Core Issue
After a Cisco IOS voice gateway upgrade, IP phones have an echo on both inbound and outbound calls from the PSTN
Resolution
This problem is tracked in Cisco bug ID CSCsd54344.
This defect is fixed in DSPWare version 4.4(18), which is integrated in Cisco IOS® Software Release 12.4(8).
As a workaround, downgrade to DSPWare 4.4.12 or an earlier version which resolves the echo issue, or upgrade to DSPWare 8.4.0, which also has the fix for this bug.
TFTP the file (dsp_c5510_flex.rbf) to the Flash and reload the gateway. Once the gateway reloads, it recognizes the name of the DSP in Flash and upgrades the DSP firmware automatically. No additional configuration is needed. Refer to the Upgrading DSP Firmware section of Managing and Troubleshooting the Voice Feature Card for more information.
Open a case with Cisco Technical Support with the TAC Service Request Tool in order to obtain the DSP filedsp_c5510_flex.rbf.
In order to update the firmware for the DSPs on the NM-HDV2 module, complete these steps:
Save the dsp_c5510_flex.rbf file to the PC.
Copy this file across to the router that has the problem.
Based on the voice card or router type, save the file on the Flash memory with this naming convention:
Voice Card/Platform Required DSP firmware filename on Flash
NM-HD-2VE guido.dsp
NM-HDV2 hdv2.dsp
C28xx dsp_c5510_flex.rbf
C38xx dsp_c5510_flex.rbf
IAD243X dsp_c5510_flex.rbf
VG224 dsp_c5510_flex.rbf
Command: copy tftp:kctsai/dsp_c5510_flex.rbf flash:
Once this file is on the Flash, reload the router.
Note: The same DSPWare on the router Flash is loaded whenever the router is reloaded, even if the Cisco IOS image is upgraded. Remember to remove the .rbf file if bundled DSPWare within Cisco IOS is needed.
Some tracebacks can occur as the router boots. But, this does not seem to affect the operation. Issue theshow voice dsp command when the router is up in order to confirm that the DSP firmware runs.
If an NM-HDV2 module and DSPs are used on the motherboard as well, two files in the Flash are needed for the DSPWare upgrade.
The first file is already on the Flash and must be kept there so that the DSPs on the motherboard are upgraded. Rename that file based on the network module on which it sits.
For the NM-HDV2, make a copy of the dsp_c5510_flex.rbf file and rename the new file hdv2.dsp. Then, load it onto the Flash.
Reload the router, so it upgrades the DSPs on both the motherboard and the NM-HDV2.
Cisco bug ID CSCsb68986 documents the same issue for Cisco IOS gateways that run Cisco IOS Software Release 12.3T, which can experience brief convergence echo at the start of a call when connected to high ERL PSTN loops. There is no known workaround for this issue other than to reduce the PSTN ERL which is not usually under one's control. This issue is fixed in these software releases:
- Cisco IOS Software Release 12.4(3e) and later
- DSP 4.4.24 and later
In order to obtain the appropriate DSPWare version, open a service request with Cisco Technical Support through the TAC Service Request Tool.
Download the relevant Cisco IOS software from Cisco Downloads.
Also, refer to these Cisco TAC Case Collection cases:
- TAC Case Collection Case #K11733387—IP phone user hears an echo of his voice on a call to a PSTN phone
- TAC Case Collection Case #K10011923—How to troubleshoot the echo problems between IP phones and Cisco IOS gateways
