[cisco-voip] vg224 sanity check

[Countryman, Edward]

We just went through something similar at one of our sites. 

 

This site has a large amount of analog so in order to allow feature access through a VG224 the ports have to be configured as SCCP.  What we found the hard way is the SCCP and fax machines do not play nice.    

 

The most reliable way to assure faxing works with Cisco is to use t38 protocol.  Trying to fax through a G711 connection is a nightmare.  

 

However, Cisco doesn’t really support T38 on sccp (there are some contrived config’s that tell you to use cisco NSE’s etc but we never could get that to work.)

 

Ultimately, our solution was to configure the ports used for faxing as MGCP.  Also as important, configure the T38 protocol the same on both the (mgcp) VG224 and your router that has the PRI on it.  

 

If done correctly, you will actually see the codec change from G711 once the call connects and the fax machines start to negotiate.

 

Good luck

 

From: cisco-voip [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Ed Leatherman
Sent: Thursday, June 13, 2013 1:37 PM
To: Carlo Calabrese
Cc: Cisco VOIP
Subject: Re: [cisco-voip] vg224 sanity check

 

Thanks for the suggestions everyone!

 

They are able to make voice calls out OK with their fax machines so RTP is at least working both ways. 

 

Story changes the more questions I ask... Faxes between any VoIP endpoints (VG and ATA) work OK, it seems like just faxes over their PRI's now are the problem (but its any faxes, VG or ATA both). Their PSTN gateway is H.323, pretty basic config but that's my next point to start looking at. The VG224 and the PRI gateway are literally right next to each other off the same L3 switch, no firewalls and ethernet interfaces are error/drop free. I asked them to check with the local phone company to check their PRI circuits, error counters are relatively clean on their local side though.

 

All this has been working up till a day ago or so, everyone swears to me nothing has been changed :)

 

Time to start reading up on my Fax, Modem, and Text for IP Telephony book.

 

On Thu, Jun 13, 2013 at 11:54 AM, Carlo Calabrese <carlo_calabrese2006 at yahoo.com> wrote:

Can you check your mgcp config. Do you have

Mgcp default-package fxr-package

 

This will cause problems with faxes training up.

 

Carlo

 

From: cisco-voip [mailto:cisco-voip-bounces at puck.nether.net] On Behalf Of Ed Leatherman
Sent: Thursday, June 13, 2013 5:57 AM
To: Cisco VOIP
Subject: [cisco-voip] vg224 sanity check

 

Good morning!

 

I have a remote campus with 1 VG224 (SCCP controlled) and a handful of ATA's for analog service to fax machines etc.

 

IT staff on-site is complaining now that faxes on the VG can no longer send faxes (they fail usually during the first page), whereas faxes via ATA are ok oddly enough.

 

Kicker to me is they've also stated that even faxes between two devices on the VG224 are having the same issue.

 

To me this along with the ATA's actually working OK seems to make a PRI or network issue less likely although not ruling it out in case they are just reporting things wrong to me. They also say no changes were made to gateway (which I believe cause they prob don't have the login for it) or on their CUCM.

 

My question though for anyone familiar with these is, if two devices on the gateway are talking to each other via FXS ports, is this signal just getting switched natively on the gateway? Is any signal conversion happening or DSP's engaged at this point, assuming there aren't any conferencing or such going on?

 

Thanks!

 

-- 
Ed Leatherman





 

-- 
Ed Leatherman

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