Clarification of FXO port behavior with Caller ID

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Jul 25th, 2007
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Confused about something...

To quote one of the Cisco study books:

"When you are using FXO and FXS ports to set up connections to a PBX it is important to remember that FXS ports SEND caller ID and FXO ports RECEIVE caller ID. Because of this relationship caller ID is sent only one way when used on this type of connection - from FXS to FXO"

Now the quote above refers to PBX's but I am presuming the same rule applies with any FXO port on a voice gateway RECEIVING caller ID info FROM a FXS port on a Telco switch.

I understand you use the "station-id" command to configure a station name and number for Caller ID purposes.

What doesn't make sense to me it that on my 2801's this option can seemingly be configured on both FXS... AND FXO ports.

My question is why is it an option on FXO ports?? I can understand it being an option with the FXS ports because the SEND it out but if FXO ports only ever RECEIVE the information why would you ever need to configure the "station-id" command on an FXO port?

No doubt I'm missing something here but any help would be appreciated.


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gogasca Wed, 07/25/2007 - 22:11
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I understand the following: that command will overwrite the CallerID that was recieved and will just -forward- this number to the final destination, but internally...

PSTN (CallerID 4082599090) - FXO - (we get 4082599090) station-id configured to 666 -

IP Phone gets 666.

attention with fwd, since this fwd is not travelling via FXO but internally...

flash2200 Thu, 07/26/2007 - 03:12
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Hi Gonzalo,

Thanks for the response (and testing!) on this. So just to clarify is appears the station-id coming from the PSTN is over-written by the FXO port if the "Station ID" command is configured on it and your testing appears to bear that out. Not clear on what you mean in your last sentence though?

I suppose I'm just wondering why someone would want to overwrite the caller ID coming in from the PSTN but I guess that's another story...

Thanks again.


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