Cisco press cisco voice gateways and gatekeepers aug 2006 ISBN 158705258x

CiscoVoiceGatewaysandGatekeepers
ByDeniseDonohue,DavidMallory,KenSalhoff
...............................................
Publisher:CiscoPress
PubDate:August17,2006
PrintISBN-10:1-58705-258-X
PrintISBN-13:978-1-58705-258-3
Pages:648

TableofContents|Index

CiscoVoiceGatewaysandGatekeepers

UnderstandingandconfiguringGW/GKincomplexVoIPnetworks

DeniseDonohue,CCIE®No.9566
DavidMallory,CCIENo.1933
KenSalhoff,CCIENo.4915

DeploymentsofvoiceoverIP(VoIP)networkscontinueatarapidpace.Voice
gatewaysareanessentialpartofVoIPnetworks,handlingthemanytasks
involvedintranslatingbetweentransmissionformatsandprotocolsandacting
astheinterfacebetweenanIPtelephonynetworkandthePSTNorPBX.
GatekeepersandIP-to-IPgatewayshelpthesenetworksscale.Gatekeepers
providecalladmissioncontrol,callrouting,addressresolution,andbandwidth
managementbetweenH.323endpointsincludingCiscoIOS®voicegateways
andCisco®UnifiedCallManagerclusters.IP-to-IPgatewaysallowVoIPcalls


totraversedisparateIPnetworks.

CiscoVoiceGatewaysandGatekeepersprovidesdetailedsolutionstorealworldproblemsencounteredwhenimplementingaVoIPnetwork.Thispractical
guidehelpsyouunderstandCiscogatewaysandgatekeepersandconfigurethem
properly.Gatewayselection,designissues,featureconfiguration,andsecurity
andhigh-availabilityissuesareallcoveredindepth.Theabundantexamples,
screenshots,configurationsnips,andcasestudiesmakethisatrulypractical
andusefulguideforanyoneinterestedintheproperimplementationof
gatewaysandgatekeepersinaVoIPnetwork.Emphasisisplacedonthe
acceptedbestpracticesandcommonissuesencounteredinreal-world
deployments.

CiscoVoiceGatewaysandGatekeepersisdividedintofourparts.PartI
providesanoverviewofanIPvoicenetwork.PartIIisdedicatedtovoice
gateways,includingdiscussionsofMediaGatewayControlProtocol(MGCP);
H.323;SessionInitiationProtocol(SIP);voicecircuitoptions;connectingtothe
PSTN,PBX,andIPWAN;dialplans;digitmanipulation;routeselection;class
ofrestriction;SurvivableRemoteSiteTelephony(SRST)andMGCPfallback;
digitalsignalprocessor(DSP)resources;andToolCommandLanguaue(Tcl)
scriptsandVoiceXML(VXML).PartIIIaddressesvoicegatekeepers,
includingdetaileddeploymentandconfiguration.PartIVisdedicatedtoIP-toIPgateways.

"Withthisbook,theauthorsprovideanin-depthlookatthebreadthofvoice
gatewayfeaturesandcapabilities,aswellasprovidingvoicegateway
configurationguidance."
ChristinaHattingh,AccessTechnologyGroup,CiscoSystems®

DeniseDonohue,CCIE®No.9566,isadesignengineerwithAT&T.Sheis
responsiblefordesigningandimplementingdataandVoIPnetworksforSBC


andAT&Tcustomers.

DavidL.Mallory,CCIENo.1933,isatechnicaleducationconsultantwith
CiscoSystems,supportingCiscovoicecertifications.Priortothisrole,David
wasasystemsengineersupportingseveralglobalenterprisecustomers.

KenSalhoff,CCIENo.4915,isasystemsengineerwithCiscoSystems.Ken
hasbeenspecializinginvoicetechnologiesatCiscoforthepastsixyears.

