Subject: [Mip6] Comments on draft-wakikawa-mobileip-multiplecoa-02.txt

From: "James Kempf" <[email-masked]>
Date: Fri, 31 Oct 2003 18:42:22 -0800

Thierry,

I looked at draft-wakikawa-mobileip-multiplecoa-02.txt and the fundamental
architectural idea here seems to be to introduce a new namespace, the BID,
to tie together multiple CoAs to one HA. I can see a couple issues with this
approach.

1) On the one hand, the CoAs are not exposed to the transport layer on the
two hosts, so the transport layer doesn't have the opportunity to assess
such connection characteristics as congestion, reachability, bandwidth, etc.
when determining which CoA to use, or whether to use multiple
CoAs (draft-matsuoka-multilink-transport-requirement-00.txt). An
example is the MPEG streaming video example I cited in previous email. If
the transport layer has access to the multiple addresses and information on
the connection, it can decide whether to send the extra layers to improve
video quality over a high bandwidth v.s. low bandwidth connection.  Another
example is SCTP which uses multiple addresses to good advantage, switching
to a new address if unrecahability develops on the currently active one.

2) On the other hand, although the BID is halfway to being an endpoint
identifier, yet there's still the HoA to deal with. Proposals such as MAST
(draft-crocker-mast-analysis-01.txt) and HIP
(draft-moskowitz-hip-arch-05.txt) go all the way in this regard and
introduce endpoint identifiers that are independent of IP addresses and are
utilized for session identification. The endpoint identifier is visible to
the transport layer and is used for transport session identification, rather
than an IP address. They use different approaches - MAST identifiers are
session specific and negotiated while HIP identifiers are global - but the
basic architectural idea is the same.

            jak

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From: Ryuji Wakikawa<[email-masked]>
Date: Tue, 04 Nov 2003 03:13:28 +0900

Hi James

At Fri, 31 Oct 2003 18:42:22 -0800,
> to tie together multiple CoAs to one HA. I can see a couple issues with this

Well, I am not sure whether BID is the new name space or not. The
identifier of MN is still HoA.  BID is nothing to do with session or
endpoint identifier. BID is identifier to distinguish bindings for the
same HoA. BID is used only for binding management (registration, de-,
refresh) and binding selection only. 

The name of BID might be wrong, we should name like nonce index
(i.e. just index each binding). If the name of "BID" is reason to
cause misunderstanding, I can change the name of BID to "binding
index, etc" in the next version.

> to a new address if unrecahability develops on the currently active one.

We use this BID only to register multiple CoAs bound to the same
HoA. Therefore, upper layers might not be aware of even multihoming
(multiple bindings). see more below.

> basic architectural idea is the same.

The MN's identifier is still HoA in my draft. After session
establishment with HoA, MN and CN need to select the best BID or use
multiple BIDs for single communication depending on each flow type.

This decision shouldn't be taken only by MIP6, but also other
factors. I know there are several approaches proposed to MIP6WG to use
filter/policy for this decision (I basically agree with them), but
management of these policy/filters is _not_ MIP6 specific
issue. Carrying policy by MIP signaling is not only solution. There
are several ways to manage these policies at end-nodes.

We need to discuss combination of other transport protocols like you
listed, but what MIP6 lacks for multihoming now is multiple CoAs
registration for the same HoA. This draft try to solve the issue.
Even if other approach is taken for multihoming, multiple bindings
registration is still needed at MIP6 layer. 

regards,
ryuji

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From: Vijay Devarapalli <[email-masked]>
Date: Mon, 03 Nov 2003 10:29:50 -0800

Jim,

I think draft-wakikawa-mobileip-multiplecoa-02.txt deals with a
very specific problem. it deals with how to register mutliple
care-of addresses for a single home address.  it is very MIPv6
specific. Mobile IPv6 currently does not allow more than one
care-of address in a binding cache entry.

nothing to do with endpoint identifiers.

