H3.23 PSTN gateway problem - Urgent

Unanswered Question
Jan 14th, 2009

Hi all,

My set-up is one like this:

Ip phones are registered to a cisco callmanager,an H3.23 gateway is also registered to the same callmanager-the gateway is a cisco 2821 cisco router-which has a number of FXO ports where the pstn providers have terminated their links.

Now the problem is that whenever one wants to call out to the PSTN there is a certain noise(doooooh)that comes from the phone when you finish inputing the numbers-at this stage the call shows up as connected on the screen of the phone.

The other thing is this does not happen all the times-sometimes the call is successful,but of late all am getting is the doooooh sound-i have tried all manner of configs/research without any success.

Please find the running configs of the voice gateway attached.

Please help,

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Paolo Bevilacqua Thu, 01/15/2009 - 04:07

Configure an incoming voip DP:

dial-peer voice 1 voip

incoming called-number .

codec g711

no vad

Also, you can reduce all the pots DP to a single one, just configure the voice-port under a trunk-group, eg "pots", and reference it instead of individual ports in the DP.

Hope this helps, please rate post if it does!

nickolaskoiser Thu, 01/15/2009 - 07:03

I applied both of these configs on the Voice gateway and nothing much changed,when you pick a phone and dial a PSTN number,the noise is still there(the noise is one like this:dooooo..h).

I have never seen such a thing before.

am using the route pattern:9.! on the callmanger.

The callmanager is in Rwanda.

Please help.

Nicholas Matthews Thu, 01/15/2009 - 07:53

Hi Nickolas,

I think there is a fair chance this is coming from the provider. Find out what happens if you dial from a normal analog phone instead of the router, and see if the problem persists.

You may also want to remove this command: voice call send-alert



nickolaskoiser Thu, 01/15/2009 - 08:11

Thanks for that,

However,this is the first thing that i tried out,I picked an analog phone connected it directly to the FXO ports and tried making a call and it was going successfully.

So to me,the provider was out of question.

Nicholas Matthews Thu, 01/15/2009 - 09:40

You can try removing the configuration from the voice-port such as caller-id and the other things on there. See if the problem persists with just the CP tone. (Is CPtone FR correct for Rwanda?)

Also try removing the send-alerting command.



Paolo Bevilacqua Thu, 01/15/2009 - 10:11

How strong the noise is ? does it sound like dialtone if you compare ? Can you dial some calls ? Does it change swapping tip and ring ?

mparra.fusionet Thu, 01/15/2009 - 10:59

Hello nickolaskoiser/team,

Could you please gather a sniffer trace from a PC connected to the back of an IP Phone that performs an outbound call with wireshark/ethereal so you can get uploaded the audio of that call as an au. file (you can talk as well so that we can get to know you better :) ) In this manner we can hear it, that doooh sound it is very interesting, I'm not sure though if the calls that get affected by this sound actually work or not? (meaning that you place the call and you hear during the conversation this sound, but still the call works) because all of us are assuming that is the case, could you please clarify that.

I'm asking that because if they do not work, there's a big chance that simply the router is sending DTMF so fast that the PSTN does not detect them and plays dial tone to you (from the IP phone perspective the call will show up connected due to the H225 Connect being sent to CCM once the FXO port goes off-hook) and since there is no dtmf-relay commands on the dial-peers when you try to break the dial tone by pressing the digits of the IP phone it does not break. (timing digit under the voiceport tweaks how long the in ms the DTMF is played to the provider and timing interdigit defines how much time there should be between each digit is played). I believe this is the poing where p.bevilacqua was going for by asking about the sound.

If the call works with the weird sound, I can tell you that from my experience weird sounds on analog lines, tend to come from either adding input gain/output attennuation commands under the voice-ports or having the impedance command that you have there, when the electric impedance of the line is different than the impedance defined on the port and finally a DSPware problem on the router (the DSPware comes with the IOS).

So if the call works with the sound try to get rid of the "impedance complex2" and even the cptone/caller-id commands as nicmatth suggested on all the voiceports, then make sure you do shut/no shut under the voice ports after removing the commands to ensure that the settings get applied, then try again please.

nickolaskoiser Thu, 01/15/2009 - 22:39

Hi all,

Very many thanks for your input(s).

One problem is:the voice gateway is in Rwanda while am in Kenya and so most of the time i have to get the support guy on the phone and tell him to input the commands as we test-so far we have taken out the caller-id setting,cp-tone and reset the voice-ports.We did the test after doing this-we made 5 PSTN calls-two were okay but three were still having the problem.

The noise as i mentioned is one that goes like this:doooooo.....h-this happens when the PSTN call shows up as connected on the IP phone-the sound goes on to the point where you finally get a busy tone and the call finally disconnects on its own.The strength of the noise-i can say its fairly strong(dooooo..h).

What's worse is at times,the calls go in well without any problms.

Once the call is set up successfully the quality is good without any kind of noise.

It does not compare with the sound of a dial tone in any way.

Unfortunately am i not be able to send the sound at this stage-let me see how i can get the sound to you.

I have not done any changes to the dmtf-relay,input-gain/output because as i mentioned,some calls through the same gateway are successful and without any problems.

Thanks,let me work on further troubleshooting-i'll post an update incase of anything.

Thank you.

Nicholas Matthews Fri, 01/16/2009 - 04:31

Hi Nickolas,

You may try adding this command to your pots dial peer:

prefix ,,,

This will add 3 seconds of silence before the digits are sent. It's possible you're sending the right digits, but just too fast after you go offhook for the carrier.



mparra.fusionet Fri, 01/16/2009 - 07:18

Thanks for answering, so pretty much, the call does not work when this happens, to me it sounds like what I said, maybe one or two of the lines are more

sensitive to how fast we (the FXO port) sends the DTMF tones to the PSTN (hence the random behavior), so the PSTN does not recognize the DTMF, they play a dial tone (the dial tone sound in Rwanda could be way different than the dialtone on Kenya) for a period of time and finally fast busy, that has happened to me before so it would not be surprising that it is the root cause.

Here's my recommendation

voice-port x/x/x ! Where x/x/x is a FXO port

timing digit 200

timing interdigit 200


no shut

Do this on all the FXO ports, basically what it does is send DTMF every 200 ms (timing interdigit) and each digit is played for a duration of 200ms (timing digit) the default values for this parameters (sh vo po x/x/x) is 100ms, have your tech guy do this and have him try it several times until we can confirm that the issue is solved or persists.

Hope this Helps



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