introduction to lan

7212019 Introduction to LAN

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Introduction

This lesson covers the definition of a Local Area Network (LAN) The history of LANswith regard to how the inventors of LANs tried to solve a problem (sharing ofinformation) is also covered LANs were created to save time money and enable users

to share information and resources more easily ome advantages that LANs provideinclude

bull imple and inepensive connections

bull upport for multiple media protocols

bull leibility to provide any$to$any connections

bull upport for new applications

bull Ability to grow easily

These advantages are outlined in detail in this lesson

Objectives

pon successful completion of this lesson you should be able to do the following

bull ampefine the purpose of a Local Area Network (LAN)

bull ampiscuss the history and evolution of the Local Area Network (LAN)

bull dentify the advantages of implementing a Local Area Network (LAN)



LAN Overview

irst let us answer the uestion hat is a LAN+ and discuss the history of how LANscame into eistence

LAN stands for Local Area Network A LAN is a communications system that allowsusers to access and share resources (computers printers servers) with other users

LANs provide companies with time$ and money$ saving ways to share resources andinformation They are simple inepensive and support many types of protocols therfeatures include the ability to handle connections to different types of network euipmentand to support many applications n addition LANs can be easily etended to allow forchanges in the number of users for an organi-ation that is epanding



LAN Overview

ow far is local+

Normally what limits the distance a LAN can travel is the type of cable used The most

common type of cable is unshielded twisted pair (UTP) which is similar to the roundtelephone wire found in your home T can carry signals up to 011 meters without toomuch trouble ther types of cable can carry signals for longer distances

2ou will learn more about cables later in this course

LAN Overview

The area serviced by a LAN may be some physical area like the floor of a building or itmay be logically grouped according to the function of the computers served erhapsharsh operating conditions on the plant floor reuire the manufacturing group to have adifferent physical LAN than the administrative group erhaps the programming groupneeds a faster LAN than the marketing group erhaps the product testing group isisolated from the production group for security reasons urther folks may need toconnect to one LAN for a session and then move to another LAN later t is common for alarge site to have several LANs in the same building each serving a slightly different purpose Later there will be a discussion about how LANs are inter$connected usingdevices like switches and routers



LAN Overview

The network is private and under the control of the LAN Administrator(s) as opposed toa Wide Area Network (WAN) which is regulated by the government(s) and public utilities (3ore information about ANs can be found in the companion course WAN

Theory) The private control of a LAN enables the LAN Administrator to apply preferredconventions for naming addressing and identifying network entities hile this allowsfor greater customi-ation the differing conventions may be a problem if two LANs try tocommunicate or merge together

3ore recently the distinction between a LAN and a AN is starting to blur istoricallythe different environments dictated that the LAN and AN use different rules ofcommunication known as protocols and different addressing schemes reviously to go

from a LAN (eg ampenver) through a AN (eg 34) and then back to another LAN(eg ittsburgh) it was necessary to change protocols and addresses (and you were often painfully aware of the change over and back) As the deployment of new networkingtechnologies increases protocols are becoming unified end$to$end so that the network hasthe appearance of one great big nationwide LAN



istor o LANs

n the 0561s there were large room$si-ed ainrae computers that had specialterminal displays and keyboards An eample of a mainframe was the 73 891 or 73ystem89 which was commonly running a traditional business application like payroll orinventory These dumb terminals were of a single fied function and often reuiredspecial wiring (coaial cable similar to the type used for cable T was common) To adda new application (for eample sales analysis) reuired months of programming erylittle off$the$shelf software was available and most programs were custom$written oftentailored to accommodate the proprietary terminals

istor o LANs

ith the arrival of the 051s came the ini$coputer (typified by a amplt4 amp$= oramp$01) which made use of a standard terminal interface and a slow but cheap ASCII serial (asynchronous) connection hile the terminals were dropping in si-e and pricethey still relied completely on the mini$computer for any intelligence nfortunately the



cabling for the mainframe terminals was different from the cabling for the mini$computers

