Understanding DSCP Values and Marking

Posted on 2012-03-18
Last Modified: 2012-03-21
I am currently configuring Lync for our enterprise. I have it running but I want to implement QOS so that it has priority over certain data types and less than other.
These are the port ranges.

Audio      49,152 – 57,500
Video      57,501 – 65,535
Application Sharing      32,768 – 49,151
Client File Transfer       24,733 – 32,767

Now, in QOS policy, it asks for a DSCP value for each. How do I know what value to use and what it means?

If someone can explain the significance (Ive read articles but still dont really understand), it would help me out a lot.

Question by:Network_Padawan
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Accepted Solution

mccarl earned 500 total points
ID: 37736000
Basically, it is the priority, but not necessarily in numerical order. Different values have specific meanings, and therefore specific priorities. Have a look at the Wiki for this and you will see that 0 is the default traffic and the lowest priority (best-effort), 46 is for "expedited forwarding" and will have the highest priority, and then the values in the table (10, 12, 14, 18, 20, 22, 26, 28, 30, 34, 36, 38) are for "assured forwarding" which will have a priority inbetween the default and 'expedited' but also has different classes of priority within itself.

Author Comment

ID: 37736043
so if i place a 46 on video and audio, what will that do for the rest of data traffic? Do I need to prioritise the rest as well?
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Expert Comment

ID: 37736050
No, that's why the 0 is default, all traffic that isn't given a specific value, will be classed as default, and will then be lower priority to your video and audio.
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Author Comment

ID: 37736062
Ok, thanks, just lastly, does DSCP have anything to do with TOS? Or are they seperate things?
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Assisted Solution

mccarl earned 500 total points
ID: 37736072
DSCP is a newer concept than TOS, but it reuses the same field, in a way that is backwards-compatible to the older TOS. In the wiki link that I gave you above, it talks about this in the section on the 'Class selector' PHB, but basically use of TOS gives values that are distinct from the ones defined for DSCP.

However, if you are just setting this all up from scratch, you shouldn't need to worry about TOS.

Author Closing Comment

ID: 37736115
Thanks. Makes much more sense.
LVL 36

Expert Comment

ID: 37736119
Not a problem!
LVL 12

Expert Comment

ID: 37750433
Take a look at this blog article which describes this concept in detail as it pertains to Lync Server:

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