Almost forgot. Please do not post patches (if any) in this list, but
attach them to the SS7-27 issue instead with proper license agreement,
so it can be included in Asterisk codebase
On 2013-06-26 14:57, Kaloyan Kovachev wrote:
> Hi all,
> sorry for joining so late, but i am on holidays (by the end of the
> week) and rarely checking my mailbox. Thanks to bad weather i did that
> today :)
>
> To the OP:
> while reading the first posts i thought it is an old problem with
> REL/RSC loop (persistent on start with ANSI signaling) which was fixed
> in libss7 instead of sig_ss7, but not sure if it is a similar yet
> different one or it is the same issue. It really is a (remaining)
> problem if we receive RLC on previous REL, but after we have sent RSC.
> I was thinking to clear the old status bits after we receive RLC, but
> this will not fix the double RLC received problem and we can't ignore
> the first one (or just clear the SENT_REL flag), because we may never
> get a second one, so it should probably be better to ignore sending
> second RSC inside isup_handle_unexpected() if the previous one was
> sent T17 (timer seconds) ago. Because the timer is stopped on RLC it
> should be another timer or some flag to ignore it's expiration and not
> reset again ... will work on this next week when i am back.
>
> The code in my branch is actually Domjan Attila's version (the patches
> attached to the SS7-27 issue) ported to later Asterisk versions with
> very few additions/modifications, so the muffins are for him, while
> the bugs are from me :)
>
> P.S.
> apologies for top posting - the connection is unstable and i had to
> write the post offline and just copy/paste it
>
> On 2013-06-26 06:42, Pavel Troller wrote:
> 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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