PSTN-A --> VoIP --> PSTN-B Problem

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Oct 9th, 2005
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Hi,can anyone help me with my VoIP setup? I currently have two branches, Branch-A and Branch-B in two different cities. I'm trying to setup an infrastructure whereby I can call into my local Branch via PSTN into my Cisco voice gateway... go through the Internet.. routed to the other Branch and out the Cisco voice gateway to the remote PSTN. Here,s what it looks like.

PSTNA -> CiscoGW -> Internet -> CiscoGW ->PSTNB

Branch-A has a CiscoGW with 4 FXO ports connected to 1FLs and Branch-B CiscoGW has a NM-HDV(VWIC-1MFT-T1) connected to a T1 PRI. My problem is I can dial from PSTNB to Branch-B and out to PSTNA, it would ring but I get no voice. And when I say no voice I mean on either side.

By the way, I'm just using simple Dial-Peer statements to point from one site to the other. Using Codec G.711. I actually followed steps from this link below but I made it even simplier as I don't have SIP configured.

Thanks for your help!

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Overall Rating: 5 (4 ratings)
venkekri Mon, 10/10/2005 - 00:32
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This is a pretty straight forward setup.

You have mention that you are able to make the far end phone ring, however when the person picks up the phone there is No Audio on either end.

That clearly states that the signalling is good but there is a trouble in RTP cut through.

You can intiate the following command.

voice rtp send-recv

voice call send-alert

On both the routers.

Also when both party have picked up, do a show call active voice brief, and check the status of the call legs. It should ideally show 'active'. However if shows 'connecting or connected' then we have issue.

Also to make sure your dial peers are correct, you can run "debug voice ccapi inout" on either routers. This will show that which dial peer is getting invoked and wat digits are being sent across.

Also check if the symptoms are same when you call from Pstn A--Branch A -- Branch B ---PSTN B.

lexiainfo Tue, 10/11/2005 - 00:09
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I have similiar problem unable to send and receive calls.

lexiainfo Tue, 10/11/2005 - 01:53
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Thanks for your quick responce.

But i am testing on only one site. I have no gatway at other end.

First i want to test at site A.

Following Things i got at site A

=> router 2620 register with CCM

=> 7940 IP Phone.

When i make a call bell is ringing but both person cannot hear each other.

venkekri Tue, 10/11/2005 - 03:21
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If i understood correctly, your setup is as follows.


From the logs you have attached, it seems that your gateway is registered with CCM as MGCP. If thats the case, it would be a good idea to bind the media with an interface. Check the below link.

Hope that helps.Also clarify if my deduction of your gateway registered as mgcp is correct or not.

There are some known bugs on no audio issue. Check:

Also check the routing.



lexiainfo Tue, 10/11/2005 - 03:51
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1. Phone===2620===CCCM===7940

2. Yes you are right it registered as MGCP.

3. How do i check the routing

4. "it would be a good idea to bind the media with an interface" What is the purpose of bindind. Presently i am unable to make and receive call from IP phone.

Sorry i am new to cisco. Trying to learn IT Telephony. I would appreciate you could assist me.


lexiainfo Wed, 10/12/2005 - 14:59
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Can anyone reply to my question. IP Phone is ringing but unable to hear and make calls.

The caller can make call from pots phone but unable to hear from the receiver.

Hin Lee Wed, 10/12/2005 - 21:30
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Please post you gateway config (sh run).

Hin Lee Fri, 10/14/2005 - 00:01
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mgcp call-agent which means that your callmanager is

So that means that this is probably your issue

ip route

If your ccm is also your gateway, then that is also a problem because it cannot have two separate network connected.

lexiainfo Fri, 10/14/2005 - 01:32
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Thanks for the reply.

So what should i do to work the things perfectly?

Hin Lee Fri, 10/14/2005 - 01:52
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Hard to say. The reason is that I don't know how you have your network setup.

This line

ip route

should be

ip route < ip-address-of-default-gateway for 192.168.0.x subnet >

Is this your config?

ip phone --> CCM --> MGCP Gateway () --> PSTN via FXO?

lexiainfo Sat, 10/15/2005 - 17:44
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I tried but still didnt work.

ip route

Here is my current network setup.

Internet=>Netgear Modem=>Pix501=>Inside Network


Here is my current config

IP Phones and Gateway Registered with CCM 4.1.2

PSTN line via FXO (Cisco 2620 Router)


Bell is ringing on IP phone but cannot hear, Even the caller cant hear.

Cannot make a call from IP Phone.



Erick Bergquist Sat, 10/15/2005 - 20:32
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What is inside IP on the PIX? is it

If not, does have route back to your phone IP?

Is PIX doing VPN tunnel to other site? Is other site using PIX also or netgear?

Also, on the PIX do you have fixup skinny? I also recall that you may new PIX software if you're on a newer version of CCM due to some changes with skinny the older PIX software did not fixup right. I had a customer whose IP phones on other sides of PIX would just ring and ring due to PIX software being old and once they put new 6.3 (If I recall right they were on 6.2 when it did not work) it worked fine.

Hin Lee Sat, 10/15/2005 - 20:46
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Hi Erik:

Actually I don't think that the problem relates to the pix. The ip address of the 2620 is, the CCM is, and I presume that the ip address of the phone is 192.168.0.x with mask of


Would you consider changing the config to H.323?

lexiainfo Sat, 10/15/2005 - 22:02
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Yes you are right "Actually I don't think that the problem relates to the pix. The ip address of the 2620 is, the CCM is, and I presume that the ip address of the phone is with mask of "

Add new gateway as H.323. Then i believe i have to change in router config too. What will be the config if i change it to h.323?

lexiainfo Sat, 10/15/2005 - 23:37
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Thanks for quick reply

I only have gateway at site A. Presently testing on Site A. So basically i am facing the problem at site A. There is no gateway setup at Site b and Site C.

As per your instructions i am providing you the PIX


Hin Lee Sun, 10/16/2005 - 01:55
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open this page http://ccmserver/CCMService/main.asp

Select Trace, Configuration, your server, and Cisco CallManager Service.

Debug Trace Level should be detailed.

The location of the files will be in Trace Output Settings

The last file should contain the logs.

lexiainfo Sun, 10/16/2005 - 02:58
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Please check email. I have just sent traces.


cau Mon, 10/17/2005 - 12:46
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Hi Everyone... been working on this problem and now now I'm running into a new related problem. I upgraded my BranchA site with the 4 FXO to an E1 PRI. so now my diagram looks like:

PSTNA -> (E1-PRI)CiscoGW -> Internet -> CiscoGW(T1-PRI) ->PSTNB

My problem now is I can call from PSTNB thru to PSTNA and th person on PSTNA would ring and he would pickup and hear me from PSTNB.. but I don't hear anything from PSTNA. One way audio. I'm not using CM or anything so I don't think it's a routing issue. I tried pinging and pings went thru. I actually see the call being set up but no voice. I even used RTP cut-thru but nothing... anyone have any suggestions?


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