Subject: Re: IP flow def'n: unidirectional, "host pair", "host port quadruple" (was "Re: Standard Flow Export - definition of 'flows'")

From: Remco van de Meent <[email-masked]>
Date: Tue, 27 Mar 2001 15:29:15 +0200

Remco Poortinga wrote:
> > In my mind, the IP flow definition would go something more along
> > these lines:
> > 
> >    An IP flow is a unidirectional series of IP packets of a given
> >    protocol,
> 
> [insert]
> and Class of Service
> (and maybe more/others if we look at the IPv6 header?)

Is "Class of Service" well-defined? I think a more detailed description
would be useful. Adding CoS to the definition sounds good. However,
some thoughts.

Trying to define CoS. IP packets that have the same TOS and/or DSCP
bits set? Also within other (but possibly irrelevant?) domains, the
proposed 4-tuple itself is used for classification (i.e. setting those
bits) of the service.

I'm trying to think of an example where adding CoS to the definition of
a flow would add to its strength. In other words, a scenario where
classification is not based on parts already mentioned in the proposed
definition for an IP flow. Theoratically, classification could be done
using any of the bits in the IP header, "some" parts of the lower layer
protocol (e.g. transport protocol, ethernet mac address) as well as the
physical environment the IP packet lives in (e.g. the port it has been
received on). In that view adding CoS is useful, IMHO. From a more
practical viewpoint, I'm not really sure. 

> >traveling between a source and destination, within a
> >    certain period of time.
> >    The source and destination are defined, at least, by IP address,
> >    forming a "host pair".
> > 
> >    For IP protocols which further qualify the source and destination
> >    endpoints with a /port/ number, those port numbers become part of
> >    the source and destination, forming a "host and port quadruple"
> >    (source-address, source-port, destination-address,
> >    destination-port).

cheers,
Remco.
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