Cisco Cisco IOS Software Release 12.2(13)ZH

This document describes the third-party G.168 extended echo canceller (EC) used in Cisco gateways 
with Cisco IOS Release 12.2(13)ZH. The extended EC uses the Cisco voice digital signal processor 
(DSP) code base (DSPWare). 

The Enhanced ITU-T G.168 Echo Cancellation feature provides an alternative to the default 
Cisco-proprietary G.165 EC. The new extended EC provides improved performance for trunking 
gateway applications and provides a configurable tail length that supports up to 64 ms of echo 
cancellation. 

The extended EC offers the following improvements over the Cisco default EC:

Complies with the ITU-T G.168 (2000) standard in addition to maintaining support for the old 
ITU-T G.165 standard. 

Increases the configurable tail length from a maximum of 32 ms to a maximum of 64 ms.

Tone detection and echo disabling are performed outside the EC automatically in the DSP firmware.

Cisco IOS software supports the following improvements with the extended EC:

Configuration and reporting of extended echo path capacity

Configuration and reporting of worst-case echo return loss (ERL)

Test mode support for manually freezing, thawing, and clearing the EC h-register

Reporting of statistics for location of the largest reflector

Reporting of the internal state of the EC

This feature provides the following additional benefits:

No changes to platform—Improves platform functionality by updating the EC module through a 
DSPWare upgrade and a Cisco IOS software upgrade

Enabling and disabling of nonlinear processor—Enables and disables nonlinear processor (NLP) 
spectrally matched comfort noise

Echo return loss (ERL) configuration—Can be set to three values: 0 dB, 3 dB, and 6 dB

Expansion of Echo Canceller Capacity—EC capacity is expanded to 64 ms 

 contains specific high-complexity and medium-complexity support listed by platform. For 

hardware support documentation, refer to links provided in the 

.