Subject: [Sigtran] M3UA IG: section 3.15 reworked

From: "Javier Pastor-Balbas (ECE)" <[email-masked]>
Date: Tue, 17 Jun 2003 16:17:17 +0200

Hi guys, 

Here is the proposed rework for section 3.15 of the IG. We have included 

This proposal includes the latest agreements: arrive to AS-ACTIVE only after n ASPs are in ASP-ACTIVE state but moving to AS-PENDING only when all the ASPs have failed (state != ASP-ACTIVE). Changes with the previous version are therefore concentrated on AS-ACTIVE and AS-PENDING states and their transitions.

Cheers // Javier.

--------- 
Old text: (Section 4.3.2) 
---------

AS-DOWN: The Application Server is unavailable.  This state implies 
that all related ASPs are in the ASP-DOWN state for this AS. Initially the AS will be in this state. An Application Server is in the AS-DOWN state when it is removed from a configuration.

AS-INACTIVE: The Application Server is available but no application 
traffic is active (i.e., one or more related ASPs are in the ASP-
INACTIVE state, but none in the ASP-ACTIVE state).  The recovery 
timer T(r) is not running or has expired. 

AS-ACTIVE: The Application Server is available and application traffic is active.  This state implies that at least one ASP is in the ASP-ACTIVE state.

AS-PENDING: An active ASP has transitioned to ASP-INACTIVE or ASP-DOWN  and it was the last remaining active ASP in the AS.  A recovery timer T(r) SHOULD be started and all incoming signalling messages SHOULD be queued by the SGP. If an ASP becomes ASP-ACTIVE before T(r) expires, the AS is moved to the AS-ACTIVE state and all the queued messages will be sent to the ASP. 

If T(r) expires before an ASP becomes ASP-ACTIVE, and the SGP has no 
alternative, the SGP may stops queuing messages and discards all 
previously queued messages. The AS will move to the AS-INACTIVE state 
if at least one ASP is in ASP-INACTIVE state, otherwise it will move 
to AS-DOWN state. 

Figure 5 shows an example AS state machine for the case where the 
AS/ASP data is preconfigured.  For other cases where the AS/ASP 
configuration data is created dynamically, there would be differences 
in the state machine, especially at creation of the AS.  

                 Figure 5: AS State Transition Diagram

     +----------+   one ASP trans to ACTIVE   +-------------+
     |    AS-   |---------------------------->|     AS-     |      
     | INACTIVE |                             |   ACTIVE    |
     |          |<---                         |             |
     +----------+    \                        +-------------+
        ^   |         \ Tr Expiry,                ^    |
        |   |          \ at least one             |    |
        |   |           \ ASP in ASP-INACTIVE     |    |
        |   |            \                        |    |
        |   |             \                       |    |
        |   |              \                      |    |
one ASP |   | all ASP       \            one ASP  |    | Last ACTIVE
trans   |   | trans to       \           trans to |    | ASP trans to
to      |   | ASP-DOWN        -------\   ASP-     |    | ASP-INACTIVE
ASP-    |   |                         \  ACTIVE   |    | or ASP-DOWN
INACTIVE|   |                          \          |    |  (start Tr)
        |   |                           \         |    |
        |   |                            \        |    |
        |   v                             \       |    v         
     +----------+                          \  +-------------+
     |          |                           --|             |      
     | AS-DOWN  |                             | AS-PENDING  |
     |          |                             |  (queueing) |
     |          |<----------------------------|             |
     +----------+    Tr Expiry and no ASP     +-------------+
                     in ASP-INACTIVE state)   

 Tr = Recovery Timer

For example, where the AS/ASP configuration data is not created until 
Registration of the first ASP, the AS-INACTIVE state is entered 
directly upon the first successful REG REQ from an ASP.  Another 
example is where the AS/ASP configuration data is not created until the first ASP successfully enters the ASP-ACTIVE state.  In this case the AS-ACTIVE state is entered directly.

--------- 
New text: (Section 4.3.2) 
---------

AS-DOWN: The Application Server is unavailable.  This state implies that the number of ASPs being in ASP-INACTIVE or ASP-ACTIVE is less than "n". Initially the AS will be in this state. An Application Server is in the AS-DOWN state when it is removed from a configuration.

AS-INACTIVE: The Application Server is available but no application traffic is active. This implies that there are at least n ASPs in either ASP-INACTIVE or ASP-ACTIVE but the total number of ASPs in ASP-ACTIVE state has not reach n.  The recovery timer T(r) is not running or has expired. 

AS-ACTIVE: The Application Server is available and application traffic is active. The AS moves to this state after being in AS-INACTIVE and getting n ASPs in ASP-ACTIVE state or, after reaching AS-ACTIVE and keeping one or more ASPs in ASP-ACTIVE state. 

