class value in label

Unanswered Question
Jul 7th, 2010

Hi Guys,

  Came across some doc for DSCP on MPLs which states label can carry class values and  mpls EXP bits carry drop value. If thats the case how can i see the class value in label and here are they mentioning 20 bits label? And is there any pre-defined values DSCP to EXP  values?


Regards,

V Dinesh Kumar

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shivlu jain Wed, 07/07/2010 - 11:00

In MPLS we are having only 3 bit which means not more than 8 combinations of offering class of service. If you want to map DSCP to MPLS QOS then you can imagine mappings will like 0-7 DSCP belongs to MPLS EXP bit 1 then 8 to 15 DSCO belongs to 2 and upto 64.


regards

shivlu jain

http://www.mplsvpn.info

inderdeeps Tue, 07/20/2010 - 01:37

Hello Dinesh,


We have specific combination of the 3 bits in EXP, For there combination we have the DSCP range from 0 to 63.We are defining the Class of the label as follows:-


Code Point
Forwarding Class
Loss Priority

000

best-effort

low

001

best-effort

high

010

expedited-forwarding

low

011

expedited-forwarding

high

100

assured-forwarding

low

101

assured-forwarding

high

110

network-control

low

111

network-control

high


But in actual the Diffserv model uses 6 bits of IP tos value to define the Diffserv code points(DSCP) which distinguishes how packet can be treated by the network. The first 3 bits are of EXP bits and the other 3 bits are provided by the Service Provider named as IP prec Bits, so we have two modes now:-


  • Default A  simple best-effort class, with a DSCP value of 000000. Packets with no  defined DSCP are mapped to the default class for best-effort service.

  • Class  Selector Provides for backward compatibility with 3-bit IP PREC  classes. Basically, it defines a DCSP of XXX000,  where XXX represent the PREC bits.


For further, Pls go through the below link:-

http://www.atslog.dp.ua/ch04lev1sec5.html


Cheers!!!

Inderdeep

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