Re: DATA msg from SGP to ASP in DOWN state.

Mahantesh,

Consider that ASPDN and ASPDN Ack messages are sent on stream 0 whereas
DATA, SNMM on other than stream 0, and ASPTM can be sent on a stream
other than zero.  This means that DATA, SNMM and ASPTM can always be
delayed until after the ASPDN or ASPDN Ack arrives, even when they were
transmitted ahead of these messages.  Therefore, it cannot be considered
and error simply because a DATA, SNMM or ASPTM (sent on other than
stream 0) arrives when the ASP is in the ASP-DOWN state, either at the
ASP or at the SGP.  Sending an ERROR would be IMO inappropriate.

Normally, within a platform, queues would be flushed before deactivating
in this manner.  A similar procedure to flushing of queues could be
performed as follows:

1. ASP stops traffic to the SGP and sends a BEAT on each traffic stream
   and awaits a BEAT Ack.

2. Once all the BEAT Acks have been received, send ASPDN.

3. On receipt of the ASPDN, the SGP stops traffic and sends a BEAT on
   each traffic stream and awaits BEAT Ack.

4. Once all the BEAT Acks have been received, send ASPDN Ack.

These procedures are described in

 http://www.ietf.org/internet-drafts/draft-bidulock-sigtran-corid-04.pdf

This procedure could ensure that there is no DATA, SNMM or ASPTM queued
on a traffic stream before the ASP Down procedure is initiated or
completed.  However, some standards bodies (ETSI), in their infinite
wisdom, forbade the BEAT/Ack messages.

Therefore, either an ASP or and SGP receiving DATA, SNMM or ASPTM when
the ASP is in the ASP-DOWN state should process the message (if
possible) or, otherwise, discard it.  The pertinent reference is
RFC4666 4.3.4.1 (ASP Up Procedures):

>  The ASP must wait for the ASP Up Ack message before sending any other
>  M3UA messages (e.g., ASP Active or REG REQ).  If the SGP receives any
>  other M3UA messages before an ASP Up message is received (other than
>  ASP Down; see Section 4.3.4.2), the SGP MAY discard them.

So, all messages (other than ASP Down) MAY be discarded in the ASP-DOWN
state.

Note that the same situation is true for ASP Inactive and ASP Inactive
Ack, as described in RFC4666 4.3.4.3. (ASP Active Procedures):

>                                        ...  If the SGP or IPSP
>  receives any Data messages before an ASP Active message is received,
>  the SGP or IPSP MAY discard them.  ...

Also the situation is alluded to in RFC 4666 section 3.8.1. (Error):

>  The "Unexpected Message" error MAY be sent if a defined and
>  recognized message is received that is not expected in the current
>  state (in some cases, the ASP may optionally silently discard the
>  message and not send an Error message).  For example, silent discard
>  is used by an ASP if it received a DATA message from an SGP while it
>  was in the ASP-INACTIVE state.  ...

The reason for the "MAY" associated with the discard of messages is
because the SGP (and ASP for that matter) must always be permitted to
process the message if it is capable of doing so.

Hope that helps.

--brian

On Fri, 15 Dec 2006, Mahantesh wrote:

> 
>    Hi there,
> 
> 
> 
>    In ASP-DOWN procedure,
> 
>    It  is  mentioned that if ASP receives a message from any of the below
>    mentioned CLASSES
> 
>     1. TRANSFER [DATA]
>     2. SSNM
>     3. ASPTM.
> 
>    it shouldn't be received at ASP.
> 
>    Whereit will go. Whether to DISCARD it or send an ERROR msg.
> 
> 
> 
>    Can I add this perticular one as a testcase at ASP side?
> 
>    -Mahantesh 
> 
>    IntelliNet Technologies

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-- 
Brian F. G. Bidulock    ¦ The reasonable man adapts himself to the ¦
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http://www.openss7.org/ ¦ trying  to adapt the  world  to himself. ¦
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