Cell Relay Archive

[swb@newbridge.com (Scott Brim)]

On Fri, 23 Apr 1999 10:01:13 +0200, Mudassir Tufail
<mtufail@run.montefiore.ulg.ac.be> wrote:

>Hello
>
>I am looking for some pointers, papers or any material that
>discuss different possible mapping of IP-DiffServ classes
>(EF, AF1, AF2, AF3 and AF4) to ATM service categories.
>
>Please refer me the contributions other than those submitted
>to ATM Forum.

Let me try to summarize current thinking.  First, recall that
diff-serv services depend both on the per-hop behaviors, some of which
you've listed above, and the traffic treatment at the edge of the
network.  So you can't map IP PHBs to ATM service classes, rather you
map IP service offerings to ATM service classes.  An AF PHB can be
used for everything from a guaranteed load service to a simple
priority scheme, depending on the way admission control is handled,
and obviously you would want different ATM service classes for the
different ways in which you're using it.  

Now, add the general principle that IP flows covered by service
agreements  which offer hard guarantees are best placed in their own
VCCs (most probably CBR or rtVBR), while those covered by relative
agreements can share VCCs (UBR, GFR, ABR).  EF, since it doesn't
tolerate bursts, will almost always be used for quantitative services,
but AF can be used for both.

We're trying to make it easier to share resources by adding a new
setup information element which will say what behavior class a
particular VCC belongs to.  Basically you use end-to-end signaling
(ATM setup) to communicate desired per-hop behavior to the switches.
Anyway, a switch then manages resources for a particular class, e.g.
AF1, and shares those resources among the VCCs in that class.  That
way a VCC could be set up with minimum cell rate of 0 (since it
doesn't reserve any resources for the VCC itself) but switches could
be configured with per-class resource allocations.  This is all still
being worked out.  We know what we want to do in principle but there
are nits like error conditions and messages to be dealt with.  Some
switches allow you to turn off CAC on a per-class basis, e.g. for UBR,
so you could take signaled MCR as a kind of a weight, but that's only
a temporary measure while we get appropriate signaling worked out.

...Scott (Newbridge Networks)

--
Scott Brim    <swb@newbridge.com>