istor o LANs

The personal coputer came on the scene in 05=1 with the Apple and then into the business world with the 73 4 in 05=0 ildly popular software programs oftenreferred to as killer apps were isi4alc (an early spreadsheet) and ordtar (an earlyword processor) haring of these spreadsheet and document files was accomplished bywalking the diskette from machine to machine a process gtokingly referred to as sneaker$net Not only was this method inefficient it created version control problems henthere were several copies of a file floating around which one was the official versionwhen updates occurred+

ide Area Networks were still in place for the mini and mainframes and the new 4scould emulate (look like or pretend to be) those older AN protocols for sharing filesThe 4 could emulate a fied function terminal and be able to run isi4alc as well twas the best of both worlds owever there was still no central repository for files

istor o LANs

ltventually Novell and 3icrosoft (and also Apple 7anyan ero and others)independently came up with the idea of LANs to connect the 4s together 7ecause disksand printers were so epensive at the time the original intent of a LAN was to allowusers to share disk and printer resources As a result the first LANs were designed simplyto avoid having to get up to hand someone a diskette of new files you gtust created Later4 LANs improved to the point where they were no longer dependent on mainframe andmini computers As LANs continue to develop they share more kinds of resources andmore kinds of data



iple and Ineamppensive onnections

hen 4s first emerged in the early 05=1s installing an adapter card to connect yourcomputer on a LAN was a complicated process ince the advent of the 3icrosoftindows operating system most LAN adapters are either pre$installed or recogni-ed bythe operating system as soon as they are installed n most cases the softwareaccompanying a LAN adapter is automatically configured to allow the computer to begincommunicating immediately This auto$recognition and auto$configuration is called plu$

and$pla compatibility ith plug$and$play the software asks you a few uestions sothat it can define the parameters reuired to get your 4 communicating with other 4son the network owever sometimes this process does not work and you need to go back and tweak the parameters a process that is derisively referred to as plug$and$pray

or eample you may have a three$hole electrical outlet and a two$prong plug r worseyet what if you have a three$prong plug and a two$hole outlet+ There are similar featuresin LANs that could potentially cause compatibility problems As a general rule if you getall of the LAN adapters from the same vendor you eliminate potential problems andconflicts




There are several items that go into the total cost of a complete set of euipment for asingle LAN user also known as a seat The LAN adapter card that goes inside the 4 iscalled a Network Interace ard (NI) ampepending on the speed of the card this cardmay cost as little as 1 or as much as =11 The cost of the LAN cable from the 4 tothe central distribution point varies based on the speed and distance of the transmissionstarting as low as B and going as high as B11

hile it is possible to hook two computers back$to$back using cross$over cables toechange the receive and the transmit cables such an arrangement is not really a LAN inthe strictest sense Typically the computers are connected to a central distribution pointsuch as a LAN switch or a hub These distribution devices operate much like a phone

switchboard in that they have multiple ports which provide inputs and outputs for thecables coming to and from the attached 4s Those ports go for as low as 0B8port to ashigh as 0B118port depending on the speed and intelligence of the device

The economies of scale may work for you or against you when building a LAN orinstance to buy a new N4 with 01 times the speed of a slower one may be only doublethe cost

owever it may cost 01 times more to double the ports on a switch As a result careful planning must be considered before deploying the euipment for a new LAN

2ou will learn more about port cost later in this course



upports ultiple edia

ecurity issues aside a LAN is usually wired or cabled so that each 4 can talk to anyother 4 on the network These wires have different characteristics and different costs both of which will be addressed later in this course

At the top end there are several kinds of iber optic cables that transmit light signalsthrough glass strands Lasers may be used to drive this signal great distances perhapseven to 1 kilometers or more

iber cable has the advantage of being immune to electrical interference andeavesdropping owever the disadvantage of fiber is the difficulty of splicing cable andthe higher epense relative to other transmission media till if money is no obgtect fiber

is the way to go




The part of a cable that plugs into a port or interface to connect one device to another iscalled a connector 4onnectors can either be male (containing one or more eposed pins)or female (containing holes in which the male connector can be inserted)

