Subject: [Sigtran] M3UA : How to deal whit Unexpected ASPSM/ASTM Message (Jacky Chen)

From: [email-masked]
Date: Thu, 21 Jun 2007 08:54:10 +0800

Thanks,brain

but new questions are :
1: for  question One,when received unexpected ASP INACTIVE Ack message,ASP
should Send ASP-DWON Message to
return itself to its previous state???

2: for question Two: why not discard the unexpected  ASP UP ACK or ASP
INACTIVE ACK OR ASP ACTIVEACK
  When ASP IS IN ASP-DOWN Status?
because when ASP ENTER ASP INACTIVE When received  unexpected ASP Up Ack
message,the AS Contain THE ASP maybe enter into AS-INATIVE Status
temporarily ,This is not reasonable.

i think in rfc4666,it need to explain how to deal with every unexpected
ASPSM/TM Message in every as/asp status .

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Thu, 21 Jun 2007 00:05:48 -0600

chen.puran,

[email-masked] wrote:               (Thu, 21 Jun 2007 08:54:10)
> return itself to its previous state???

Quite simply, when the ASP receives an unsolicited ASP Inactive Ack message
it places the ASP in the ASP-INACTIVE State for the AS indicated in the ASP
Inactive Ack message.  If the ASP was not already in the ASP-INACTIVE State
for the AS indicated in the unsolicited ASP Inactive Ack message, then the
ASP should initiate steps to return the ASP to the previous state for the AS.
If that previous state was ASP-DOWN (for _all_ AS), the way to initiate
returning the ASP to the appropriate state for the AS is to send an ASP Down 
message.

>   When ASP IS IN ASP-DOWN Status?

Why do you have ASP Active Ack message in this list?  Nowhere does it say
in the RFC to use these unsolicited procedures for ASP Active Ack.  Also,
they really just pertain to ASP Inactive Ack and ASP Down Ack, where the
SGP is using these messages to force the ASP to the ASP-INACTIVE or ASP-DOWN
states.

> temporarily ,This is not reasonable.

Completely reasonable: the SGP is required to send ASP Up Ack in
response to ASP Up, in which case the ASP Up Ack is always expected
by the ASP, cf. RFC 4666 4.3.4.1.  The only reason for an unexpected
ASP Up Ack is some sort of error, in which case the procedure will
attempt to properly resynchronize state.

> ASPSM/TM Message in every as/asp status .

It does: but you need to thoroughly read the RFC to see that.

--brian

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

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From: [email-masked]
Date: Thu, 21 Jun 2007 14:17:52 +0800

Thanks,brain
your anser:

1) Quite simply, when the ASP receives an unsolicited ASP Inactive Ack
message
it places the ASP in the ASP-INACTIVE State for the AS indicated in the ASP
Inactive Ack message.  If the ASP was not already in the ASP-INACTIVE State
for the AS indicated in the unsolicited ASP Inactive Ack message, then the
ASP should initiate steps to return the ASP to the previous state for the
AS.
If that previous state was ASP-DOWN (for _all_ AS), the way to initiate
returning the ASP to the appropriate state for the AS is to send an ASP
Down
message.

 my question:
    jack chen:if do as you say,Then One unsolicited ASP Inactive Ack(for
one AS) message will affet all AS(s)'s
status,it is good idea?

2)  Completely reasonable: the SGP is required to send ASP Up Ack in

   my question:
    jack chen:because it is unexpected message,we can not think it is
expected message just only of sort ?!

    maybe because of the error of the sgp' softward code.
       so I think ASP should make itself stronger and not to  affect all
AS's Status.

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Thu, 21 Jun 2007 02:43:24 -0600

chen.puran,

[email-masked] wrote:                                    (Thu, 21 Jun 2007 14:17:52)
> one AS) message will affet all AS(s)'s

No, because the ASP is ASP-DOWN for all the other AS.  See the state
diagram in RFC 4666 Figure 3 and the description above the diagram
and the description in 4.3.4.1.  Note that the only transition from
ASP-INACTIVE to ASP-DOWN is using the ASP Down message which results
in the ASP moving to the ASP-DOWN state for _all_ AS.  So, if a given
AS is in the ASP-DOWN state and the ASP receives an ASP Inactive Ack,
_all_ the AS are in the ASP-DOWN state.  Sending an ASP Down message
in this case has precisely the desired effect.

> expected message just only of sort ?!

Whenever there is an ASP Up Ack outstanding for sent ASP Up message (no
matter how many ASP Up messages were sent without an ASP Up Ack response),
the ASP UP Ack message is "expected", because the specification REQUIRES
the SGP to send it.

>        so I think ASP should make itself stronger and not to  affect all

Read the procedures from 4.3.4.1 for the _SGP_side.  When the SGP sends
ASP Up Ack it is required to place all of the AS for the ASP in the
ASP-INACTIVE state.  If the ASP does not do the same thing whenever it
receives an ASP Up Ack, its state will not match that of the SGP.  So, in
fact the ASP makes itself stronger by synchronizing its state with the SGP
in such an unexpected event rather than blindly assuming that the SGP
should know its state by some telepathic means outside the protocol.

--brian

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