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Concern on the M3UA SSNM request, DUPU

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I was referring the rfc4666 for M3UA and have few concerns regarding the DUPU SSNM message. The specification says that a DUPU indicates the unavailability of a certain user part.
If I may quote "The DUPU message is used by an SGP to inform concerned ASPs that a remote peer MTP3-User Part (e.g., ISUP or SCCP) at an SS7 node is unavailable"
I have two questions.
1. How these concerned ASPs are identified. Is it upon receiving a MTP-Transfer for a particular user part (say SCCP) or can it be sent periodically for a given ASP ?
2. I could not find any SSNM message that indicates a User Parts Availability. Am I wrong here to expect such a message and if so how come a concerned ASP know if a certain User Part is available at a given point code.

It would be an immense help if anyone could clarify the aforementioned concerns.

posted Jul 21, 2016 by anonymous

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Saw a SS7/Sigtran query after a long time,
1. This is part of network configuration.
2. In MTP3 there is something called UPU for unavailability, UPA for availability and UPT for user part test if UPA is missed as MTP3 is a connection-less protocol.
commented Jul 21, 2016 by Salil Agrawal

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