Contents

• Configuring Echo Cancellation
• Finding Feature Information
• Information About Echo Cancellation
• Voice Call Transmit and Receive Paths
• Echo Cancellation
• Echo Canceller Operation
• Echo Canceller Components
• Echo Canceller Coverage
• ITU-T Echo Cancellation History
• Extended G.168 Echo Canceller Features
• Extended EC Comparison
• Extended Echo Canceller Support by Platform
• Extended G.168 Echo Canceller
• How to Configure the Extended G.168 Echo Canceller
• Restrictions for G.168 Extended Echo Canceller
• Changing Echo Cancellers on Digital Voice Ports
• Enabling the Extended G.168 EC in Cisco IOS Release 12.2(13)T
• Enabling the Extended G.168 EC in Cisco IOS Release 12.2(13)ZH
• Configuring the Extended G.168 EC on the Cisco AS5300
• Modifying Echo Cancellation Default Settings
• Configuration Examples for Extended G.168 Echo Cancellation
• Enabling the Extended EC on the Cisco 1700 Series and Cisco ICS 7750 Example
• Enabling the Extended EC Prior to Cisco IOS Release 12.3(4)XD Example
• Enabling the Extended EC on the Cisco 7200 and Cisco 7500 Series Example
• Enabling the Extended Echo Canceller on the Cisco AS5300 Example
• Adjusting the Echo Canceller Size Example
• Worst-Case Echo Return Loss Example

Configuring Echo Cancellation

---

Echo cancellation is a key function in packet voice. Much of the perceived quality of the connection depends on the performance of the echo canceller. The G.168 extended echo cancellation (EC) provides an alternative to the proprietary Cisco G.165 EC with improved performance for trunking gateway applications.

The following sections provide configuration information for echo cancellation:

• Finding Feature Information
• Information About Echo Cancellation
• How to Configure the Extended G.168 Echo Canceller
• Restrictions for G.168 Extended Echo Canceller
• Configuration Examples for Extended G.168 Echo Cancellation

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest caveats and feature information, see Bug Search Tool and the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the feature information table at the end of this module.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/​go/​cfn. An account on Cisco.com is not required.

Information About Echo Cancellation

• Voice Call Transmit and Receive Paths
• Echo Cancellation
• Echo Canceller Operation
• Echo Canceller Components
• Echo Canceller Coverage
• ITU-T Echo Cancellation History
• Extended G.168 Echo Canceller Features
• Extended EC Comparison
• Extended Echo Canceller Support by Platform
• Extended G.168 Echo Canceller

Voice Call Transmit and Receive Paths

Every voice conversation has at least two participants. From the perspective of each participant, there are two voice paths in every call:

• Transmit path (also called the send or Tx path)--The transmit path is created when a person speaks. The sound is transmitted from the mouth of the speaker to the ear of the listener.
• Receive path (also called the return or Rx path)--The receive path is created when a person hears the conversation. The sound is received by the ear of the listener from the mouth of the speaker.

The figure below shows a simple voice call between caller A and caller B. The top line represents the Tx path for caller A, which becomes the Rx path for caller B. The bottom line represents the Tx path for caller B, which becomes the Rx path for caller A.

Figure 1. Transmit and Receive Paths in a Voice Network

Echo Cancellation

Echo is the sound of your own voice reverberating in the telephone receiver while you are talking. When timed properly, echo is not a problem in the conversation; however, if the echo interval exceeds approximately 25 milliseconds (ms), it can be distracting to the speaker. In the traditional telephony network, echo is generally caused by an impedance mismatch when the four-wire network is converted to the two-wire local loop. Echo is controlled by echo cancellers (ECs).

A packet voice gateway, which operates between a digital packet network and the PSTN, can include both digital (time division multiplexing [TDM]) and analog links. The analog circuit is known as the tail circuit. It forms the tail or termination of the call from the perspective of the person experiencing the echo. The tail circuit is everything connected to the PSTN side of a packet voice gateway--all the switches, multiplexers, cabling, and PBXs between the voice gateway and the telephone.

The figure below shows a common voice network where echo cancellation might be used.

Figure 2. Echo Cancellation Network

An echo canceller reduces the level of echoes that leak from the Rx path (from the gateway out into the tail circuit) into the Tx path (from the tail circuit into the gateway). From the perspective of the echo canceller in a voice gateway, the Rx signal is a voice coming across the network from another location. The Tx signal is a mixture of the voice call in the other location and the echo of the original voice, which comes from the tail circuit on the initiating end and is sent to the receiving end.

