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1© 1999, Cisco Systems, Inc.
Course NumberPresentation_ID
Voice Data Voice Data IntegrationIntegration
Cisco do BrasilCisco do BrasilJonio CavalcantiJonio Cavalcanti
[email protected]@cisco.com
VoIP Network Design
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2Presentation_ID © 1999, Cisco Systems, Inc.
AgendaAgenda
• IntroductionIntroduction
• Codecs
• Voice Over Packets
• Characteristics for VoIP, VoATM and VoFR
• QoS and Signaling for VoIP
• Conclusions
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3Presentation_ID © 1999, Cisco Systems, Inc.
AgendaAgenda
• IntroductionIntroduction
• Codecs
• Voice Over Packets
• Characteristics for VoIP, VoATM and VoFR
• QoS and Signaling for VoIP
• Conclusions
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4Presentation_ID © 1999, Cisco Systems, Inc.
VoCoders (VoCoders (AUDIO CODECSAUDIO CODECS))
• Quality often measured using MOS
• Standards vs Entrepreneurial
• DTMF tones
• Language sensitivity
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5Presentation_ID © 1999, Cisco Systems, Inc.
Voice Quality: Compression Voice Quality: Compression StandardsStandards
Unacceptable Utility Business Toll
PCM
Quality
8
16
24
32
40
48
56
64
0
ADPCM 32(G.723)
LD CELP 16(G.728) LDCELP 16
(G.728)
ADPCM 16(G.726)LPC 4.8
CS-ACELP 8(G.729)
MPMLQ(G.723.1)
Ban
dw
idth
(kb
ps)
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6Presentation_ID © 1999, Cisco Systems, Inc.
AgendaAgenda
• IntroductionIntroduction
• Codecs
• Voice Over Packets
• Characteristics for VoIP, VoATM and VoFR
• QoS and Signaling for VoIP
• Conclusions
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7Presentation_ID © 1999, Cisco Systems, Inc.
Route Replacement Route Replacement
Branch Office
PSTN
Main Office
T1,E1
QoSWAN
(Intranet/Internet)
VV
VV
Telco Switch
PBXPBX
PBXPBX
Voice GWVoiceGW
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8Presentation_ID © 1999, Cisco Systems, Inc.
VoX TransportVoX Transport
PSTN
Branch Office Main Office
Analog/Digital
Fax
Voice GWs
QoSWAN
VV
VV
Telco Switch
PBXPBX
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9Presentation_ID © 1999, Cisco Systems, Inc.
Enterprise Voice VPNEnterprise Voice VPN
Philadelphia
Typical Building
PSTN
Data Center
T1,E1
QoSWAN
(Intranet/Internet)
VV
VV
Telco Switch
PBXPBX PBXPBX
PSTN PSTNVV
PSTNV
Phoenix Charlotte
Call Comes In
BypassPSTN
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10Presentation_ID © 1999, Cisco Systems, Inc.
Dial Plan DesignDial Plan Design
IP QoSWAN
3600A
AS5300
PSTNVV
3600BVV
NXX555-xxxx
1111
NXX556-xxxx
1111
1111
Netmeeting PC
NXX559-xxxx
NXX557-xxxx
1111
10.1.5.0
.4
.10
.2
.3
PBXPBX
7 and 7 digits for Local PSTN71 and 10 digits for Long Distance to PSTN7 digits of “on net” Location
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11Presentation_ID © 1999, Cisco Systems, Inc.
AgendaAgenda
• IntroductionIntroduction
• Codecs
• Voice Over Packets
• Characteristics for VoIP, VoATM and VoFR
• QoS and Signaling for VoIP
• Conclusions
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12Presentation_ID © 1999, Cisco Systems, Inc.
VoFR, VoATM, VoIP QualityVoFR, VoATM, VoIP Quality
Cost ($)
Quality
Unacceptable BusinessQuality
TollQuality
CS-ACELP 8 Kbps (G.729)
Cellular
UtilityQuality
VoATM(8 Kbps)
VoFR
VoIP
VoATM(PCM/AAL1)
InternetInternet IntranetIntranet
PSTNVOICE
VoFR, VoATM, VoIP QualityVoFR, VoATM, VoIP Quality
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13Presentation_ID © 1999, Cisco Systems, Inc.
L3/L2 Transport CharacteristicsL3/L2 Transport Characteristics
• L3—VoIPFlexible—IP is ubiquitous
“Soft” form of QoS
IP/UDP/RTP overhead (RTP compression)
Quickly emerging technology
• L2—VoFR, VoATM“Hard” Qos
Infrastructure can be rigid
Better suited for high volume bulk voice
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14Presentation_ID © 1999, Cisco Systems, Inc.
AgendaAgenda
• IntroductionIntroduction
• Codecs
• Voice Over Packets
• Characteristics for VoIP, VoATM and VoFR
• QoS and Signaling for VoIP
• Conclusions
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15Presentation_ID © 1999, Cisco Systems, Inc.
