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DescribeCiscoVoIPImplementationsCalculatingBandwidthRequirements
ImpactofVoiceSamplesandPacketSizeonBandwidth
FactorsInfluencingBandwidthFactorDescriptionPacketrateDerivedfrompacketizationperiod(theperiodoverwhichencodedvoicebitsarecollectedforencapsulation)Packetizationsize
(payloadsize)DependsonpacketizationperiodDependsoncodecbandwidth
(bitspersample)IPoverhead
(includingUDPandRTP)DependsontheuseofcRTPData-linkoverheadDependsonprotocol
(differentperlink)Tunnelingoverhead(ifused)Dependsonprotocol(IPsec,GRE,orMPLS)
BandwidthImplicationsofCodecsCodecbandwidthisforvoiceinformationonlyNopacketizationoverheadincludedCodecBandwidthG.71164kbpsG.726r3232kbpsG.726r2424kbpsG.726r1616kbpsG.72816kbpsG.7298kbps
HowthePacketizationPeriodImpacts
VoIPPacketSizeandRateHighpacketizationperiodresultsin:LargerIPpacketsize(addingtothepayload)Lowerpacketrate(reducingtheIPoverhead)
VoIPPacketSizeandPacketRateExamplesCodecand
PacketizationPeriodG.711
20msG.711
30msG.729
20msG.729
40msCodecbandwidth(kbps)646488Packetizationsize(bytes)1602402040IPoverhead
(bytesoIPpacketsize(bytes)2002806080Packetrate
(pps)5033.335025
DataLinkOverhead
DataLinkOverheadIsDifferentperLinkDataLinkProtocolEthernetFrameRelayMLPEthernetTrunk(802.1Q)Overhead[bytes]186622
SecurityandTunnelingOverhead
SecurityandTunnelingOverheadIPpacketscanbesecuredbyIPsec.Additionally,IPpacketsordata-linkframescanbetunneledoveravarietyofprotocols.CharacteristicsofIPsecandtunnelingprotocolsare:Theoriginalframeorpacketisencapsulatedintoanotherprotocol.Theaddedheadersresultinlargerpacketsandhigherbandwidthrequirements.Theextrabandwidthcanbeextremelycriticalforvoicepacketsbecauseofthetransmissionofsmallpacketsata
highrate.
ExtraHeadersinSecurityandTunnelingProtocolsProtocolHeaderSize(bytes)IPsectra
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