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Networking
Technologies
CERTIFICATION OBJECTIVES
✓
1.01 Networks Two-Minute Drill
1.02 Topologies Q&A Self Test
1.03 Network Types
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2 Chapter1: Networking Technologies
T
hischapteroffersabriefintroductiontonetworkingandsomebasicnetworkingterms
andconcepts.Thismaterialshouldbeareviewofmanyalreadyknownconcepts.You
shouldbefamiliarwiththevariousnetworkingtopologiesusedinnetworks,aswellas
differenttypesofnetworks,suchaslocalareanetworks(LANs)andwideareanetworks(WANs).
CERTIFICATION OBJECTIVE 1.01
Networks
Anetworkis basically all of the components (hardware and software) involved in
connectingcomputersacrosssmallandlargedistances.Networksareusedtoprovide
easyaccesstoinformation,thusincreasingproductivityforusers.Thissectioncovers
some of the components involved with networking, as well as the basic types of
topologies used to connect networking devices, including computers.
Components
Oneofthemaincomponentsofnetworkingisapplications,whichenableusersto
performvarioustasks.Manyapplicationsarenetwork-aware.Theseapplicationsallow
youtoaccessanduseresourcesthatarenotlocatedonyourlocalcomputer.Someof
themorecommonnetworkingapplicationsincludee-mail(sendingmailelectronically),
FTP(transferringfiles),andWWW(providingagraphicalrepresentationtoinformation).
Thenumberofnetworkingapplicationsrangesinthethousands,butthoselistedarethe
mostcommonlyused.
To build a network, you need three types of devices or components: computers,
networking devices, and cabling. Computers—devices such as PCs and file servers
running Microsoft Windows, Macintosh OS, Unix (including Linux), or other
operatingsystems—areresponsibleforprovidingapplicationstotheusers.Networking
devices—suchashubs,bridges,switches,routers,firewalls,modems,NT1s(anISDN
network termination device), and channel service units / data service units (CSU/
DSUs)—are responsible for moving information between computers.. Cabling, such
ascopperorfibercabling,isneededtoconnectthecomputersandnetworkingdevices
sothatinformationcanbesharedbetweencomponents.Wirelesscommunicationalso
fallsinthiscategory.
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Topologies 3
TABLE 1-1
Term Definition
Networking Small office/home office Users working from a home or small office (a handful of
Locations (SOHO) people)
Branch office A small group of users connected in a small area, called
a LAN, geographically separated from a corporate office
Mobile users Users who can connect to a network from any location,
LAN or WAN
Corporate office The location where most users in an organization and
their resources are located
Locations
Networkcomponentscanbelocatedinvariouslocations.Table1-1showssome
commontermsusedtodescribethelocationofnetworkcomponents.
CERTIFICATION OBJECTIVE 1.02
Topologies
Whenyouarecablingupyourcomputersandnetworkingdevices,varioustypesof
topologiescanbeused.Atopologydefineshowthedevicesareconnected.Figure1-1
showsexamplesoftopologiesthatdifferentmediatypesuse.
Apoint-to-pointtopologyhasasingleconnectionbetweentwodevices.Inthis
topology,twodevicescandirectlycommunicatewithoutinterferencefromother
devices. These types of connections are not common when many devices need to be
connected together. An example of a point-to-point topology is when you connect
two routers across a dedicated WAN circuit.
In astartopology, a central device has many point-to-point connections to other
devices. Star topologies are used in environments where many devices need to be
connected.Anexampleofamediatypethatusesastartopologyis10BaseTEthernet.
When connecting devices together, you connect your computers to a hub or switch
(thecenterofthestar).Anextendedstartopologyisbasicallymultiplestartopologies
interconnected.
Abustopology uses a single connection or wire to connect all devices. Certain
mediatypes,like10Base5and10Base2Ethernet,useabustopology.Typically,special
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FIGURE 1-1 Network topologies
typesofconnectorsortransceiversareusedtoconnectthecablesinordertoprovide
thebustopology.In10Base2,forexample,eachdeviceconnectstoasinglestrandof
coaxialcableviaavampiretap.Thisdevicetapsintothesinglestrandofcoaxialcable
and provides the physical connection from a networking device to the single strand
of cable.
