Subject: [Capwap] Proposed resolution to issue 73

From: "Michael Montemurro" <[email-masked]>
Date: Tue, 16 Jan 2007 06:35:36 -0500

Issue 73 deals with problems with the WTP not being able to indicate
to the AC that a configuration has not been applied.

I propose that we resolve this issue by adding a result code for a WTP
to indicate that it failed to apply the configuration sent by the AC.

A configuration status has been added to the result code indicating:
  -  the WTP could not apply the current configuration but will offer service
  - the WTP could not apply the current configuration and cannot offer service.

Cheers,

Mike
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---

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Wed, 17 Jan 2007 04:00:23 -0800

Michael,

I have sent text which I do believe addresses the issue. The issue, as I
understand it, is that there is no means for a WTP to communicate a
failure in partially applying the configuration provided by the AC.
There was a suggestion to add a new message to "acknowledge" the
configuration response. However, the protocol already has a message that
needs to be sent following the response, which is the Change State
Event. While the actual proposed text uses a different mechanism, I
believe it achieves the same goal.

I now include my proposed text and a commentary:

I have introduced a new message element, which is described below:
<text>
4.5.  CAPWAP Protocol Message Elements
[...]
   Returned Message Element                             46
</text>

Here I have defined new result codes that allow the WTP to communicate
why it was unable to apply the configuration, and two different reasons:
<text>
4.5.31.  Result Code
[...]
   Result Code:   The following values are defined:
[...]
      10 Failure (Unable to Apply Requested Configuration - Service
         Provided Anyhow)

      11 Failure (Unable to Apply Requested Configuration - Service Not
         Provided)
</text>

In the event that the WTP is unable to partially apply the requested
configuration, the Change State Event includes one or more "Returned
Message Element" which includes the offending information element.

<text>
4.5.32.  Returned Message Element

   The Returned Message Element is sent by the WTP within the Change
   State Event Request in order to communicate to the AC which message
   elements in the Configuration Status Response it was unable to apply
   locally.  The Returned Message Element contains a result code that is
   used to indicate the reason why the configuration could not be
   applied, and encapsulates the offending message element.

      0                   1                   2
      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |    Reason     |       Message Element...
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Reason:   The reason why the configuration in the offending message
      element could not be applied by the WTP

      1 -  Unknown Message Element

      2 -  Unsupported Message Element

      3 -  Unknown Message Element Value

      4 -  Unsupported Message Element Value

   Message Element:   The Message Element field encapsulates the message
      element sent by the AC in the Configuration Status Response
      message that caused the error.
</text>

Finally, the Change State Event text has been modified to indicate its
expanded purpose, and the new message elements it may carry:
<text>
8.7.  Change State Event Request

   The Change State Event Request message is used by the WTP for two
   main purposes:

   o  When sent by the WTP following the reception Configuration Status
      Response from the AC, the WTP uses the Change State Event to
      provide an update on the WTP radio's operational state as well as
      to confirm that the configuration provided by the AC was
      successfully applied.

   o  When sent during the Run state, the WTP uses the Change State
      Event to notify the AC of an unexpected change in the WTP's radio
      operational state.

   When an AC receives a Change State Event Request message it will
   respond with a Change State Event Response message and make any
   necessary modifications to internal WTP data structures. The AC MAY
   decide not to provide service to the WTP if it receives an error,
   based on local policy, which is done by transitioning to the
   CAPWAP Reset state.

   The Change State Event Request is sent by a WTP to acknowledge or
   report an error condition to the AC for a requested configuration
   through the Configuration Status Response.  The Change State Event
   Request includes the Result Code message element, which indicates
   whether the configuration was successfully applied.  If the WTP is
   unable to apply a specfic configuration request, it indicates the
   failure by including one or more Returned Message Element message
   elements (see Section 4.5.32).

   The following message elements MUST be present in the Change State
   Event Request message.

   o  Radio Operational State, see Section 4.5.30

   o  Result Code, see Section 4.5.31

   One or more of the following message elements MAY be present in the
   Change State Event Request message.

   o  Returned Message Element, see Section 4.5.32
</text>

Therefore, I believe the request defined in issue 73 has been satisfied.