Echo cancellers face into the PSTN tail circuit. They eliminate echoes in the tail circuit on its side of the network.The echo canceller in the originating gateway looks out into the tail circuit and is responsible for eliminating the echo signal from the initiation Tx signal and allowing a voice call to go through unimpeded. By design, ECs are limited by the total amount of time they wait for the reflected speech to be received, which is known as an echo tail. The echo tail is normally 32 ms.

Note	Delay and jitter in the WAN do not affect the operation of the echo canceller because the tail circuit, where the echo canceller operates, is static.

Echo cancellation is implemented in digital signal processor (DSP) firmware (DSPWare) on Cisco voice gateways and is independent of other functions implemented in the DSP (the DSP protocol and compression algorithm). In voice packet-based networks, ECs are built into the low-bit-rate codecs and are operated on each DSP.

The figure below shows a typical DSP channel configured for voice processing.

Figure 3. DSP Channel Configured for Voice Processing

Echo Canceller Operation

An echo canceller removes the echo portion of the signal coming out of the tail circuit and headed into the WAN. It does so by learning the electrical characteristics of the tail circuit and forming its own model of the tail circuit in its memory, and creating an estimated echo signal based on the current and past Rx signal. It subtracts the estimated echo from the actual Tx signal coming out of the tail circuit. The quality of the estimation is continuously improved by monitoring the estimation error.

Following are descriptions of the primary measurements of relative signal levels used by echo cancellers. They are all expressed in decibels (dB).

• Echo return loss (ERL)--Reduction in the echo level produced by the tail circuit without the use of an echo canceller. If an Rx speech signal enters the tail circuit from the network at a level of X dB, the echo coming back from the tail circuit into the echo canceller is X less ERL.
• Echo return loss enhancement (ERLE)--Additional reduction in echo level accomplished by the echo canceller. An echo canceller is not a perfect device; the best it can do is attenuate the level of the returning echo. ERLE is a measure of this echo attenuation. It is the difference between the echo level arriving from the tail circuit at the echo canceller and the level of the signal leaving the echo canceller.
• Acombined (ACOM)--Total ERL seen across the terminals of the echo canceller. ACOM is the sum of ERL + ERLE, or the total ERL seen by the network.

For more information about the echo canceller, refer to the "Echo Analysis for Voice over IP" document.

Echo Canceller Components

A typical echo canceller includes two components: convolution processor (CP) and a nonlinear processor (NLP).

Convolution Processor

The CP first stage captures and stores the outgoing signal toward the far-end hybrid. The CP then switches to monitoring mode and, when the echo signal returns, estimates the level of the incoming echo signal and subtracts the attenuated original voice signal from the echo signal.

The time required to adjust the level of attenuation needed in the original signal is called the convergence time. Because the convergence process requires that the voice signal be stored in memory, the EC has limited coverage of tail circuit delay, normally 64, 96, and up to 128 ms. After convergence, the CP provides about 18 dB of ERLE. Because a typical analog phone circuit provides at least 12 dB of ERL (that is, the echo path loss between the echo canceller and the far-end hybrid), the expected permanent ERL of the converged echo canceller is about 30 dB or greater.

Nonlinear Processor

In single-talk mode, that is, when one person is talking and the other is silent, the NLP replaces the residual echo at the output of the echo canceller with comfort noise based on the actual background noise of the voice path. The background noise normally changes over the course of a phone conversation, so the NLP must adapt over time. The NLP provides an additional loss of at least 25 dB when activated. In double-talk mode, the NLP must be deactivated because it would create a one-way voice effect by adding 25 to 30 dB of loss in only one direction.

To completely eliminate the perception of echo, the talker echo loudness rating (TELR) should be greater than 65 dB in all situations. To reflect this reality, ITU-T standard G.168 requires an ERL equal to or greater than 55 dB. Segmentation local reference (SLR), receive loudness rating (RLR), and cell loss ratio (CLR) along the echo path should allow another 10 dB to meet the expected TELR. CP, NLP and loudness ratings (LRs) must be optimized to make sure that echo is canceled effectively.

Echo Canceller Coverage

Echo canceller coverage (also known as tail coverage or tail length) is the length of time that the echo canceller stores its approximation of an echo in memory. It is the maximum echo delay that an echo canceller is able to eliminate.

The echo canceller faces into a static tail circuit with input and an output. If a word enters a tail circuit, the echo is a series of delayed and attenuated versions of that word, depending on the number of echo sources and the delays associated with them. After a certain period of time, no signal comes out. This time period is known as the ringing time of the tail circuit--the time required for all of the ripples to disperse. To fully eliminate all echoes, the coverage of the echo canceller must be as long as the ringing time of the tail circuit.

ITU-T Echo Cancellation History

ITU-T standard G.164 defines the performance of echo suppressors, which are the predecessors of echo cancellation technology. G.164 also defines the disabling of echo suppressors in the presence of 2100 Hz tones (which precede low bit rate modems).

