4321 SIP Gateway w/ FXS Ports for Faxes

[mumbles202]

Currently have a 4321 that will be the new gateway for inbound calls via my ITSP and will have a SIP connection to CUCM 11.5.  There is also a VG224 that was legacy and only has a handful of connections still.  The 4321 already has a FXO card installed which was just used for the PVDMs.  If I want to install a FXS card as well, would I think need to have the same device in CUCM twice, once as a SIP trunk and another as a H.323 gateway so that I can send/receive calls to/from fax machines connected?

[Roger Kallberg]

Why can you not send the fax via the SIP trunk?

[mumbles202]

I can send the fax back to same 4321 and have it route out the FXS that are installed on it?

[Roger Kallberg · Accepted solution]

In the gateway you would have dial peers for both the options that you listed in your OP. So using SIP or H.323 between the CM and the GW would be no difference with regards to this. However using both protocols creates a much more complex system setup, so it’s not really recommended. If you configure your dial peer in an optimal way the call would not even touch CM.

[Jonathan Schulenberg · Accepted solution]

H.323 is deprecated as of IOS-XE 17.6(1); it will stop working when you upgrade a chassis. It seems short-sighted to implement it on something new. Interworking a call between SIP and H.323 also complicates the call flow considerably.

As others have suggested, just configure a POTS dial-peer so the router can send calls directly out the FXS port instead of hair-pinning through CUCM. If you really want to use the CUCM admin GUI to manage the FXS port, add it as an MGCP gateway instead of H.323.

[mumbles202]

If I have the need to send these calls to CUCM so that I can rollover inbound calls from 1 FXS port to another if the first is busy would MGCP be the best option? Wasn't clear how I'd send the call back to the 4321 if only using SIP. I was able to get the dial peers on the 4321 to have the calls go out directly without having to go to CUCM first but the issue now is if you call the same line back to back the 2nd call gets an error.

[mumbles202]

Good point about making POTS dial-peers and doing it that way so the call never goes to CUCM.  I'll give that a try.

I've never been a fan of MGCP (possibly just a lack of exposure) so my default has always been H.323 or SIP.