3ost LANs support fiber optic connections There are two common connector types usedto plug fiber optic cable into a port

bull tick$and$lick () connectors consist of suare plastic plugs

bull tick$and$Turn (T) connectors consist of a pair of bayonets


opper cable is another common wiring solution which typically comes in one of twoforms

bull Twisted pair cable consists of two wires twisted around each other similar to the

type of cabling used for telephones

bull oaampial cable consists of single stiff copper wire surrounded by insulation and a

concentric braided copper mesh similar to the cabling used for 4able T

hile copper is cheaper than fiber and easier to install there are distance limitationswhen compared to fiber Cenerally coaial cable can run farther (11$B11 meters) thantwisted pair (011 meters) 3ost LANs support twisted pair connections and very fewsupport coaial connections




Dust as cell phones have broken the cable barrier for voice wireless (roaming) LANadapters are decreasing the dependency on physical network cabling 4ompanies arecontinuing to eperiment with inrared radio and other forms of wireless LANtechnology hile distance and line$of$sight limitations remain issues increasedstandardi-ation and advances in mobile transmission technology are making wireless aincreasingly viable option for LAN connectivity


The good news about all of these options for transmission media is that the process ofdeciding which type(s) to use is made relatively independent of other aspects of LANoperations The bad news is that with so many prevalent types of media in use there area myriad of inter$connection possibilities that must be considered when purchasing LANeuipment



upports ultiple Protocols

A protocol is a method or procedure used for the echange of information between twocommunications devices Like its political counterpart if you do not speak the right way(that is according to the rules of my protocol) will not talk to you ince a LAN isoften shared by many people peaceul coeampistence becomes the goal


ome protocols actually cooperate and inform each other of what the other one is doingn the graphic shown rotocol and rotocol 2 work together to enable communicationacross the LAN

Eouters which will be discussed later are particularly good at handling cooperative protocols The information discovered within a protocol by one router may be sharedwith other routers that are speaking different protocols




ome other protocols coeampist but may not cooperate n this case rotocol F does notcooperate with rotocol or rotocol 2 but it may coeist on the same LAN The protocols do not talk to each other at all but they do not harm each other either

or instance both voice and video traffic may pass through the same switch oweveryou would not epect to receive video signals on your telephone ideo traffic gtust goesfrom T to T while voice traffic gtust goes from phone to phone The two data types pass each other in the switch without complaining


ome protocols cannot coeampist on the same wire with each other and therefore need to be segregated in some fashion n the graphic shown rotocol A cannot coeist with oneor more of the eisting protocols already in use on the LAN



An eample of this is G 3bps and 06 3bps Token$Eing protocols both of which aredefined later in this course These two protocols simply cannot operate on the same wirefor the same reason you cannot drive your car at 11 mph on the same one$lane road asothers driving their cars at 1 mph The lowest speed dictates the pace

An$to$An onnectivit

There are standards in place to define what is the proper protocol 7ecause most networksutili-e hardware and software from multiple vendors interoperabilit is the goal of anymied$vendor network

To this end there are several international groups that publish interoperability standards

bull The Institute o +lectrical and +lectronics +nineers (I+++) has developed aset of 011 or so documents called I+++ - x specifications which define manyaspects of LAN operations

bull TheInternet +nineerin Task orce (I+T) has issued thousands of 0e1uests

or oents (0) that identify interoperability problems and offer technicalsolutions

bull The International Orani2ation or tandardi2ation (IO) has defined a

communications framework known as the Open stes Interconnection (OI) model which divides LAN functions into several layers of protocol hile the model is no longer a defacto industry standard it remains useful as a tool for

identifying the function of new protocols

There are do-ens of additional standards bodies 7ut the ltltlt ltT and are the7ig Three that are relevant to understanding LAN Theory 3arconi and many othernetwork vendors participate in the open discussions hosted by these groups



