[asterisk-ss7] KNK SS7-27 - first experiences - part 1

Pavel Troller patrol at sinus.cz
Mon Jun 24 07:02:16 CDT 2013

  I would like to share my expiernce with deployment of this experimental SS7
  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,

More information about the asterisk-ss7 mailing list