Subject: [MOBILE-IP] Encapsulating delivery style in reverse tunnel draft

From: Samita Chakrabarti <[email-masked]>
Date: Mon, 8 May 2000 12:32:06 -0700

Hello folks:

Currently rfc2344-bis requires foreign agent to support EDS (encapsulating
delivery style) and DDS (direct delivery style) when 'T' bit is
turned on in the agent advertisement.

" A foreign agent that sets the 'T' bit MUST support the two delivery
   styles currently supported: Direct and Encapsulating Delivery Style
   (section 5)."

Since we are revisiting the draft, I wonder if it makes sense to relax
the 'MUST' to 'SHOULD' for simplicity in FA.

I understand that, it may introduce some delay in MN side, if a MN
wants to use EDS and the FA  is a DDS only agent. Also I know that
there are not enough bits left in the agent advertisement to distinguish
between two reverse tunnel modes.

On the other hand, if most MNs use DDS only then perhaps, EDS support may
be an optional choice for FA's implementation. I have discussed this question
internally with some folks and would like to know if the working group
has any strong opinion in changing the requirement from 'MUST' to 'SHOULD'.
Attached is excerpt of Gabriel's response on this discussion.

-Samita
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Date: Thu, 4 May 2000 13:55:31 -0700 (PDT)
From: Gabriel Montenegro <[email-masked]>
Subject: Re: Encapsulating delivery style in reverse tunnel draft
To: Samita Chakrabarti <[email-masked]>
MIME-Version: 1.0

about EDS (encapsulating delivery style) vs DDS (direct delivery style):

the consensus was that it was simpler (at least from one point of view)
to require EDS and DDS as a unified 'reverse tunneling'
bundle instead of then having the
additional problem of resolving which flavor of it was supported. so yes, you'd
need additional error codes, at least. perhaps you'd need additional
info in the advertisement if you want the mobile node to not attempt
registration with a DDS-only FA, if what it needs is EDS. We even joked
once that this could be accomplished by overloading the 'T' bit thus:

        capital 'T': EDS (and DDS) supported
        small 't': DDS only

the alternative was to use more than one bit in the advertisement, but
that's probably out of the question. i had at one time defined an
extension to the advertisement with which the FA explicitly announced
support for EDS (in addition to DDS).

the 'T' bit by itself would then only imply DDS support.

we'd need new error codes as well. not a major thing, though.

as always, it's a tradeoff, perhaps it's worth revisiting. i'd suggest
you bring this up in the mailing list, and if there's strong sentiment
that we should allow DDS-only FA's then we could do that now that we're
revising rfc2344.

feel free to forward some or part of this email if you wish.

-gabriel

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