Hey, voice gateway, that’s *my* call!

It’s not often that people ask me to keep calls from being answered by a voice gateway, but recently I got privilege of addressing just that issue.

The scenario here is not all that common, but if you should find yourself in similar jam, you are going to want to send me candy and flowers for this tip.

Say that you have a voice gateway and the only reason it’s there is so that some archaic fax machine can send and receive (die, fax, die!!), and so that outgoing user 911 calls are routed out the local PSTN.

Say that for whatever reason, an FXS card was not used for the fax machine, but instead, wiring wizards split off the PSTN connection at the demarc so currently both the router and the FAX machine share dial-tone from the same line.

Say that you determine not to question the setup so much as focus on making sure that when calls come in from the PSTN, the FAX machine takes the call and the router just sits there, pretending like nothing’s going on.

Here is the magical command you need to make this happen:

voice-port 0/0/3 (or whatever voice-port your PSTN connection is cabled to)
ring number 10

This sweet little command tells the router not to pick up when the call rings in initially.   This gives the FAX machine plenty of time to jump in there and take the call without the router interference.

Granted you won’t see this everyday. If you’re lucky you may never see it.  I, on the other hand, need to have a long talk with karma…

Be sure to check out this support forum, which led me to the above solution: https://learningnetwork.cisco.com/thread/9357

Published 03/26/2012

10 thoughts on “Hey, voice gateway, that’s *my* call!

  1. I love how you don’t question (but you really question) why the #%*! Someone would wire that up. I LOL’d

    So, I’m assuming thats a 10 second timeout while the fax auto-answers to see if it’s another hot fax girl? And if still idle, pickup the caller?

    1. Actually looked it up, the 10 is the number of rings to wait before answering to see if it’s a hot fax girl. 😉

      And yes, the real question is WHY??!!

  2. One of several other places you may see this is with an alarm panel, one like you would have for a house alarm. This also is incorrect wiring. I should use have the analog line wired through the panel. That is the panel is wire first and in series with the router. The alarm may seize the line if it is in use. It’s not fool proof. It is good engineering pratice and risk management.

    1. I wouldn’t have thought of that, but yes, I can see this being a helpful command in that situation as well – if someone insist on wiring it that way! Thanks for bringing that up!

  3. “I should use have the analog” should read “It should have the analog”

    Yes, I see some other minor mistakes. I bow to the word smiths of the world.

    Jerry you are sentenced to proof reading 101 detention for ten days.

  4. Hola Amy,
    “Say that for whatever reason, an FXS card was not used for the fax machine”

    This is something I’ve had to learn the hard way, when my employer decided to go VOIP, we setup ATA187’s all throughout the network connected to FAX machines. Being that the faxes are RARELY if ever used at all, the tickets started trickling in as the months went by with “We can’t fax”.
    In your experience, are ATA’s that horrible at working with Fax machines? According to the oh so truthful Cisco documentation, ATA’s are BFF’s with Fax machines.

    1. I despise ATAs with faxing – so many unpleasant memories! The older ATAs didn’t have official support for faxing, the newer ones were supposed to be better, but still a horrible experience. There’s only so much tuning you can do, and it’s usually not enough. I personally recommend a standard POTs line, which usually gets rejected, then I recommend FXS or one of the VG devices. Those are usually easier to tune and can get to a reasonably decent level of reliability. Did I mention die fax die?

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