Inaringtopology,deviceoneconnectstodevicetwo,devicetwoconnects
todevicethree,andsoontothelastdevice,whichconnectsbacktodeviceone.
Ring topologies can be implemented with a single ring or a dual ring. Dual rings are
typicallyusedwhenyouneedredundancy.Forexample,ifoneofthedevicesfails
inthering,theringcanwrapitself,asshowninFigure1-2,toprovideasingle,
functional, ring. Fiber Distributed Data Interface (FDDI) is an example of a media
technology that uses dual rings to connect computer devices.
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Topologies 5
FIGURE 1-2 Dual rings and redundancy
Physical Versus Logical Topologies
Adistinctionneedstobemadebetweenphysicalandlogicaltopologies.Aphysical
topologydescribeshowdevicesarephysicallycabledtogether.Forinstance,10BaseThas
aphysicalstartopologyandFDDIhasaphysicaldualringtopology.Alogicaltopology
describeshowdevicescommunicateacrossthephysicaltopology.Thephysicaland
logicaltopologiesareindependentofeachother.Forexample,anyvarietyofEthernet
usesalogicalbustopologywhendevicescommunicate.ThismeansthatinEthernet,
youmightbeusing10BaseTwithaphysicalstartopologytoconnectdevicestogether;
however,thesedevicesareusingalogicalbustopologytocommunicate.
TokenRingisactuallyagoodexampleofamediatypethathasadifferent
physical topology from its logical one. Physically, Token Ring uses a star topology,
similar to 10BaseT Ethernet. Logically, however, Token Ring devices use a ring
topologytocommunicate.Thiscancreateconfusionwhenyouaretryingto
determine how devices are connected together and how they communicate. FDDI,
ontheotherhand,isstraightforward.FDDI’sphysicalandlogicaltopologiesare
thesame:aring.Table1-2showscommonmediatypesandtheirphysicaland
logical topologies.
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TABLE 1-2 Examples of Physical and Logical Topologies
Media Type Physical Topology Logical Topology
Ethernet Bus, Star, or Point-to-Point Bus
FDDI Ring Ring
Token Ring Star Ring
Meshing
Meshinggenericallydescribeshowdevicesareconnectedtogether.Therearetwotypesof
meshedtopologies:partialandfull.Inapartiallymeshedenvironment,everydeviceisnot
connectedtoeveryotherdevice.Inafullymeshedenvironment,everydeviceisconnected
toeveryotherdevice.Figure1-3showsexamplesofthesetwotypesoftopologies.
Notethatlikethetopologiesintheprecedingsection,partialandfullmesh
can be seen from both a physical view and a logical one. For example, in a physical
bustopology,allthedevicesarefullymeshed,sincetheyareallconnectedtothe
same piece of wire—this is both a physical and logical fully meshed topology. This
iscommoninLANtopologies.WANs,ontheotherhand,becauseoftheircost,
commonly use partially meshed topologies to reduce the cost of connected devices.
For example, in the partially meshed network shown in the top part of Figure 1-3,
thetop,right,andbottomdevicescanallcommunicateviathedeviceonthe
right-hand side. This communication introduces a delay in the transmission, but
it reduces the cost, since not as many connections are needed.
FIGURE 1-3 Partial- and full-mesh topologies
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Network Types 7
CERTIFICATION OBJECTIVE 1.03
Network Types
Networkscomeinawidevarietyoftypes.ThemostcommonareLANsandWANs,but
therearemanyothertypesofnetworks,includingmetropolitanareanetworks(MANs),
storageareanetworks(SANs),contentnetworks(CNs),intranetsandextranets,VPNs,
andothers.Thefollowingsectionsprovideabriefoverviewofeachofthesenetworktypes.
Local Area Networks
Local area networks (LANs) are used to connect networking devices that are in a
veryclosegeographicarea,suchasafloorofabuilding,abuildingitself,oracampus
environment.InaLAN,you’llfindPCs,fileservers,hubs,bridges,switches,routers,
multilayerswitches,voicegateways,firewalls,andotherdevices.Themediatypesused
inLANsincludeEthernet,FastEthernet(FE),GigabitEthernet(GE),TokenRing,
and FDDI. Today, most networks use some form of Ethernet. Ethernet is discussed
inChapter2.
