Subject: [Pana] issue 57 (resolution)

From: Yoshihiro Ohba <[email-masked]>
Date: Tue, 16 Mar 2004 15:18:13 -0800

This is the resolution for issue 57 (PSR retransmission strategy).
Basically the same as what I had proposed on the mailing list in
February and presented in the IETF59 meeting.  Further comments are
appreciated.

- Change the following paragraph in section 

"
   A PANA-Start-Request message is never retransmitted. A
   PANA-Start-Answer message is retransmitted based on timer in the same
   manner as other messages retransmitted at PANA-layer.
"

to:

"
   A PANA-Start-Request message that carries a Cookie AVP is never
   retransmitted.  A PANA-Start-Request message that does not carry a
   Cookie AVP is retransmitted based on timer.  A PANA-Start-Answer
   message that carries a Cookie AVP is retransmitted based on timer.
   A PANA-Start-Answer message that does not carry a Cookie AVP is
   never retransmitted based on timer.
"

Change the first paragraph of section 10 to:

   "The PANA protocol provides retransmissions for all the message
   exchanges except PANA-Auth-Request/Answer. PANA-Auth-Request messages
   carry EAP requests which are retransmitted by the EAP protocol
   entities when needed. The messages that need PANA-level
   retransmissions are listed below:

         PANA-PAA-Discover (PDI)
         PANA-Start-Request (PSR)*
         PANA-Start-Answer (PSA)**
         PANA-Bind-Request (PBR)
         PANA-FirstAuth-End-Request (PFER)
         PANA-Reauth-Request (PRAR)
         PANA-Termination-Request (PTR)

   *)  PSR that carries a Cookie AVP is not retransmitted.
   **) PSA that does not carry a Cookie AVP is not retransmitted."

(Note: PFER message is introduced for issue 52.)

Regards,
Yoshihiro Ohba

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From: Alper Yegin <[email-masked]>
Date: Wed, 17 Mar 2004 04:27:44 -0800

Yoshi,

Thinking a bit more on this (or confusing myself :)...

I think whether a PDI/PSR/PSA retransmitted or not should not be indexed
to cookie usage, but to solicited vs. unsolicited PSR.

When PaC performs active discovery of PAAs by sending PDI, both PDI and
PSA messages are retransmitted as needed, whereas PSR is not
retransmitted by the PAA. 

When PAA discovery is performed in unsolicited fashion, PSR is
retransmitted, and PSA is not.

Does this make sense?

Alper

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From: Alper Yegin <[email-masked]>
Date: Wed, 17 Mar 2004 04:27:44 -0800

Yoshi,

Does this make sense?

Alper

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From: Yoshihiro Ohba <[email-masked]>
Date: Tue, 16 Mar 2004 17:50:04 -0800

> retransmitted, and PSA is not.

I think indexing to solicited vs. unsolicited PSR also works.

A difference from indexing to cookie usage is that it is possible that
PaC can operate in solicited mode while PAA is operating in
unsolicited mode at the same time.  For example, PaC operating in
solicited mode sends PDI, while at the same time PAA operating in
unsolicited mode sends PSR.  If it happens, I think all PDI, PSR and
PSA will be retransmitted if the retransmission strategy is based on
solicited vs. unsolicited PSR, which seems to be less efficient.

By indexing to cookie usage (or indexing to stateless vs stateful
PAA), both PaC and PAA can always be synchronized to have the same
mode of operation about the retransmission strategy, i.e., when PSR is
retransmitted PSA is never retransmitted, and vise versa.

What do you think?

Yoshihiro Ohba
-

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From: Yoshihiro Ohba <[email-masked]>
Date: Tue, 16 Mar 2004 17:50:04 -0800

What do you think?

Yoshihiro Ohba
-

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From: Alper Yegin <[email-masked]>
Date: Wed, 17 Mar 2004 17:00:49 -0800

> retransmitted PSA is never retransmitted, and vise versa.

I see. You are using cookie as a tie-breaker. My concern, unless I'm
missing something, is that there is no semantic relevance between the
cookie usage and the retransmission policy. Some other clue could be
used to stop one side from retransmitting. For example in my case,
receipt of PDI by the PAA could cease the PSR retransmissions on the
PAA. 

Alper

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From: Alper Yegin <[email-masked]>
Date: Wed, 17 Mar 2004 17:00:49 -0800

Alper

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From: Yoshihiro Ohba <[email-masked]>
Date: Tue, 16 Mar 2004 21:19:15 -0800

On Wed, Mar 17, 2004 at 05:00:49PM -0800, Alper Yegin wrote:
> cookie usage and the retransmission policy. 

I understand your concern.  Let me explain a semantic relevance as
follows:

- PDI is retransmitted whatever information is used as a tie-breaker.

- As a general retransmission policy, in a request/answer exchange, the
requester should take the responsibility of retransmission.

- There is an exception.  If the requester remains stateless after
sending a request, the responder should take the responsibility of
retransmission.  This cases occurs only for PSR/PSA exchange, and
retransmission of PDI and PSA can archieve the responsibility.  The
presence of the cookie indicates that the requester remains stateless.

> Some other clue could be

That is also possible.  Which strategy do you think is better?

Yoshihiro Ohba

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From: Yoshihiro Ohba <[email-masked]>
Date: Tue, 16 Mar 2004 21:19:15 -0800

Yoshihiro Ohba