Subject: [mobile-ip] Heterogeneous Handover - How Would it Work?

From: James Kempf <[email-masked]>
Date: Mon, 6 Aug 2001 23:54:39 -0700

There has been alot of talk about handover between two different technology
interfaces over the last year, and it has been used as a justification 
for alot of work in both Seamoby and MIP WGs. However, it is entirely
unclear to me exactly how this would work. For example, it seems to me
that to handover between an interface running on one radio link
configured with the global home address and an active CoA to another
interface which is unconfigured, the MN would have to effectively
transfer the global home address from the active interface to the
unconfigured interface, then obtain a new CoA on the new interface.
But, presumably  the home address was registered in the home network
associated with a particular radio link technology. Does this imply that there
must also be a heterogeneous technology network back in the home
network? Are there any security implications of this? If the 
MN is authenticated through one interface, perhaps including
L2 authentication, what would be needed to transfer that to
the second interface? And would that matter to the binding between
the L2 address and global home address back in the home network?

There are probably alot of other details involved in doing heterogenous
technology handover. Maybe I'm just being too paranoid, but I think it 
would be prudent to actually figure out how it would work from a systems 
perspective before we go further in using heterogeneous handover as a 
justification for adding various features or removing them. Otherwise, we 
may end up with lots of features that basically don't reflect reality. A 
simple, clear description of how heterogeneous handover would work is needed,
IMHO.

		jak

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From: Mattias Pettersson <[email-masked]>
Date: Tue, 07 Aug 2001 09:51:28 +0200

> the L2 address and global home address back in the home network?

I can speak from an implementation perspective. In the Ericsson MIPv6
contribution to KAME we used CoAs bound to physical interfaces, while
the home address would be bound to a virtual interface (say loopback).

The MN would be considered "home" whenever any of the interfaces was at
the home subnet. No particular interface was associated with the home
subnet.

On the other hand, the home address must belong to some ISP/operator.
That ISP must provide a home agent and an ip address, and a CoA when the
MN is connected to other than the home subnet. Other ISPs that are used
are only access providers, and would give the MN its CoA. This of course
would cause political problems. Who are the ISPs that are willing to be
access providers only, and who will be providing home agent and home
address as well?

Another approach is to have a home address for every interface that the
MN uses. If MN has a cellular interface, it will have a home address
from the cellular operator. If the MN also has a WLAN interface, it will
have a second home address from the WLAN ISP. But now, which home
address will the MN use? The MN will in practice have two identities.
Should it register both? Both registrations would use the same CoA if
only one access is available.

/Mattias

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From: "alper" <[email-masked]>
Date: Tue, 7 Aug 2001 05:52:03 -0700

Jim,

This is a good subject to discuss. Although I don't see any issues with
this,
it'd be good to see if everybody agrees, and if there are any issues we are
missing.

comments start with "aey >"...

-----Original Message-----
From: [email-masked]
[mailto:[email-masked]]On Behalf Of Mattias
Pettersson
Sent: 07 Aðustos 2001 Salý 00:51
To: [email-masked]
Subject: Re: [mobile-ip] Heterogeneous Handover - How Would it Work?

aey > yes, that makes sense to me as well. as soon as an interface is
attached to a radio link, it can configure a CoA. And after this point,
MN can send a BU mapping its home address to this newCoA.

aey > from home agent point of view, all it sees is that MN has moved.
Hoem agent doesn't have to even know that mn is multihomed, or what
L2 technoologies it's using.

aey > right. at this point, mobile node can configure the home address
on this interface.

aey > it seems like there are two kind of services here. one is providing
a home address and home agent service. the other is providing a topological
correct address, (coA), service. I think an ISP should be able to provide
any or both.

aey > distinguishing two services (as above) makes more sense to me.

/Mattias

alper

---

From: Tom Weckström <[email-masked]>
Date: Tue, 7 Aug 2001 17:48:23 +0300 (EET DST)

On Tue, 7 Aug 2001, Mattias Pettersson wrote:

mattia >Another approach is to have a home address for every interface that the
mattia >MN uses. If MN has a cellular interface, it will have a home address
mattia >from the cellular operator. If the MN also has a WLAN interface, it will
mattia >have a second home address from the WLAN ISP. But now, which home
mattia >address will the MN use? The MN will in practice have two identities.
mattia >Should it register both? Both registrations would use the same CoA if
mattia >only one access is available.
mattia >
mattia >/Mattias
mattia >

Hello Mattias.

One of the strengths of MIP is that it preserves the sessions while the
mobile terminal moves, because the home IP adress remains the same.

Taking this another approach would result in broken sessions while making
heterogenous technology handovers, because the home IP address of the MN
would be different in each technology.

So, I would not implement the second approach at all. The first one (not
quoted above, but available in the original email) looks better.

Regards,
-- 
	Tom Weckström		Dynamics group
				Helsinki University of Technology
				[email-masked]
				http://www.cs.hut.fi/Research/Dynamics/