An$to$An onnectivit

ithout interoperability standards euipment purchased from one vendor might notcommunicate with euipment purchased from another vendor or eample the 4adapter purchased from endor A may epect each network message to end with a -eroThe 4 adapter purchased from endor 7 is epecting the message to end with a one Asa result of the different standards there will be confusion and they will not talk to eachother reliably

hen interoperability standards are followed everybody wins and there are no surprises

owever a standard is by definition the lowest common denominator 3ost vendorsaugment the standards with their own etensions which result in new incompatibilities

until those etensions become so popular they are added to the standards o standardsdevelopment is an ongoing process that struggles to keep up with new technologies andideas



upports New Applications

The first and probably still the most common application for LANs is to share

resources such as files and printers among the 4s f several people are working on thesame progtect they can store the common file in a common location (like a library) ther

individuals may then check out the file work on it and put it back when they are done

imilarly a user may need access to a printer but does not need one all the time osharing a printer among multiple users makes more sense


3any software programs charge by the number of simultaneous users of their package

4onsider a company with 011 employees that all reuire occasional use of the 2F package

The company might buy only ten licenses and share them among the 011 peopleallowing access to no more than ten users at a time hen one person is done using alicense they release it making it available for use by the net person o in turn each ofthe 011 people could use the package by waiting their turn 3any LAN administration programs allow software use to be policed and monitored The cost savings of suchefficiency is immediate

oftware sharing alone may gtustify the cost of installing a LAN




e all use e$ail to communicate and LANs can make that process faster and easier byeliminating the need to dial up a modem n the same way we send e$mail many LANsnow support voice$mail videoconferencing and distance learning As you can imaginevideo eats up much if not all of the available bandwidth capacity of a LAN

owever e$mail is a very low bandwidth albeit high value consumer of LAN resources

3rows +asil

As shown in the graph getting two 4s to talk to each other costs about 011 on the lowend (Heep in mind that this estimate makes many assumptions about needs and speeds)n addition to the 1 cost of a network interface for each 4 there is an initial cost ofabout 61 for a simple =$port hub (The hub a common connection point for devices in anetwork will be discussed in more detail later in this course) Adding up to si more 4swill cost an additional 1 each



3rows +asil

f more than eight 4s are connected another central hub needs to be connected at themain distribution point ampue to the cost of purchasing an additional distribution hubdevice (which can usually connect to the first one as a stack) there is a marked increasein cost when epanding beyond the number of available ports on the central hub

3rows +asil

The two$hub solution is usually sufficient until the LAN grows beyond fourteen 4sThen a different kind of distribution device called a sart hub needs to be consideredThe smart hub is considerably more epensive than a standard hub because the smart hubneeds additional intelligence to manage a large number of ports As a result there is a big gtump in the price when the network grows to the point where intelligent port managementis reuired o while the cost per seat appears to be fairly flat it is actually increasing



This should not be a surprise really 4onsider a bus that carries twenty passengers The bus may actually cost less than the four cars it replaces 7ut when an airplane is neededthat costs more than the cars it replaces owever it also provides the added benefit ofincreased speed to reach the destinationI

n any case the initial cost to get into a simple LAN is relatively low owever as thesi-e of your network increases more sophisticated and intelligent devices are needed tomanage the flow of information through the network

uar

This lesson eamined the history and definition of the LAN The purpose of creating aLAN could be as simple as replacing an aging mainframe computer or as comple as

supporting the development of a new application n either cases LANs are easy to setup easy to epand and could allow any 4 to talk with any other 4



LAN Overview

irst let us answer the uestion hat is a LAN+ and discuss the history of how LANscame into eistence

LAN stands for Local Area Network A LAN is a communications system that allowsusers to access and share resources (computers printers servers) with other users

LANs provide companies with time$ and money$ saving ways to share resources andinformation They are simple inepensive and support many types of protocols therfeatures include the ability to handle connections to different types of network euipmentand to support many applications n addition LANs can be easily etended to allow forchanges in the number of users for an organi-ation that is epanding



LAN Overview

ow far is local+




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LAN Overview

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