Re: M3UA: SCON: congestion condition never abates

urte,

Please see comments inline...

urte plesske wrote:                                         (Tue, 23 Oct 2012 16:58:27)
>    Hello, I'm faced with a problem based on the following architecture:
>    AS connected to two SGs
>       AS
>      /  \
>     /    \
>    SG1---SG2
>    SCCP: SGs are making GTTs to route to the ss7 network.
>    MTP configurations on AS:
>    There are two routesets defined on AS, one to SG1 (containing direct
>    route and route over SG2) and to SG2 (containing direct route and route
>    over SG1)
> 
>    SCON message was received by AS from SG2 with affected PC SG1.
>    On AS the route set (PC SG1) was inhibited. No traffic was sent to SG1
>    by AS any more.

This, to begin with, is somewhat peculiar.  The circumstances
under which SG2 would send SCON to the AS concerning SG1's point
code would be:

 - traffic on the association from AS to SG2 is overloading;

 - SG2's SMH function is overloading (in which case it should
   have first attempted a DRST in ANSI-based networks);

 - the C-links between SG2 and SG1 are congested.

Which begs the question, why is the AS sending messages with DPC
of SG1 to SG2?  Is not the direct route between AS and SG1
available and unrestricted?  Perhaps you have already received a
DRST from SG1 concerning its own point-code? (which would not be
correct).

So, that's number 1 problem: Why are you sending M3UA-User
messages from the AS to SG1 via the indirect route through SG2
when there exists a direct route to SG1?

>    Usually the AS would start sending periodic DAUDs messages as a result
>    of the congestion, but because SG1 was got to know as adjacent node, no
>    DAUDs with affected Point Code = Point Code SG1 were sent by any ASP.
>    No SCON messages were sent by SG2 to AS because no DATA and DAUD
>    messages were received to react.
>    The congestion condition never abates.

No, that is incorrect.  You should audit even though the
destination is adjacent.  Following on on my first issue,
you should be auditing SG1 already because there is something
the matter with the direct route for you to have been sending
messages on the indirect route.  The direct route must be
restricted or unavailable, or the AS is doing the wrong thing.

> 
>    Could you please help me with the following questions:
>    How to solve this situation (timer on AS?)?

Send periodic DAUD while point codes are marked congested.
The period should be 1.4 to 2.0 seconds.

>    Is it correct not to audit adjacent nodes?

No it is not.  Adjacent nodes need not be audited for
availability, but they do need to be audited for restriction and
congestion.

>    Can (should) SG2 send a SCON message even there are no DATA and DAUD
>    messages to react?

No, is does not have to.  SG2 only need send SCON to the AS
under the same conditions as an STP would send TFC to an
adjacent signalling point.

>    Where can I find (rfc) the information, that SCON is like TFC and not
>    TFR?

In the sections describing SCON and DRST.  SCON is equivalent
to TFC, DRST is equivalent to TFR.

--brian