Subject: [Pana] Some clarifications in PANA cxtp draft

From: Sasikanth Bharadwaj <[email-masked]>
Date: Wed, 30 Nov 2005 10:56:45 +0530

Hi

As I see, there are a few more problems with the PANA cxtp draft
(draft-ietf-pana-cxtp-00).
For one, it does not mention how the PSA message sent by the PaC is to be
sent to the pPAA. Should it be put in the form of a CDB and sent in the next
requested data block field?
Another issue is, in the normal CXTP exchanges (as per rfc 4067), the MN's
previous COA field is used to identify the MN to which a particular context
corresponds. This information is obtained at the nAR from the CTAR message
and is included in the CT-Req message. But the CTAR message is not used in
PANA cxtp. So, how is the nPAA supposed to know the MN's previous COA? Note
that the pPAA can still identify the context from the session id in the PSA
message (assuming we somehow send the PSA message from the nPAA in the
CT-Req message). But, when the nPAA receives a CTD message, it has no way of
telling to which PaC this context belongs.

Thanks and Regards

Sasikanth

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From: Julien Bournelle <[email-masked]>
Date: Wed, 30 Nov 2005 10:49:05 +0100

Hi,

 thanks a lot for reading it,

 I create 2 threads to respond to your questions.

> requested data block field?

 We plan to specify deeper this in the next version so that's nice that
 you bring it up.

 To answer to your question I think that the CT-Req message should be
 fulfilled with:

 - MN PCoA set to 0 since the Pac doesn't give its IP address.
 - Sequence Number
 - MN Authz token also be set to zero. The authorization is done using PSA
 message. Maybe we should explicit this in the draft.

 and yes, the PSA should be sent in the CTB. 
 
 We need to allocate a number for PANA for FPT.
 While receiving the CT-Req, the pPAA knows that the PSA is in the CTB.
 In response, the FTP is the same but the CTB content is different.

 Does it make sense ?

 Julien

ps: I'll answer to the rest of your mail in a separate thread.

-- 
julien.bournelle at int-evry.fr

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From: Julien Bournelle <[email-masked]>
Date: Wed, 30 Nov 2005 11:41:27 +0100

Hi again,

 answer to the other issue.

<snip>

> CT-Req message). 

 yes, we assume that the pPAA gets the context based on the PSA. For
 this, the PSA must contain the previous Session-Id (PaC-pPAA).

> But, when the nPAA receives a CTD message, it has no way of

 that's a interesting point. I think it depends on the transport
 protocol that we use. (4067 currently proposes SCTP)

 If it's UDP, we can match request and response based on Port source and
 destination.

 If it's TCP, it depends on how we use it.

 Either we have only one TCP connection on which we send all our CT-Req/CTD or we
 open TCP connection for each transfer. 

 In the latter solution which seems inefficient, we can match request
 and response.

 In the former approach, I think that as you noted something is missing.
 So, in this case, it appears that we need to add an identifier in the
 CTD message. Either we add something in both CT-Req and CTD or only in
 the CTD.

 I'm not familiar with SCTP so I can't tell. This need investigation.

 Any comments on this ?
 
 Julien

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From: Sasikanth Bharadwaj <[email-masked]>
Date: Wed, 30 Nov 2005 16:53:34 +0530

Hi

>  I'm not familiar with SCTP so I can't tell. This need investigation.

As I mentioned earlier, rfc 4067 prescribes MN's previous COA to be used for
this purpose.
Since we are tailoring CXTP to suit our purpose, I think we should specify
an alternate mechanism using which this mapping can be achieved rather than
rely on external mechanisms. Two alternatives come to my mind - either
include the MN's previous COA in an AVP in the PSA so that the nPAA can copy
the same to the CT-Req message or let the nPAA send the MN's new COA instead
of the previous COA in the CT-Req message. The pPAA will then have to copy
the address into the CTD message.

Sasikanth

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From: Julien Bournelle <[email-masked]>
Date: Wed, 30 Nov 2005 13:11:58 +0100

hi,

> the address into the CTD message.

 Another alternative could be to use the MN's pCoA field. Thus the nPAA
 puts an identifier in it (Session identifier) and the pPAA replies with
 the same identifier. 

 Julien

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From: Sasikanth Bharadwaj <[email-masked]>
Date: Wed, 30 Nov 2005 18:17:11 +0530

Hi

>  puts an identifier in it (Session identifier) and the pPAA replies with
Since the field is supposed to carry an address, I said new COA but as you
said, any identifier should serve the purpose.

Sasikanth

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From: Sasikanth Bharadwaj <[email-masked]>
Date: Wed, 30 Nov 2005 18:23:54 +0530

Hi

>  message. Maybe we should explicit this in the draft.

Yes, I think it would be better to explicitly mention these things in the
draft

>  In response, the FTP is the same but the CTB content is different.
Yes. That was what I had in mind.

Thanks and Regards

Sasikanth

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From: Julien Bournelle <[email-masked]>
Date: Wed, 30 Nov 2005 14:59:27 +0100

Hi,

> said, any identifier should serve the purpose.

 so it appears that we have 3 alternatives:

 1/ leave this to the transport protocol.
	
	this is not a solution if we want to use one TCP connection for
	all CT-Req/CTD exchange between pPAA and nPAA.
	
 2/ the PaC provides its pCoA in the PSA message sent to the nPAA

 	it requires to modify the current PANA specs (pana-mobopts and
	pana-statemachine)

 3/ nPAA and pPAA uses the MN's pCoA field of CT-Req and CTD as an
 identifier to match response to request.

	in a sense it is compliant with RFC4067 since this field is used
	by the nAR to match the response (as far as I understand)

	in another sense it is not compliant since it is not the pCoA

 Any comments ?

 Julien

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From: "Alper Yegin" <[email-masked]>
Date: Wed, 30 Nov 2005 17:57:43 +0200

> > telling to which PaC this context belongs.

Doesn't CTP provide a way to match responses with the requests? If it
does (I'd be surprised if it didn't), then do we still have a problem?

Alper

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From: Julien Bournelle <[email-masked]>
Date: Wed, 30 Nov 2005 17:06:20 +0100

On Wed, Nov 30, 2005 at 05:57:43PM +0200, Alper Yegin wrote:
> Doesn't CTP provide a way to match responses with the requests? 

 CXTP uses the MN's pCoA field for this. The MN sends its pCoA in the
 CTAR message and the nAR copy it in the CT-Req. The pAR replies and
 also set this field with pCoA. (cf. Section 2.5 "Messages")

 As we don't use CTAR message, the PaC doesn't currently provide its
 pCoA and thus we can't use this mechanism.

 Julien

> If it

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From: Yoshihiro Ohba <[email-masked]>
Date: Wed, 30 Nov 2005 23:28:48 -0500

Julien,

>  	it requires to modify the current PANA specs (pana-mobopts and

This will not work if pCoA=PRPA=link-local address.  In this case,
pCoA can conflict if two PaCs moving from two different previous
networks to the same new network, but happened to have the same link
local address in their previous networks.

Yoshihiro Ohba