class value in label

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Jul 7th, 2010
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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
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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
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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

Giuseppe Larosa Wed, 07/21/2010 - 13:14
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Hello Dinesh,

you are probably referring to E LSPs versus L LSPs idea


to be able to map the 6 bits wide DSCP you need to use multiple LSPs with the same destination


see the following document from networkers 2008


http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6557/ps6607/prod_presentation0900aecd8031280f.pdf


silde 6


Hope to help

Giuseppe

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