Cell Relay Archive

[Geert Goossens <gagoosse@info.vub.ac.be>]

ronald h. davis wrote:
> 
> Geert Goossens wrote:
> >
> > Patrick Hurley wrote:
> > >
> > > What is the standard way in which a switch deals with prioritization of
> > > traffic based upon whether it is configured as CBR, VBR-rt or VBR-nrt?
> >
> > The switch uses the following priorities:
> >         CBR
> >         VBR-rt
> >         VBR-nrt
> >         UBR
> >         ABR
> > as defined in the Traffic Management Specification version 4
> > (af-tm-0056_000), April 1996 by the ATM Forum.
> >
> 
> i don't think that this priority ranking is correct.  if compliant traffic is
> received from a cbr connection, and a vbr-rt connection, and they have the same
> qos (as defined by maximum ctd, cdv, and clr) how does the switch prioritize
> between traffic from connections with the same qos specification?
> furthermore, would a switch really handle traffic from an abr connection (if
> it is within bounds of the specified mcr) at a lower priority than traffic
> from a ubr connection which has no such specification?  this point is debatable
> either way, however, since according to the traffic management specification
> there is no qos guarantee allocated to either abr or ubr traffic so a switch
> could treat them at the same priority, or different priorities depending upon
> the implementation.
> 
I'm afraid I've answered this question w/o checking the actual
documents. I though I remember this being defined this way, but now I
can't find it back. Maybe I saw it somewhere else or in a specific
implementation, I don't remember.
Anyway, it would be logical to prioritize real-time traffic (CBR and
rt-VRB). I agree that ABR probably should come before UBR.

Geert.