Subject: [MOBILE-IP] Questions/Comments on Buffer Management draft

From: "BINAR, Simon" <[email-masked]>
Date: Thu, 28 Oct 1999 14:58:26 +0100

Hi.

I have read the buffer management draft, and would have a couple of
questions/comments:

First, it is not clear to me from Figures (1) and (2) whether the MN is
communicating directly with the old FA (after it has exchanged messages
with the new FA), or whether it is communicating via the new FA. If the
first case applies (direct communications), then the implementation of
the protocol might be problematic in TDMA-based networks, as it would
mean that the MN would need to switch several times between different
frequencies. This would be very inefficient, and could significantly
increase handover latency. In some cases, it may not be possible at all.
I think that IP-based solution for handover should not be optimised for
a particular radio technology (which would be rather CDMA-based networks
in this case).

I think there are also two major issues with this proposal, and I would
be happy to hear anyone's views on this.

The first issue is related to billing and charging and network
operator's control over QoS. In public service provider networks, the
allocation of specific resources to customers (such as bandwidth)
usually will be reflected in the cost of the service. A buffer is also
clearly such a resource. Thus, if a MN requests usage of a buffer from a
service provider, this normally should result in higher cost of the
wireless service - not only because of usage of dedicated resources in
the network, but also because the sensed QoS probably will be higher
(customers cannot be charged the same price for different QoS).

The problem with this approach is that control over the provided QoS is
in the control of the user rather than the network operator (this is
what the draft seems to suggest, anyway). If a user requests usage of
buffers, he will need to be made aware of the higher cost. How shall
this happen? I think this is a very difficult issue to resolve. The
easier way would be for the user to *sign-up* a priori for a service
with a specified QoS. A foreign agent could then decide whether it
should allocate buffer space based on the QoS class that is specified in
IP packet headers (e.g., the DS field in the case of DiffServ, I guess).

Furthermore, if the network operator knows a priori how many customers
have signed up for a specific class of service, it will have a rough
idea of how to dimension its network, and especially about how much
buffer space to allocate in its foreign agents. How shall the network
operator do network dimensioning when *anyone* could use available
buffer space? How could the operator then provide different levels of
service to different customers? If anyone can request use of buffers,
then users that otherwise would have payed more money for higher service
might not get the service they expect, because someone else is using up
their resources... These are all quite tough issues, I think.

My point here is that control over QoS should be for a large part in the
hands of the network operator, and not of the user.

Another problem is from the perspective of application developers. The
proposed buffer management draft provides a lot of flexibility to the
mobile node to request or not usage of buffer space, to specify how much
buffer space is needed, to request or not whether the foreign agent
should send a Buffer Control Response or not, etc... This high level of
flexibility in my view also means a lot of headaches for application
developers, because they will be confronted with the basic question: how
should they choose which values to use for all of these
options/parameters?

Comments are most welcome...

----------------------------------------------
Simon Binar
NEC Europe Ltd.
Tel:   +44 (0)1753 606933
Fax:   +44 (0)1753 606901
EMail: [email-masked]
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From: Claude Castelluccia <[email-masked]>
Date: Thu, 28 Oct 1999 18:12:29 +0200

> their resources... These are all quite tough issues, I think.
Hello,

the same problem occurs when trying to use DiffServ in a mobile
environment...
we just have to hope that statistical multiplexing will help us ...

Claude.

----------------------------------------
Claude CASTELLUCCIA, INRIA Rhone-Alpes
ph:  +33 4.76.61.52.15 (fax: 52.52)
http://www.inrialpes.fr/planete/