RE: [Diffserv] [OFFLIST] MPLS+Diffserv(mapping DSCP to EXP)

[Shahram Davari <Shahram_Davari@pmc-sierra.com>]

> -----Original Message-----
> From: Mark Duffy [mailto:mduffy@quarrytech.com]
> Sent: Tuesday, February 04, 2003 7:29 AM
> To: nerdboy@rediffmail.com; Diffserv@ietf.org

> >2. Further, since the DSCP  ( pow(2,8) = 256 combinations ) 
> is 8 bits and
> >provides 22 different PHB's(or roughly 7 different classes),
> >      and the EXP is just 3 bits and therefore can provide 
> only upto 8
> >different classes, wouldnt there be loss of info while 
> mapping DSCP->EXP ?
> >

No because in MPLS we do DSCP=> PHB translation and PHB=> EXP+Label encoding. The label gives you the context info, so each label can support up to 8 PHBs. To support all 64 PHBs (which are not defined yet) you need 8 parallel LSPs.


-Shahram
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