Wide Area Networks
Wideareanetworks(WANs)areusedtoconnectLANstogether.Typically,WANs
are used when the LANs that must be connected are separated by a large distance.
Whereas a corporation provides its own infrastructure for a LAN, WANs are leased
fromcarriernetworks,suchastelephonecompanies.Fourbasictypesofconnections,
orcircuits,areusedinWANservices:circuit-switched,cell-switched,packet-switched,
anddedicatedconnections.
AwidearrayofWANservicesareavailable,includinganalogdialup,ATM,dedicated
circuits,cable,DSL(digitalsubscriberline)FrameRelay,ISDN,SwitchedMulti-megabit
DataServices(SMDS),andX.25.Here,analogdialupandISDNareexamplesofcircuit-
switchedservices,ATMandSMDSareexamplesofcell-switchedservices,andFrame
RelayandX.25areexamplesofpacket-switchedservices.
Circuit-switchedservicesprovideatemporaryconnectionacrossaphonecircuit.
Thesearetypicallyusedforbackupofprimarycircuitsandfortemporarybootsof
bandwidth. A dedicated circuit is a permanent connection between two sites where
the bandwidth is dedicated. These circuits are common where you have a variety of
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services, such as voice, video, and data, that must traverse the connection and you
are concerned about delay issues with the traffic and guaranteed bandwidth.
Cell-switchedservicescanprovidethesamefeaturesthatdedicatedcircuitsoffer.Their
advantageoverdedicatedcircuitsisthatasingledevicecanconnecttomultipledevices
onthesameinterface.Thedownsideoftheseservicesisthattheyarenotavailableatall
locations,theyaredifficulttosetupandtroubleshoot,andtheequipmentisexpensive
whencomparedtousingdedicatedcircuits.
Packet-switchedservicesaresimilartocell-switchedservices.Whereascell-switched
services switch fixed-length packets, called cells, packet-switched services switch
variable-lengthpackets.Thisfeaturemakesthembettersuitedfordataservices,but
they can nonetheless provide some of the Quality of Service (QoS) features that
cell-switchedservicesprovide.Alloftheseservicetypesarediscussedinmoredepth
in Chapter 15.
Circuit-switched partially or full-meshed network. Cell-
connections, like analog and ISDN switched services, like ATM and SMDS,
are typically used for temporary or can provide a granular level of quality of
backup connections. Dedicated circuits, service (QoS) for an application and are
like leased lines, are used to provide typically used to provide voice and video
guaranteed bandwidth for applications connections. Packet-switched services,
across short distances. Cell-switched like Frame Relay and X.25, provide a more
services and cell-switches services are cost-effective solution than cell-switched
used when you only want to use a single services, but not with the same level of
connection to the WAN, but provide a QoS support.
TwonewerWANservicesthatareverypopularintheU.S.arecableandDSL.DSL
providesspeedsupto2MbpsandcostsmuchlessthanatypicalWANcircuitfrom
thecarrier.Itsupportsbothvoiceandvideoanddoesn’trequireadialupconnection
(it’salwaysenabled).Cableaccessusescoaxialcopperconnections—thesamemedium
usedtoprovidetelevisionbroadcastservices.ItsupportshigherdataratesthanDSL,but
likeDSL,itprovidesafull-timeconnection.However,ithasonemajordrawback:itis
asharedserviceandfunctionsinalogicalbustopology(discussedinChapter2)much
likeEthernet—themorecustomersinanareathatconnectviacable,thelessbandwidth
eachcustomerhas.
Examples of networking devices used in WAN connections include cable and
DSL modems, carrier switches, CSU/DSUs, firewalls, modems, NT1s, and routers.
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Network Types 9
Metropolitan Area Networks
Ametropolitanareanetwork(MAN)isahybridbetweenaLANandaWAN.Likea
WAN,itconnectstwoormoreLANsinthesamegeographicarea.AMAN,forexample,
mightconnecttwodifferentbuildingsorofficesinthesamecity.However,whereasWANs
typicallyprovidelow-tomedium-speedaccess,MANsprovidehigh-speedconnections,
suchasT1(1.544Mbps)andopticalservices.
TheopticalservicesprovidedincludeSONET(theSynchronousOpticalNetwork
standard)andSDH(theSynchronousDigitalHierarchystandard).Withtheseoptical
services,carrierscanprovidehigh-speedservices,includingATMandGigabitEthernet.
