Subject: [NSIS] CAR Discovery: find an AR with satisfying/better QoS

From: Xiaoming Fu <[email-masked]>
Date: Thu, 8 Nov 2001 14:06:58 -0800 (PST)

Hi,

Well, the problem of finding a "good" AR which provides a
satisfying/better QoS (than current one) possibly will be resolved by
candidate AR (CAR) discovery solution as suggested in
seamoby-cardiscovery-issues-01 draft. 

This explains why this requirement is not listed in the
mip-qos-requirement draft. Provided such CAR discovery solution is
going to be available, we only need to coordinate between the the QoS
signaling solution and CAR here(for this problem)?!

Regards,
Xiaoming

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From: Holger Karl <[email-masked]>
Date: Fri, 09 Nov 2001 08:40:34 +0100

> signaling solution and CAR here(for this problem)?!

No, I do not agree with this. I am not convinced that some generic,
LOCAL candidate AR protocol will be suitable. What I imagine will happen
is the following, with two main possibilities:

1.) CAR is oblivious of QoS requests/reservations:

- CAR discovers a new AR. It talks to the AR about connecting the MN to
the new AR. This needs some radio resources, but likely nothing will be
reserved. 

- The network layer will attempt to do a handover. If QoS can not be
reservered on the radio link, what would happen? Abort the handover?
Likely. 
If QoS can be reserved on the radio link, handover will proceed. But the
QoS reservations could still fail further on in the network. The CAR has
no chance whatsoever of knowing this. 

- Hence, we end up with a new AR with insufficient QoS resources. Even
worse, we have overprovisioned on the radio link, which is really going
to waste customer's money.

2.) CAR knows about QoS requests:

Essentially similar to above, with the excpetion that only such ARs will
be considered that are capable of supporting the requested QoS.
Nevertheless, this most certainly will only be a local descision about
the radio link. Hence, again we might end up with expensive reservations
on the radio link which can not be supported further on in the network.

To cut a long story short: I am seriously worried by a tendency to treat
some parts of the network in some special fashion (here the radio link),
when QoS signaling by definition is something that only makes sense in
larger contexts. 

And in general: radio link QoS reservations is a QoS signaling protocol
problem! And a complicated one on top of it, if you want the protocol to
be compatible with a multitude of emerging radio link technologies. I am
in favor of having some black box that tells about possible ARs, and
here a concept like CAR is very useful. 

Regards

Holger

-- 
Holger Karl
TKN, Technische Universität Berlin

"If you had to identify, in one word, the reason why the human race
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word would be 'meetings'."
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