

1. A fairly strong firewall or Unified Threat Management System2. Strong Antivirus software and Internet Security Software.3. For authentication, use strong passwords and change it on a

monthly basis.4. When using a wireless connection, use a robust password.5. Raise awareness about physical security to employees.6. Use an optional network analyzer or network monitor.7. An enlightened administrator or manager.8. Clear employee guidelines should be implemented for using the

Internet, including access to non-work related websites,sending and receiving information.

9. Individual accounts to log on and access company intranet andInternet with monitoring for accountability.

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10. Have a back-up policy to recover data in the event of ahardware failure or a security breach that changes, damages ordeletes data.

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IP ADDRESSING

An IP address is a numeric identifier assigned to each machine on anIP network. It designates the specific location of a device on thenetwork. An IP address is a software address. IP addressing wasdesigned to allow a host on one network to communicate with a hoston a different network, regardless of the type of LANs the hosts areparticipating in.

IP TerminologyImportant terms vital to the understanding of the Internet Protocolare:Bit - A bit is one digit; either a 1 or a 0.

Byte - A byte is 7 or 8 bits, depending on whether parity is used. Itis always assume that a byte is 8 bits.

Octet - An octet, made up of 8 bits, is just an ordinary 8-bitbinary number. The terms byte and octet are completelyinterchangeable.

Network address - This is the designation used in routing to sendpackets to a remote network— for example, 10.0.0.0, 172.16.0.0, and192.168.10.0.

Broadcast address - The address used by applications and hosts tosend information to all nodes on a network is called the broadcastaddress. Examples include 255.255.255.255, which is all networks,all nodes; 172.16.255.255, which is all subnets and hosts onnetwork 172.16.0.0; and 10.255.255.255, which broadcasts to allsubnets and hosts on network 10.0.0.0.

An IP address consists of 32 bits of information. These bits aredivided into four sections, referred to as octets or bytes, eachcontaining 1 byte (8 bits). You can depict an IP address using oneof three methods:

1. Dotted-decimal, as in 172.16.30.562. Binary, as in 10101100.00010000.00011110.001110003. Hexadecimal, as in AC.10.1E.38

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All these examples truly represent the same IP address. Hexadecimalisn’t used as often as dotted-decimal or binary when IP addressingis discussed, but you still might find an IP address stored inhexadecimal in some programs. The Windows Registry is a goodexample of a program that stores a machine’s IP address in hex.

Network AddressingThe network address (which can also be called the network number)uniquely identifies each network. Every machine on the same networkshares that network address as part of its IP address. In the IPaddress 172.16.30.56, for example, 172.16 is the network address.

The node address is assigned to, and uniquely identifies, each machineon a network. This part of the address must be unique because itidentifies a particular machine—an individual— as opposed to anetwork, which is a group. This number can also be referred to as ahost address. In the sample IP address 172.16.30.56, the 30.56 is thenode address.

The designers of the Internet decided to create classes of networksbased on network size. For the small number of networks possessinga very large number of nodes, they created the rank Class A network. Atthe other extreme is the Class C network, which is reserved for thenumerous networks with a small number of nodes. The classdistinction for networks between very large and very small ispredictably called the Class B network.

Subdividing an IP address into a network and node address isdetermined by the class designation of one’s network. The tablebelow summarizes the three classes of networks.

Class DMulticast

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8 bits 8 bits 8 bits 8bits

ClassA

Network

Host Host Host

ClassB

Network

Network

Host Host

ClassC

Network

Network

Network

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Class E Research

Network Address Range

Class AThe designers of the IP address scheme said that the first bit ofthe first byte in a Class A network address must always be off, or0. This means a Class A address must be between 0 and 127inclusive. Consider the following network address:0xxxxxxxIf we turn the other 7 bits all off and then turn them all on,we’ll find the Class A range of network addresses:00000000 = 001111111 = 127So, a Class A network is defined in the first octet between 0 and127, and it can’t be less or more.

Class BIn a Class B network, the scheme said that the first bit of thefirst byte must always be turned on, but the second bit must alwaysbe turned off. If you turn the other 6 bits all off and then allon, you will find the range for a Class B network:10000000 = 12810111111 = 191As you can see, a Class B network is defined when the first byte isconfigured from 128 to 191.

