Re: [tsvwg] COMMENT PLEASE: Which DSCP value should we use for LE PHB?

[<[e-mail]>]

Hi Roland,

in an MPLS domain, one generally may assign a bunch of DSCP to a 
single Treatment Aggregate / PHB. That I think is quite useful. 
Unfortunately the top label is removed before the last MPLS 
domain router is reached. Then an unknown and not re-marked 
DSCP is not acceptable. Hence your guidance below isn't applicable in 
all networks.

There is a fairly simple and useful option allowing to combine Treatment 
Aggregates, Diffserv forwarding across an MPLS domain and 
maintenance of multiple DSCP. Per Treatment Aggregate:
- classify DSCPs by bit-mask at ingress.
- re-mark DSCPs by bit mask at ingress.
- Diffserv forwarding by Treatment Aggregate
- classify and forward by individual DSCP at the egress (if desired)
- same holds for next domain

The other simple option I see without bit mask based re-mark is, 
again per Treatment Aggregate:
- classify DSCPs by bit-mask at ingress.
- re-mark to _a single DSCP_ at ingress.
- Diffserv forwarding by Treatment Aggregate 
- classify and forward by this single DSCP at the egress
- same holds for next domain

I prefer a simple solution (and a standardized one, if possible). 

Of course it is technically possible to set up and maintain per DSCP to 
PHB and individual DSCP re-mark tables, customized for each 
interconnection. Interconnection DSCPs are not standardized.
Many carriers operate multiple interconnections. 

Regards, 

Ruediger

>> IMHO it shouldn't be difficult to have a mapping table from each DSCP 
>> to a PHB. The mapping table should initially only contain mappings to 
>> the default PHB (no need to remark anything then).
>> Configuring DSCP remarking by using bitmasks is IMHO not RFC2474 
>> compliant and a broken concept causing the trouble we just ran into.
> 
> And you shouldn't fix broken products by fiddling with a standard; 
> that rewards the makers of broken products.

+1

Regards,
 Roland