ITU-T standard G.165 defines echo cancellation and provides a number of objective tests that ensure a minimum level of performance. These tests check convergence speed of the echo canceller, stability of the echo canceller filter, performance of the nonlinear processor, and a limited amount of double talk testing. The signal used to perform these tests is white noise. Additionally, G.165 defines the disabling of echo cancellers in the presence of 2100 Hz signals with periodic phase reversals in order to support echo cancelling modem technology (V.34, for example), which does not work if line echo cancellation is performed in the connection.

ITU-T standard G.168 allows more rigorous testing and satisfies more testing requirements. White noise is replaced with a pseudospeech signal for the convergence tests. Most echo cancellation algorithms use a least mean square (LMS) algorithm to adapt the echo cancellation filter. LMS works best with random signals, and slows down with more correlated signals such as speech. Using the pseudospeech signal in testing provides a more realistic portrayal of the echo cancellers performance in real use.

In Cisco IOS Release 12.3(4)XD and later releases, the G.168 EC is the default and you can no longer select the Cisco G.165 EC on any supported platform except the Cisco AS5300. The Cisco AS5300 still supports the Cisco G.165 EC and the extended G.168 EC. provides a summary of the Extended ITU-T G.168 Echo Cancellation feature availability in Cisco IOS releases.

Table 1 Feature History for Extended ITU-T G.168 Echo Cancellation

Release	Modification
12.2(13)T	This feature was introduced.
12.2(13)ZH	The extended G.168 EC became the default on the Cisco 1700 series and the Cisco ICS 7750.
12.2(15)ZJ	The extended G.168 EC became the default on the Cisco 2600 series, Cisco 3600 series, Cisco 3700 series. Note    The extended G.168 EC is not supported on the High-Density Analog Network Modules (NM-HDA) and Asynchronous Interface Module (AIM)-Voice modules on the Cisco 2600 series in this release.
12.3(1)	The extended G.168 EC became the default on the Cisco IAD2420, Cisco MC3810, and Cisco VG200.
12.3(4)T	The extended G.168 EC became the default on the Cisco 7200 series and Cisco Catalyst 4000 AGM.
12.3(4)XD	The G.168 extended EC became the only EC on all voice packet platforms that support the extended G.168 EC; the Cisco G.165 EC is no longer a selectable option. Note    The Cisco AS5300 still supported choosing between the Cisco G.165 EC and the extended G.168 EC.
12.3(3)	The G.148 extended EC was configurable with no codec restriction on the Cisco AS5300.
12.3(8)XY	The G.168 extended EC was supported for the WS-SVC-CMM-6T1, WS-SVC-CMM-6E1, and WS-SVC-CMM-24FXS port adapters on the Cisco Communication Media Module (WS-SVC-CMM).
12.3(9)	The extended G.168 EC was supported for the NM-HDA and AIM-Voice modules on the Cisco 2600 series.
12.3(11)T	The dual-filter G.168 echo canceller capability was added to NextPort SPE firmware (SPEware) version 10.2.2 and later versions with Cisco IOS Release 12.3(11)T and later releases. See the chapter "NextPort-Based Voice Tuning and Echo Cancellation".
12.4(20)T	Software-configurable echo cancel coverage was extended to 80, 96, 112, and 128 ms. The default parameter is 128 ms.

Extended G.168 Echo Canceller Features

• Configuration and reporting of extended echo path capacity and worst-case ERL
• Test mode support for manually freezing, thawing, and clearing the EC h-register
• Reporting of statistics for location of the largest reflector and the internal state of the EC
• 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 NLP spectrally matched comfort noise
• ERL configuration--Can be set to three values: 0 dB, 3 dB, and 6 dB
• Expansion of EC capacity--EC capacity is expanded to 64 ms (128 ms in Release 12.4(20)T or later)

Extended EC Comparison

The table below contains comparison information for G.165 and G.168 echo cancellation.

Table 2 Echo Canceller Comparison

Feature	G.165 EC	G.168 EC
Tail Coverage	Up to 32 ms	Up to 64 ms (128 ms in Release 12.4(20)T or later
Minimum ERL	Greater than or equal to 6 dB	Configurable to greater than or equal to 0 dB, 3 dB, or 6 dB
Echo Suppression	Up to 10 seconds	Not required because of faster convergence

Extended Echo Canceller Support by Platform

The table below lists the support for the extended G.168 EC by platform, network module, high-complexity and medium-complexity codecs, and minimum Cisco IOS release.