Class CFor Class C networks, the scheme defines the first 2 bits of thefirst octet as always turned on, but the third bit can never be on.Following the same process as the previous classes, convert frombinary to decimal to find the range. Here’s the range for a Class Cnetwork:11000000 = 19211011111 = 223So, if you see an IP address that starts at 192 and goes to 223,you’ll know it is a Class C IP address.

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Network Address Ranges: Classes D and EThe addresses between 224 and 255 are reserved for Class D and Enetworks. Class D (224– 239) is used for multicast addresses andClass E (240–255) for scientific purposes.

Network Addresses: Special PurposeSome IP addresses are reserved for special purposes, so networkadministrators can’t ever assign these addresses to nodes. Thetable below lists the members of this exclusive little club and thereasons why they’re included in it.

Reserved IP AddressesADDRESS FUNCTION

Network address of all 0s Interpreted to mean “this network orsegment.”

Network address of all 1s Interpreted to mean “all networks.”

Network 127.0.0.1 Reserved for loopback tests. Designatesthe local node and allows that node tosend a test packet to itself withoutgenerating network traffic.

Node address of all 0s Interpreted to mean “network address” orany host on specified network.

Node address of all 1s Interpreted to mean “all nodes” on thespecified network; for example,128.2.255.255 means “all nodes” onnetwork 128.2 (Class B address).

Entire IP address set to Used by Cisco routers to designate thedefault route. Could also mean “anynetwork.”

Entire IP address set to all 1s (same as

255.255.255.255)

Broadcast to all nodes on the currentnetwork; sometimes called an “all 1sbroadcast” or limited broadcast.

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Class A AddressesIn a Class A network address, the first byte is assigned to thenetwork address and the three remaining bytes are used for the nodeaddresses. The Class A format is:

Network . Node . Node . Node

For example, in the IP address 49.22.102.70, the 49 is the networkaddress, and 22.102.70 is the node address. Every machine on thisparticular network would have the distinctive network address of49.

Class A network addresses are one byte long, with the first bit ofthat byte reserved and the 7 remaining bits available formanipulation (addressing). As a result, the maximum number of ClassA networks that can be created is 128. Why? Because each of the 7bit positions can be either a 0 or a 1, thus 27 or 128.

The network address of all 0s (0000 0000) is reserved (see abovetable). Additionally, the address 127, which is reserved fordiagnostics, can’t be used either, which means that you can reallyonly use the numbers 1 to 126 to designate Class A networkaddresses. This means the actual number of usable Class A networkaddresses is 128 minus 2, or 126.

Each Class A address has three bytes (24-bit positions) for thenode address of a machine. This means there are 224—or 16,777,216—unique combinations and, therefore, precisely that many possibleunique node addresses for each Class A network. Because nodeaddresses with the two patterns of all 0s and all 1s are reserved,the actual maximum usable number of nodes for a Class A network is224 minus 2, which equals 16,777,214. That’s a huge amount of hostson a network segment.

Class A Valid Host IDsHere’s an example of how to figure out the valid host IDs in aClass A network address:

All host bits off is the network address: 10.0.0.0. All host bits on is the broadcast address: 10.255.255.255.

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The valid hosts are the numbers in between the network address andthe broadcast address: 10.0.0.1 through 10.255.255.254. Notice that0s and 255s can be valid host IDs. All you need to remember whentrying to find valid host addresses is that the host bits can’t allbe turned off or all be on at the same time.

Class B AddressesIn a Class B network address, the first two bytes are assigned tothe network address and the remaining two bytes are used for nodeaddresses. The format is:

Network . Network . Node . Node

For example, in the IP address 172.16.30.56, the network address is172.16, and the node address is 30.56.

With a network address being two bytes (8 bits each); there wouldbe 216 unique combinations. But the Internet designers decided thatall Class B network addresses should start with the binary digit 1,then 0. This leaves 14 bit positions to manipulate, therefore16,384 (that is, 214) unique Class B network addresses.

A Class B address uses two bytes for node addresses. This is 216

minus the two reserved patterns (all 0s and all 1s), for a total of65,534 possible node addresses for each Class B network.

