Subject: [Sigtran] M3UA - What state for AS in loadshare mode?

From: Peter Woodhouse <[email-masked]>
Date: Mon, 24 Oct 2005 14:56:18 +0100

I have a question regarding the state of the AS in an N+K redundancy 
model and the sending of NTFYs.

Consider the situation where the AS requires 2 ASPs to be active before 
the AS is considered active when operating in loadshare mode.
Both ASPs are brought into an ACTIVE state.

What happens when one of the ASPs becomes INACTIVE?  The RFC doesn't 
appear to be clear.
It looks like we should send a NTFY (Insufficient resources).
If the AS state goes to PENDING and then to INACIVE after Tr, we should 
also send a NTFY (PENDING) as well?

The other 2 possibilities are
1) The AS state goes straight to INACTIVE - we send a NTFY (INACTIVE)
2) The AS state stays ACTIVE - this would seem a bit strange to me. Why 
would you consider the AS ACTIVE when you only have 1 ACTIVE association 
when associations are becomeing INACTIVE, but consider the AS INACTIVE
when associations are coming up?

 From the state transition diagram Figure 4, it implies we should always 
go PENDING then INACTIVE. However, the text in 4.3.2 states "AS-PENDING: 
An active ASP has transitioned to ASP-INACTIVE or ASP DOWN and it was 
the last remaining active ASP in the AS."
Additionally in 4.3.4.4 "If no other ASPs in the Application Server are 
in the state ASP-ACTIVE, the SGP MUST send a Notify message 
("AS-Pending") to all of the ASPs in the AS which are in the state 
ASP-INACTIVE.

So in summary, what NTFY messages should be sent and what state is the 
AS when one of the associations becomes INACTIVE.

Pete

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From: "Barry Nagelberg" <[email-masked]>
Date: Mon, 24 Oct 2005 10:22:24 -0400

Pete,

I think that draft-ietf-sigtran-rfc3332bis-05.txt is clear. The procedures are as follows:

1. If the AS moves to the INACTIVE state, the SG MAY send NTFY(Insufficient resources). See Section 4.3.4.4 (ASP
Inactive Procedures).

2. Upon an AS state change, SG should always send a NTFY(AS state change) msg to the ASP. So if the AS moves to the
PENDING state, the SG should send a NTFY(AS-PENDING) msg to the ASP. See section 3.8.2 (Notify)

<snip>
      The Status Information parameter contains more detailed
      information for the notification, based on the value of the Status
      Type. If the Status Type is AS-State_Change the following Status
      Information values are used:

         1    reserved
         2    Application Server Inactive (AS-INACTIVE)
         3    Application Server Active (AS-ACTIVE)
         4    Application Server Pending (AS-PENDING)

      These notifications are sent from an SGP to an ASP upon a change
      in status of a particular Application Server. The value reflects
      the new state of the Application Server.
<snip>

3. The AS state never goes from ACTIVE straight to INACTIVE. It always goes through PENDING.

Barry Nagelberg
Adax, Inc.

-----Original Message-----
From: [email-masked] [mailto:[email-masked]]On
Behalf Of Peter Woodhouse
Sent: Monday, October 24, 2005 9:56 AM
To: [email-masked]
Subject: [Sigtran] M3UA - What state for AS in loadshare mode?

Pete