Subject: [Capwap] ImageDataStartTimer in draft-ietf-capwap-protocol-specification-10.txt

From: "Yong Zhang" <[email-masked]>
Date: Mon, 23 Jun 2008 11:14:48 -0700

I have a question on this ImageDataStartTimer. What's the purpose of it?

Is it used to define the AC waiting time for the first WTP image data
req after it sends the join resp? After the first image data req is
received from WTP,  this timer will be no use any more after the AC
start image data push to WTP?

Refer to figure 4/6 in chapter 9, the WTP will only send the first
image data req message, then it will receive image data req from AC,
and reply with image data resp.

Page 24 Join to Image Data (f): AC: ImageDataStartTimer is started
after the AC receives the Image Data Request message from the WTP

Page 25 Image Data to Image Data (j):AC This state transition occurs
when the AC receives the Image
         Data Request message from the WTP while already in the Image
         Data state.  The AC resets the ImageDataStartTimer timer.

         Here you want to say the first Image data req from WTP, or
the image data response from WTP for AC's image data req? If it is the
first one, there is no image data req from WTP when the FSM is in
Image Data state.

         Reset timer is the timer to be restarted or canceled?

Thanks!

Yong

In this spec., most of req messages are send by WTP. The image data
req is an exception, which is mainly used by AC.
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---

From: "Pat Calhoun (pacalhou)" <[email-masked]>
Date: Thu, 26 Jun 2008 05:11:46 -0700

Yes, I believe you are once again correct. The issue was created when
the Image Data Request/Response became bi-directional, and the timers
were not adjusted correctly. The proper fix is, I believe, to make use
of the timer on both the AC and the WTP:

<text>
2.3.  CAPWAP State Machine Definition
[...]
   Image Data to Image Data (j):  The Image Data state is used by the
      WTP and the AC during the firmware download phase.

      WTP:  The WTP enters the Image Data state when it receives an
         Image Data Response message indicating that the AC has more
         data to send.  This state transition also occurs when the WTP
         receives the subsequent Image Data Requests, at which time it
         resets the ImageDataStartTimer time to ensure it receives the
         next expected Image Data Request from the AC.

      AC:  This state transition occurs when the AC receives the Image
         Data Response message from the WTP while already in the Image
         Data state.  The AC disables the ImageDataStartTimer timer.

   Image Data to Reset (k):  This state transition is used to reset the
      DTLS connection prior to restarting the WTP after an image
      download.

      WTP:  When an image download completes, or if the
         ImageDataStartTimer timer expires, the WTP enters the Reset
         state.  The WTP MAY also transition to this state upon
         receiving an Image Data Response message from the AC (see
         Section 9.1.2) indicating a failure.

      AC:  The AC enters the Reset state when an error occurs during the
         image download process or if the ImageDataStartTimer timer
         expires.

4.7.8.  ImageDataStartTimer

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

PatC
-----Original Message-----
From: Yong Zhang [mailto:[email-masked]] 
Sent: Monday, June 23, 2008 11:15 AM
To: [email-masked]
Subject: [Capwap] ImageDataStartTimer
indraft-ietf-capwap-protocol-specification-10.txt

Refer to figure 4/6 in chapter 9, the WTP will only send the first image
data req message, then it will receive image data req from AC, and reply
with image data resp.

Page 24 Join to Image Data (f): AC: ImageDataStartTimer is started after
the AC receives the Image Data Request message from the WTP

         Here you want to say the first Image data req from WTP, or the
image data response from WTP for AC's image data req? If it is the first
one, there is no image data req from WTP when the FSM is in Image Data
state.

Thanks!

Yong

In this spec., most of req messages are send by WTP. The image data req
is an exception, which is mainly used by AC.
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