Class B Valid Host IDsHere’s an example of how to find the valid hosts in a Class Bnetwork:

All host bits turned off is the network address: 172.16.0.0. All host bits turned on is the broadcast address:

172.16.255.255.

The valid hosts would be the numbers in between the network addressand the broadcast address: 172.16.0.1 through 172.16.255.254.

Class C Addresses

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The first three bytes of a Class C network address are dedicated tothe network portion of the address, with only one measly byteremaining for the node address. The format is:

Network . Network . Network . Node

Using the example IP address 192.168.100.102, the network addressis 192.168.100, and the node address is 102.

In a Class C network address, the first three bit positions arealways the binary 110. The calculation is: 3 bytes, or 24 bits,minus 3 reserved positions, leaves 21 positions. Hence, there are221, or 2,097,152, possible Class C networks.

Each unique Class C network has one byte to use for node addresses.This leads to 28 or 256, minus the two reserved patterns of all 0sand all 1s, for a total of 254 node addresses for each Class Cnetwork.

Class C Valid Host IDsHere’s an example of how to find a valid host ID in a Class Cnetwork:

All host bits turned off is the network ID: 192.168.100.0. All host bits turned on is the broadcast address:

192.168.100.255.

The valid hosts would be the numbers in between the network addressand the broadcast address: 192.168.100.1 through 192.168.100.254.

Static and Dynamic AddressingStatic IP addressing occurs when you permanently assign one or moreIP addresses for each user. These addresses do not change overtime. However, if a static address is assigned but not in use, itis effectively wasted.

Dynamic IP addressing allows you to efficiently utilize the addressspace. Using dynamic IP addressing, the IP addresses of individualuser computers may change over time. If a dynamic address is not inuse, it can be automatically reassigned to another computer as

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needed. Dynamic IP addresses are usually assigned by DHCP (DynamicHost Configuration Protocol). Dynamic Host Configuration Protocol(DHCP) is a network protocol that enables a server/computer toautomatically assign an IP address to an individual computer'sTCP/IP stack software. DHCP assigns a number dynamically from adefined range of numbers configured for a given network.

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NETWORK PROBLEMS AND TROUBLESHOOTING

Wireless or Ethernet, almost everyone has had their share ofnetwork connection problems.  It could be anything from not beingable to access the Internet despite being connected to the network,to not being able to connect to the network at all. Unfortunately,network connection problems are sometimes hard to diagnose. If acomputer is unable to connect to a network or see other computerson a network, it may be necessary to troubleshoot the network.

The five most common network problems are:1. Cable Problem: Cables that connect different parts of a networkcan be cut or shorted. A short can happen when the wire conductorcomes in contact with another conductive surface, changing the pathof the signal. Cable testers can be used to test for many types ofcable problems such asCut cable, incorrect cable connections, Cable shorts, Interferencelevel, Connector Problem.

2. Connectivity Problem: A connectivity problem with one or moredevices in a network can occur after a change is made inconfiguration or by a malfunction of a connectivity component, suchas hub, a router or a Switch.

3. Excessive Network Collisions: These often lead to slowconnectivity. The problem can occur as a result of bad networksetup/plan, a user transferring a lot of information or jabberingnetwork card.

NB: A jabbering Network card is a network card that is stuck in atransmit mode. This will be evident because the transmit light willremain on constantly, indicating that the Network card is alwaystransmitting.

4, Software Problem: Network problems can often be traced tosoftware configuration such as DNS configuration, WINSconfiguration, the registry etc.

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5. Duplicate IP Addressing: A common problem in many networkingenvironments occurs when two machines try to use the same IPaddress. This can result in intermittent communications.

Others are: Network card not connected properly. Bad network card drivers or software settings. Firewall preventing computers from seeing each other. Bad network hardware.

Solutions to Common Windows Networking and Hardware Problems

Nothing will stall your workday faster than a dropped networkconnection or recalcitrant peripheral. There's a good chance that justa few tweaked Windows settings will get you rolling again. With someluck, the tools built into the OS will be all the help you need.