Voice Transport RequirementsVoice Transport Requirements
• Background noise
• Silence suppression
Comfort noise
• Language sensitivity
• Subjective quality (MOS)
MOS
• Delay and delay variation
• Echo cancellation
Loss
Bandwidth
Delay
VoIP Challenges in the WAN
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16Presentation_ID © 1999, Cisco Systems, Inc.
missin
g p
acket
G.729 vocoder algorithm
VoIP (G.729) Is Tolerant of VoIP (G.729) Is Tolerant of “Occasional” Packet Loss“Occasional” Packet Loss
• The friendly “retransmission” is of no use in the Voice world… late is as good as never
• Complex “concealment strategy” in algorithm interpolates lost packets based on context
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17Presentation_ID © 1999, Cisco Systems, Inc.
How Does Echo Happen?How Does Echo Happen?
Echo is due to a reflection
Impedance mismatch at the 2w-4w hybridis the most common reason for echo
2 Wire Local Loop
Central Office
2w-4wHybrid
ReceiveDirection
TransmitDirection
Rx & TxSuperimposed
Echo is always present and as a problem is a functionof the echo delay, and the magnitude of the echo
Echo is always present and as a problem is a functionof the echo delay, and the magnitude of the echo
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18Presentation_ID © 1999, Cisco Systems, Inc.
Delay—How Much Is Too Much? Delay—How Much Is Too Much?
Cumulative Transmission Path Delay
Time (msec)
0 100 200 300 400
CB ZoneCB Zone
Satellite QualitySatellite Quality
Fax Relay, BroadcastFax Relay, BroadcastHigh QualityHigh Quality
Delay Target
500 600 700 800
ITU’s G.114 Recommendation = 0 – 150msec 1-way delay
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19Presentation_ID © 1999, Cisco Systems, Inc.
Fixed Delay ComponentsFixed Delay Components
• Propagation—six microseconds per kilometer
• Serialization
• ProcessingCoding/compression/decompression/decoding
Packetization
Processing Delay
Propagation Delay
Serialization Delay—Buffer to Serial Link
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20Presentation_ID © 1999, Cisco Systems, Inc.
Fixed Frame Serialization Delay MatrixFixed Frame Serialization Delay Matrix
Frame Size
LinkSpeed
56kbps
64kbps
128kbps
256kbps
512kbps
768kbps
1536kbs
1Byte
143us
125us
62.5us
31us
15.5us
10us
5us
64Bytes
9ms
8ms
4ms
2ms
1ms
640us
320us
18ms
128Bytes
16ms
8ms
4ms
2ms
1.28ms
640us
36ms
256Bytes
32ms
16ms
8ms
4ms
2.56ms
1.28ms
72ms
512Bytes
64ms
32ms
16ms
8ms
5.12ms
2.56ms
144ms
1024Bytes
128ms
64ms
32ms
16ms
10.24ms
5.12ms
1500Bytes
46ms
214ms
187ms
93ms
23ms
15mss
7.5ms
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21Presentation_ID © 1999, Cisco Systems, Inc.
Variable Delay Components Variable Delay Components
• Queuing delay
• Dejitter buffers
• Variable packet sizes
DejitterBuffer
Queuing Delay
Queuing Delay
Queuing Delay
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22Presentation_ID © 1999, Cisco Systems, Inc.
Delay Variation—“Jitter”Delay Variation—“Jitter”
t
t
Sender Transmits
Sink Receives
AA BB CC
AA BB CC
D1 D2 = D1
SenderReceiver
Network
D3 = D2D3 = D2
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23Presentation_ID © 1999, Cisco Systems, Inc.
QoS Networking ToolsQoS Networking Tools
• Congestion Management (WFQ)
• QoS Signaling (IP Prec / RSVP)
• Packet Residency (MLPPP/MTU Size Reduction)
• Bandwidth (RTP Header Compression, Silence Suppression, VAD)
• Generic Traffic Shaping
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24Presentation_ID © 1999, Cisco Systems, Inc.
Presentation
Session
Transport
Network
Link
Physical
G.729(A)/G.723(.1)/G.711
H.323/SIP/SGCP/IPDC
RTP/UDP
IP
MLPPP/FR/ATM AAL1
– – –
Voice over IP ProtocolsVoice over IP Protocols
Constant - Voice Packets ride on UDP/RTPVariable - Several Signaling Methods
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25Presentation_ID © 1999, Cisco Systems, Inc.
ITU H.323 InfrastructureITU H.323 Infrastructure
Intranet
Gatekeeper
Gatewaye
H.323 Terminals
V
- User Interface
- Gateway
- Video Terminal
TelephoneNetwork
H.320(Over ISDN)
H.324(Over POTs)
Speech Only(PSTN)
Proxy
Real-Time Network
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26Presentation_ID © 1999, Cisco Systems, Inc.
AgendaAgenda
• IntroductionIntroduction
• Codecs
• Voice Over Packets
• Characteristics for VoIP, VoATM and VoFR
• QoS and Signaling for VoIP
• Conclusions