FXO Centrex Line with FXS Port for Fax Machine

[Daniel Isham]

We have a location with one Centrex line coming into an FXO port. There is a fax machine that will be using this line, and they will also be using this for 911 calls only since that is the only line at that location. How would I go about configuring the FXS port for the fax machine to plug into? I have already created the DN for the DID but wasn't sure if there was anything else I need to watch out for..fax

[Jonathan Schulenberg · Accepted solution]

You're best off just configuring the FXS port locally on the router and not forcing the call through CUCM. If you push it through CUCM you'll need to deal with protocol interop and avoiding MTPs to get faxing working reliably. They wrote a whole book on this topic and the answer depends on CUCM version and protocols in play.

If it's locally patched on the router it can just pass through the backplane and be much more simplistic. Build a dial-peer for the fax DID that has the FXS port on it directly and ensure that get chosen.

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[Daniel Isham]

I still need a DN in CUCM for sharing the line with people who need to use it here and there. Can I do what you stated and still associate a line to a device?

[Jonathan Schulenberg]

Sure; just build a SIP trunk or H323 gateway to the router and the appropriate VoIP dial-peer to receive calls from CUCM.

Please remember to rate helpful responses and identify helpful or correct answers.

[Daniel Isham]

Thank you for the good information Jonathan.