AS-PENDING: The last active ASP has transitioned from ASP-ACTIVE to ASP-INACTIVE or ASP-DOWN.  A recovery timer T(r) SHOULD be started and all incoming signalling messages SHOULD be queued by the SGP. If an ASP becomes ASP-ACTIVE before T(r) expires, the AS is moved to the AS-ACTIVE state and all the queued messages will be sent to the ASP. 

If T(r) expires before an ASP becomes ASP-ACTIVE, the SGP MAY stops queuing messages and discards all 
previously queued messages. The AS will move to the AS-INACTIVE state 
if at least the number of ASPs in either ASP-INACTIVE or ASP-ACTIVE sum n, otherwise it will move to AS-DOWN state. 

Figure 5 shows an example AS state machine for the case where the 
AS/ASP data is preconfigured and an n+k redundancy model. 

             Figure 5: AS State Transition Diagram

     +----------+          IA2AC              +-------------+
     |    AS-   |---------------------------->|     AS-     |
     | INACTIVE |                             |   ACTIVE    |
     |          |<-----------                 |             |
     +----------+            \                +-------------+
        ^   |                 \                    ^   |
        |   | IA2DN            \ PN2IA             |   | AC2PN
        |   |                   \                  |   | 
  DN2IA |   |                    \          PN2AC  |   | 
        |   v                     \                |   v
     +----------+                  \          +-------------+
     |          |                   ----------|             |
     | AS-DOWN  |                             | AS-PENDING  |
     |          |                  PN2DN      |  (queueing) |
     |          |<----------------------------|             |
     +----------+                             +-------------+

DN2IA: One ASP moves to ASP-INACTIVE causing that n ASPs are in either ASP-ACTIVE or ASP-INACTIVE states.

IA2DN: One ASP moves to ASP-DOWN causing that the number of ASPs in either ASP-ACTIVE or ASP-INACTIVE drops below n.

IA2AC: one ASP moves to ASP-ACTIVE, causing number of ASPs in the ASP-ACTIVE state to be n.

AC2PN: the last ASP in ASP-ACTIVE state moves to ASP-INACTIVE or ASP-DOWN states, causing the number of ASPs in ASP-ACTIVE drop below 1.

PN2AC: One ASP moves to ASP-ACTIVE.

PN2IA: T(r) Expiry, n or more ASPs are in either ASP-INACTIVE.

PN2DN: T(r) Expiry, the number of ASPs in either ASP-INACTIVE state is less than n.

As a general rule, an AS becomes AS-ACTIVE right after n ASPs reach the ASP-ACTIVE state during the start-up phase. Once the traffic is flowing, an AS keeps the AS-ACTIVE state till the last ASP turns to another state different to ASP-ACTIVE. As "n" is considered to be the maximum engineered load, this will avoid

There are other cases where the AS/ASP configuration data is created dynamically. In those cases there would be differences in the state machine, especially at creation of the AS. For example, where the AS/ASP configuration data is not created until Registration of the first ASP, the AS-INACTIVE state is entered directly upon the nth successful REG REQ from an ASP belonging to that AS.  Another example is where the AS/ASP configuration data is not created until the nth ASP successfully enters the ASP-ACTIVE state.  In this latter case the AS-ACTIVE state is entered directly.

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---

From: [email-masked]
Date: Wed, 18 Jun 2003 10:15:23 +0530

Hi Javier
  If AS has transitioned to AS-PENDING as a result of ASP inactive being
received
  from last ASP.Now  during T(r) if one of the ASP becomes active.According
to the changed
  text AS transitions  to AS - ACTIVE even though total number of active
ASP's is 1 and n is greater than 1.
  So if configuration of active ASP's remain same there after AS will have
insufficient active
  ASP's to handle the engineered application server traffic. IMO it is not
a fear assumtion to follow
  1 + k redundancy after AS state transitions from AS - ACTIVE state to any
other state.

Regards
Kamesh
Hughes Software Systems

"Javier Pastor-Balbas (ECE)"
<[email-masked]>@ietf.org on 06/17/2003 08:21:16 PM

Sent by:    [email-masked]

To:    "Javier Pastor-Balbas (ECE)" <[email-masked]>,
       "[email-masked]'" <[email-masked]>
cc:    "Ken Morneault (E-mail)" <[email-masked]>, Antonio Cañete (ECE)
       <[email-masked]>

Subject:    [Sigtran] RE: M3UA IG: section 3.15 reworked

This is the last version. There were still some unfinished sentences and
inconsistences in the first text I sent. Now, they are fixed.

Cheers // Javier.

---------

AS-DOWN: The Application Server is unavailable.  This state implies
that all related ASPs are in the ASP-DOWN state for this AS. Initially the
AS will be in this state. An Application Server is in the AS-DOWN state
when it is removed from a configuration.

AS-ACTIVE: The Application Server is available and application traffic is
active.  This state implies that at least one ASP is in the ASP-ACTIVE
state.