UnderstandtheprosandconsofMGCP,H.323,andSIP,howthey
implementcallsignalinganddescribecallflow,andhowtoconfigureeach
protocol
Learnthevariousanaloganddigitalvoicecircuitoptionsusedtoconnecta
VoIPnetworktothePSTN
ConfigureandtroubleshootPSTN,PBX,andIPWANconnections
Buildscalabledialplansandunderstandthedifferenttypesofdialpeers
Understandthevariouswaysgatewayscontrolcalledandcallingphone
numbers
Examinecalladmissioncontrol(CAC)techniques
ConfigureClassofRestrictions(CoR)forbothinboundandoutboundcalls
DeployandtroubleshootSRSTandMGCPfallback
EvaluateDSPconsiderationsandresources
Supportinteractivevoiceresponse(IVR)andadvancedcall-handing
applicationsusingTclscriptsandVXML
Deployandconfigurebasicandadvancedgatekeeperfunctions


ConfigureandtroubleshootIP-to-IPgateways

ThisIPcommunicationsbookispartoftheCiscoPress®Networking
TechnologySeries.IPcommunicationstitlesfromCiscoPresshelpnetworking

professionalsunderstandvoiceandIPtelephonytechnologies,plananddesign
convergednetworks,andimplementnetworksolutionsforincreased
productivity.

Category:CiscoPressIPCommunications
Covers:VoIPgatewaysandgatekeepers

$65.00USA/$81.00CAN


CiscoVoiceGatewaysandGatekeepers
ByDeniseDonohue,DavidMallory,KenSalhoff
...............................................
Publisher:CiscoPress
PubDate:August17,2006
PrintISBN-10:1-58705-258-X
PrintISBN-13:978-1-58705-258-3
Pages:648

TableofContents|Index

Copyright
AbouttheAuthors
AbouttheTechnicalReviewers
Acknowledgments
IconsUsedinThisBook
CommandSyntaxConventions
Foreword

Introduction
HowThisBookIsOrganized
PartI:VoiceGatewaysandGatekeepers
Chapter1.GatewaysandGatekeepers
TheRoleofVoiceGateways
TheRoleofVoiceGatekeepers
TheRoleofIP-to-IPGateways
IntroductiontoVoiceProtocols
CallControlAgents
DeploymentScenarios
CaseStudy:Introduction
ChapterReviewQuestions
PartII:Gateways
Chapter2.MediaGatewayControlProtocol

IntroductiontoMGCP
MGCPOperation
CallFlowwithMGCP
DialPlanConsiderations
ImplementingMGCPGateways
SecuringMGCPGateways
TroubleshootingTools
CaseStudy:ConfiguringanMGCPGateway

ReviewQuestions
Chapter3.H.323
H.323Specifications
H.323NetworkComponents
CallFlow
H.323ProtocolProsandCons
WhentoUseH.323
DialPlanConsiderations
ImplementingH.323Gateways
SecuringH.323Gateways
TroubleshootingTools
CaseStudy:ConfiguringanH.323Gateway
ReviewQuestions
Chapter4.SessionInitiationProtocol
DescriptionofSIP
SIPCallFlow
SIPProsandCons
WhentoUseSIP
DialPlanConsiderations
ImplementingSIPGateways
SecuringSIPGateways
AllowingH.323toSIPConnections
TroubleshootingTools
CaseStudy:ConfiguringSIPBetweenaGatewayandCallManager
5.x

ReviewQuestions
Chapter5.CircuitOptions
CircuitSignaling
AnalogCircuits
DigitalCircuits
ReviewQuestions
Chapter6.ConnectingtothePSTN
PSTNCircuitSelectionOverview
AnalogTrunks
DigitalTrunks
CaseStudy:AddanE1R2ConnectiontotheLeedsGateway
ReviewQuestions
Chapter7.ConnectingtoPBXs
AnalogTrunks
DigitalTrunks
ConfiguringTransparentCommonChannelSignaling
CaseStudy:ImplementingaCiscoVoiceGatewayattheShanghai
Office
ReviewQuestions
Chapter8.ConnectingtoanIPWAN
ApplicationsforConnectingtoanIPWAN
DesignConsiderations
QualityofService
ProvidingFaxandModemServices
Security
CaseStudy:UsingaT1LinkasaTieLine
ReviewQuestions
Chapter9.DialPlans

