Subject: Re: line-side answer supervision

From: Al Varney <[email-masked]>
Date: Thu, 7 Sep 2000 11:25:41 -0500

At 17:18 08/29/2000 -0500, Mario Monteiro wrote:
>For analog circuits, answer indication in some cases needs to be
>returned towards the originating side for billing purposes.
>
>Question: Once answer is detected at the terminating side, how is this
>answer event communicated to the originating side so that the
>originating AGW may apply line-side answer supervision? That is, what
>type of Megaco signal is sent by the Softswitch to the originating AGW?

As Tom pointed out, there is no package defining such things for analog lines.  I recall seeing a proposal for Digital Loop Carrier Gateway (TR-303) control, which would support the needed capabilities, using the ABCD codes such as RLCF (reverse loop current feed).

Anyway, a package extending the Analog Line support is needed to control all aspects of the DC interface to the analog line for both loop-start and ground-start signaling, including:
 - reverse loop battery [a common means of providing line-side answer superv.]
 - normal loop battery (unless the above is a toggle -- yuck)
 - loop open (no current feed, battery remains)
 - loop closed
 - short open (This is a common indication to called parties, also known as CPC, that the caller has disconnected.  If "loop open" is a signal, rather than a line state, then you could just use a short timer with "loop open" to do this, and assume "loop closed" is the default condition.)

Note that reverse loop battery is also used as a "toll-diversion" indicator on analog lines and on some analog (reverse-battery) trunks.  So the package might also apply to analog trunks??  It's unfortunate that
    draft-brown-supplpkgs-00
specified only Robbed-bit-signaled trunks, since "seize" and "unseize" could be considered useful signals for any in-band-signaling trunk.  (Note that "supplpkgs" also considers these "brief" signals -- probably a typo).

I'm not sure if/how these would be extended to emulated analog lines (derived voice via DSL/cable, IP phones, or digital phones on a PBX) as described in
    draft-ietf-megaco-basicpkg-00.

Al Varney - Lucent Technologies  +1 630 224-7493    [email-masked]