Table 3 Extended Echo Canceller Algorithm Coverage by Platform

Platform	Network Module	High Complexity Codec	Medium Complexity Codec	Comments
		Analog	Digital	Analog	Digital
Cisco 1700 series	--	12.2(8)YN 12.2(13)T	12.2(8)YN 12.2(13)T	12.2(8)YN 12.3(2)T	12.2(8)YN 12.3(2)T	Flexi6 support in Cisco IOS Release 12.2(8)YN.
Cisco 2600 series Cisco 2600XM Cisco 3600 series Cisco 3700 series Cisco VG200	NM-HDV (C549)	--	12.2(13)T	--	12.2(13)T	Full support.
Cisco 2600 series Cisco 2691 Cisco 3600 series Cisco 3700 series Cisco VG200	NM-1V, NM-2V (C542)	--	--	--	--	Not supported.
Cisco 2600XM Cisco 2691 Cisco 3640 Cisco 3660 Cisco 3700 series	NM-HDxx	12.3(4)XD	12.3(4)XD	12.3(4)XD	12.3(4)XD	--
Cisco 2600XM Cisco 2691 Cisco 3640 Cisco 3660 Cisco 3700 series	AIM-Voice (C5421), AIM-Voice-30 (C542)	--	12.2(15)ZJ 12.3(4)T	--	12.2(15)ZJ 12.3(4)T	AIM.
Cisco 2600XM Cisco 2691 Cisco 3640 Cisco 3660 Cisco 3700 series	NM-HDA (C5421)	12.2(15)ZJ 12.3(4)T	--	12.2(15)ZJ, 12.3(4)T	12.2(15)ZJ 12.3(4)T	NM-HDA. Note    G.728 high complexity is not supported.
Cisco 2600 series	NM-HDA (C5421)	12.3(9)	--	12.3(9)	--	--
Cisco 2600 series	AIM-Voice (C5421)	--	12.3(9)	--	12.3(9)	--
Cisco 7200 series	PA-VXx-2TE1+ and PA-MCX-nTE1	--	12.2(13)T	--	12.2(13)T	PA-MCX-nTE1 port adapters do not have their own DSPs, so they use the DSPs of PA-VXx-2TE1+ port adapters.
Cisco 7500 series	--	--	12.2(13)T	--	--	No medium complexity.
Cisco 7600 series	Communiction Media Module (WS-SVC-CMM) with one of the following port adapters: WS-SVC-CMM-6T1 WS-SVC-CMM-6E1	--	12.3(8)XY 12.3(14)T	--	--	--
	WS-SVC-CMM-24FXS	12.3(8)XY 12.3(14)T	--	--	--	--
Cisco AS5300	--	--	12.2(13)T (restricted) 12.3(3) (unrestricted)	--	--	1-channel DSP on C549 with extended EC, any codec (unrestricted).
Cisco AS5350 Cisco AS5400 Cisco AS5850	NextPort DFC modules: DFC60 DFC108 1 CT3_UPC 216 UPC324	--	Digital - 12.3(11)T	--	12.3(11)T	See the "NextPort-Based Voice Tuning and Echo Cancellation" chapter in this guide.
Cisco Catalyst 4000	AGM	12.3(4)T	--	--	12.3(4)T	High-complexity analog and medium-complexity digital is planned.
Cisco Catalyst 6000	Cisco 6624	A002040- 00002	--	A002040- 00002	--	--
	Cisco 6608	--	A004040- 00002	--	A004040- 00002	--
Cisco Catalyst 6500 series	Communiction Media Module (WS-SVC-CMM) with one of the following port adapters: WS-SVC-CMM-6T1 WS-SVC-CMM-6E1	--	12.3(8)XY 12.3(14)T	--	--	--
	WS-SVC-CMM-24FXS	12.3(8)XY 12.3(14)T	--	--	--	--
Cisco IAD2420	--	12.2(13)T	12.2(13)T	12.3(1) mainline	12.3(1) mainline	--
Cisco IAD243x	VIC2-4FXO onboard T1	12.3(4)XD	12.3(4)XD	12.3(4)XD	12.3(4)XD	--
Cisco ICS 7750	--	12.2(13)T	12.2(13)T	12.2(13)T	12.2(13)T	Flexi6 support.
Cisco MC3810	HCM 549	12.2(13)T	12.2(13)T	12.3(1) mainline	12.3(1) mainline	--

Extended G.168 Echo Canceller

The Extended ITU-T standard G.168 Echo Cancellation feature provides an alternative to the default proprietary Cisco G.165 EC. Beginning in Release 12.4(20)T, the extended EC provides improved performance for trunking gateway applications and provides a configurable tail length that supports up to 128 ms of echo cancellation. The G.165 EC is not configurable in Cisco IOS Release 12.3(4)XD and later releases, except on the Cisco AS5300.

