[cisco-voip] Intercom in Callmanager

[Lelio Fulgenzi]

We have a VG248 and were told by Cisco to use one of the aforementioned  adapters for call supervision. Only after did I find out that that VG248 has the following Call Supervision modes: drop loop current, reverse polarity. Would either of them worked in out situation? Who knows. Something to consider, however.

  ----- Original Message ----- 
  From: John Osmon 
  To: cisco-voip at puck.nether.net 
  Sent: Friday, October 28, 2005 5:25 PM
  Subject: Re: [cisco-voip] Intercom in Callmanager


  On Fri, Oct 28, 2005 at 02:21:41PM -0500, Schuett, Court (MBNAP it) wrote:
  > That's what we did.  We ran from an ATA 186 port into the amplifier that ran
  > into the speakers.  We had a wiring company set up the amp and speakers for
  > us.  It was pretty simple and it sounded like they had done it before.
  > Connecting it to the ATA was also very simple.  Just assigned the ATA a
  > number and when people want to announce over the speakers, they just call
  > that number.  There was a catch to it though.  When the number was called,
  > the speakers would pick up, but they wouldn't let go.  What happened was the
  > person would call, make the announcement and then hang up.  But the speakers
  > would still be broadcasting and would eventually go to a busy signal.  To
  > fix this, you have to go in and change the polarity on the ATA to 0x00008 I
  > believe.  Might want to call TAC and confirm that though.

  Classic disconnect supervision problem.  When you have an analog line
  it is difficult to tell something at the other end that the call is
  over.  (Humans are easy -- the 'goodbye' protocol signals the end of
  the conversation, so they hang up.)

  Disconnect supervision on analog lines is typically handled by:
    - shorting the line (removing voltage)
    - reversing polarity of the line
    - playing special tones (rare)

  Don't forget that the end device has to support that particular
  disconnect supervision as well...

  Last I'd heard is that the ATAs have *NO* disconnect supervision, but if
  you've gotten them to break with the speakers, obviously *something*
  is working.  Thanks for the tip.
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