AS-PENDING: An active ASP has transitioned to ASP-INACTIVE or ASP-DOWN  and
it was the last remaining active ASP in the AS.  A recovery timer T(r)
SHOULD be started and all incoming signalling messages SHOULD be queued by
the SGP. If an ASP becomes ASP-ACTIVE before T(r) expires, the AS is moved
to the AS-ACTIVE state and all the queued messages will be sent to the ASP.

 Tr = Recovery Timer

For example, where the AS/ASP configuration data is not created until
Registration of the first ASP, the AS-INACTIVE state is entered
directly upon the first successful REG REQ from an ASP.  Another
example is where the AS/ASP configuration data is not created until the
first ASP successfully enters the ASP-ACTIVE state.  In this case the
AS-ACTIVE state is entered directly.

---------

AS-DOWN: The Application Server is unavailable.  This state implies that
the number of ASPs being in ASP-INACTIVE or ASP-ACTIVE is less than "n".
Initially the AS will be in this state. An Application Server is in the
AS-DOWN state when it is removed from a configuration.

AS-INACTIVE: The Application Server is available but no application traffic
is active. This implies that there are at least n ASPs in either
ASP-INACTIVE or ASP-ACTIVE but the total number of ASPs in ASP-ACTIVE state
has not reach n.  The recovery timer T(r) is not running or has expired.

AS-ACTIVE: The Application Server is available and application traffic is
active. The AS moves to this state after being in AS-INACTIVE and getting n
ASPs in ASP-ACTIVE state or, after reaching AS-ACTIVE and keeping one or
more ASPs in ASP-ACTIVE state.

AS-PENDING: The last active ASP has transitioned from ASP-ACTIVE to
ASP-INACTIVE or ASP-DOWN.  A recovery timer T(r) SHOULD be started and all
incoming signalling messages SHOULD be queued by the SGP. If an ASP becomes
ASP-ACTIVE before T(r) expires, the AS is moved to the AS-ACTIVE state and
all the queued messages will be sent to the ASP.

If T(r) expires before an ASP becomes ASP-ACTIVE, the SGP MAY stops queuing
messages and discards all
previously queued messages. The AS will move to the AS-INACTIVE state
if at least the number of ASPs in ASP-INACTIVE sum n, otherwise it will
move to AS-DOWN state.

DN2IA: One ASP moves to ASP-INACTIVE causing that n ASPs are in either
ASP-ACTIVE or ASP-INACTIVE states.

IA2DN: One ASP moves to ASP-DOWN causing that the number of ASPs in either
ASP-ACTIVE or ASP-INACTIVE drops below n.

IA2AC: one ASP moves to ASP-ACTIVE, causing number of ASPs in the
ASP-ACTIVE state to be n.

AC2PN: the last ASP in ASP-ACTIVE state moves to ASP-INACTIVE or ASP-DOWN
states, causing the number of ASPs in ASP-ACTIVE drop below 1.

PN2IA: T(r) Expiry, n or more ASPs are in ASP-INACTIVE.

PN2DN: T(r) Expiry, the number of ASPs in ASP-INACTIVE state is less than
n.

As "n" ASPs are needed to handle the maximum engineered load of the AS, an
AS becomes AS-ACTIVE right after n ASPs reach the ASP-ACTIVE state during
the start-up phase. Once the traffic is flowing, an AS keeps the AS-ACTIVE
state till the last ASP turns to another state different to ASP-ACTIVE,
avoiding unnecessary traffic disturbances as long as there are ASPs
available, in the assumption that the AS will not always be exposed to the
maximum load.

There are other cases where the AS/ASP configuration data is created
dynamically. In those cases there would be differences in the state
machine, especially at creation of the AS. For example, where the AS/ASP
configuration data is not created until Registration of the first ASP, the
AS-INACTIVE state is entered directly upon the nth successful REG REQ from
an ASP belonging to that AS.  Another example is where the AS/ASP
configuration data is not created until the nth ASP successfully enters the
ASP-ACTIVE state.  In this latter case the AS-ACTIVE state is entered
directly.

---

From: "Javier Pastor-Balbas (ECE)" <[email-masked]>
Date: Wed, 18 Jun 2003 12:01:05 +0200

Hi Kamesh, 

The main objective is keeping the system working as long as possible. NTFY messages give the AS the clue that the system is not working fine and operator will have to decide whether stop traffic or not. When the number of ASPs is below "n", AS side should take steps ASAP to activate new ASPs. 

Cheers // Javier.

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]]
> Sent: miércoles, 18 de junio de 2003 6:45
> To: Javier Pastor-Balbas (ECE)
> Cc: [email-masked]
> Subject: Re: [Sigtran] RE: M3UA IG: section 3.15 reworked
> 
> 
> 
> 
> 
> 
> Hi Javier