Troubleshooting Voice Quality Issues © 2004 Cisco Systems, Inc. All rights reserved. IPTT v4.05-1 Troubleshooting VoIP Quality Problems. - презентация

1 Troubleshooting Voice Quality Issues © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Troubleshooting VoIP Quality Problems

2 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Troubleshooting VoIP Quality Problems: Objectives Upon completing this lesson, you will be able to: Discuss potential voice quality problems and troubleshoot using the Cisco Recommended methodologies Describe how and when to use the Quality Report Tool List the potential problems regarding Layer 2 Voice Quality using Ciscos Recommended troubleshooting methodology List the potential problems regarding Layer 3 Voice Quality using Ciscos Recommended troubleshooting methodology Describe the usage of Call Admission Control solutions Demonstrate the effect of VAD on bandwidth and List the Cisco IOS commands to reliably transmit DTMF tones

3 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Overview Identifying and Isolating Voice Quality Problems Quality Report Tool for IP Phones Troubleshooting Layer 2 Voice Quality Problems Troubleshooting Layer 3 Voice Quality Problems Additional Considerations Summary Quiz Outline

4 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Troubleshooting VoIP Quality Problems Ensure call connects first Check voice quality next – Adequate bandwidth for codec – Do not exceed Frame Relay CIR – Use fragmentation as needed

5 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v RTCP Call Information Displays RTCP call statistics

6 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Packet Loss Normal Packet Loss X Frame Relay

7 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Jitter Normal Jitter Frame Relay

8 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Latency Normal Latency Frame Relay

9 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Quality Report Tool The Quality Report Tool (QRT) is a voice quality and general problem-reporting tool for Cisco CallManager IP Phones. QRT is a feature that extends to IP Phones as an Microsoft Windows NT service. The Cisco Extended Functions service supports the QRT feature. Make sure that the Cisco Extended Functions service is activated.

10 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Configuring QRT Cisco CallManager 3.3, 4.0 Copy softkey template from the standard user template. Add QRT from Connected and Connected Conference. Modify IP Phone softkey template. Ensure that Extended Services function is activated.

11 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Configuring QRT

12 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Configuring QRT (Cont.)

13 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Identifying Layer 2 Bottlenecks Bandwidth is typically not an issue. Buffer congestion is an issue. Buffer congestion occurs when there is a rate change or if many interfaces are aggregated to a single uplink.

14 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Dat a Threshold 4 Threshold 3 Threshold 2 Threshold 1 Buffer Drop Packets with CoS 6 and 7 CoS 4 and 5 Drop Packets with CoS 2 and 3 Drop Packets with CoS 0 and 1 Incoming Packet Monitoring Performance of Layer 2 Devices

15 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Selecting Layer 2 QoS Tools Port is set to trust-cos Input Scheduling Port untrusted? ISL or 802.1Q? Get CoS from ISL/dot1o Frame enters switch Apply port CoS Port set to trust- ipprec? Port set to trust-dscp? To switching engine YesNo Yes No Port Trust States: trust-cos trust-ipprec trust-dscp untrusted Apply port CoS

16 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Identifying Layer 3 Bottlenecks Normal Packet Loss X Jitter Latency Insufficient WAN bandwidth causes: Buffer overflows Queuing delay Serialization delay Layer 3 Bottleneck Frame Relay

17 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Monitoring Performance of Layer 3 Devices Router#show interfaces random-detect FastEthernet1/0/0 queue size 0 packets output 29692, drops 0 WRED: queue average 0 weight 1/512 Precedence 0: 109 min threshold, 218 max threshold, 1/10 mark weight 1 packets output, drops: 0 random, 0 threshold Precedence 1: 122 min threshold, 218 max threshold, 1/10 mark weight (no traffic) Precedence 2: 135 min threshold, 218 max threshold, 1/10 mark weight packets output, drops: 0 random, 0 threshold Precedence 3: 148 min threshold, 218 max threshold, 1/10 mark weight (no traffic) Precedence 4: 161 min threshold, 218 max threshold, 1/10 mark weight (no traffic) Precedence 5: 174 min threshold, 218 max threshold, 1/10 mark weight (no traffic) Precedence 6: 187 min threshold, 218 max threshold, 1/10 mark weight packets output, drops: 0 random, 0 threshold Precedence 7: 200 min threshold, 218 max threshold, 1/10 mark weight (no traffic)

18 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Selecting Layer 3 QoS Tools WRED 40% 25% 10% Gold Silver Bronze Priority Delivery Guaranteed Bandwidth Best Effort LLQ Cisco 3600 Headquarters PBX Larger Branch Office Cisco 3600 Frag 1500-byte Packet 1500-byte Packets LFI Queue Minimum Threshold Maximum Threshold WAN

19 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Additional Considerations Voice activity detection DTMF relay Frame Relay CIR

20 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v QoS Recommendations CampusBranch Office SRST Router IP WAN Building AccessBuilding DistributionWAN ModuleBranch RouterBranch Switch PSTN Multiple queues 802.1Q/p DSCP Fast link convergence Multiple queues 802.1Q/p DSCP LLQ CBWFQ WRED LFI/FRF.12 cRTP FRTS, dTS DSCP LLQ CBWFQ WRED LFI/FRF.12 cRTP FRTS 802.1Q/p DSCP NBAR Multiple queues 802.1Q/p

21 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Commands show interface show access-lists show class-map show frame-relay fragment show policy-map

22 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Some models of Cisco IP Phones can display RTCP information, which can be useful in troubleshooting voice quality. The main voice quality problems that you face are packet loss, jitter (variable delay), and latency. When troubleshooting voice quality at Layer 2, consider queuing configurations on switches. To combat loss, delays, and jitter at Layer 3, consider queuing, WRED, and LFI mechanisms. Besides protecting voice from data, voice quality also requires that you protect voice from other voice traffic. Other voice quality troubleshooting targets include VAD, DTMF relay, and Frame Relay traffic shaping. Summary

23 © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Lesson Review 1. Which link fragmentation and interleaving tool is useful for VoIPovFR? 2. Which two of the following are valid port-trust states? 3. Which command displays the RED profile (for example, drop thresholds) for each interface on a router? 4. Which three of the following are categories of CAC mechanisms? 5. What is the function of dtmf-relay?

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