NumberingPlans
OverlappingNumberingPlans
BuildingaScalableDialPlan
DialPeers
DialPeerMatching

CaseStudy:ConfiguringPSTNAccess
ReviewQuestions
Chapter10.DigitManipulation
BasicDigitManipulation
NumberExpansion
VoiceTranslationRulesandProfiles
ManipulatingCallerID
OrderofOperationinDigitManipulation
TroubleshootingDigitManipulation
CaseStudy
ReviewQuestions
Chapter11.InfluencingPathSelection
HuntGroups
UsingTrunkGroups
Tail-EndHop-Off
CallAdmissionControl

POTS-to-POTSCallRoutingConsiderations
CaseStudy:ImplementingGateway-ControlledRSVP
ReviewQuestions
Chapter12.ConfiguringClassofRestrictions
COROverview
COROperation
ImplementingCOR
AssigningCORListswithSRST
AssigningCORListswithCiscoCallManagerExpress
RestrictingInboundCalls
CaseStudy:ImplementingCORforMiami
ReviewQuestions
Chapter13.SRSTandMGCPGatewayFallback
SRSTOverview
ConfiguringSRST
DialPlanConsiderations
SRSTFeatures




SIPSRST



CallPreservation

SecureSRST
MGCPGatewayFallback

ConfiguringMGCPGatewayFallback
VerifyingandTroubleshootingSRST
VerifyingandTroubleshootingMGCPGatewayFallback
CaseStudy:IntegratingSRSTwithanAnalogVoice-MailSystem
ReviewQuestions
Chapter14.DSPResources
NeedforDSPResources
DeterminingtheDSPResourcesRequired
ConfiguringDSPResources
TranscodingforCallManagerExpress
CaseStudy:AddDSPResourcestotheMiamiGateway
ReviewQuestions
Chapter15.UsingTclScriptsandVoiceXML
TclIVRandVoiceXMLApplicationOverview
SampleApplications
DownloadingTclScriptsfromCisco.com
ConfiguringtheGatewaytoUseaTclScript
ImplementingtheAATclScript
CreatingAudioFiles
RestrictionsandCaveats
CaseStudy:ImplementingACDApplication
ReviewQuestions
PartIII:Gatekeepers
Chapter16.DeployingGatekeepers
GatekeeperFunctionality
GatekeeperSignaling
E.164NumberResolution
CallAdmissionControl

GatekeeperDeploymentModels




GatekeeperswithCallManager
SecuritywithGatekeepers

ReviewQuestions
Chapter17.GatekeeperConfiguration
ConfiguringBasicGatekeeperFunctionality
MultipleGatekeeperConfigurations
ConfiguringDirectoryGatekeepers
TroubleshootingGatekeepers
CallManagerandGatekeepers
GatekeeperRedundancy
ConfiguringResourceAvailabilityIndicator
ConfiguringGatekeeperSecurity
CaseStudy:DeployingGatekeeperstoAssistinMigrationtoVoIP
ReviewQuestions
PartIV:IP-to-IPGateways
Chapter18.CiscoMultiserviceIP-to-IPGateway
IP-to-IPGatewayOverview
CiscoMultiserviceIP-to-IPGateway
BasicConfiguration
IP-to-IPGatewayFeatures
CaseStudy:ProvidingEnterpriseVoIPTrunkingtoVoIPServiceof
theServiceProvider
ReviewQuestions
AppendixA.AnswerstoChapter-EndingReviewQuestions
Chapter1
Chapter2

Chapter3
Chapter4
Chapter5
Chapter6
Chapter7




Chapter8



Chapter9





Chapter10
Chapter11
Chapter12

Chapter13
Chapter14
Chapter15
Chapter16
Chapter17
Chapter18
Index


Copyright
CiscoVoiceGatewaysandGatekeepers
DeniseDonohue,DavidMallory,KenSalhoff
Copyright©2007CiscoSystems,Inc.
Publishedby:
CiscoPress
800East96thStreet
Indianapolis,IN46240USA

