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Understanding DSCP Values and Marking

Posted on 2012-03-18
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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.

Thanks
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Question by:Network_Padawan
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mccarl earned 500 total points
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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.
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by:Network_Padawan
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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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by:mccarl
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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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by:Network_Padawan
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Ok, thanks, just lastly, does DSCP have anything to do with TOS? Or are they seperate things?
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by:mccarl
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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.
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by:Network_Padawan
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Thanks. Makes much more sense.
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by:mccarl
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Not a problem!
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by:Jeff_Schertz
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Take a look at this blog article which describes this concept in detail as it pertains to Lync Server:
http://blog.schertz.name/2011/08/lync-qos-behavior
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