Re: [AVT] 2833bis - hook events

[Henning Schulzrinne <hgs@cs.columbia.edu>]

> Flash-hook is a transition from off-hook to on-hook and then, within 
> 200-300
> ms to 1100-1550 ms, another transition back to on-hook. Thus all we are
> really observing is off-hook and on-hook, just with certain durations. To
> make things more complicated, there is something called flash response
> enabled timing and flash response disabled timing. In the flash response
> disabled case, a transition to on-hook lasting from 200-400 ms and up will
> be a disconnect and hence a subsequent off-hook transition will never 
> imply
> a flash. In the flash response enable case, the previously mentioned 
> timing
> considerations apply and hence we may see a flash.
>
> Thus, if we are sending on-hook and off-hook events, then we can detect if
> there is flash or not (or more accurately, I believe we are in just a good
> or bad position as the sending party to determine whether a flash occurred
> or not). This in itself makes the flash event redundant when used with the
> on-hook and off-hook events. Secondly, it's not clear that the sending 
> party
> actually knows whether we want flash response enabled timing or not. This
> also argues for only sending the raw on-hook and off-hook states and 
> not the
> flash event.
However, there are devices that have a "flash" button (seems to be 
popular in Europe). For these devices, sending a single event seems 
easiest. I thought Flash was used to switch between parties during call 
waiting?

> Now it might be useful to keep the event so you can simply monitor for
> flash-hook (without general on-hook and off-hook state), however I'm not
> sure what the application for this is. I vaguely recall some operator
> services looking for a customer flash-hook to get the operator back 
> on-line,
> but could be wrong. Whether RFC 2833 would be the right solution for 
> this is
> perhaps another question.
Flash hook it seems to be part of the possible AT command (D) modem 
dialing sequences, shown as a !, as in ATD123!45. See, for example, 
http://supportmech.virtualave.net/at-command.htm

That said, I'm not quite sure what your suggestion is for 2833bis.

> -- Flemming
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