The MPLS WG Archive

[David Charlap <david.charlap@marconi.com>]

Shahram Davari wrote:
> David Charlap wrote:
>>
>> You really can't.  There is no defined meaning for COS-type
>> values other than zero (best effort).  Any other value may be
>> ignored, rejected, or handled in a way you don't want.
> 
> Yes off course you can. You could map any COS-Type to a local
> (non-standard) DSCP value.

And ensure that every router along the LSP accepts the non-zero COS-type
and handles it in the intended way.

A human administrator may be able to make that guarantee, but there's no
way switch software can do so on its own.

In other words, any use of these COS-types to map DS classes would have
to be through explicit administrative control.  Such mappings can not be
made automatically, because successful implementation requres
meta-knowledge of how the entire cloud will support this non-standard
feature.

(Of course, a new draft may come along to solve this problem, if people
really care.  But that changes the problem - after approval of such a
draft, use of the COS-type would no longer be non-standard.)

-- David