Subject: [nemo] Including prefix information in BU in explicit mode

From: Vijay Devarapalli <[email-masked]>
Date: Fri, 13 Aug 2004 13:18:21 -0700

hi all,

Pascal brought this issue up.

In the explicit mode, can the MR avoid including prefix information
in binding updates that just refresh an existing binding cache entry?

a brief summary of the discussion is at
http://people.nokia.net/vijayd/nemo/issue42.txt

we have 2 options.

1. mandate that the MR include prefix information in every BU in
    explicit mode. the prefix information should only contain those
    prefixes for which the MR wants forwarding setup.

2. the MR can avoid including prefix information in the BU, if
    it is not updating the list of prefixes for which it needs
    forwarding setup at the HA. if it is updating (removing a prefix
    or adding a prefix), then it needs to include the prefix
    information in the BU.

option 1) is simpler for the Home Agent, but option 2) saves bits
over the air.

comments are welcome.

Vijay

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From: Ryuji Wakikawa <[email-masked]>
Date: Sat, 14 Aug 2004 15:43:27 +0900

Hello Vijay

I support option-1.
If MR-HA want to save bits over the air, please simply use implicit 
mode :-)

The problem of option-2 is when MR sends BU w/out prefix option,
but HA already discards binding for the MR.
In such case, HA does not have any prefix information for the MR and
it returns BA with 143 status code.
After MR receiving the BA, it'll try to register another HA.

We can also say that R-bit cannot be set in BU when there is no mobile 
network prefix in explicit mode.
As alex pointed out, HA always knows explicit or implicit by checking R 
bit and prefix options.

regards,
ryuji

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From: Mattias Pettersson <[email-masked]>
Date: Mon, 16 Aug 2004 10:27:57 +0200

>    or adding a prefix), then it needs to include the prefix

I prefer 1.

/Mattias

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From: Vijay Devarapalli <[email-masked]>
Date: Mon, 16 Aug 2004 10:58:30 -0700

Ryuji

> but HA already discards binding for the MR.

did the HA discard the binding cache entry because it expired
or for some other reason? if it discarded the binding cache
entry because it expired, then there isnt an issue. the MR also
knows when the binding expires and includes the prefix
information accordingly.

Vijay

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From: Ryuji Wakikawa <[email-masked]>
Date: Tue, 17 Aug 2004 03:05:19 +0900

Hi Vijay

> knows when the binding expires and includes the prefix

While operating MIP6/NEMO, I found the situation where HA
discards BC before MR successfully updating BC.
For example, when a BU sent by MR is dropped due to network trouble,
MR retries to send another BU.  However, it's possibly happened that
the lifetime of BC is expired before the second BU.
It is totally up to timing between HA's BC lifetime and BU arrival time.

In MIP and NEMO, it's fine, because HA re-creates BC right after 
receiving the second BU.

If we go with option-2, HA can not create BC due to lack of prefix 
information.
Although HA may keep prefix information for a while after removing BC,
I don't think we should bring these new status for option-2.

ryuji

---

From: Vijay Devarapalli <[email-masked]>
Date: Mon, 16 Aug 2004 11:21:07 -0700

you are right. this could lead to the MR trying another HA.

Vijay

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From: Vijay Devarapalli <[email-masked]>
Date: Mon, 16 Aug 2004 11:36:55 -0700

hi all,

looks like there is concensus for option 1).

I think we should add some text to clarify this. here is a suggestion.
add the following to the end of section 5.2

    In explicit mode, the Mobile Router MUST include
    prefix information in all binding updates, including those sent to
    refresh existing binding cache entres, if it wants forwarding enabled
    for the corresponding Mobile Network Prefixes.

comments are welcome.

Vijay

---

From: Ryuji Wakikawa <[email-masked]>
Date: Tue, 17 Aug 2004 03:50:00 +0900

Vijay

We can also add MUST in section 5.2.

       Explicit:

          In this mode, the Mobile Router "MUST" include one or more 
Mobile
          Network Prefix Options in the Binding Update.  These options
          contain information about the Mobile Network Prefix(es)
          configured on the mobile network.

ryuji

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From: Vijay Devarapalli <[email-masked]>
Date: Mon, 16 Aug 2004 12:12:08 -0700

Ryuji,

I think we can avoid the additional "MUST". this MUST does not
increase interoperability.

>          In this mode, the Mobile Router "MUST" include one or more Mobile

Vijay

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From: Alexandru Petrescu <[email-masked]>
Date: Tue, 17 Aug 2004 11:35:59 +0200

Vijay Devarapalli wrote:

> I think we should add some text to clarify this. here is a
> suggestion. add the following to the end of section 5.2
> 
> In explicit mode, the Mobile Router MUST include prefix information
> in all binding updates, including those sent to refresh existing
> binding cache entres, if it wants forwarding enabled for the
> corresponding Mobile Network Prefixes.

Yes, I agree with option 1 and with this text at the end of section 5.2.

note "entres" to "entries", capitalized BU's, etc...

Alex