When simple changes aren’t…tales of MGCP to h.323 conversions

02 Jul

Maintenance windows have a way of reminding you that simple changes aren’t always so simple.

Take a recent after hours task of switching over some MGCP gateways to h.323.  The primary inbound gateway was already h.323 and the MGCP gateways were – well, MGCP – so it made sense to make everything uniform and do the conversion.

So I changed all my calls to route in and out the primary gateway, which was already h.323, and set about making my changes.  In case you haven’t done this before, here is a brief outline of the process – not meant to be a step-by-step, all inclusive list, just a general idea of the process.

On the gateway side:

-set isdn switch type on the router (you can get this from the MGCP configuration in CUCM)
-bind h323 to source interface
-create inbound and outbound dial peers on the router
-remove MGCP bind command and other MGCP configuration (you will need to shutdown the voice port to do this)
-reconfigure the T1 controller
-put in place any translation patterns required
-add commands for calling name and/or Facility IE support if required

On the Cisco Unified Call Manager side:

-create the gateway 
-add the gateway to a route group
-add the gateway to a test route list
-create a few route patterns to send calls out the gateway
-add gateway to production route list(s)

My plan was proceeding perfectly up until I needed to send a long distance call out one of the recently converted gateways.  The call received a reorder tone from the carrier even though the debug isdn q931 output showed my call going out with the proper digit format. I knew long distance calls were working going out this gateway before, so I was pretty sure it had to be something with my configuration even though it looked like a carrier issue.  

After comparing configurations with the current h.323 gateway (PRI to the same carrier), uttering a lot of fairly creative yet non repeatable curses, and wasting an hour of my life with a clueless carrier tech who swore I wasn’t sending the 1 required for long distance, the obvious finally hit me.  And it was annoyingly painful.

See, I had made the assumption that long distance calling had been tested out the primary gateway when it was installed.  I foolishly believed that outbound long distance via the primary h.323 gateway had been tested at installation, as this is pretty much standard and *should* be part of any voice gateway install process.  Once I wised up and tested that theory, however, I realized that all long distance calling to the carrier was broken from every gateway, including the old h.323 one which I hadn’t changed anything on.  Knowing this couldn’t be the result of my conversion efforts, I was now able to think through what the real source of the issue could be.

When you send the carrier the right digit format and yet they emphatically insist you most definitely aren’t, you are likely hitting an issue I blogged about in my first ever post.  In some cases, a carrier switch reads your ISDN plan type and takes digit stripping action based on it. They seem to be completely unaware they are even doing it, so don’t expect the carrier to ever discover this is your problem. The solution is simply to set a translation pattern that changes the plan type to UNKNOWN and then the carrier switch doesn’t try to do you any favors and manipulate the digits. Problem solved.

I am now adding testing inbound and outbound calling from ALL gateways before making changes to my check list.  Pass the bourbon please.

Bonus material:
At the time, I didn’t think about the 8945 phones (and newer phones with video capabilities) that often require you add a specific command to the ISDN voice port, otherwise outbound calls from the device fail. I discovered this while finishing up my testing plan and was able to fix it before anyone noticed.  A very good reason to have a thorough testing plan no matter how small the changes being made. Here’s a link to a forum post on this type of issue and the command you need to fix it:

voice-port 0/1/0:23
bearer-cap speech

Also, your lucky day, some commands for calling name when carrier is using the Facility IE:

voice service voip
h225 display-ie ccm-compatible
interface Serial0/1/0:23
isdn supp-service name calling
isdn outgoing display-ie

Published 7/2/2014


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4 responses to “When simple changes aren’t…tales of MGCP to h.323 conversions

  1. Rolando Valenzuela

    2014/07/03 at 10:54

    Just awesome!!

  2. Rolando Valenzuela

    2014/07/03 at 11:03

    Amy, I adding another comment just in case you want to delete it 😛
    Quick question… I’m having problem with an ISP not giving me the calling ID for every international call, the information is there if it is a local call, I already opened a case with them and they said they are OK, I’m still pushing for additional tests…

    Progress Ind i = 0x8281 – Call not end-to-end ISDN, may have in-band info
    Calling Party Number i = 0x00A3, N/A
    Plan:Unknown, Type:Unknown

    Can be something in my end?
    Thanks! 🙂

    • Scott L

      2014/07/11 at 17:38

      Had a similar problem to you at a previous company where I worked where caller ID wouldn’t be displayed to the called party unless you had ISDN set up as the Plan and International set up as the Type. You could try setting that at Route Pattern level or at Gateway level (if using H.323). Failing that, speak to your carrier about what settings they expect.

  3. Max

    2014/08/06 at 04:01

    Very nice Read


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