# DSCP - QOS value

Oct 11th, 2007

DSCP Value conversion to PHB Value mechanism and details required.

Hi,

It was detailed calculation:

AFXY, CSX and EF are just PHB codes for the corresponding DSCP in binary or decimal representation.

AFXY where X is the class (3bits)

Y is the priority (2bits)

AF calculation example: PHB codeAF33=011 11 0(binary)=30(decimal)

EF calculation example: PHB code EF =101 11 0(binary)=46(decimal)

101 is the precedence

11 is the class of service

0 remain 0

and so one for other values, I attached another more detailed table that resume all calculations of the DSCP binary and the equivalent decimal value from the precedence and class of service

Hello Guarav.

What zou are looking for is NOT mathematical. "AF" and "EF" is just a NAME defined in Standard. AF means Assured Forwarding, and EF means Expedited Forwarding. They could have named it "Very Important" and instead of EF we would use "VI"

So DSCP EF 46 is really DSCP 46. Standard defines how should numbers be used and what they are named. Please refer to the following documents:

Hope this helps.

Overall Rating: 5 (3 ratings)

## Replies

Martin Parry Thu, 10/11/2007 - 06:12
• Silver, 250 points or more

Hope this helps

Martin

Attachment:
gaurav_thapar79 Thu, 10/11/2007 - 10:21

Dear Parry,

Thats of great help but i am looking for mathematical calculas to do the conversion part.

i can do the DSCP to IP precedence but cld not achieve DSCP to PHB.

Can you help on this?

gaurav_thapar79 Thu, 10/11/2007 - 21:36

Hi matrin,

can you share the calculas of converting DSCP values to Assured Forwarding Classes and drop precedence.

DSCP 31 to AFxy.

How to convert 31 to xy? pls share the URL or method of doing it so.

abdel_n Fri, 10/12/2007 - 07:29

Hi,

Take a look at the enclosed document I hope this will help.

Good Work,

Abdel

Attachment:
gaurav_thapar79 Fri, 10/12/2007 - 09:46

Hi abdel,

I am looking for methodology of calculating AFxy using given DSCP value instead of using table.

Like DSCP 46 means

a.) IP precedence =4

b.) TOS value = 184

c.) PHB = EF =101 but how have i derived 46 = EF?

Any possible calculation against this.

Mohamed Sobair Fri, 10/12/2007 - 11:06
• Gold, 750 points or more

Hi,

Great question,

I was asking the same, How is PHP is converted to Diffserv Code point?

the point here is that IP-Precedence 5 is equal to EF 46.

Regards,

Mohamed Sobair

Attachment:
gaurav_thapar79 Fri, 10/12/2007 - 11:30

Dear Sobair,

My apologies for writing IP precedence 4 instead of 5. But still my query hasn't been addressed.

How would i come to know that DSCP 36 is equal to AFxy?

how would i calculate that 36 = xy?

x= class service

y= drop precedence.

Hope you understand my question. please share any possible calculas.

Pavel Bykov Fri, 10/12/2007 - 11:25
• Silver, 250 points or more

Hello Guarav.

What zou are looking for is NOT mathematical. "AF" and "EF" is just a NAME defined in Standard. AF means Assured Forwarding, and EF means Expedited Forwarding. They could have named it "Very Important" and instead of EF we would use "VI"

So DSCP EF 46 is really DSCP 46. Standard defines how should numbers be used and what they are named. Please refer to the following documents:

Hope this helps.

abdel_n Fri, 10/12/2007 - 11:40

Hi,

It was detailed calculation:

AFXY, CSX and EF are just PHB codes for the corresponding DSCP in binary or decimal representation.

AFXY where X is the class (3bits)

Y is the priority (2bits)

AF calculation example: PHB codeAF33=011 11 0(binary)=30(decimal)

EF calculation example: PHB code EF =101 11 0(binary)=46(decimal)

101 is the precedence

11 is the class of service

0 remain 0

and so one for other values, I attached another more detailed table that resume all calculations of the DSCP binary and the equivalent decimal value from the precedence and class of service

Attachment:
Mohamed Sobair Fri, 10/12/2007 - 12:16
• Gold, 750 points or more

Hi,

Great Explanation,

Deserve Full Rate.

Regards,

Mohamed Sobair

Pavel Bykov Sat, 10/13/2007 - 07:50
• Silver, 250 points or more

A little correction to Abdel's post: IP Precedence are not called CS0, CS1, and so forth. That's DSCP code. The following list describes the Codes (Names) of IP Precedence values in format "Binary (decimal) - Name":

000 (0) - Routine

001 (1) - Priority

010 (2) - Immediate

011 (3) - Flash

100 (4) - Flash Override

101 (5) - Critical

110 (6) - Internetwork Control

111 (7) - Network Control