1 © 1999, Cisco Systems, Inc. Course Number Presentation_ID Voice Data Integration Cisco do Brasil Jonio Cavalcanti [email protected] VoIP Network Design

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

2Presentation_ID © 1999, Cisco Systems, Inc.

AgendaAgenda

• IntroductionIntroduction

• Codecs

• Voice Over Packets

• Characteristics for VoIP, VoATM and VoFR

• QoS and Signaling for VoIP

• Conclusions


AgendaAgenda


• Codecs




• Conclusions


VoCoders (VoCoders (AUDIO CODECSAUDIO CODECS))

• Quality often measured using MOS

• Standards vs Entrepreneurial

• DTMF tones

• Language sensitivity


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)


AgendaAgenda


• Codecs




• Conclusions


Route Replacement Route Replacement

Branch Office

PSTN

Main Office

T1,E1

QoSWAN

(Intranet/Internet)

VV

VV

Telco Switch

PBXPBX

PBXPBX

Voice GWVoiceGW


VoX TransportVoX Transport

PSTN

Branch Office Main Office

Analog/Digital

Fax

Voice GWs

QoSWAN

VV

VV

Telco Switch

PBXPBX


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


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


AgendaAgenda


• Codecs




• Conclusions


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


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


AgendaAgenda


• Codecs




• Conclusions


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


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


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


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


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


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


Variable Delay Components Variable Delay Components

• Queuing delay

• Dejitter buffers

• Variable packet sizes

DejitterBuffer

Queuing Delay

Queuing Delay

Queuing Delay


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


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


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


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


AgendaAgenda


• Codecs




• Conclusions

Documents

1 © 1999, Cisco Systems, Inc. Course Number Presentation_ID Voice Data Integration Cisco do Brasil Jonio Cavalcanti [email protected] VoIP Network Design