[asterisk-dev] ISDN gurus - getting isdn call progress ??

[Kai Militzer]

Hi,

On 15.11.2006 01:36, Steve Kennedy wrote:
> On Tue, Nov 14, 2006 at 04:35:49PM -0600, Kevin P. Fleming wrote:
>> Julian Lyndon-Smith wrote:
>>> we have an ISDN-30 Euro connection. When dialling out is it possible to
>>> stop a call when it is about to start ringing ? (i.e is there an ISDN
>>> message that says "yup, this is a valid number, starting to ring now" ?)
>> The message tells you that the call has _begun_ ringing, not that the
>> call is being placed. I don't know of any signaling that you could use
>> just to verify that numbers are dialable, without actually placing the
>> calls and then dropping them.

> You should be able to do that at the ISDN signalling layer, or via SS7.

Via SS7 you can use the ACM (Address Complete Message) which tells the
initiating side of the call, that the number is complete. In theory that
message should arrive before the called side begins to ring as before
ringing a CPG should be received, but for example in auto answer
configurations, an ANM could be sent directly after the IAM.

Best regards,
Kai

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