Note

Extended echo cancellation is configured differently depending on the version of Cisco IOS software that you are using. If you are using Cisco IOS Release 12.3(4)XD or a later release, you do not have to use any Cisco IOS commands to enable the Extended ITU-T standard G.168 Echo Cancellation feature because the extended G.168 EC is the only available echo canceller. You have the option of disabling the extended EC, but it is highly recommended that you leave it enabled.

To configure the NextPort dual-filter G.168 echo canceller, see the "NextPort-Based Voice Tuning and Echo Cancellation" chapter in this guide.

The table below lists the Cisco IOS commands that are used for selecting the extended G.168 EC based on your platform and Cisco IOS release.

Table 4 Cisco IOS Commands for Selecting Extended E.168 EC by Platform and Cisco IOS Release

Cisco IOS Release	Cisco IOS Command
Cisco 1700 Series and Cisco ICS 7750
12.2(13)T	Router(config)# voice echo-canceller extended
12.2(13)ZH 12.2(15)ZJ 12.3(1)	Router(voice-card)# codec complexity medium
12.3(4)T and later	No configuration necessary. G.168 EC enabled by default.
Cisco 2600 Series, Cisco 3600 Series, Cisco 3700 Series, Cisco MC3810, Cisco VG200
12.2(13)T 12.2(13)ZH 12.3(1)	Router(voice-card)# codec complexity medium ecan-extended or Router(voice-card)# codec complexity high ecan-extended
12.2(15)ZJ 12.3(4)T	Router(voice-card)# codec complexity medium
12.3(4)XD and later	No configuration necessary. G.168 EC enabled by default.
Cisco 7200 Series and Cisco 7500 Series
12.2(13)T	Router(config-dspfarm)# codec complexity medium ecan-extended
12.2(13)ZH and later	No configuration necessary. G.168 EC enabled by default.
Cisco 7600 Series with Communication Media Modules
12.3(8)XY and later	No configuration necessary. G.168 EC enabled by default.
Cisco AS5300
12.2(13)T	Router(config)# voice echo-canceller extended codec small codec large codec
12.3(3)	Router(config)# voice echo-canceller extended [codec small codec large codec]
Cisco Catalyst 6500 Series with Communication Media Modules
12.3(8)XY and later	No configuration necessary. G.168 EC enabled by default.
Cisco Catalyst 4000 AGM
12.3(4)T and later	No configuration necessary. G.168 EC enabled by default.

How to Configure the Extended G.168 Echo Canceller

Restrictions for G.168 Extended Echo Canceller

• Not all Cisco platforms that use C542 or C549 DSPs support the extended EC.
• The G.168 extended EC is not supported on the Cisco AS5300 in Cisco IOS Release 12.2(13)ZH.
• The Cisco 1700 series does not support the T1/E1 card in Cisco IOS Release 12.2(13)T.

• Changing Echo Cancellers on Digital Voice Ports
• Configuring the Extended G.168 EC on the Cisco AS5300
• Modifying Echo Cancellation Default Settings

Changing Echo Cancellers on Digital Voice Ports

To use the G.168 extended EC in a release prior to Cisco IOS Release 12.3(4)XD, perform one of the following tasks depending on your hardware platform:

Cisco 1700 or Cisco ICS 7750

Cisco 2600 Series, Cisco 3600 Series, Cisco 3700 Series, Cisco MC3810, and Cisco VG200

• Changing Codec Complexity on Cisco 2600 Series, Cisco 3600 Series, Cisco 3700 Series, and Cisco MC3810 in the "Configuring Digital Voice Ports" chapter.

Cisco 7200 Series and Cisco 7500 Series

• Configuring Codec Complexity on Cisco 7200 Series and Cisco 7500 Series Routers in the "Configuring Digital Voice Ports" chapter

Note	See the table above for extended EC algorithm coverage by platform.

• Enabling the Extended G.168 EC in Cisco IOS Release 12.2(13)T
• Enabling the Extended G.168 EC in Cisco IOS Release 12.2(13)ZH

Enabling the Extended G.168 EC in Cisco IOS Release 12.2(13)T

To change codec complexity on the Cisco 1700 series and Cisco ICS 7750 and switch between the proprietary Cisco EC and the extended G.168 EC, use the following commands.

Note	You must clear all calls on the system before using the following commands. If there are active calls on the system, the commands are ignored and a warning message is issued.

