Cisco Support Community
Showing results for 
Search instead for 
Did you mean: 
New Member

3640 Gateway with VWIC and VIC-2FXS

Does anyone know the best way to go about this.

I have a 3640 with a VWIC running my PRI for my gateway out to the PSTN.

I also have a VIC-2FXS module installed. I would like to have the Fxs ports run my faxes. How can I have the gateway do a U turn when someone calls one of my DIDs into the PRI then have it go out the FXS ports.

Just like a ATA module (I dont want to spend the money if I have the fxs card)

Take Care


Cisco Employee

Re: 3640 Gateway with VWIC and VIC-2FXS


You can configure a dial-peer with a destination-pattern you want and route it

out the FXS voice port.

For example, let said one of your PRI DID number is 4081112222 and you would like this number to be dedicated to the fax machine on FXS voice port.

You can create the following port dial-peer:

dial-peer voice 2 pots

destination-pattern 4081112222

port x/y/z

where x/y/z is the slot and port number for one of the FXS interface.

As for the PRI line, you can create

dial-peer voice 1 pots

incoming called-number .

destination-pattern 9T


port x/y:23



New Member

Re: 3640 Gateway with VWIC and VIC-2FXS

Hi Neil,

The first example will work fine just have a dest patern on your pots dial-peer pointing to your fxs port/s example 45111 this will match before 45...

The chances are you are tranlating called party to 4 or 5digit extensions on PRI 1/0:23 or 1/0:15

And make sure you do not have a 4 wire rj 11 cable plugged into port 0/0 because the router monitors all four pins on that port and you will get severe issues looping problems.

example someone dials in to fax on fxs 0/1

sh voice call sum will show connect and 0/1 wil show digit collect on 0/0 dial-tone which shouldnt happen on FXS ports but does in this scenario.

I experienced this problem and it was a nightmare.

This aside it is a basic config that will work fine.

Port 0 on a VIC-2FXS is designed to accommodate a US style 2-line phone, instead of the usual European style 1-line phone.

This means that in addition to pins 3 and 4 being used, pins 2 and 5 are also monitored. With some phone handsets it is possible that pins 2 and 5 are wired up to allow last number re-call or call-forwarding. If this is the case, Port 0 on the VIC will assume you have a 2-line phone, and shutdown port 1.

To check this, use only two wires in the cable from the VIC to the Phone and verify that Port 1 becomes active again.

Pin 1 No Connection

Pin 2 line-2 tip

Pin 3 line-1 ring

Pin 4 line-1 tip

Pin 5 line-2 ring

Pin 6 Non Connection

Re: 3640 Gateway with VWIC and VIC-2FXS

Do NOT do this if you want faxes to work.

You MUST send the incoming call to call manager and then back to the router / FXS port to make sure that fax-passthrough operates correctly.

The 26/3600 series routers require a fax call to leave the DSP proccessing and re-enter to operate correctly, but local hairpinning on the box does not do this and so you end up with unreliable fax.

I would also configure your route patterns to send a number other than your normal access code to the router to match the outbound dial-peer statement. this way you can have your FXS ports send all outbound calls to call manager which hairpins the calls back to the router.


New Member

Re: 3640 Gateway with VWIC and VIC-2FXS

I totally disagree with Paul on this occasion.

Look at the debugs the call doesnt do a u turn a more explicit match is the fxs port.

I have set this up many times and it works fine for me.

just last weekend i did an install and have not received any complaints all this week with regards to any issues.

The faxes and FXS ports have nothing to do with CM useing H.323.

dial-peer voice 23 pots destination pattern 35000 port 0/1

why send the call to CM, absoloute waste of time Callmanager doesnt need to know about faxes been sent from FXS ports on the 2600 H.323.

when you send faxes it will just match your outbound dial-peer

0 0T 9T or which ever yuou use.

Like I said I have done this on many occasions with no reported issues most recently on the 7th June.

New Member

Re: 3640 Gateway with VWIC and VIC-2FXS


for correct fax transmission especially for "Super G3" (V.34) faxes you need correct fax detection by DSPs (disable echo cancellation, disable vad etc.)

with V.34 fax machines pass through mode is the only way !!


under dial-per voice xy voip configuration you configure :

modem passthrough nse codec g711ulaw

disable fax rate => because cisco fax relay will not work with V.34 faxes !

there is no other possibility (e.g. under pots dial peer) to configure these parameters


you need ccm !!

like paul mentioned before

by the way you generate cdr in ccm (maybe you need them for billing)



Re: 3640 Gateway with VWIC and VIC-2FXS

> I have set this up many times and it works fine for me.

You mentioned a 2600 below - have you done this on a 36xx? It's a documented problem and I have had problems trying to do hairpinning of fax calls on a 3660. Fax calls would negotiate as low rates with lots of dropped calls. The problem was immediately resolved with routing the call to CM and having it come back. What IOS version is this working for you?

> why send the call to CM, absoloute waste of time Callmanager

> doesnt need to know about faxes been sent from FXS ports on the

> 2600 H.323.

In my case, I'd prefer CM know about the call so that I can audit calls. Otherwise, I have no way of knowing about calls that the gateway handles locally.


Re: 3640 Gateway with VWIC and VIC-2FXS


Well it looks like I'm not the only one who recommends sending faxes in and out of Call Manager.

In response to your comments, you are right Call manager has no idea that the call is a fax, and indeed it has no reason to, however the architecture of the DSP modules means that fax transmissions are in the majority of cases extremely unreliable and slow speeds are the norm. (you appear to have been lucky)

I usually set the pots dial peer for outgoing on the router to use something like 801 as the destination pattern and then use call manager to translate the PSTN access code (9) to 801 before sending to the router. Then on the router I set up a voip dial peer with a DP of 9 to point at call manager. Then configure up pots DP with extension numbers for the FXS ports and matching RP on CM.

This serves a number of purposes.

1.) it gets round the fax problem.

2.) You can send calls from multiple gateways to the fax machines

3.) All Fax calls are logged in the CDRs

4.) you can test the fxs ports work by dialing them from IP phones (and then whistle fax tones if you want :-))

I'm not saying your way doesn't work, just that I've always found it unreliable whereas you've had no problems.


Re: 3640 Gateway with VWIC and VIC-2FXS

As you can see there are several opinions on how to configure this, just keep in mind if your using mgcp w/ pri-backhauling, you will have to have ccm control the call, if your running h323 as the gateway primary protocol, the dial-peer will work fine. Another think to keep in mind is if your running srst on the router, you may need some translation-rules to accomidate the call routing if in fall-back mode. Either way it should work fine, you should test extensively of course.

A nice advantage of using call manager, you can build a hunt group of all your fax machines, so if one is busy receiving/send, the next inbound will be routed to the next fax machine to receive the call.

New Member

Re: 3640 Gateway with VWIC and VIC-2FXS

you can have it hunt without CCM

interesting to see the different theories.

CreatePlease to create content