Subject: [Capwap] Proposed resolution to Issue 85/ wasRe: Issue with state machine

From: "Dorothy Stanley" <[email-masked]>
Date: Tue, 3 Oct 2006 08:39:33 -0700

All,

Issue 85 was closed in -02 and then re-opened to address the following
comment:

I just noticed that the latest specification's state machine requires that
in order to perform a firmware download, the state must transition from the
join to configure to image data. This is a departure from the original
protocol, and I believe introduces some challenges. One of the benefits of
bypassing the configure state is that it maximizes interoperability across
version numbers. If we require the configure state to be run, then we need
to ensure that the configure message does not introduce any new message
elements that can create a backward compatiblity issue. However, the way the
protocol used to be only required that the Join state have to deal with
backward compatibility.

I'd like to see this changed back to the old way. Sorry I missed this in my
reviews.

The -02 specification has state transitions from Join to Configure to Image
data, with corresponding text descriptions.
This is unchanged from the -01  specification. The -00 specification had a
transition from
DTLS-Complete to Configure and to Image Data.

The current text description includes:

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

      WTP: The WTP enters the Configure state when it successfully
         completes the Join operation.  If it determines that its
         version number and the version number advertised by the AC are
         the same, 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 4.5) If the version numbers are not the same,
         the WTP will immediately transition to Image Data state (see
         transition (i)).

and for the AC:

      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.  If the AC
         instead receives the Image Data Request from the WTP, it
         immediately transitions to the Image Data state (see transition
         (i)).

In the current specification, if the WTP received a Discovery Response
message from the AC, it has the AC descriptor data, including the
AC Hardware and Software version numbers, and does not need
to exchange configuration messages to obtain AC HW & SW version info.

If the WTP does not execute the Discovery exchange, then it will
need to obtain the data.

Proposed Resolution:  Insert the following text at the end of 6.2 "Join
Response",
so that in all cases, the Configuration messages are not sent:

"The following message element MUST be included in the Join Response
message:

- AC Descriptor, see Section 4.4.1"
------------------------------------------------------------------------------------------------
Related observation 1: The current text states that
" If it [WTP] determines that its
         version number and the version number advertised by the AC are
         the same, the WTP transmits the Configuration Status message
         (see Section 8.2) to the AC with a snapshot of its current
         configuration."

This can't be correct - multiple vendors will have different version
numbering
schemes.

Proposed change:

from

If it determines that its
         version number and the version number advertised by the AC are
         the same, the WTP transmits the Configuration Status message
         (see Section 8.2) to the AC with a snapshot of its current
         configuration.

to

If it determines that its
         version number and the version number advertised by the AC are
         compatible, the WTP transmits the Configuration Status message
         (see Section 8.2) to the AC with a snapshot of its current
         configuration.

----------------------------------------------------------------------------------------------------------------------
Related observation 2: The current specification provides a means for the
WTP to
initiate the move to Image Data from the Configure State, but does not
provide the AC with a similar capability. The current text expects that
the WTP has knowledge of all of the AC versions that it can interoperate
with.
How the WTP would make this determination is of course out of scope.
It is also likely that the AC would have similar knowledge, in one central
location.

Proposed Change:

Insert the following sentence as indicated:

      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.  If the AC
         instead receives the Image Data Request from the WTP, it
         immediately transitions to the Image Data state (see transition
         (i)). If the AC determines that a new firmware image should be
         installed on the WTP, the AC initiates a firmware download by
sending an Image Data Request
         Message with an Initiate Download message element to the WTP.

Comments welcome,

Thanks,

Dorothy

On 6/30/06, Michael Montemurro <[email-masked]> wrote:
>
> Pat,
>
> I re-openned issue 85 to deal with this issue.
>
> Cheers,
>
> Mike
>
>
> On 6/27/06, Pat Calhoun (pacalhou) <[email-masked]> wrote:
>
> >  I just noticed that the latest specification's state machine requires
> > that in order to perform a firmware download, the state must transition from
> > the join to configure to image data. This is a departure from the original
> > protocol, and I believe introduces some challenges. One of the benefits of
> > bypassing the configure state is that it maximizes interoperability across
> > version numbers. If we require the configure state to be run, then we need
> > to ensure that the configure message does not introduce any new message
> > elements that can create a backward compatiblity issue. However, the way the
> > protocol used to be only required that the Join state have to deal with
> > backward compatibility.
> >
> > I'd like to see this changed back to the old way. Sorry I missed this in
> > my reviews.
> >
> >
> > Pat Calhoun
> > CTO, Wireless Networking Business Unit
> > Cisco Systems
> >
> >
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