Applying Quality of Service in VoIP Networks © 2004 Cisco Systems, Inc. All rights reserved. IPTT v Troubleshooting Echo in a VoIP Network

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Troubleshooting Echo: Objectives Upon completing this lesson, you will be able to: Identify what makes Echo a issue Describe the sources and types of echo List Echo Canceller Characteristics List Echo measuring techniques for different platforms Describe how to adjust levels for solving echo issues

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Outline Overview Defining in an IP Telephony Network Echo Sources and Types of Echo Defining the Echo Canceller Measuring in an IP Telephony Network Echo Adjusting in an IP Telephony Network Echo Summary Quiz

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Where Can Echo Occur? Headquarters Branch B Branch C Cisco CallManager VM/UM Cisco CallManager VM/UM Cisco CallManager VM/UM ? ? ? ? ? What is the probability of Echo? ?? ? ? IP WAN PSTN VM = voice messaging UM = unified messaging

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Echo Is Always Present Echo as a problem is a function of the echo delay and the loudness of the echo.

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Source and Types of Echo Talker Echo (most common) IP Phone PSTN/PBX User PSTN Hybrid Rx Tx Rx

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Source and Types of Echo (Cont.) Listener Echo (less common) IP Phone PSTN/PBX User PSTN Hybrid Rx Tx Rx

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Due to a reflection Impedance mismatch at the two-wire to four-wire hybrid Most common reason for echo Found mostly in tail-end circuits Hybrid Two-Wire Subscriber Loop Two-Wire Subscriber Loop Four-Wire Trunk Echo Two- to Four-Wire Conversion and Echo

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Echo Canceller Characteristics IP Network Sout H(t) ^ y(t) ^ - ACOM ERLE ERL Output attenuation Input gain Echo Cancel Coverage (Tail length) Tail Circuit

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Router / Gateway Cisco CallManager Measuring Echo Using IP Phone Hz Tone Measure Off-Hook PSTN

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Measuring Echo in Cisco IOS (H.323 Gateways) Gateway#sh call active voice - snip - OutSignalLevel=-15 InSignalLevel=-15 ERLLevel=25 - snip - Use the Cisco IOS command show call active voice to look at the input and output levels for your call. The following is a call that echoes back the signal with no attenuation.

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Measuring Echo in Cisco IOS (H.323 Gateways)(Cont.) Gateway#sh call active voice - snip - OutSignalLevel=-16 InSignalLevel=-17 ERLLevel=11 - snip - If you configure 1 dB of attenuation in each direction as follows: The resulting levels are as follows: voice-port 1/1:23 input gain -1 output attenuation 1

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Gateway#sh call active voice - snip - OutSignalLevel=-17 InSignalLevel=-19 ERLLevel=4 -snip - Measuring Echo in Cisco IOS (H.323 Gateways)(Cont.) If you configure 2 dB of attenuation in each direction as follows: The resulting levels are as follows: voice-port 1/1:23 input gain -2 output attenuation 2

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Measuring Echo on the 6608 From the Catalyst software prompt, use the show port voice active / command to see the active calls on that port. The 6608 does not show you input and output levels; however, it does show the ERL and ACOM. Echo tuning is done from Cisco CallManager in the Gateway Configuration page.

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Measuring Echo on the 6608 (Cont.) vdtl-Cat6k-PBX1> (enable) sh port voice active 4/8 Port 4/8 : Channel #23: Remote IP address : Remote UDP Port : ACOM Level Current : 370 Call State : voice Codec Type : G711 ULAW PCM Coder Type Rate : 20 ERL Level : 60 Voice Activity Detection : disabled Echo Cancellation : enabled Fax Transmit Duration (ms) : 0 Hi Water Playout Delay : 65 Low Water Playout Delay : 64 Receive Bytes : Receive Delay : 64 Receive Packets : 1972 Transmit Bytes : Transmit Packets : 1973 Tx Duration (ms) : Voice Tx Duration (ms) : 37990

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Important Considerations Be sure to check the levels going into and out of Cisco Unity or other voic system when you are done tuning for echo.

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v T1/E1 (Cisco CallManager 4.0(1) MGCP voice-port 1/1:23 input gain -3 output attenuation 3 echo-cancel coverage 32 echo-cancel suppression 5 Cisco IOS H.323 Adjusting Levels on Various Gateways

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Eliminating Echo So, how do you get rid of echo? You need to ensure that you give the echo canceller enough information to distinguish between echo and normal conversation. The only parameters you have control over are: Input level (Input gain) Output level (Output attenuation) Minimum ERL Echo canceller coverage Echo suppressor (Cisco IOS Release 12.2[11]T) for convergence issues

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Summary The most common type of echo is talker echo. Identify the source and type of echo. Reproduce the echo whenever possible. Isolate where echo is not coming from. Trace the call flow to the source of echo. Eliminate and or reduce the echo by applying basic port tuning techniques.

© 2004 Cisco Systems, Inc. All rights reserved. IPTT v Lesson Review: 1. Which is the most common type of echo in a VOIP network? 2. When applying an input gain change to a voice- port, you must do what to apply the change? 3. _______ echo occurs when a talker's speech energy, transmitted down the primary signal path, is coupled into the receive path from the far end? 4._______ echo is generally caused by the 2-wire and 4-wire 'hybrid' transformers? 5. The source of echo is generally located at: