Re: What are the chances that SG may not send Notify messages to AS (M3UA)

Deepak,

AS state is maintained on an SG-wide basis.  That is, there is one
coordinated AS state that is the same for all SGP that make up an
SG.  When this AS state changes, each ASP that is not in the
ASP-Down state (for some SGP) must be sent a notify message
informing the ASP of the change of AS state.

When an ASP moves from the ASP-DOWN to ASP-INACTIVE state within an
AS, the SG should inform the ASP of the coordinated AS state
provided that it hasn't done so already.  It is not optional.  It is
recommended and you need a very good reason not to do so in each
circumstance.

What are some reasons for not sending a Notify message when an
ASP-DOWN to ASP-INACTIVE transition occurs:

1. ASP-DOWN to ASP-INACTIVE transitions are per-SGP.  AS state is
   coordinated SG-wide.  The SG need only inform the ASP of AS state
   once (not once for each SGP in the SG).

2. The ASP-DOWN to ASP-INACTIVE transition causes the AS state to
   move from AS Down to AS Inactive.  In this case a Notify message
   must be send to signal the AS state transition and a separate
   message to inform the ASP of the current state is unnecessary.

I can't think of any more of the top of my head.

So what can you do if you are faced with a broken SG implementation
that ignores this recommendation?  First, tell them to fix it or
present the very good reasons why they are not sending it.  Then, if
you are forced to deal with such a broken implementation, consider
the following:

If the ASP-DOWN to ASP-INACTIVE state transition causes the AS to
change state from AS-DOWN to AS-INACTIVE then the Notify message
MUST be sent per 4.3.4.5.  Therefore, if the ASP does not receive a
Notify message, the SG is either terribly broken or the AS was not
in the AS-DOWN state previously: that is, the ASP is not the first
ASP in the AS.  This is actually a lot of information.  If no Notify
is received, there exists some other ASP in the AS that is aware of
the SG's view of AS state.  ASPs in an AS need to coordinate
themselves.  The ASP might obtain the AS state from this other ASP.

I actually brought this passage up as a last call issue on M3UAv02
(where is was added).  The issue was not resolved at last call.  In
fact there were many issues brought up at last call that were not
resolved.  The issue was that the ASP-DOWN to ASP-INACTIVE state
transition is not necessarily due to the ASP Up procedure  (it can
also occur as a result of the Registration procedure).  Therefore,
mention of the "ASP-UP receptor" is misleading.

When an ASP transitions from the ASP-DOWN to ASP-INACTIVE state for
the first time in a particular AS (for whatever reason) the ASP
should be informed by the SG of the current AS state with a Notify
message, unless it has already or will otherwise be notified of the
AS state.

Can you think of any good reason not to do that in a given
circumstance?

The danger of an SG not sending this Notify message is that the
ASP might sit around waiting for one.  This could be a bad thing
if the current AS state happens to be AS-ACTIVE (with insufficient
ASPs active), AS-PENDING or AS-INACTIVE.

--brian




Deepak Gunjal wrote:                         (Wed, 23 Dec 2009 12:39:16)
> 
>    Hi Chris,
> 
> 
> Thanks for your detailed reply. From the same section, 2^nd
> paragraph "When an ASP moves from ASP-DOWN to ASP-INACTIVE within
> a particular AS, a Notify message SHOULD be sent, by the ASP-UP
> receptor, after  sending the ASP-UP-ACK, in ord er to inform the
> ASP of the current AS state."
>  
> 
>    Now as per the above statement when an ASP moves from ASP-DOWN
>    to ASP-INACTIVE it seems that the Notify could be optional
>    (SHOULD clause) and this is the cause of my doubt which a bit
>    is an contradictory statement what has been written in the
>    beginning of this section 4.3.4.5.
> 
> 
>    Can you please confirm if there is some misinterpretation from
>    my side?
> 
> 
>    Thanks
> 
>    Deepak
> 


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