Re: M3UA ASP mode vs IPSP mode

> Hi there, 
> 
> When not using a signalling gateway, IPSP mode, do I still 
> need to worry
> about SSNM messages e.g. 
>  1        Destination Unavailable (DUNA)
>  2        Destination Available (DAVA)

My interpretation of the RFC is that these messages are only sent
by an SGP, so will not appear on an IPSP connection.
This also implies that it is inappropriate to send a DAUD on an
IPSP connection.
Since M3UA is carrying the MTP3 service interface, and DUNA/DAVA
carry the MTP pause/resume events there is also no where for
event to originate from.
(This is all similar to the fact that they cannot originate from
an ASP.)

> Are such messages only raised if the DPC goes out of service

In IPSP mode the existance of the SCTP connection (and the
non-rejection of the ASP messages) is enough to indicate that
the users are in service.

OTOH I'm not at all clear about the implications of the last
paragraph of section 4.6 (MTP3 restart).
The MTP3 restart section itself doesn't seem to allow for
'white book' restart - where, in order to avoid large amounts
of network traffic, destinations are assumed to be accessible
at restart.

> I have seen such messages in ASP mode directly following 
> SSP/SSA messages. 

Even in AS-SG mode the SG shouldn't really be sending DAVA/DUNA
except when the MTP3 state changes - except in response to a DAUD
or a message being sent to an inaccessible destination.

	David

Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)  
P Please consider the environment and don't print this e-mail unless you really need to