Thesetwoopticalservices(coveredinChapter2)providespeedsrangingintothe
hundredsorthousandsofmegabitspersecond(Mbps).Devicesusedtoprovide
connectionsforMANsincludehigh-endrouters,ATMswitches,andopticalswitches.
Storage Area Networks
Storageareanetworks(SANs)provideahigh-speedinfrastructuretomovedatabetween
storagedevicesandfileservers.Astoragedevice,sometimesreferredtoasastorageunit,
includesdiskdrives,diskcontrollers,andanynecessarycabling.Thisinfrastructurecan
bededicatedtojustthesedevicesorcanincludeotherdevices.Typically,fiberchannels
areusedfortheconnections.Afiberchannelisanopticalcablethatconnectsthefile
servers,diskcontrollers,andharddrivesatratesexceeding1gigabitpersecond(Gbps).
Theadvantagesofseparatingthestoragedevicefromthefileservicesaremoreflexibility
andcentralizationofstorage,whicheasesmanagement.
SANsarebecomingverypopularinLANenvironments,andsomeISPsandcarrier
companiesarestartingtooffertheseservicesinMANenvironments.However,SANs
arenotcurrentlybeingusedinWANenvironments,becauseoftheconnectiontypes
andaccessspeedsrequired.
Sinceopticalconnectionsareused,yougainthefollowingadvantagesovernormal
storagetechniques(keepingthedatalocaltotheserver):
■ Performance is fast.
■ Availability is high because of the redundancy features available.
■ Distances can span up to 10 kilometers.
■ Management is easy because of the centralization of data resources.
■ Overhead is low (uses a thin protocol).
The main disadvantage of SANs is their cost. If you are using fiber channels,
youmustbuyspecialdiskcontrollercardsforyourfileserversandbuyaSANstorage
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unit,andyoumustlaydownthenecessaryfiber.Ofcourse,ifyouareusingyourown
networkinfrastructure,youonlyneedtobuyastorageunitandlaydownanynecessary
cabling for it. Plus, if you are concerned about redundancy, your cost will increase
because you’ll need to ensure that your network infrastructure has redundant paths
between your servers and the SAN storage unit(s).
Content Networks
Contentnetworks(CNs)weredevelopedtoeaseusers’accesstoInternetresources.CNs
areawareoflayers4–7oftheOSIReferenceModel(discussedinChapter2)andusethis
informationtomakeintelligentdecisionsabouthowtoobtaintheinformationfortheuser
orusers.CNscomeinthefollowingcategories:contentdistribution,contentrouting,
contentswitching,contentmanagement,contentdelivery,andintelligentnetwork
services,whichincludeQoS,security,multicasting,andvirtualprivatenetworks(VPNs).
Companies deploy basically two types of CNs:
■ Caching downloaded Internet information
■ Distributing Internet traffic loads across multiple servers
Forthefirstitem,CNsareusedtoreducetheamountofbandwidththatyouneed
foryourusers’Internetconnections.Whenusersdownloadcontent,itiscachedona
localserver.Andthenwhenausermakeanotherrequest,thatrequestisfirstchecked
withthelocalservertodetermineifthecontentexiststhere.Ifitdoes,thelocalserver
sends the information to the user, thus providing higher data rates, since the client is
acquiring its information from the LAN instead of having to download it again from
the Internet. If not, the local server will obtain the information from the Internet
resource.Becausemanyitems,especiallyGIFsandJPEGs,areincludedoneverypage
fromawebsite,thisinformationdoesn’thavetoberepeatedlydownloaded.Themain
problem with this solution, however, is that all traffic to and from the network must
go through a CN device, commonly called a proxy server, which can reduce your
throughput.
CNs are also used to reduce the overhead for external users that want to access
internal resources in your network. In the old days of networking, if your web server
wasoverwhelmedwithrequests,youronlysolutionwastoupgradeitsprocessor,
memory,diskdrive,andinterfacecardtolargersizesorfasterspeeds.Andifyou
have ever upgraded a server, you know that this is not always an easy process. With
theintroductionofCNs,youcandistributethetrafficloadfromexternalusers
acrossmultipleinternalservers,thusreducingnetworkcongestiontotheservers
and reducing the resources required to handle the external users’ requests.
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