SUMMARY STEPS

1.    enable


2.    configure terminal


3.    voice echo-canceller extended


4.    exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	voice echo-canceller extended Example: Router(config)# voice echo-canceller extended	Enables the G.168 extended echo canceller on the Cisco 1700 series or Cisco ICS 7750. You do not have to shut down all the voice ports on the Cisco 1700 or Cisco ICS 7750 to switch the echo canceller, but you should make sure that when you switch the echo canceller, there are no active calls on the router. To return to the proprietary Cisco G.165 default EC, use the no form of the command.
Step 4	exit Example: Router(config)# exit	Exits global configuration mode.

Enabling the Extended G.168 EC in Cisco IOS Release 12.2(13)ZH

The codec complexity medium command enables the extended echo canceller by default on the Cisco 1700 series and the Cisco ICS 7750 in Cisco IOS Release 12.2(13)ZH.

Note	You must clear all calls on the system before using the following commands. If there are active calls on the system, the commands are ignored and a warning message is issued.

SUMMARY STEPS

1.    enable


2.    configure terminal


3.    voice-card slot


4.    codec complexity medium


5.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables higher privilege levels, such as privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	voice-card slot Example: Router(config)# voice-card 1	Enters voice card configuration mode on the specified slot.
Step 4	codec complexity medium Example: Router(voice-card)# codec complexity medium	Enables the extended EC (default).
Step 5	end Example: Router(voice-card)# end	Exits voice-card configuration mode and completes the steps for configuring the extended EC on the Cisco 1700 series and Cisco ICS 7750.

Configuring the Extended G.168 EC on the Cisco AS5300

Perform this task to enable the Extended ITU-T standard G.168 Echo Cancellation feature on the Cisco AS5300. You must designate which EC to use on the Cisco AS5300 C542 and C549 DSPM high-complexity platform. You can use the extended EC with codec restrictions on the C542 DSP firmware or with or without codec restrictions on the C549 DSP firmware.

Note	A firmware upgrade can be made by upgrading Cisco VCWare. For upgrade information, refer to the Combined Version Release Notes and Compatibility Matrix for Cisco VCWare on Cisco AS5300 Universal Access Servers/Voice Gateways .

Before You Begin

Extended EC with Restricted Codecs on C542 or C549 DSP:

• Create a backup of your router configuration.
• Determine which codecs are required when enabling the extended echo canceller. For this information, see the codec restriction options for the voice echo-canceller extended command.

  • Specify a single small codec (g711 or g726) and a single large codec (g723, g728, GSM FR, GSM EFR, g729, or fax-relay). Any call setup involving other codecs is rejected.
  • If fax-relay is not selected as the large codec, the VoIP dial peer requires that you use the fax rate disabled command in dial-peer configuration mode to reset the dial peer for voice calls.
• Review your existing configuration and look for all dial peers that select codecs or fax-relay specification that are different from the codecs that you decide on. After choosing the codecs to be supported by the extended echo canceller, either remove all dial peers with different codecs not supported by your new configuration or modify the dial-peer codec selection by selecting a voice codec or fax-relay that is supported by the new configuration.
• Ensure that modem relay is not configured in any of the dial-peer configurations. If modem relay is configured, it should be disabled using the no modem relaycommand.

Extended EC with Unrestricted Codecs on C549 DSP:

• Create a backup of your router configuration.
• Ensure that modem relay is not configured in any of the dial-peer configurations. If modem relay is configured, it should be disabled using the no modem relaycommand.

Note

The extended G.168 EC can be used only in one of the following ways on the Cisco AS5300: With a restricted set of codecs with C542 or C549 DSP firmware. Two channels of voice are supported per DSP, and full call handling capacity is supported. With no restrictions on codecs with C549 DSP firmware. One channel of voice is supported per DSP, and call handling capacity is reduced by half. Not all Cisco platforms that use C542 or C549 DSPs support the extended EC. Other platforms continue to use the proprietary Cisco G.165 EC if they do not support the extended EC. >

SUMMARY STEPS

1.    enable


2.    configure terminal


3.    no dial-peer voice tag voip


4.    dial-peer voice tag voip


5.    codec {g711alaw | g711ulaw | g723ar53 | g723ar63 | g723r53 | g723r63 | g726r16 | g726r24 | g726r32 | g726r53 | g726r63 | g728 | g729abr8 | g729ar8 | g729br8 | g729r8 | gsmefr | gsmfr} [bytes payload-size]


6.    exit


7.    Do one of the following:

• voice echo-canceller extended
• voice echo-canceller extended [codec small codec large codec]

