Cisco Catalyst 6000 Series Switches

Document ID: 15259

Contents

Introduction
Prerequisites
      Requirements
      Components Used
      Conventions
Step-By-Step
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Related Information

Introduction

This document troubleshoots and alleviates echo where possible on the Catalyst 6608 T1/E1 blade.

Echo within the first couple of seconds of a call is normal and expected behavior as the echo canceller trains. If there is persistent echo after this on a number of calls to different areas/exchanges, you might potentially need to adjust the padding to and from the Public Switched Telephone Network (PSTN).

If you need assistance configuring a 6608 T1/E1 blade, refer to Configuring a Catalyst WS-X6608-T1 Port as a T1 VoIP Gateway with Cisco CallManager 3.0.

Prerequisites

Requirements

There are no specific requirements for this document.

Components Used

This document is not restricted to specific software and hardware versions.

Conventions

For more information on document conventions, refer to the Cisco Technicßal Tips Conventions.

Step-By-Step

Complete these steps:

1. Make a call through the gateway to a destination number that is known to cause echo. While the call is up and audio present (say "check" or "test" repeatedly), issue the show port voice active mod/port command.

   Search for an Echo Return Loss (ERL). This figure needs to be higher than 60 (ERL and ACOM values are displayed as 10x the dB value, so a value of 60 is really 6db), and preferably higher than 120 (12db) for a safer margin of error.

2. On the Gateway Configuration page configure "Audio Signal Adjustment from IP Network" (TX) to -2db as the initial setting. Be sure to click Update, and then reset the port.

3. Make another test call. Perform an audio test and issue the show port voice active mod/port command. Listen to the echo and compare the values.

   Console> show port voice active 3/2
   
   Port 3/2:
   Channel #1:
     Remote IP address                         : 165.34.234.111
     Remote UDP port                           : 124
     Call state                                : Ringing 
     Codec Type                                : G.711
     Coder Type Rate                           : 35243
     Tx duration                               : 438543 sec
     Voice Tx duration                         : 34534 sec
     ACOM Level Current                        : 123213
     ERL Level                                 : 123 dB       
     Fax Transmit Duration                     : 332433
     Hi Water Playout Delay                    : 23004 ms
     Logical If index                          : 4
     Low water playout delay                   : 234 ms 
     Receive delay                             : 23423 ms
     Receive bytes                             : 2342342332423
     Receive packets                           : 23423423402384
     Transmit bytes                            : 23472377
     Transmit packets                          : 94540p

4. If the ERL is low, or echo is still reported, try to change the Audio Signal Adjustment into IP Network (RX) on the Cisco CallManager Gateway port configuration menu to -1db.

5. Perform the ERL/audio test again and adjust the parameters as necessary. Try to alternate between TX and RX padding by –1db increments until the desired result is achieved.

   Note: If you go below –3db for each TX and RX, it raises the possibility of the voice levels being unacceptably low.

   The quality of PSTN connections is unique to each environment. Settings that work for for one customer might possibly not be acceptable in another’s environment.

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Related Information

• Voice Technology Support
• Voice and Unified Communications Product Support
• Recommended Reading: Troubleshooting Cisco IP Telephony
• Technical Support - Cisco Systems