Allrightsreserved.Nopartofthisbookmaybereproducedortransmittedinany
formorbyanymeans,electronicormechanical,includingphotocopying,
recording,orbyanyinformationstorageandretrievalsystem,withoutwritten
permissionfromthepublisher,exceptfortheinclusionofbriefquotationsina

review.
PrintedintheUnitedStatesofAmerica1234567890
FirstPrintingAugust2006
LibraryofCongressCataloging-in-PublicationNumber:2005935269

WarningandDisclaimer
ThisbookisdesignedtoprovideinformationaboutconfiguringCiscoroutersto
actasVoiceoverIPgatewaysandgatekeepers.Everyefforthasbeenmadeto
makethisbookascompleteandasaccurateaspossible,butnowarrantyor
fitnessisimplied.
Theinformationisprovidedonan"asis"basis.Theauthors,CiscoPress,and
CiscoSystems,Inc.shallhaveneitherliabilitynorresponsibilitytoanyperson
orentitywithrespecttoanylossordamagesarisingfromtheinformation
containedinthisbookorfromtheuseofthediscsorprogramsthatmay
accompanyit.


Theopinionsexpressedinthisbookbelongtotheauthorandarenotnecessarily
thoseofCiscoSystems,Inc.

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Alltermsmentionedinthisbookthatareknowntobetrademarksorservice
markshavebeenappropriatelycapitalized.CiscoPressorCiscoSystems,Inc.
cannotattesttotheaccuracyofthisinformation.Useofaterminthisbook
shouldnotberegardedasaffectingthevalidityofanytrademarkorservice
mark.

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PrintedintheUSA

Dedications
DeniseDonohue:Thisbookisdedicatedtomyincrediblypatientfamily,
especiallymyhusband,Kevin,whohasdoneagood,ifnotenthusiastic,jobof
cookingdinnersthepastfewmonths.I'dalsoliketodedicatethisbooktoallthe
peoplewhohavebeensogenerousinsharingtheirknowledgewithmeoverthe
years.
DavidMallory:Thisbookisdedicatedtomywife,Tammy,andmychildren,
MelissaandLaura,whosacrificemuchformyendeavors.
KenSalhoff:Thisbookisdedicatedtomywife,Jan,andmychildren,Jeffand
Dani,whohavebeenencouragingandsupportivethroughthisentireprocess.
DuringthemanyhoursI'vespentlockedinthelab,Janhashandledtheadded
familyworkloadwithoutcomplaint,andforthatIwillbeforevergrateful.

AbouttheAuthors
DeniseDonohue,CCIENo.9566,isadesignengineerwithAT&T.Sheis
responsiblefordesigningandimplementingdataandVoIPnetworksforSBC
andAT&Tcustomers.Priortothat,shewasaCiscoinstructorandcourse
directorforGlobalKnowledge.HerCCIEisinRoutingandSwitching.
DavidL.Mallory,CCIENo.1933,isatechnicaleducationconsultantwith
CiscoSystems,Inc.supportingCiscovoicecertifications.Priortothisrole,
Davidwasasystemsengineersupportingseveralglobalenterprisecustomers.
DavidhaspresentedonvoicegatewaysandgatekeepersatNetworkersandhas
achievedfourCCIEcertifications:RoutingandSwitching,WANSwitching,
Security,andVoice.
KenSalhoff,CCIENo.4915,isasystemsengineerwithCiscoSystems,Inc.
KenhasbeenspecializinginvoicetechnologieswithCiscoforthepastsixyears.
Inthesystemsengineeringrole,Kenhassupportedseveralglobalenterprise
customersusingCiscovoicetechnologies.KenhasachievedtwoCCIE
certifications:RoutingandSwitching,andVoice.

ContributingAuthor
JayeshChokshihasworkedinthefieldofnetworkingforabout10yearsandhas
beenwithCiscoSystems,Inc.forthelast6years.Hehasworkedinthefieldof
VoiceoverIPaspartoftheSolutionsEngineeringandTechnicalMarketing
Teamandhelpeddesignanddeploymultiplecustomervoicenetworks.
Currently,heworksasaTechnicalMarketingEngineerandfocusesonCisco
MultiserviceIP-to-IPGatewayproductdevelopmentandcustomerdeployments.


AbouttheTechnicalReviewers
DanelleAuisaproductmanagerintheAccessTechnologyGroupatCisco

Systems.Shedefinesthestrategyandroadmapanddrivesproductrequirements
intheareasofIPcommunications.Shewasinvolvedintheproductmanagement
andmarketingactivitiesfortheintroductionoftheCiscoCallManagerExpress
(CME)andSurvivableRemoteSiteTelephonyproducts.Sheiscurrently
responsibleforIPCommunicationssecurity,thevoicegatewaymoduleportfolio,
andDSPtechnologiesontheCiscoIntegratedServicesRouters.DanelleisacoauthoroftheCiscoIPCommunicationsExpressbook(ISBN158705180X)and
holdsanM.S.inElectricalEngineeringfromUniversityofCalifornia,Berkeley.
ChristinaHattinghisamemberofthetechnicalstaffinthebranchofficeIP
CommunicationsgroupatCiscoSystems.Theproductsinthisgroup,including
theCisco2600,2800,3600,3700,and3800seriesplatforms,weresomeofthe
firstCiscoplatformstoconvergevoiceanddatabyofferingPSTNandPBX
voicegatewayinterfacesandcriticalQoSfeaturesonWANinterfaces,while
morerecentlyintegratingnumerousIPnetworkvoiceservices,callcontrol,and
applicationelementssuchasconferencing/transcodingservices,RSVPAgent,
IP-IPgateway,CiscoCME,andCiscoUEintotherouter-basedplatform.Inthis
role,shehelpsguidedevelopmentprojects,trainsCiscosalesstaffandCisco
resalepartnersonnewrouter-basedvoicetechnologies,andadvisescustomers
onvoicenetworkdeploymentanddesign.
SibrinaShafique,CCIENo.10871,isamemberofthetechnicalmarketingteam
thatworksontheCiscovoicegateways.Sheworkscloselywithengineering
teamstoguidevoice-relatedprojectsandsalesstafftoprovidetrainingand
technicalassistance.Inherpreviousroleasatechnicalsupportengineerhertask
wastoanalyze,configure,andtroubleshootcomplexproductandnetwork
problemsoncustomernetworksonallCiscoVoicegatewaysandtheir
interactionwithPSTN,third-partyPBXsystems.Shehasend-to-end
understandingofvoicenetworksandhasassistedwithlargevoicedeployments.
LinglingZhanghasbeenworkinginCiscoSystemsasProductManagerforfive
years.Theprimaryfocusofherroleistoleaddefinitionanddevelopmentof
VoiceoverIPproductsandservicesintheportfolioofCiscoaccessroutersand
developCiscocompetitivestrategyandpositioninginthelow-endaccess

market.BeforejoiningCisco,LinglingZhangworkedinChinaNetworkWorld


asareporterandeditorfortwoyears.
BrandonTa,CCIENo.2494,isaConsultingSystemsEngineerforthe
EnterpriseEastVoiceGroupatCiscoSystems,Inc.BrandonworkedforCisco
Systems,Inc.fornineyearsandhasbeenfocusingonunifiedcommunicationfor
thelastsixyears.HehasworkedonsomeoflargerIPTelephonydesignsand
networksthatspanfrom16,000tomorethan100,000CiscoIPphones.Beside
theCISSPcertificationandahandfulofothertechnicalcertifications,Brandon
hasfourCCIEsandwasthefirstintheworldtoreceivethreeCCIEsbackin
2000,wherehewasfeaturedinCiscoPacketmagazine.Brandonhaspresented
attheCiscoIPTelecommunicationUserGroup(CIPTUG)conferenceaswellas
theCiscoNetworkersConferenceonUnifiedCommunicationTechnology.


