Subject: RE: [NSIS] Two kinds of requirements

From: [email-masked]
Date: Fri, 25 Jan 2002 16:46:40 +0200

Brian,

> My concern is that there must be sufficient information of some type to
> allow the derivation of what is required for the layer 2. However, the
> typical set of parameters currently in Intserv is not sufficient to
> allow a spectrum efficient bearer, and more information is needed.

I'd be very interested in know what kind of parameters you mean.
Is there a reason why the layer 2 technology cannot handle the
specifics for setting up of layer 2?  Are applications sitting over
layer 3 so demanding / fussy that the need very precise details?

My feeling is that we should generalize the layer 3 needs, and
that layer 2 (or the service provider) can interpret them to
its needs.  

John

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From: Brian Williams <[email-masked]>
Date: 26 Jan 2002 03:59:35 +1100

Hi John.
> layer 3 so demanding / fussy that the need very precise details?
A layer 2 management entity (at either end of the L2 connection) would
be responsible for establishing the layer 2 connection using the layer 2
specific protocol. If you look at UMTS, this protocol has a large number
of parameters; the aim of which is to allow spectrum efficiency which is
_the_key_concern_ for cellular. So, it is not the layer 3 that is
demanding, it is the need to make the most of the spectrum (read as best
QoS possible for lowest possible cost).

The layer 2 can trade off some characteristics against others:
eg.- to get a lower delay, you may accept a higher bit error rate
- in some cases you want the radio link to build in more error
correction (possible increase in delay, but much better characteristics
than end-to-end error recovery). In other cases you want to have packets
delivered even with errors to get lowest delay (eg a speech application
can be tolerant to errors in codec bits).

There are many of these that need to be set. If you only provide the
typical parameters from layer 3 (eg. traffic rate, delay) then the layer
2 management function cannot identify the optimal (ie cheapest that best
meets your needs) bearer. That is because fixed networks typically
assume error rates are low enough to be ignored, and it is _only_
bandwidth, delay and congestion loss that determine QoS. For cellular,
we believe there are more factors that affect QoS, and there are more
details. 

We have two drafts which 
1) identify the problem
http://search.ietf.org/internet-drafts/draft-fodor-intserv-wireless-issues-00.txt
and
2) give an indication of the parameters we are considering 
http://search.ietf.org/internet-drafts/draft-fodor-intserv-wireless-params-00.txt
 
These drafts look at Intserv, and are not tailored to NSIS though. We
are currently working on a new draft discussing the cellular network
problem focused more towards NSIS.
/brian