Subject: RE: [Sigtran] ASP Identifier

From: "Goel, Soni" <[email-masked]>
Date: Fri, 1 Mar 2002 12:30:19 -0800

Hi,

Please see my comments below.

- Soni
-----Original Message-----
From: Brian F. G. Bidulock [mailto:[email-masked]]
Sent: Thursday, February 28, 2002 6:05 PM
To: Goel, Soni
Cc: Sigtran (E-mail)
Subject: Re: [Sigtran] ASP Identifier

Soni,

Goel, Soni wrote:                                           (Thu, 28 Feb
2002 16:52:20)
> Hi,
> 
> Why will an ASP need to know the identity of another ASP to decide which
> traffic it wants to take over ? After the ASP receives the identity of
> Application Servers, it becomes a local decision at ASP to determine which
> AS it wants to be active for.

RC is not part of the ERR("ASP Failure") message.The ASP does not receive
the identify of the AS.  
[Soni] RC is a parameter in Notify message.
If the ASP failure does not change the overall state
of the AS (e.g. loadshare with ASPs > n), the ASP will not receive AS
notification either.  This still means that some AS are running
"vulnerable".
[Soni] In such a case the minimum number of ASPs required should be (n+1).
So that if an ASP goes down and the AS becomes "vulnerable" then the Notify
message with state "Insufficient Resources Active for an AS" can be sent
with the RC to the Inactive ASPs in the AS. This removes the need for "ASP
Failure".

If the ASP has the identify of the failed ASP, it can determine for which AS
it is sparing the other ASP and become active for those AS before things
become critical.  
[Soni] For the ASP to determine for which AS is has to come Active, it needs
to know only the identity of the AS.
Unfortunately, the SG does not notify when the AS only has
`n' processors, just when it has `n-1'.
[Soni] Please see the first two comments.

> Moreover, once an ASP becomes active for an AS in Override mode, it has to
> handle all the AS traffic. And if the AS is in Loadshare mode then it is
the
> SGP which decides the traffic distribution based on the Loadshare
algorithm.

But you forget, as above, that the ASPs are still responsible for
determining
how many ASPs are serving a loadshare AS.
[Soni] ASPs need to know the AS which is getting affected because some ASP
has failed, so that it can come active for this AS.

Also, in broadcast mode, the ASPs determine which traffic distribution they
are serving, not the SG.  So, broadcast mode is another example of where an
ASP needs to know the identify of the failed ASP to determine the traffic
that
it needs to assume.
[Soni] It seems that ASP Id and ASP Failure status in Notify message are
only required for Broadcast mode.
Thus, ASP Id in ASP Failure is again necessary.

[Soni] Draft states that ASP Id MUST be present in Notify message in case of
AS State Change and "Alternate ASP Active". This is also not required.

--brian

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

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---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Fri, 1 Mar 2002 15:14:20 -0600

Soni,

Please see comments below...

Goel, Soni wrote:                                           (Fri, 01 Mar 2002 12:30:19)
> Goel, Soni wrote:                                           (Thu, 28 Feb

Well, no.  The behavior of the SG in this case could be to move to AS_PENDING.
insufficient resources and just sufficient resources are two different things.
ASP Failure is still required to avoid pending at the SG.

> to know only the identity of the AS.

RC is not in the NTFY("ASP Failure") message.  And for good reason in SUA
where the number of AS supported by an ASP could be a very large number.

> only required for Broadcast mode.

ASP Id is also required in loadshare as above.

> AS State Change and "Alternate ASP Active". This is also not required.

This is required in Override so that the ASP can determine the identity
of the overriding ASP.  The ASP can use this information to inform local
management of who took over, as well as permitting the now INACTIVE ASP
to determine its next course of action.  (For example, for some ASPs it
could be persistent and override again.)

An example scenario would be where two ASPs are sparing each other on a
given AS: ASP1 is active and ASP2 is not.  A third ASP3 overrides the
AS even though it has no business doing so.  ASP1 gets NTFY("Alternate
ASP Active", ASP3) and can determine that the override was in error and
perform its own ASPAC REQ to override back.

Soni, ASP Id is a useful feature of the protocol, but only when included
in the proper messages.  It is an extra piece of information that the SGP
has at its disposal which permits ASPs to make informed decisions about
what action to take in response to these events.  The focus of the protocol
has always been to put the ASPs in control of activation and deactivation
and have the SG just satisfy those requests.  That is why NTFY messages
are largely adivisory only.  As advisory messages, they should contain as
pertinent information.  The Id of an ASP in an ASP related notification
message must include the ASP Id, otherwise it is worthless to the receiver.

--brian

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