8.    exit

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	no dial-peer voice tag voip Example: Router(config)# no dial-peer voice 1 voip	(Optional) Removes VoIP dial peers, one dial peer at a time. When configuring the extended EC in global configuration mode, you must remove or modify all existing VoIP dial peers before the voice echo-canceller extendedcommand is accepted.
Step 4	dial-peer voice tag voip Example: Router(config)# dial-peer voice 1 voip	Enters dial-peer configuration mode so that you can modify a codec type.
Step 5	codec {g711alaw | g711ulaw | g723ar53 | g723ar63 | g723r53 | g723r63 | g726r16 | g726r24 | g726r32 | g726r53 | g726r63 | g728 | g729abr8 | g729ar8 | g729br8 | g729r8 | gsmefr | gsmfr} [bytes payload-size] Example: Router(config-dialpeer)# codec g711alaw	Specifies the voice codec rate for the dial peer.
Step 6	exit Example: Router(config-dialpeer)# exit	Exits dial-peer configuration mode and returns to global configuration mode.
Step 7	Do one of the following: voice echo-canceller extended voice echo-canceller extended [codec small codec large codec] Example: Router(config)# voice echo-canceller extended Example: Router(config)# voice echo-canceller extended codec small g711 large fax-relay Example:	Enables the extended echo canceller with no restriction on codecs. or Enables the extended echo canceller with restricted codecs. The following codec choices are valid: Small footprint codec--G.711 or G.726. Large footprint codec--G.729, G.726, G.728, G.723, fax-relay, GSM FR, or GSM EFR. Note    The voice echo-canceller extended command enables the extended EC without codec restrictions on a Cisco AS5300 with C549 DSP firmware. One channel of voice is supported per DSP. Any codec is supported. Note    The voice echo-canceller extended codec command restricts codecs on the Cisco AS5300 with C542 and C549 DSP firmware. Two channels of voice are supported per DSP. Only specific codecs are supported.
Step 8	exit Example: Router(config)# exit	Exits global configuration mode.

Modifying Echo Cancellation Default Settings

Perform this task to modify the default settings for echo cancellation parameters.

SUMMARY STEPS

1.    enable


2.    configure terminal


3.    voice-port slot / port:ds0-group-number


4.    echo-cancel enable


5.    echo-cancel coverage {24 | 32 | 48 | 64 | 80 | 96 | 112 | 128}


6.    echo-cancel erl worst-case [0 | 3 | 6]


7.    non-linear


8.    echo-cancel suppressor seconds


9.    end

DETAILED STEPS

	Command or Action	Purpose
Step 1	enable Example: Router> enable	Enables higher privilege levels, such as privileged EXEC mode. Enter your password if prompted.
Step 2	configure terminal Example: Router# configure terminal	Enters global configuration mode.
Step 3	voice-port slot / port:ds0-group-number Example: Router(config)# voice-port 1/0:0	Enters voice-port configuration mode on the selected slot, port, and DS0 group. Note    The syntax of this command is platform-specific. For the syntax for your platform, refer to the Cisco IOS Voice Command Reference.
Step 4	echo-cancel enable Example: Router(config-voiceport)# echo-cancel enable	Enables echo cancellation. Echo cancellation is enabled by default. Use the no form of this command to disable echo cancellation. The extended G.168 EC is the default EC for all supported platforms in Cisco IOS Release 12.3(4)XD and later releases, except the Cisco AS5300. On the Cisco AS5300, the Cisco G.165 EC is enabled by default with echo suppression disabled. Note    This command is supported only when the echo-cancel coverage command is enabled.
Step 5	echo-cancel coverage {24 | 32 | 48 | 64 | 80 | 96 | 112 | 128} Example: Router(config-voiceport)# echo-cancel coverage 64	Adjusts the size of the echo canceller (echo path capacity coverage). 128 is the default in Cisco IOS Release 12.4(20)T and later releases. Prior to this release, the default is 64 ms. Note    This command is supported only when echo cancellation is enabled. See Step 4 of this procedure.
Step 6	echo-cancel erl worst-case [0 | 3 | 6] Example: Router(config-voiceport)# echo-cancel erl worst-case 6	(Optional) Determines worst-case ERL in dB. Worst-case ERL is the minimum expected attenuation in the voice path. For example, if you have a worst-case ERL of 6 (erl worst-case 6), when you speak into the phone you can expect at least 6 dB of attenuation on the signal by the time it gets back to the original source (echo). In general you do not need to change this value from 6, which is the default. Worst-case ERL does not directly modify the inbound or outbound signals. This is purely a configuration parameter for the EC to help it distinguish between echo and a new signal. Note    This command is supported for the extended G.168 EC only; it is not supported for the G.165 EC.
Step 7	non-linear Example: Router(config-voiceport)# non-linear	(Optional) Selects nonlinear processing (residual echo suppression) in the EC, which either shuts off any signal or mixes in comfort noise if no near-end speech is detected. Note    This command is supported only when echo cancellation is enabled. See Step 4 . Nonlinear processing is enabled when the extended G.168 EC is enabled. Use the no form of this command to disable the NLP.
Step 8	echo-cancel suppressor seconds Example: Router(config-voiceport)# echo-cancel suppressor 10	(Optional) Applies echo suppression for the number of seconds specified when using the G.165 EC. This command cannot be used with the extended G.168 EC in Cisco IOS Release 12.2(15)ZJ or later releases, or on NextPort (Cisco AS5350 and Cisco AS5400) platforms. Note    This command is required to configure the Extended ITU-T standard G.168 Echo Cancellation feature in Cisco IOS Release 12.2(13)T. For the AS5300, the Cisco G.165 EC is enabled by default with echo suppression disabled. The echo suppressor can be used only on T1 DSPs when the default Cisco G.165 EC is used. This command enables echo cancellation for voice that is sent out an interface and received back on the same interface within the configured amount of time. This command reduces the initial echo before the echo canceller can converge. In case of double-talk in the first number of seconds, the code automatically disables the suppressor. The echo-cancel suppressor command is visible when the G.168 extended EC is selected but it has no effect. Note    This command is supported only when echo cancellation is enabled.
Step 9	end Example: Router(config-voiceport)# end	Exits voice-port configuration mode and completes the configuration.

