Re: M3UA AS override mode from SGP perspective

Andrew,

Does the RFC make you think that you could get away with forming
two associations from the same `ASP'?  Pretty much assuming that
ASP designers would be netheads and SG designers would be bellheads
we provided the SGP with the power to enforce a single association
from an ASP at all times:

RFC4666/3.8.1 Error (p.65)

  The "ASP Identifier Required" error is sent by an SGP in response to
  an ASP Up message that does not contain an ASP Idetifier parameter
  when the SGP requires one.  The ASP SHOULD resend the ASP Up message
  with an ASP Identifier.

  The "Invalid ASP Identifier" error is sent by an SGP in response to
  an ASP Up message with an invalid (i.e., non-unique) ASP Identifier.

Also, the typical arrangement forseen was that the SGP would act as a
server and the ASP as a client for SCTP connections.

So, when the SGP gets a association attempt from, say, Host A that is
configured for 1 ASP, and has already formed an association and is
ASP Up, it is fully within its rights to simply refuse the second
association.

When Host A is configured for more than one ASP, and the SGP cannot
tell which ASP is connecting at any given time from its source or
destination address and port, it can demand an ASP Identifier (when
one is not provided by the ASP) using the error, "ASP Identifier
Required".  Should the ASP respond with the same ASP Id that was
provided for another association, the SGP sends the error, "Invalid
ASP Identifier".  Because the ASP Id is always unique and because it
MUST be placed in the Notify(Alternate ASP_Active) when available,
there will nevery be any confusion.  One association, one ASP.

Nevertheless, the SGP might not care what the ASP Id's are, and might
not care to have one supplied.  It might just assume that they are
all unique and treat your two associations as going to different ASPs
regardless of whether you view them as the same or not.  In this case
if you view them as one ASP from your end, the SGP will be sending
you Notify(Alternate ASP_Active) on one association when the other
goes ASP Active, with with no ASP Id (you didn't care to provide one).
But then it will be your fault: just view them as two different ASPs,
the same way that the SGP does and you will not have a problem.

Which then begs the question: "Why would you ever need to form two
associations _from_ _the_ _same_ _ASP_??"  Why not simply consider
one association as coming from ASP#1 and the other from ASP#2?  There
is no requirements placed on the mapping of ASPs to hosts or processes
(and the term "process instance" in the ASP definition is really
really vague).

The only need is for the SGP to identify the ASPs at the end of each
association so that it can run its state machines and provide
notifications within the requirements of the RFC.

--brian


Andrew Booth wrote:                         (Fri, 08 Oct 2010 15:44:26)
> 
>    Hi Brian,
>    I've certainly always thought about it that way, but I don't see this
>    as a requirement in the RFC.  Did I miss it?
>    Will anything break if an ASP has more than one association to an SGP?
>    Thanks for any info,
>    Andrew

-- 
Brian F. G. Bidulock
[email protected]
http://www.openss7.org/