Subject: Re: [MOBILE-IP] simultaneous mobility bindings: 'tunnels a copy t o each'

From: "Karim El-Malki (ERA)" <[email-masked]>
Date: Tue, 15 Feb 2000 18:43:14 +0100

I agree it is 'quite a complex issue':
>  we are talking about QoS routing, which is so hard most folks have
>  given up on it; and then compounding the problem by not merely
>  selecting the one 'best' route, but rather forwarding packets
>  over multiple concurrent paths.

Well, simultaneous bindings are definitely not a means of "compounding
the problem" as you put it, but quite the opposite. In many cases,
having multiple concurrent paths is a good thing.
If a MN is making a handoff between FAs, having copies of the
same packets reaching both FAs for a short period will help
in improving the quality of handoffs. Therefore your specific
requirements are not the only ones we should be considering.

Regards,
Karim

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From: "[email-masked]" <[email-masked]>
Date: Tue, 15 Feb 2000 09:55:32 -0800

> requirements are not the only ones we should be considering.

Yes, but in a hierarchical scheme, wouldn't it be nice if a parent FA could
handle the distribution of packets to multiple lower layer children FAs?

PatC

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From: Stuart Card <[email-masked]>
Date: Tue, 15 Feb 2000 14:22:10 -0500

[email-masked] wrote --

>> ... In many cases, having multiple concurrent paths is a good thing...
>> your specific requirements are not the only ones we should be considering.

Agreed!

>handle the distribution of packets to multiple lower layer children FAs?

Indeed! The general case is rather complex, and a FA hierarchy could help.

We have:

  Correspondent Host (CH);

  Mobile Host (MH);

  Home Agent of the Mobile Host (HAmh);

  Foreign Agent of the Mobile Host (FAmh);

  Mobile Router (MR);

  Home Agent of the Mobile Router (HAmr); and

  Foreign Agents of the Mobile Router (FAmr0..FAmrN).

Typically, FAmh = MR.

If we tell HAmr only about FAmr0, and have the latter
act as a parent FAmr for all the other FAmr1..FAmrN, we
could limit distribution of link status to the FAmr net:
each FAmrJ need know only about MR and FAmr0; and FAmr0
is the only node that needs to know about all the other
FAmr1..FAmrN (and, for each, whether its link to MR is
currently usable, or better still, its current link QoS).

MR, of course, must also know about each FAmr1..FAmrN,
but that is nothing new if it is registered with each;
further, it is only 1 hop from each, across the wireless
links, knowledge of whose current QoS is our major concern.

Interposing the parent FAmr does not reduce the complexity,
but it _hides_ it from HAmr, allowing HAmr to be 'merely' a
standard HA with mobile router support, rather than also a
QoS-aware, load-balancing, concurrent multipath router
(as FAmr takes on that responsibility).  This buys us nothing
if we own (and thus can put fancy QoS routing code in) HAmr;
but if we don't own HAmr, it buys us much.

Our approach here is to _use_ Mobile-IP to provide multiple
concurrent tunnels; but not to _burden_ Mobile-IP itself
(the baseline HA and FA functionalities) with our fancy
routing.  Once the HA has constructed the tunnels, the
decision as to which tunnel to use for a given packet
(or [micro]flow) is left to the forwarding process.

A HA is, in essence, a router; but typically it has
only one route to the mobile node -- the tunnel defined
by a single registration.  Allowing multiple simultaneous
registrations merely allows for multiple tunnels, thus
multiple paths, yielding a situation more akin to that
normally found in core routers.  We can then use tricks
used in core routers to select among those paths.

***

What this boils down to, IMHO, is this:

FA hierarchies allow us to _optimize_ this, and are generally
A Good Thing;

but the current option for multiple simultaneous registrations at
the HA allows us to do this _without_ introducing a requirement
for FA heirarchies;

and furthermore, that option supports at least one straightforward
approach for _creating_ FA heirarchies.

Thus, that option should _NOT_ be removed from RFC 2002!

------------------------------------------------------------------------
Stuart W. Card, Chief Scientist & Vice-Pres., Critical Technologies Inc.
Suite 400 Technology Center, 4th Floor 1001 Broad Street, Utica NY 13501
315-793-0248   FAX -9710    <[email-masked]>   http://www.critical.com

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From: "Tom K. Weckström" <[email-masked]>
Date: Wed, 16 Feb 2000 08:11:05 +0200

> handle the distribution of packets to multiple lower layer children FAs?

Exactly. I haven't seen anyone mentioning packet duplication here. Has
the current suggestion been to let the HA to duplicate the packets to
all the tunnels it has for the MN? That is at least what a standard
implementation would do, if it had multiple tunnels for a single MN.

OTOH, using FA hierarchies is more like multicasting; the HA sends the
packets to one destination (the Highest FA) which could then do a policy
decision, whether to duplicate packets to multiplse lower FAs. If FA
functionality were improved, some QoS style balancing for the different
tunnels could be added.

If one of the problem to be solved was how to multiply the bandwith over
the _Internet_, then this scheme would not help. If the goal was to
multiply the BW inside a FA hierarchy, then my point is valid.

My point was to make this transparent for the HA, reduce the number of
packets (duplicates) traversing the Internet, and also provide fast
localized handoffs in the FA hierarchy while also giving a possibility
to multiply BW inside the FA hierarchy (with additional QoS logic in the
FA).

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