Acknowledgments
Thisbookistheproductofafewauthorsandmanybehind-the-scenesworkers
whodeserverecognition.Ourthanksgotooureditor,BrettBartow,whodidhis
besttokeepusontrackandontime,inspiteofourselves.Thanksalsoto
ChristopherClevelandandDanYoung,ourdevelopmenteditors,forensuring
thatourwordsmadesense.Theeditingandproductionstaffhadtheunenviable
jobofmakingsureallspelling,grammar,punctuation,andillustrationswere
correct,andwearegratefulfortheirwork.
Ourtechnicaleditorsonthisbookdidagreatjobofmakingsurethebookwas
technicallycorrectandsuggestingwaystoimprovethecontent.Thebookwould
nothavebeenasgoodwithoutthem.AbigthankyoutoDanelleAu,Christina
Hattingh,SibrinaShafique,BrandonTa,andLinglingZhang!
DenisewouldliketothanktheAESEngineeringandCallismagroupswithin
AT&Tfortheloanoflabequipment.ThanksalsotoTomPetzoldforhelping

keepthisrelevant.
DavidwouldliketothankthevoiceTECteamfortheirreviewsandsuggestions
andfortheirinsightsoninstructionandcertification.Healsowantstothankhis
manager,DrewRosen,forsupportinghiminthisandallhisotherefforts.
Kenwouldliketothankhismanager,MichaelAaron,forhissupportduringthis
process.


IconsUsedinThisBook
[Viewfullsizeimage]


CommandSyntaxConventions
Theconventionsusedtopresentcommandsyntaxinthisbookarethesame
conventionsusedintheCiscoIOSCommandReference.TheCommand
Referencedescribestheseconventionsasfollows:
Boldfaceindicatescommandsandkeywordsthatyouenterliterallyas
shown.Inactualconfigurationexamplesandoutput(notgeneralcommand
syntax),boldfaceindicatescommandsthatyouinputmanually(suchasa
showcommand).
Italicindicatesargumentsforwhichyousupplyactualvalues.
Verticalbars|separatealternative,mutuallyexclusiveelements.
Squarebrackets[]indicateoptionalelements.
Braces{}indicatearequiredchoice.
Braceswithinbrackets[{}]indicatearequiredchoicewithinanoptional
element.


Foreword
CiscoIOSroutershaveshippedwithvoiceinterfacecardssince1997,andafter

thiscapabilitywasavailablethetermvoicegatewaybecamepartoftheVoIP
vernacular,seeminglyovernight.Thevoiceinterfacesallowedrouterstoprovide
acriticalinterconnectivitylinkbetweenthetraditionaldataIPnetworksandthe
traditionalvoice(PSTN,PBXs,andkeysystems)networks.Withthis
technology,theindustrywidelybuilttollbypassnetworksduringthelate1990s:
EnterprisesconnectedtheirPBXsatdifferentsiteswithVoIP"trunks"insteadof
withTIElinesorthePSTN,andserviceprovidersleveragedIPbackbone
networkstooffercalling-cardservicesandcut-ratelong-distanceand
internationalcalling.
VoIPdidnotfascinatethepopularimaginationofthelikesofJeffPulverof
Voice-on-theNet(VON)andotherindustryobserversuntilend-uservisible
devices,suchasIPphones,andIP-basedapplicationsbroughtthetechnologyto
theforefront.VoicegatewaytechnologyisstillthepalesiblingoftheIP
telephonyworldthatcreatesnobuzz,andyetitisalsotheworkhorseofevery
singleVoIPnetwork.EvenasVoIPendpointsbecomeevermoreprevalentin
businessesandresidences,voicegatewaysstillprovidecriticalinterconnectivity
withbillionsoftraditionalPSTNandPBXvoiceendpoints,withoutwhich
companiescannotoperatetheircommunicationsnetworks.
Althoughtheideaofavoicegatewayisconceptuallysimpleenoughit'sa
demarcationbetweentwonetworksandtranslatestheprotocolsfromone(the
TDMworld)totheother(theIPworld)thetechnologyhasbecomeincreasingly
sophisticatedandthefeaturesmoreintertwinedovertheyears.Choosingthe
"right"voicegatewayandconfiguringthe"right"setoffeaturesforaparticular
networkisnolongerthetaskfortheuninitiated.ThequestionIhearmost
frequentlyiswhethertodeployMGCP,H.323,orSIPgateways.Ciscogateways
areprotocolagnosticandsupportalloftheseprotocolsandseveralvariations
thereof,andtheanswertothequestionposedisnotasimpleone:Theoptimal
networkdesigndependsonalargenumberofconsiderations.Someprotocols
anddesignsarebettersuitedtoparticulartypesofnetworks,partlyowingtothe
architectureoftheprotocolsthemselvesandpartlyduetothefeaturesthathave