Diagnose Network Disconnections in Vista And XPOne of Vista's most useful new tools is the revamped Network Diagnostics utility. When a Web page won't load in Internet Explorer, you may be prompted to run the utility by clicking Tools > Diagnose Connection Problems. You can also open the program by clicking the network icon in the system tray, choosing Network and Sharing Center, and clicking Diagnose and Repair in the left pane.

Some problems the program will fix automatically, but it may alsodisplay instructions for correcting the glitch manually, or itmight simply point to Vista's Help and Support file. The tool can'tdiagnose problems outside of the local PC, such as your ISP'sservers being down, but it helps you determine whether the sourceis in your system or something else.

XP's Network Diagnostics tool lacks the troubleshooting chops ofits Vista counterpart, but it can help you pinpoint the location ofthe failure. To run it from Internet Explorer, click Tools >Diagnose Connection Problems. To open it without IE, click Start >Run, type %windir%\network diagnostic\xpnetdiag.exe, and pressEnter.

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If everything checks out with your PC's network settings, ping yourISP's servers to make sure the connection is working. Click Start >All Programs > Accessories > Command Prompt, type ping yahoo.com(or any domain name), and press Enter. If your network link isworking, you'll see four lines of replies, followed by a list ofping statistics. A failed ping test indicates a lost connection toyour ISP. Before you get on the horn to your ISP, try turning offyour router and then turning it back on again. This is sometimessufficient to reset the device. (To get a more detailed look of thepath packets take from your PC to a Web site, type tracert, thedomain name, and press Enter to see a list of all the stops thepackets make along the way to their destination.) When you're done,type exit and press Enter to close the Command Prompt window.

Pinging a Web site from Windows' Command Prompt to determine whether the link to your ISP is working

Some Solutions to Windows Network Connection ProblemsHere are four easy solutions you can try to get your Internetaccess back.

1. Check Your Hosts FileWindows can use the hosts file to set IP addresses to particulardomains.  This means though that it can be used to redirect oreffectively cut off your Internet access.When you need to troubleshoot an Internet connection, this is couldbe the first place to look.

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To view the file, just open up Notepad and go to File->Open.  Then,navigate to your C drive, then to the “Windows” Folder, then“System32” folder, then “drivers” folder, then “etc” folder andfinally, open the file named “hosts“.

After you have the file open, it should look something like what wehave below and anything else should be deleted.

Note: To edit this in Windows Vista and 7, you need to right click onthe notepad icon and select Run as Administrator.

# Copyright (c) 1993-2009 Microsoft Corp.## This is a sample HOSTS file used by Microsoft TCP/IP for Windows.## This file contains the mappings of IP addresses to host names. Each# entry should be kept on an individual line. The IP address should# be placed in the first column followed by the corresponding host name.# The IP address and the host name should be separated by at least one# space.## Additionally, comments (such as these) may be inserted on individual# lines or following the machine name denoted by a '#' symbol.## For example:## 102.54.94.97 rhino.acme.com # source server# 38.25.63.10 x.acme.com # x client host

# localhost name resolution is handled within DNS itself.# 127.0.0.1 localhost# ::1 localhost

2. Check Your TCP/IP SettingsAnother issue may be that your TCP/IP settings were altered in someway.To do this in XP , got to Control Panel and then Network Connections.In Windows Vista/7, go to the Control Panel and then the Network andSharing Center.  In 7, click on “Change Adapter Settings.” In Vista, clickon “manage network connections“.In all versions of Windows, after you get to the places designatedabove, right click the device giving you trouble, either theWireless card or Ethernet card.  Then select “Properties.”

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If either the IP or DNS server address are not set to automatic,set them to be automatic.

Repeat this for Internet Protocol Version 4.

3. Reset Your TCP/IP ManuallySometimes, you may just need to reset your TCP/IP.  This can easilybe done at the command line in Windows.

For Windows XP, go to Start->Run.  Type “cmd” and press enter.  Acommand window should pop up.  Then type “netsh int ip reset c:\resetlog.txt”and press enter.  You will then have to restart your computer.

For Windows Vista/7, you have to run the Command Prompt as anadministrator.  To do that, just type “cmd” in your start menu’ssearch bar.  Right click the “cmd” icon that should come up andselect “Run as administrator.”  Then type the same as indicated above,press enter, and restart.

