One way voice issue

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Jun 14th, 2007
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I have installed a new Voice-Gateway 2801 at a branch office. This Gateway is connected to the PSTN with multiple ISDN BRI voice interfaces. The gateway is also connected to a Callmanager-Cluster at the central location over a private vpn connection. All local phones (7911 IP Phones) are registered at the central callmanager which is version 4.1(3).

There are voice quailty problems with incoming calls over the PSTN. In this case the called party at the branch office hear a strong hissing. The calling party from the pstn can hear the called party clear. All other calls from the branch office to the pstn and to other phones in the central location are fine. Only incoming calls from the pstn are hissing for the called party in the branch office only.

Other branch office voice gateways with nearly the same configuration doesn't have any problems, so it is confusing.

These are the relevant parts of the configuration:

------------------ show running-config ------------------

boot system flash:c2801-advipservicesk9-mz.124-11.T2.bin


network-clock-participate wic 0

network-clock-participate wic 1

network-clock-participate wic 2

ip cef

isdn switch-type basic-net3


voice-card 0



voice call convert-discpi-to-prog


voice service voip


voice class h323 1

h225 timeout tcp establish 3


voice translation-rule 1

rule 1 /\(^.*\)/ /00\1/ plan isdn national



voice translation-profile callback

translate calling 1


interface BRI0/0/0

no ip address

isdn switch-type basic-net3

isdn timer T310 10000

isdn overlap-receiving T302 10000

isdn point-to-point-setup

isdn incoming-voice voice

isdn send-alerting

isdn sending-complete

isdn outgoing-voice info-transfer-capability 3.1kHz-audio

isdn static-tei 0


voice-port 0/0/0

compand-type a-law

cptone DE


dial-peer voice 1 voip

description PSTN -> VoIP

translation-profile outgoing callback

destination-pattern 52087..

voice-class h323 1

session target ipv4:

dtmf-relay h245-alphanumeric

codec g711alaw

no vad


dial-peer voice 700 pots

tone ringback alert-no-PI

description VoIP -> PSTN

destination-pattern 0T

incoming called-number 52087..


port 0/0/0


Thanks for any suggestions


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dgoodridge Thu, 06/14/2007 - 08:22
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Poor quality (hissing rather than choppy traffic) is unlikely to be a configuration issue.

If the gateway has multiple BRI connections I would disconnect all but one and test individually. If you find the culprit then contact the telco and get them to fix it.

stlieser Thu, 06/14/2007 - 23:07
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I've tried that, but without success. In the next step we replace the router and see what happens.

Thanks for your reply


MARTIN STREULE Tue, 06/19/2007 - 06:59
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check your clocking...

you have configured "network-clock-participate wic 0"

but no "network-clock-select 1 BRI0/0/0"

Check with "show network-clocks" where the clocking is sourced. Should be interface, not PLL/backplane

The other thing:

Be sure that "trust" is set properly at the switchport to which the gateway is connected.

A good starting point for this kind of problems:


stlieser Tue, 06/19/2007 - 07:47
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thanks for your reply. The problem was the codec-command, because g711alaw is not supported by the callmanager. But I have to change the clocking too...

Thanks again


paolo bevilacqua Tue, 06/19/2007 - 07:58
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be vary setting clock source from BRI. If telco deactivates layer 1 on inactivity, you will end having a lot of clock source transactions from interface to backplane and viceversa. You may find it necessary for fax only, and in that case you will have to live with a logging filled by clock entries.

gfolens Mon, 06/25/2007 - 11:31
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Hi, I think the 124-11.T2 is very buggy.

I had seriuous problems to get an E1 working after changing some params (number type) on the CCM (v5.1) side.

On another customer site cm v4.2, I had similar problems with activation of E1's.

rgds, Geert FOlens.

kumarjeet.acharya Wed, 06/27/2007 - 06:21
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Hi marcus,

Please check the ERL value while u have active calls on the voice GW.Also add the commands like 'input gain' and 'output attenuation' in voice ports u r using for incoming calls.Hope this will help u.

Please refer this link:

Let me know if it helps....


russell.sage Fri, 07/20/2007 - 15:04
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In your config you have stated which interface can particpate in the clock table. However you haven't told it which one to use so it defaults to its internal oscillator.

use the show network-clocks statement to see the active clock source.

You need to use the network-clock-select command to force it use a particular interface

dford333 Tue, 08/07/2007 - 08:55
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internal g711

external g729

I seen this design approach evade many ppl.

assuming the PSTN codec is set properlyto what the CM is expecting.


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