beenchosenforimplementationovertheyears.
ACiscoPressbookwithcomprehensivecoveragefocusedentirelyonvoice


gatewaytechnologyandfeatureswasalongtimecoming,andatlastwiththis
book,theauthorsprovideanin-depthlookatthebreadthofvoicegateway
featuresandcapabilities,aswellasprovidingvoicegatewayconfiguration
guidance.ThebookexplainsthemajorVoIPprotocols,MGCP,H.323,andSIP,
theirstructureandoperation,andtheconsiderationstochooseamongthem.It
discussesindetailthePSTNandPBXcircuitconnectiontechnologiesand
choices.Thereareoftenmultipleconnectionchoicesonthecentralofficeor
PBXswitchaswellasonthevoicegatewaysideofthecircuit,andwhichof
thesewouldprovidethefeatures,costpoints,andmanageabilitythatareoptimal
foryournetworkmightnotbeobviousatfirstglance.
Thebookgoesontoprovideinsightsintomanyotherareasofgatewayselection
anddeployment,includingthemyriadchoicesincarryingfaxandmodemtraffic
overIP,dialplanfeaturesanddigitmanipulationtools,calladmissioncontrol
capabilitiestokeepvoicetrafficofftheIPnetworkwhenitdoesnothavethe
qualitylevelstocarryit,areviewofDSPtechnologyandoperation,andan
examinationofIPconnectivityimplicationsandQoSfeaturesrequiredtocarry
voicetrafficwithdecentquality.Laterchaptersinthebookalsoinclude
discussionsonpureIP-orientedtopicssuchasTCLandVXMLapplications
capabilities,conferencemixing,transcoding,gatekeeperfunctionsand
connectivity,andIP-to-IPgateway(sessionbordercontroller)servicesand
features.AllofthesepureVoIPservicesareofferedbythesameplatformsthat
arealsovoicegateways,eventhoughTDMconnectivityisnotanecessary
componentfortheIP-onlyservices.
Thebookalsocoverskeyareasofinterestinanynetwork,includingsecurity
measuresandhighavailability.VoIPnetworksecurityisawidetopicfully
deservingofitsownbook-lengthtreatment,butthisbookprovidesenoughbasic

informationtogetyournetworkdeployed.Itcovershowvoicegatewaytraffic
passesthroughfirewallsandNATdevices,howtoencryptvoicesignalingand
mediatraffictoorfromavoicegateway,aswellasconfiguringclassofservice
restrictionssuchthatcertaincallpatternsareallowedwhileothersareblocked
perthepolicyofyournetwork.Highavailabilityisessentialinallnetworksa
chapterinthisbookisdedicatedtothediscussionofhowgatewaysfailover
whenothernetworkcomponentsareoutofcontact,aswellashowgateway
featuresinteroperatewithIPPhonefailoverfeaturessuchasSRSTtomaintain
dialtoneandPSTNnetworkaccessforyourendusersatalltimes.
Throughoutthebookisacasestudythatsolidifiesthechapterdiscussionsby


providingpractical,hands-onexamplesofhowtheconfigurationofthesystem
implementsthefeatures.This,togetherwiththedetailedchapter-by-chapter
coverageofcrucialgatewaytopics,makethisaninvaluablebookessentialtothe
toolchestofanyonecontemplatingtheimplementationofanewnetwork,
activelydesigninganetwork,orevolvingoroptimizingthefeaturesinan
existingnetwork.
ChristinaHattingh
AccessTechnologyGroup
CiscoSystems,Inc.