Hi!
So, I'm replying to my own original post, to keep the question and a
possible answer together without any excessive or unrelated information.
I hope I've found the cause of the problem and I hope I solved it. A
modified libss7 is now online and I'm waiting for busy hours to see, whether
it will help.
The problem is, that in the isup_rel() function, all the important
got_sent_msg flags are cleared, so the stack "forgets" a preceding call
state:
... isup_rel():
c->got_sent_msg |= ISUP_SENT_REL;
c->got_sent_msg &= ~(ISUP_SENT_IAM | ISUP_PENDING_IAM | ISUP_CALL_CONNECTED | ISUP_GOT_IAM | ISUP_GOT_CCR | ISUP_SENT_INR);
...
So, an incoming MSU, which was perfectly legitimate before sending REL,
is now handled as unexpected.
My solution adds the following code to the isup_receive() function for
every message, which can confuse the stack by the discovered cause
(an example for ACM message):
case ISUP_ACM:
+ if (c->got_sent_msg & ISUP_SENT_REL) {
+ ss7_message(ss7, "Got unexpected ACM after sending REL on CIC %d PC %d, ignoring ", c->cic, opc);
+ return 0;
+ }
if (!(c->got_sent_msg & ISUP_SENT_IAM)) {
ss7_message(ss7, "Got ACM but we didn't send IAM on CIC %d PC %d ", c->cic, opc);
return isup_handle_unexpected(ss7, c, opc);
}
If my change will prove good, I'm planning to remove the ss7_message() to
limit the stack verbosity, as these situations are relatively frequent under
heavy load and I think they are moreless logical and normal.
I would be glad for some words from the KNK branch maintainer(s), whether to
create a JIRA issue and put my patch there or how to proceed now in general.
With regards,
Pavel
> Hi!
> I would like to share my expiernce with deployment of this experimental SS7
> branch.
> The first impressions are good, especially the timers seem to work well,
> saving many calls from being frozen.
> However, there are still some strange things, which I would like to discuss
> here, one by one.
> The first one is, that the channel sometimes doesn't recognize a message
> (mostly RLC), even it comes from an action initiated by the channel itself.
> Typically, the following is appearing often:
>
> [Jun 24 13:33:41] ERROR[3975]: chan_dahdi.c:14406 dahdi_ss7_error: [1] ISUP timer t17 expired on CIC 27 DPC 4097
> [1] Got RLC but we didn't send REL/RSC on CIC 27 PC 4097 reseting the cic
>
> As I understand, there were some timeouts and now the channel tries to
> recover by sending RSC and firing T17. However, it seems that it immediately
> rejects RLC, which comes back as a response to the RSC which was just sent
> upon expiry of T17. And this appears again and again in the rhythm of T17,
> and the channel is not operational.
> ss7 show calls shows the following line for the misbehaving CIC:
> 27 4097 11 IAM IAM
>
> Or, a very similar situation:
> [2] Got SUS but no call on CIC 48 PC 4096 reseting the CIC
> [2] Got RLC but we didn't send REL/RSC on CIC 48 PC 4096 reseting the CIC
>
> The first question is, why there was no call while SUS was received. My
> idea is, that both the parties hung up their phones in the same time and
> that the call was undergoing destruction on Asterisk side (REL just sent
> or something like this), while SUS arrived. Maybe the call was marked as
> cleared even before RLC came back ? OK, I can understand this. But
> if the CIC was reset as the first message says (i.e. RSC was sent), why the
> RLC going back is not recognized then ?
>
> Or, just now the following appeared:
>
> [1] Got ACM but we didn't send IAM on CIC 10 PC 4097 reseting the cic
> [1] Got RLC but we didn't send REL/RSC on CIC 10 PC 4097 reseting the cic
>
> Again, it's questionable, why this happened, but the second line seems
> to indicate some brokeness again.
>
> To explain: The channel is operating on a gateway equipped with 16 E1s
> and current traffic is about 10 CAPS, there are two linksets to two
> cooperating exchanges. They are EWSDs, which have very mature and stable
> SS7, so I'm almost sure that they are not making signalling errors.
>
> With regards,
> Pavel
>
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