© 2006 Cisco Systems, Inc. All rights reserved. CVOICE v5.04-1 Improving and Maintaining Voice Quality Designing for Optimal Voice Quality. - презентация

1 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Improving and Maintaining Voice Quality Designing for Optimal Voice Quality

2 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Outline Overview IP Networking Overview Jitter Delay Acceptable Delay Packet Loss PESQ, MOS, and PSQM Objectives of QoS Using QoS to Improve Voice Quality Recognizing Common Design Faults Cisco AutoQoS Features Summary Lesson Self-Check

3 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Factors Affecting Audio Clarity Fidelity Echo Jitter Delay Sidetone Background noise

4 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Jitter in IP Networks

5 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Sources of Delay

6 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Acceptable Delay: G.114

7 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Effect of Packet Loss

8 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v MOS and PSQM MOS Acronym for mean opinion score Defined in ITU-T Recommendation P.800 Results in subjective measures Scores from 1 (worst) to 5 (best); 4.0 is toll quality PSQM Acronym for Perceptual Speech Quality Measurement Defined in ITU Standard P.861 Automated in-service measurement Scores from 6.5 (worst) to 0 (best)

9 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Perceptual Evaluation of Speech Quality

10 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Voice Quality Measurement Comparison FeatureMOSPSQMPESQ Test methodSubjectiveObjective End-to-end packet loss testInconsistentNoYes End-to-end jitter testInconsistentNoYes

11 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Objectives of QoS QoS has these objectives: Supporting dedicated bandwidth Improving loss characteristics Avoiding and managing network congestion Shaping network traffic Setting traffic priorities across the network

12 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Applying QoS

13 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v What Makes a Design Bad? Ignoring Layer 2 QoS requirements Ignoring other QoS requirements Ignoring bandwidth considerations Simply adding VoIP to an existing IP network

14 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Cisco AutoQoS Features Cisco AutoQoS addresses the five key elements of QoS deployment: Application classification Policy generation Configuration Monitoring and reporting Consistency

15 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Configuring Cisco AutoQoS

16 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Configuring Cisco AutoQoS (Cont.)

17 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Summary The factors that affect audio clarity are fidelity, echo, delay, and jitter. Jitter is a variation in the delay of received packets. End-to-end network delay must be calculated to ensure acceptable quality voice. Recommendation G.114 defines maximum acceptable delay as 150 ms. Packet loss causes conversational gaps. MOS is a subjective method of measuring voice quality, using live testers to determine quality. PSQM is an objective, automated method of measuring voice quality, originally designed for circuit-switched networks. PESQ is an objective, automated method of measuring voice quality and is the preferred method in current VoIP implementations.

18 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v Summary (Cont.) QoS supports dedicated bandwidth, improves loss characteristics, avoids and manages network congestion, shapes network traffic, and sets traffic priorities across the network. Cisco IOS software QoS for voice features can be implemented across the entire network. Ignoring Layer 2 and other QoS requirements and bandwidth considerations and simply adding VoIP to an existing IP network are poor network design elements that contribute to poor QoS. Cisco AutoQoS can be used to simplify the configuration of QoS.

19 © 2006 Cisco Systems, Inc. All rights reserved. CVOICE v