4. Reset Your Winsock ManuallyWinsock, short for Windows Socket API, is how Windows handles networkservices.  A reset of this may fix a network problem.

Resetting your Winsock is similar to resetting TCP/IP.  Open aCommand Prompt as laid out above for your version of Windows andtype “netsh winsock reset“.  Then press enter and restart your computer.

Sometimes even these steps will not fix a faulty connection.  Ifthat’s the case, you can try googling the exact problem orcontacting someone with network experience.

Tips

How to configure Internet Connection Sharing in Windows XP

This article describes how to set up and use the Internet Connection Sharing feature in Microsoft Windows XP. With Internet Connection Sharing, you can use networked computers to share a single connection to the Internet. 

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How to use Internet Connection SharingTo use Internet Connection Sharing to share your Internetconnection, the host computer must have one network adapter that isconfigured to connect to the internal network, and one networkadapter or modem that is configured to connect to the Internet.

On the host computerOn the host computer, follow these steps to share the Internetconnection:

1. Log on to the host computer as Administrator or as Owner.2. Click Start, and then click Control Panel.3. Click Network and Internet Connections.4. Click Network Connections.5. Right-click the connection that you use to connect to the

Internet. For example, if you connect to the Internet by usinga modem, right-click the connection that you want under Dial-up.

6. Click Properties.7. Click the Advanced tab.8. Under Internet Connection Sharing, select the Allow other

network users to connect through this computer's Internetconnection check box.

9. If you are sharing a dial-up Internet connection, selectthe Establish a dial-up connection whenever a computer on mynetwork attempts to access the Internet check box if you wantto permit your computer to automatically connect to theInternet.

10. Click OK. You receive the following message:When Internet Connection Sharing is enabled, your LAN adapterwill be set to use IPaddress 192.168.0.1. Your computer may lose connectivity withother computers onyour network. If these other computers have static IPaddresses, it is a good idea to set themto obtain their IP addresses automatically. Are you sure you

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want to enable InternetConnection Sharing?

11. Click Yes.The connection to the Internet is shared to other computers on thelocal area network (LAN). The network adapter that is connected tothe LAN is configured with a static IP address of 192.168.0.1 and asubnet mask of 255.255.255.0

On the client computerTo connect to the Internet by using the shared connection, you mustconfirm the LAN adapter IP configuration, and then configure theclient computer. To confirm the LAN adapter IP configuration,follow these steps:

1. Log on to the client computer as Administrator or as Owner.2. Click Start, and then click Control Panel.3. Click Network and Internet Connections.4. Click Network Connections.5. Right-click Local Area Connection, and then click Properties.6. Click the General tab, click Internet Protocol (TCP/IP) in the

connection uses the following items list, and thenclick Properties.

7. In the Internet Protocol (TCP/IP) Properties dialog box,click Obtain an IP address automatically (if it is not alreadyselected), and then click OK.

8. Note You can also assign a unique static IP address in therange of 192.168.0.2 to 192.168.0.254. For example, you canassign the following static IP address, subnet mask, anddefault gateway:

9. IP Address 192.168.0.210. Subnet mask 255.255.255.011. Default gateway 192.168.0.112. In the Local Area Connection Properties dialog box,

click OK.13. Quit Control Panel.

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To configure the client computer to use the shared Internetconnection, follow these steps:

1. Click Start, and then click Control Panel.2. Click Network and Internet Connections.3. Click Internet Options.4. In the Internet Properties dialog box, click

the Connections tab.5. Click the Setup button.

The New Connection Wizard starts.

6. On the Welcome to the New Connection Wizard page, click Next.7. Click Connect to the Internet, and then click Next.8. Click Set up my connection manually, and then click Next.9. Click Connect using a broadband connection that is always on,

and then click Next.10. On the Completing the New Connection Wizard page,

click Finish.11. Quit Control Panel.

When you now start Microsoft Internet Explorer, the client computerwill try to connect to the Internet by using the host computer'sshared Internet connection.

