Dial-peer showing Operational UP when no line connected to FXO

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Apr 7th, 2009
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I've noticed when there is no PSTN line terminated on FXO, still the dial-peer Operational status is shown as "UP". I've VIC2-4FXO where PSTN is terminated on two ports only. The dial-peers are configured for all 4 ports.

It is causing outbound calls hiting such dial-peer randomly and then falling-back to others. By the time call-reaches the working dial-peer, it seems the "timeout wait-release 3" is causing call failure.

I've shut down all such dial-peers and now everything works fine for me. I could've increased the timeout wait-release but curious to know if its a normal behavior of FXO ports.

I am trying to compare it with Dial-peers pointed to digital voice-ports (ISDN PRI), where when interface goes down, the dial-peers becomes OPERATIONAL DOWN.

I've Cisco 2811 running c2800nm-advipservicesk9-mz.124-11.T.bin.



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Overall Rating: 4 (2 ratings)
Nicholas Matthews Tue, 04/07/2009 - 14:57
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You need to think about the FXO port as if it was an analog phone.

When your phone is on hook, there isn't a reliable way of knowing whether the phone line is connected or not. This requires going off hook, checking for an off-hook voltage, and listening to dial tone.

The best practice for this scenario is to only configure dial peers that you know that are in use.



Kapil Atrish Wed, 04/08/2009 - 07:52
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Thanks for you reply Nick,

So you mean it is normal to see dial-peers pointing to Analog ports as always Operational UP?

Could you point me to some Doc highlighting this behavior? I did some research but couldn't locate one.



Kapil Atrish Wed, 04/08/2009 - 20:24
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Hi Polo,

thanks for your inputs.

I went through this doc, it talks about only the digital voice-ports. I wanted to know how dial-peers operational status behaves when pointed to Analog voice-ports.

I think based on your's and Nick's comments, I can believe there is nothing wrong and DP pointing to analog voice-port always remains up. If I've access to I'll check it in some other scenarios as well may be with FXS/E&M ports this time.

Thanks to both of you for your time.




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