[asterisk-ss7] libss7 and IAM/ACM

[Barry O'Donovan]

Kristian/Anders,

Thanks very much for the detailed and informative comments and suggestions on 
this issue.

I'll review all of what you both suggested over the next few days and report 
back with any progress/patches/etc.

 - Barry

On Thursday 19 June 2008 12:00:22 Kristian Nielsen wrote:
> Anders Baekgaard <ab at dicea.dk> writes:
> > The current behaviour of chan_ss7 where ACM is sent when there is a match
> > in the dial plan is right in most cases. It allows chan_ss7 to
> > automatically send REL with cause value UNALLOCATED when there is no
> > math.
>
> Agree.
>
> The use_connect option was made to avoid sending ACM when the dialplan
> would in any case cause ANM to be sent immediately afterwards; this
> produces an annoying cut-off dial tone for voice mail or other automatic
> answering dialplans.
>
> But if the dialplan instead is used to further route the call via SIP or
> something, sending ACM is good; once we start executing the dialplan the
> address is certainly considered complete, as there is no way to process any
> extra digits anyway.
>
> > Christian's path will ensure that ACM is sent before any CPG or ANM is
> > sent, if you also specify use_connect in the configuration file. However,
> > the patch is wrong because it implicitly changes timeout values. If
> > chan_ss7 does not receive CPG or ANM, and consequenly does not send ACM
> > to the calling swith, then the calling switch, after sending IAM, will
> > timeout waiting for ACM, rather than waiting for ANM or CON. These
> > timeout values are different.
>
> Yeah. Asterisk does not work well as a general SS7/ISUP switch/router.
>
> The use_connect option, and any implicit/explicit sending of ACM controlled
> by dialplan, is at best hacks that may be useful in special situations if
> used carefully.
>
> > There is one more issue in the patch: the chunk
> >
> > @@ -886,7 +886,13 @@ static int ss7_indicate(struct ast_channel *chan,
> > int condition, const void* dat
> >    case AST_CONTROL_RINGING:
> >      ast_log(LOG_DEBUG, "Sending ALERTING call progress for CIC=%d
> > in-band ind=%d.\n",
> >  	    pvt->cic, pvt->has_inband_ind);
> > -    ss7_send_call_progress(pvt, 0x01);
> > +    if (pvt->state == ST_GOT_IAM) {
> > +      isup_send_acm(pvt, 1);
> > +      pvt->state = ST_SENT_ACM;
> > +    } else {
> > +      ss7_send_call_progress(pvt, 0x01);
> > +    }
> > +
> >
> > should be
> >
> > @@ -886,7 +886,12 @@ static int ss7_indicate(struct ast_channel *chan,
> > int condition, const void* dat
> >    case AST_CONTROL_RINGING:
> >      ast_log(LOG_DEBUG, "Sending ALERTING call progress for CIC=%d
> > in-band ind=%d.\n",
> >  	    pvt->cic, pvt->has_inband_ind);
> > -    ss7_send_call_progress(pvt, 0x01);
> > +    if (pvt->state == ST_GOT_IAM) {
> > +      isup_send_acm(pvt, 1);
> > +      pvt->state = ST_SENT_ACM;
> > +    }
> > +     ss7_send_call_progress(pvt, 0x01);
> > +
> >
> > otherwise chan_ss7 will not pass on the first received indication.
>
> Thanks. Yes, it seems some more work is needed for this, probably any
> initial indication should be encoded as parameters in the ACM when
> possible, and sent as separate CPG when not.
>
>  - Kristian.
>
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-- 

Kind regards,
Barry O'Donovan

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