Subject: [Sigtran] Needs clarification on handling of SCON message

From: Deepak Gunjal <[email-masked]>
Date: Mon, 5 Sep 2011 00:35:15 +0530

Hi,

I have one query regarding the SCON message handling between SG and ASP.

Suppose a SG informs one of the Active ASP serving an AS that one of the point code in MTP3 network has become congested and hence sends the SCON message with congestion level say 1 to ASP.

After receiving the SCON message with congestion level 1, the ASP starts the audit procedure and starts sending the DAUD message for that destination.

Now when the destination point code in MTP3 network become uncongested, can a SGP inform the ASP by sending a DAVA message or it always informs by sending SCON message with congestion level as 0.

And what if say after sending the initial SCON message to ASP with congestion level 1, the SG gets restarted. After restart would it be a DAVA message sent to ASP, on receiving it the ASP clears the congestion level set earlier and marks the destination point available and informs the higher layers.

Regards
Deepak

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From: "Nemana, Satya" <[email-masked]>
Date: Mon, 5 Sep 2011 04:00:25 -0400

Deepak,

RFC 4666 Section 4.5.3

<snip>

The SGP SHOULD respond to a DAUD message with the MTP3
availability/congestion status of the routeset associated with each
Destination Point Codes in the DAUD message.  The status of each SS7
destination requested is indicated in a DUNA message (if
unavailable), a DAVA message (if available), or a DRST (if restricted
and the SGP supports this feature in national networks).  For
national networks, the SGP SHOULD additionally respond with a SCON
message (if the destination is congested) before the DAVA or DRST.

<snip>

So, SGP should always send DUNA/DAVA/DRST and SCON.

If there is no congestion, the level should be 0 in the SCON.

After SGP restart, I would expect the SGP to clear all the SS7 node
status to available and not congested as per standard MTP procedures.

If there are TFC messages from the SS7 network to the SGP indicating the
remote node is still congested (1/2/3) the SGP should once again
broadcast SCON and respond to DAUD accordingly with DRST/DAVA and SCON.

If the ASP had cleared the status to Unavailable/Un-congested when the
SGP was down, it should now update the status again with the received
DUNA/DRST/DAVA and SCON messages from the SGP.

As per 4.5 (MTP Restart), SCON "can" be sent by the SGP on restart.

Regards,

Satya

________________________________

From: [email-masked] [mailto:[email-masked]] On
Behalf Of Deepak Gunjal
Sent: 04 September 2011 20:05
To: [email-masked]
Subject: [Sigtran] Needs clarification on handling of SCON message

Hi,

Suppose a SG informs one of the Active ASP serving an AS that one of the
point code in MTP3 network has become congested and hence sends the SCON
message with congestion level say 1 to ASP.

After receiving the SCON message with congestion level 1, the ASP starts
the audit procedure and starts sending the DAUD message for that
destination.

Now when the destination point code in MTP3 network become uncongested,
can a SGP inform the ASP by sending a DAVA message or it always informs
by sending SCON message with congestion level as 0.

And what if say after sending the initial SCON message to ASP with
congestion level 1, the SG gets restarted. After restart would it be a
DAVA message sent to ASP, on receiving it the ASP clears the congestion
level set earlier and marks the destination point available and informs
the higher layers.

Regards

Deepak

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