Interpretation of RFC4666 regarding M3UA SCON message

Hi,


We would like to ask you to interpret of RFC4666 regarding M3UA SCON message.

Recently an M3UA congestion occurred in a telekom network under our support.

The signalling config:

SG1 and SG2 are M3UA relay between ASP1 and ASP2. There is a direct association between ASP1 and ASP2 also (no traffic on that).



                         ASP2
           /  |  \
          /   |   \
         /    |    \
        SG1   |    SG2
         \    |    /
          \   |   /
           \  |  /
             ASP1

IP backbone packet drop occurred between ASP1 and SG1/SG2.

This led to ASP1 to send M3UA SCONs to all of its M3UA peers (SG1, SG2, ASP2).

These SCONs contained SG1 and SG2 as "affected point code".

When ASP2 received SCONs it started congestion timer and stopped signalling towards SG1 and SG2. This caused disturbance in the network.

When timer expired in SG2 the traffic resumed until the next SCON from ASP1.

The vendor of ASP1 says that they sent the SCON according to RFC4666 3.4.4:

RFC4666  3.4.4.  Signalling Congestion (SCON)

   The SCON message can be sent from an SGP to all concerned ASPs to
   indicate that an SG has determined that there is congestion in the
   SS7 network to one or more destinations, or to an ASP in response to
   a DATA or DAUD message, as appropriate.  For some MTP protocol
   variants (e.g., ANSI MTP) the SCON message may be sent when the SS7
   congestion level changes.  The SCON message MAY also be sent from the
   M3UA layer of an ASP to an M3UA peer, indicating that the congestion
   level of the M3UA layer or the ASP has changed.





In our opinion SGSN (ASP) should not send SCON in this situation indicating an other node's point code as "affected point code".


RFC4666 1.4.6 Congestion Management

The M3UA layer at an ASP or IPSP MAY indicate local congestion to an M3UA peer with an SCON message.

Could you explain what exactly "local congestion" means?

What is your opinion, is it allowed for an ASP to initiate an SCON indicating other's point code as "affected point code"?




Thank you for your help

Zoltan Juhasz
Tibor Szakos

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