Subject: Re: [MOBILE-IP] MIPv6 node location detection

From: Francis Dupont <[email-masked]>
Date: Tue, 17 Oct 2000 16:15:29 +0200

In your previous mail you wrote:

   Reading through section 10.4 of the MIPv6 draft (version 12), I get the
   impression that:
   
   1. Movement detection is not a simple problem to solve.  The draft
   doesn't really specifiy what method should be used.
   
=> there are many different methods, some of them are (too) slow,
some of them can detect movements when there is no movement, this can
be a problem or not... I think we need to get results from fast/smart/...
handoff special group and from implemention experiences.

   2. Seeing an adverisement from a router with a different prefix is not a
   good way to detect movement.

=> I agree but the other way is not better.

   The preferred movement detection method seems to be loss of
   reachability of the MN's default router,

=> this is not good if there are more than one router and of course
is very bad if the number of potential default routers is large enough...

   which is noticed through neighbor unreachability detection

=> which uses neighbor solicitations, not router solicitations !

   and/or use of the router advertisement interval option.

=> this point should be added into neighbor discovery specs (ie.
it is useful in general, not only for mobility).
   
   > > I also can't find RFC or draft which define exactly address list in a
   > > MIPv6 MN. A IPv6 node have a address list and  every prefix has lifetime

=> in *theory* the list is the union of local prefixes and home prefixes,
both are in router advertisements on the local link and through the tunnel
with the home agent with the according lifetimes. In order to get the whole
list ASAP someone suggested in this list that the home agent sends router
advertisements to the MN when a home registration is done.

The issue is what happens if the home link is renumbered when the MN is
stopped. In fact this depends on how the MN knows its home prefix(es):
 - very stupid implementations believe the MN is started at home then
   the home prefixes will be prefixes of the first attached link: no
   problem with renumbering.
 - stupid implementations use a static config in order to know home
   prefixes then if the config is too old the MN will not be able to
   find its home link (and a home agent).
 - someone suggested in the list to use a name which can be updated
   when the home prefix is renumbered (but not renamed :-). It is a
   fine idea out of the scope of the mobile IPv6 draft.
I think most implementations use the second way (static config)...

An open question is what to do with DHCPv6?

Regards

[email-masked]
--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page:                      http://playground.sun.com/ipng
FTP archive:                      ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [email-masked]
--------------------------------------------------------------------

---

From: "Thomas Eklund" <[email-masked]>
Date: Wed, 18 Oct 2000 11:34:18 +0200

Hi some commente regarding the movement detection algorithm.
I agree that it might not be a good idea to tie your movement detection to
when you are seeing an advertisement from a router with a different prefix.

First of all - the statemachine for the movementdetection can be at two
places - either in the 1) mobile node (which is the case today) or 2) it can
sit in the network and then you could have network controlled handoff.

To improve handoff you must make increase mobile IP's link-layer awarness.
This is usually achived by listening on the field strengh or something
similar of the radio link. The solution is different for every different
radio link you have.

Take 802.11 ethernet for instance, there you can associate every radio cell
(and AP) to an IP subnet with a new prefix or you can associate several AP
to an IP subnet (recomended). In case 1) you can associate every radio cell
with a subnetprefix and you modify you movement detection algoritm (MDA) so
that it builds up an internal list with prefixes and subnet and associated
field strengh.

For instance:
General Parameters:
Joning treshsholds: xxx dBm
Leaving Treshholds: xxx dBm

CoA        Current Subnet   Field strengh  Active CoA
CoA1         Prefix 1                   xx dBm           ---
CoA2         Prefix 2                   xx dBm        Active
CoA3         Prefix 3                   xx dBm           ---
CoA4         Prefix 4                   xx dBm           ---
CoA5         Prefix 5                   xx dBm           ---

The intention is also to start bulding new CoA before you must switch over
to a new AP which will make you handover quicker. You listens on the field
strengh of the different radio cells or subnets and associate make you
handover based on the field strengh.

