Cisco - Deploying Voice over ATM or FR Networks 403

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© 1999, Cisco Systems, Inc.

Deploying Voice Over ATM or FR Networks Session 403

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Objectives • Understand the voice quality factors in an integrated data/voice network • Describe integrated data/voice network transport mechanisms • Understand the engineering requirements in data/voice networks to meet voice quality requirements • Know where to look for the “Gremlins” in integrated data/voice networks 403 0916_04F9_c3

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© 1999, Cisco Systems, Inc.

Agenda

• Establishing Target Parameters for Quality • Network Technology Trade-Offs • Voice Over Frame Relay Network Design • Voice Over ATM Network Design 403 0916_04F9_c3

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Establishing Target Parameters

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Voice Quality Factors

• Mean opinion score • Coding • Compression • Delay

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Mean Opinion Score Source

Channel Simulation

Impairment Codec “X”

1 2 3 4 5

“Nowadays—a Chicken Leg Is a Rare Dish” Rating

Speech Quality

Level of Distortion

5

Excellent

Imperceptible

4

Good

Just Perceptible—Not Annoying

3

Fair

Perceptible—Slightly Annoying

2

Poor

Annoying but Not Objectionable

1

Unsatisfactory

Very Annoying—Objectionable

1 2 3 4 5

MOS of 4.2 = Toll Quality 403 0916_04F9_c3

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© 1999, Cisco Systems, Inc.

Voice Quality Guidelines MOS Score

Delay (Msec)

Bit Rate (Kbps)

PCM (G.711)

4.4

0.75

64

ADPCM (G.726)

4.1

1

32–24–16

3.65

3–5

16

CS-ACELP (G.729)

3.9

15

8

CS-ACELP (G.729a)

3.65

15

8

3.8

30

6.3–5.3

Compression Method

LD-CELP (G.728)

MPMLQ or ACELP (G.723.1)

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Voice Delay Guidelines One Way Delay (Msec)

Description

0– 150

Acceptable for Most User Applications

150– 150 – 400

Acceptable Provided that Administrations Are Aware of the Transmission Time Impact On the Transmission Quality of User Applications

400 +

Unacceptable for General Network Planning Purposes—However—It Is Recognized that in Some Exceptional Cases this Limit Will Be Exceeded

ITU’s G.114 Recommendation 403 0916_04F9_c3

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Fixed Delay Components Propagation Delay Serialization Delay— Buffer to Serial Link Processing Delay

Munich

1MS 30MS Frankfurt Los Angeles

• Propagation—six microseconds per kilometer • Serialization • Processing Coding/compression/decompression Packetization 403 0916_04F9_c3

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Variable Delay Components Queuing Delay

Queuing Delay

Queuing Delay

Packets

Packets

Packets

Dejitter Delay

• Dejitter buffers • Queuing delay • Variable packet sizes 403 0916_04F9_c3

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Calculate Delay Budget Coder Queuing Delay Delay 30 ms 20 ms

Example

Dejitter Buffer 40 ms

40 ms Network Delay Serialization Delay 3 ms Fixed Delay Propagation Delay Coder Delay G.729 (15 Msec Per 10 Bytes) Packetization Delay—Included in Coder Delay Queuing Delay 64 Kbps Trunk Serialization Delay 64 Kbps Trunk Network Delay (Public Frame Relay Network) Dejitter Buffer Total 403 0916_04F9_c3

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Variable Delay

30 Msec 20 Msec 3 Msec 40 Msec 40 Msec 113 Msec 20 Msec 12

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Delay—How Much Is Too Much? Cumulative Transmission Path Delay CB Zone Satellite Quality High Quality 0

100

Fax Relay, Broadcast 200

300

400

500

600

700

800

Time (msec) Delay Target

ITU’s G.114 Recommendation = 0 – 150msec 1-way delay

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Target Parameters

• MOS—Business/toll quality • Coding—G.729, G.711 • Compression—8k, 64k • Delay—Calculate network

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Network Technology Trade-Offs

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Technology Trade-Offs

• Frame vs cell • Mesh vs star • Transport vs translate

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TDM vs Frame vs Cell TDM

Frame/Packet

Cell

• TDM—Constant delay, wasted bandwidth • Frame/packet—Variable delay, highly efficient • Cell—Improved delay, less efficient 403 0916_04F9_c3

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Packet Efficiency

Frame/Packet

OH

Payload

OH

4 Bytes

1488 Bytes

4 Bytes

Payload = 1488 OH Cell 5 Bytes

Overhead = 8

Efficiency = 99.5%

Payload 48 Bytes

Payload = 48

Overhead = 5

Efficiency = 89.6%

• Small vs large packet sizes • Fixed vs variable sized packets 403 0916_04F9_c3

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Voice Payload Options

10 ms of voice

10 ms of voice

10 ms of voice

Original Voice Information

• Small Payload crc

Low Delay High Overhead High PPS High CPU Load

10 ms of voice crc

3 Small Frames

hdr

10 ms of voice

hdr

crc 10 ms of voice

hdr

• Large Payload crc

High Delay Low Overhead Low PPS Low CPU Load 403 0916_04F9_c3

10 ms of voice

10 ms of voice

10 ms of voice

hdr

1 Large Frame

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© 1999, Cisco Systems, Inc.

Network Design Options Full Mesh of PVCs

Voice PVCs Go to One Central Site

Site D

Site C

Site D

Site C

Site A

Site B

Site A

Site B

• Separate voice and data PVCs—Maximizes quality of service • Combine voice and data on one PVC—Minimizes recurring costs • Or use some combination 403 0916_04F9_c3

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Transport vs Translate Model Transport

Translate

PBX2

PBX1

PBX2

PBX4

PBX1

PBX3

PBX3

PBX4

Network Understands PBX Signaling

• ATM • Frame Relay • Router-based backbone—such as TCP/IP • Or a mixture of the above 403 0916_04F9_c3

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Design Trade-Offs

• TDM, frame, cell-efficiency, delay, cost • Mesh vs star—Performance vs cost • Transport vs translate—Signaling

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Voice Over Frame Relay

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Voice Over Frame Relay Network Design

• A brief tour of FRF.11 • Why FRF.12? • Network design considerations • Bandwidth calculations

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Data Over Frame Relay Network VoFR Service User

Data User

Data User

FRF.3.1 Multiprotocol Encapsulation

FRF.3.1 Multiprotocol Encapsulation

Frame Relay Data Link Connection 17

Frame Relay Data Link Connection N

VoFR Service SubSubSubChannel Channel Channel 1 2 3 (Voice) (Voice) (Data)

2500

Frame Relay Carrier Network

7200

SubChannel N

Voice/Data Sub-Channel Multiplexing

Central Site

Frame Relay Data Link Connection 16

7200

7200

Frame Relay Physical Interface

High-Speed Access Port at Central Sites (T1/E1)

2500

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2500 Branch Sites

2500

2500

Low-Speed Access Port at Branch Sites (64Kbps CIR)

25

© 1999, Cisco Systems, Inc.

Data/Voice Over Frame Relay VoFR Service User

Data User

Data User

FRF.3.1 Multiprotocol Encapsulation

FRF.3.1 Multiprotocol Encapsulation

Frame Relay Data Link Connection 17

Frame Relay Data Link Connection N

VoFR Service

3600

2600

V 7200

Frame Relay Carrier Network V

SubSubSubChannel Channel Channel 1 2 3 (Voice) (Voice) (Data)

Voice/Data Sub-Channel Multiplexing

3600 V

7200

PVC Carrying Voice

Frame Relay Data Link Connection 16

7200 Central Site

Frame Relay PVC (Bc