Pat Calhoun
CTO, Wireless Networking Business Unit
Cisco Systems

> -----Original Message-----
> From: Michael Montemurro [mailto:[email-masked]] 
> Sent: Tuesday, January 16, 2007 3:36 AM
> To: capwap
> Subject: [Capwap] Proposed resolution to issue 73
> 
> Issue 73 deals with problems with the WTP not being able to 
> indicate to the AC that a configuration has not been applied.
> 
> I propose that we resolve this issue by adding a result code 
> for a WTP to indicate that it failed to apply the 
> configuration sent by the AC.
>

---

From: "Michael Montemurro" <[email-masked]>
Date: Wed, 17 Jan 2007 08:12:03 -0500

Looks good to me.

Mike

---

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Fri, 26 Jan 2007 05:01:44 -0800

This issue was discussed at the interim meeting today, and there
was agreement on the proposed text. However, the group felt that 
the following should be addressed:

Add timer on the AC to detect if the Change State Event Request was not
sent 
by the WTP in a certain amount of time. This would cause the
Configure->Reset 
state transition.

Find the text below:

2.3.  CAPWAP State Machine Definition
[...]

   Join to Configure (q):  This state transition is used by the WTP and
      the AC to exchange configuration information.

      WTP:  The WTP enters the Configure state when it receives a
         successful Join Response, and determines that the included
         Image Identifier message element is the same as its currently
         running image.  The WTP transmits the Configuration Status
         message (see Section 8.2) to the AC with a snapshot of its
         current configuration.  The WTP also starts the ResponseTimeout
         timer (see Section 4.6).

      AC:  This state transition occurs immediately after the AC
         transmits the Join Response message to the WTP.  If the AC
         receives the Configuration Status message from the WTP, the AC
         must transmit a Configuration Status Response message (see
         Section 8.3) to the WTP, and may include specific message
         elements to override the WTP's configuration.  The WTP also
         starts the ChangeStatePendingTimer timer (see Section 4.6).
[...]

   Configure to Reset (s):  This state transition is used to reset the
      connection either due to an error during the configuration phase,
      or when the WTP determines it needs to reset in order for the new
      configuration to take effect.

      WTP:  The WTP enters the Reset state when it receives a
         Configuration Status Response indicating an error or when it
         determines that a reset of the WTP is required, due to the
         characteristics of a new configuration.

      AC:  The AC transitions to the Reset state when it receives a
         Change State Event message from the WTP that contains an error
         for which the AC's policy does not permit the WTP providing
         service.  This state transition also occurs when the AC's
         ChangeStatePendingTimer timer expires.

4.6.  CAPWAP Protocol Timers

   This section contains the CAPWAP timers.

4.6.1.  ChangeStatePendingTimer

   The maximum time, in seconds, the AC will wait for the Change State
   Event Request from the WTP after having transmitted a successful
   Configuration Status Response.  The default value is 25 seconds.

Pat Calhoun

> From: Pat Calhoun (pacalhou) 
> Sent: Wednesday, January 17, 2007 4:00 AM
> To: Michael Montemurro; capwap
> Subject: Re: [Capwap] Proposed resolution to issue 73
> 
> Michael,
> 
> I have sent text which I do believe addresses the issue. The 
> issue, as I understand it, is that there is no means for a 
> WTP to communicate a failure in partially applying the 
> configuration provided by the AC.
> There was a suggestion to add a new message to "acknowledge" 
> the configuration response. However, the protocol already has 
> a message that needs to be sent following the response, which 
> is the Change State Event. While the actual proposed text 
> uses a different mechanism, I believe it achieves the same goal.
> 
> Here I have defined new result codes that allow the WTP to 
> communicate why it was unable to apply the configuration, and 
> two different reasons:
> <text>
> 4.5.31.  Result Code
> [...]
> In the event that the WTP is unable to partially apply the 
> requested configuration, the Change State Event includes one 
> or more "Returned Message Element" which includes the 
> offending information element.
> 
> <text>
> Finally, the Change State Event text has been modified to 
> indicate its expanded purpose, and the new message elements 
> it may carry:
> <text>
>    o  Returned Message Element, see Section 4.5.32 </text>
> 
> indicate 
> >   -  the WTP could not apply the current configuration but 
> will offer 
> > service
> >   - the WTP could not apply the current configuration and 
> cannot offer 
> > service.
> > 
> > Cheers,
> > 
> > Mike