Capwap Mailing List: Re: Issue 181: ImageDataStartTimer not necessary on AC

[Pat Calhoun (pacalhou) (pcalhoun]

This change is mostly about removing text, so it is hard to show the
diffs, but I will include the new state machine transitions on the AC
that no longer reference the timer.

<proposed text>
   Join to Image Data (f):  This state transition is used by the WTP and
      the AC to download executable firmware.
[...]
      AC:  This state transition occurs when the AC receives the Image
         Data Request message from the WTP, after having sent its Join
         Response to the WTP.  The AC stops the WaitJoin timer.  The AC
         MUST transmit an Image Data Response message (see
         Section 9.1.2) to the WTP, which includes a portion of the
         firmware. 

   Image Data to Image Data (j):  The Image Data state is used by the
      WTP and the AC during the firmware download phase.
[...]
      AC:  This state transition occurs when the AC receives the Image
         Data Response message from the WTP while already in the Image
         Data state.

   Image Data to Reset (k):  This state transition is used to reset the
      DTLS connection prior to restarting the WTP after an image
      download.
[...]
      AC:  The AC enters the Reset state either when the image transfer
         has successfully completed or an error occurs during the image
         download process.

4.7.9.  ImageDataStartTimer

   The number of seconds the WTP will wait for its peer to transmit the
   Image Data Request.
</proposed text> 

PatC
-----Original Message-----
From: Pat Calhoun (pacalhou) 
Sent: Thursday, September 11, 2008 2:42 PM
To: capwap [at] frascone.com
Cc: Yong Zhang
Subject: [Capwap] Issue 181: ImageDataStartTimer not necessary on AC

Yong Zhang brought up the following to my attention on draft -12. I have
created issue 181 to track this. This issue does not impact
interoperability. In fact, what happens is that the AC enables the
timer, then disables the timer at the next response it gets from the WTP
- so there is no bug per se. The only issue is that the timer is
unnecessary. If the group decides the change needs to be done, I wonder
if we could make this change post IESG Review.

> 
> 5. page 25
> 
>       AC:  This state transition occurs when the AC receives the Image
>          Data Request message from the WTP, after having sent its Join
>          Response to the WTP.  The AC stops the WaitJoin timer.  The
AC
>          MUST transmit an Image Data Response message (see
>          Section 9.1.2) to the WTP, which includes a portion of the
>          firmware.  The AC MUST start the ImageDataStartTimer timer
(see
>          Section 4.7).
> 
> Here AC will first send Image Data Response, then another Image Data
Req, which has the image data.
> 
> The ImageDataStartTimer in WTP side is used ensure wtp receives image
data req from AC.
> What is it used for in AC now? For the image data resp?

Hmmm.... That's a good question. The current text reads that the timer
is started, but it is then stopped when the AC receives the next Image
Data Response. This would obviously be covered through the normal
retransmission timer, so it appears as if this timer is completely
unnecessary on the AC.

PatC
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