Configuration Examples for Extended G.168 Echo Cancellation

• Enabling the Extended EC on the Cisco 1700 Series and Cisco ICS 7750 Example
• Enabling the Extended EC Prior to Cisco IOS Release 12.3(4)XD Example
• Enabling the Extended EC on the Cisco 7200 and Cisco 7500 Series Example

Enabling the Extended EC on the Cisco 1700 Series and Cisco ICS 7750 Example

The following example enables the G.168 extended EC on a Cisco 1700 series or a Cisco ICS 7750. The extended EC is enabled by default when the medium keyword is used in Cisco IOS Release 12.2(13)ZH and later.

voice-card 1
 codec complexity medium

Enabling the Extended EC Prior to Cisco IOS Release 12.3(4)XD Example

The following example shows that the echo canceller has been changed from the default proprietary Cisco EC to the extended EC in Cisco IOS releases prior to 12.3(4)XD. This example applies to the Cisco 2600 Series, Cisco 3600 Series, Cisco 3700 Series routers, and Cisco VG200.

Note	The extended G.168 EC is the only EC in Cisco IOS Release 12.3(4)XD and later releases. Because it is enabled by default, it does not display in the configuration output in Cisco IOS Release 12.3(4)XD and later releases.

The following is example output from an originating Cisco 3640:

.
.
.
voice-card 1
 codec complexity high ecan-extended
.
.
.
controller T1 1/0
 framing esf
 linecode b8zs
 pri-group timeslots 1-24
!
voice-port 1/0:23
.
.
.
dial-peer voice 104001 voip
 destination-pattern 104001
 session target ipv4:10.2.0.104
 dtmf-relay cisco-rtp
 codec g711alaw
 fax rate 14400
 fax protocol cisco
.
.
.

Enabling the Extended EC on the Cisco 7200 and Cisco 7500 Series Example

The following example changes codec complexity on a Cisco 7200 series or Cisco 7500 series:

dspint dspfarm 2/0
 codec medium ecan-extended

• Enabling the Extended Echo Canceller on the Cisco AS5300 Example
• Adjusting the Echo Canceller Size Example
• Worst-Case Echo Return Loss Example

Enabling the Extended Echo Canceller on the Cisco AS5300 Example

The following example enables the extended G.168 EC with restricted codecs on the Cisco AS5300 with C542 or C549 DSP firmware:

!
version 12.3
no service pad
service timestamps debug datetime msec
service timestamps log uptime
no service password-encryption
service internal
!
hostname router
!
boot-start-marker
boot-end-marker
!
enable secret 5 $123
enable password temp
!
!
resource-pool disable
!
no aaa new-model
ip subnet-zero
ip rcmd rcp-enable
ip rcmd rsh-enable
ip domain name cisco.com
ip host router1 10.10.101.14
!
!
isdn switch-type primary-5ess
!
v
oice echo-canceller extended codec small g711 large fax-relay
!
!
!
fax interface-type fax-mail
!
!
controller T1 0
 framing esf
 clock source line primary
 linecode b8zs
 pri-group timeslots 1-24
.
.
.

Adjusting the Echo Canceller Size Example

The following example adjusts the size of the extended EC to 64 ms on Cisco 3600 series routers:

voice-port 1/0:0
 echo-cancel coverage 64

Worst-Case Echo Return Loss Example

The following example sets the worst-case echo return loss to 3:

voice-port 0:D
 echo-canceller erl worst-case 3
 playout-delay mode fixed
 no comfort-noise