TroubleshootingWhen you turn on Internet Connection Sharing on the host computer,the host computer's LAN adapter is automatically assigned the IPaddress of 192.168.0.1. Therefore, one of the following situationsmay occur:

IP address conflictEach computer on the LAN must have a unique IP address. If morethan one computer has the same IP address, an IP conflict occurs, and one of the network adapters turns off until the conflict is resolved. To resolve this conflict, configure the client computer to automatically obtain an IP address, or assign it a unique IP address.

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Loss of network connectivityIf your network is configured with a different IP address rangethan Internet Connection Sharing uses, you will lose network connectivity with the host computer. To resolve this issue, configure the client computers to automatically obtain an IP address, or assign each client computer a unique IP address in the range of 192.168.0.2 to 192.168.0.254.

Other solutions are:

Verify Connections / LEDs Verify that the network cable is properly connected to the back ofthe computer. In addition, when checking the connection of thenetwork cable, ensure that the LEDs on the network are properlyilluminated. For example, a network card with a solid green LED orlight usually indicates that the card is either connected orreceiving a signal.

Note: generally, when the green light is flashing, this is anindication of data being sent or received. If, however, the carddoes not have any lights or has orange or red lights, it ispossible that either the card is bad, the card is not connectedproperly, or that the card is not receiving a signal from thenetwork. If you are on a small or local network and have thecapability of checking a hub or switch, verify that the cables areproperly connected and that the hub or switch has power.

Adapter Resources Ensure that if this is a new network card being installed into thecomputer that the card's resources are properly set and/or are notconflicting with any hardware in the computer. Users, who are usingWindows OS, verify that Device Manager has no conflicts or errors.

Adapter Functionality Verify that the network card is capable of pinging or seeing itselfby using the ping command. Windows users should ping the computer

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from a MS-DOS prompt. To ping the card or the local-host, typeeither ping 127.0.0.1 or ping local-host This should show a listingof replies from the network card. If you receive an error or if thetransmission failed, it is likely that either the network card isnot physically installed into the computer correctly, or that thecard is bad.

ProtocolVerify that the correct protocols are installed on the computer.Most networks today will utilize TCP/IP, but may also utilize orrequire IPX/SPX and NetBEUI. When the TCP/IP protocol is installed,unless a DNS server or other computer assigns the IPX address, theuser must specify an IP address as well as a Subnet Mask. To dothis, follow the instructions below:

1. Click Start / Control Panel 2. Double-click the Network icon3. Click on Local Area Connection4. Click on Properties5. Select TCP/IP v46. Click on Properties7. Enter the IP address and Subnet Mask address, an example of

such an address could be: IP Address: 102.55.92.1 Subnet Mask:255.255.255.192

8. When specifying these values, the computers on the networkmust all have the same Subnet Mask and have a different IPAddress. For example, when using the above values on onecomputer you would want to use an IP address of 102.55.92.2 onanother computer and then specify the same Subnet Mask.

FirewallIf your computer network utilizes a firewall, ensure that all portsrequired are open. If possible, close the firewall software programor disconnect the computer from the firewall to ensure it is notcausing the problem.

Additional Time

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In some cases, it may take a computer some additional time todetect or see the network. If after booting the computer you areunable to see the network, give the computer 2-3 minutes to detectthe network. Windows users may also want to try pressing the F5(refresh) key when in Network Neighborhood to refresh the networkconnections and possibly detect the network.

Additional TroubleshootingIf after following or verifying the above recommendations you arestill unable to connect or see the network, attempt one or more ofthe recommendations below.

If you have installed or are using TCP/IP as your protocol, you canattempt to ping another computer's IP address to verify if thecomputer is able to send and receive data. To do this, Windowsusers must be at a prompt. Once at the prompt, assuming, that theaddress of the computer you wish to attempt to ping is 102.55.92.2,you would type: ping 102.55.92.2125

If you receive a response back from this address (and it is adifferent computer), this demonstrates that the computer iscommunicating over the network. If you are still unable to connector see the network, it is possible that other issues may bepresent.

Another method of determining network issues is to use the tracertcommand if you are Windows user. To use this command you must be atthe command prompt. Once at the prompt, assuming that the addressis again 102.55.92.2, type: tracert 102.55.92.2. This should beginlisting the hops between the computer and network devices. When theconnection fails, determine which device is causing the issue byreviewing the tracert listing.

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