This approach could also be done from the AP or BS which would be a good
aproach o a WAN radio like GSM or CDMA. Then the movement detection
algorithm sits (it is not called that in GSM terms) in a BSC and in tells
you to do you handover but in this case you would have to interupt that let
mobile IP have that info and then mobile IP could be invoked in network
initiated handoffs. This is nice on paper and would really optimize the
radio network for IP but there is a lot of polotics here which can make it
very difficult.

You can also include QoS parameter in your handover design and you can make
it very advanced.

In other it is nothing in the spec that stops you from achieving very good
handoffs.

-- Thomas Eklund

---

From: "John F. Leser" <[email-masked]>
Date: Wed, 18 Oct 2000 11:10:50 -0400

> similar of the radio link. The solution is different for every different

[cut]

I don't doubt that there are many ways the link layer could provide
excellent movement detection.  I think the issue here is how to provide
some movement detection for MIPv6 without any special signalling from
lower layers.

I think you did touch on an important point - movement detection is really
two problems - (1) detecting movement on to a link, and (2) detecting
movement off of a link.  If the mobile node is eager to move to new
networks, then it is only critial that (1) take place quickly for smooth
handoffs.  Its somewhat less clear to me when (2) must take place, but it
should happen eventually.

With this in mind, I'd like to suggest this as an idea for movement
detection:

- Require that a home agent's router advertisements always contain all
of the prefixes on the network that are valid for home or CO addresses.

- Then, whenever a MN receives an RA with the H bit set, it will know
with certainty whether that RA came from the current home or foreign
network, or from some new network, based on whether the prefix of the MN's
home or current CO address is advertised in the RA.  This way, movement
onto a new link is detected as soon as any home agent on that link sends
an advertisement.

- Whenever an RA is received indicating movement onto a new link,
the MN transitions neigbor cache entry for the old default router(s) to
stale, to accelerate unreachability detection.

Of course, the danger here is that the network could be misconfigured so
that home agents are not advertising all prefixes.  This would be 
sub-optimal (mobility would be uses when it is not needed), but wouldn't
prevent the mobile node from communicating.  

I'm curious what people think of this.

------------------------------------------------------------------- 
John Leser 			UNH InterOperability Lab 
IP/Routing Consortium Engineer 	Morse Hall, 39 College Rd, Room 332
Tel: (603) 862-0090 (8-5 EST) 	Durham, NH 03824-3525 
Fax: (603) 862-1761		Web: www.iol.unh.edu
-------------------------------------------------------------------

---

From: Francis Dupont <[email-masked]>
Date: Fri, 20 Oct 2000 14:09:29 +0200

=> according to other messages your idea is to overload the meaning
of the H flag with "this RA announces all the prefixes"...
I don't think it is a good idea but if to know the number of prefixes
(there are some optimizations where this info is needed) is very useful
then why not a new extension with it in any RA?

=> this is not protected against a rogue RA and doesn't work with
overlapping cells (which seems to need the help of the layer two).

=> move the state to incomplete is more aggressive (faster but more
expensive if there is no real movement).

=> I think to rely on RAs for movement detection is not very good because
if this should be fast then the frequency of RAs has to be very high
(ie. higher than reasonnable). And this is dedicated to a very special
scenario (the cellular one) when there are many of them. In this list
(mobile IP) many of us did shout that cellular != wireless != mobile,
please add me...

Regards

PS: the only very clear indication you can get from a RA is to receive
an announce for the home prefix(es) where you are in visit. In other
cases you can only suspect a movement.
--------------------------------------------------------------------
IETF IPng Working Group Mailing List
IPng Home Page:                      http://playground.sun.com/ipng
FTP archive:                      ftp://playground.sun.com/pub/ipng
Direct all administrative requests to [email-masked]
--------------------------------------------------------------------