Vijay

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From: "James Kempf" <[email-masked]>
Date: Mon, 3 Nov 2003 14:21:31 -0800

> nothing to do with endpoint identifiers.

If the multiple CoAs are all on one host, then isn't the net effect of the
BID to act as an endpoint identifier for the host?

If they aren't, then my question is what is the BID intended for?

            jak

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From: Vijay Devarapalli <[email-masked]>
Date: Mon, 03 Nov 2003 14:38:13 -0800

> BID to act as an endpoint identifier for the host?

not really. the Home Address is still the identifier. infact
there is one BID per CoA. each BID identifies a particular
CoA from the set of CoAs associated with a particular home
address.

Vijay

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From: "James Kempf" <[email-masked]>
Date: Mon, 3 Nov 2003 15:21:57 -0800

> CoA from the set of CoAs associated with a particular home

Here's a quote from Section 1:

   In this document, we thus propose a new identification number called
   Binding Unique Identification number (BID) for each binding cache
   entry to accommodate multiple bindings registration.  We also propose
   extension of binding cache management to store the BID and a new
   sub-option for binding update to carry the BID. The BID is assigned
   to either the interfaces or care-of addresses bound to a single
   home address of a mobile node.  The mobile node notifies the BID
   to both its home agent and correspondent nodes by means of a BU.
   Correspondent nodes and the home agent record the BID into their
   binding cache.  The home address thus identifies a mobile node itself
   whereas the BID identifies each binding registered by a mobile node.
   By using the BID, multiple bindings can then be distinguished.

Up until the last sentence, it sounds to me as if the purpose of the BID is
to unify all the CoAs under one HoA. In fact, even the last sentence could
be read as that if a "binding" is meant to include the binding of multiple
CoAs to an HoA.

Later on in the draft (viz. Section 3) it also appears as if the BID is used
in this manner.

In Section 5.1, we finally learn:

   A mobile node assigns BID to each care-of address when it wants to
   simultaneously register with its home address.  The value should be
   generated from 1 to 65535.  Zero and negative value can not be take
   as BID. If a mobile node has only one care-of address, assignment of
   BID is not needed until it has multiple care-of addresses to register
   as a binding.

So, yes, you are right, it is not used as a partial node identifier, it is
used just to identify the binding.

Which increases my confusion about why it is needed. Couldn't the MN simply
send a HoA/CoA pair when it wanted to identify the binding?

            jak

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From: Ryuji Wakikawa<[email-masked]>
Date: Tue, 04 Nov 2003 17:54:33 +0900

At Mon, 3 Nov 2003 15:21:57 -0800,
> used just to identify the binding.

I will update BID definition in the next version.

> send a HoA/CoA pair when it wanted to identify the binding?

Here is example.

MN has two i/f and registers two CoAs for a single HoA.
When the i/f-1 is attached to a new visited link (ie.movement), MN
wants to update its binding by replacing the older CoA with the new
CoA aquired by the i/f-1.

Since the value of CoA is already changed, how can MN update the
particular binding by using newCoA and HoA set? HA can not figure out
which binding should be updated with the receiving Binding
Update(NewCoA and HoA pair).

The CoA/HoA pair does not help to identify particular binding, because
CoA is variable.

regards,
ryuji

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From: "Koojana Kuladinithi" <[email-masked]>
Date: Tue, 4 Nov 2003 11:50:05 +0100

Hi all,

Please find the answer in line

> The CoA/HoA pair does not help to identify particular binding, because

NOMADv6 draft (draft-nomadv6-mobileip-filters-01.txt) looks at this problem
in a different way. It has no separate Identifier like the BID. 

It enhances having multiple interfaces to the Internet (with one HoA), by
enabling differentiation of flows based on different filtering criteria.
NOMADv6 lets the filters define how the different bindings are used to route
flows, thereby letting a binding (that is identified as HoA-CoA pair with
filters) to expire when no refreshing. That means, for Ryuji's example, the
flows that were on the i/f 1 will be redirected to new CoA of i/f 1, after
the handoff.  

Regards
Koojana