QOS: DiffServ CodePoints vs DSCP vs CoS?

Answered Question
Aug 6th, 2010

I'm new to QoS, but I've been doing some reading and packet captures to learn.  From what I can tell (from a sniffer) my phones mark SIP signalling as Type of Service 0x68 and the RTP voice as 0xb8.


But when reading other documents about best practices, I often see references to Class of Service 3 for signalling and Class of Service 5 for RTP.  And then I've also seen references to diffserv codepoint 40 vs diffserv codepoint 46.


How do these all relate?  Any intro links/articles would be appreciated too.


Thanks

Bill

I have this problem too.
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Correct Answer by Jonathan Schulenberg about 6 years 5 months ago

COS is only a three-bit value while DSCP is a superset extending it to a six-bit value.

You are seeing a hexadecimal representation of the byte field in Wireshark. What you are seeing elsewhere are decimal representations (e.g. 46 of the first six bits of that byte field.

This document includes a table that shows the commonly used binary, decimal, and AF values matched up: http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a00800949f2.shtml

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Correct Answer
Jonathan Schulenberg Fri, 08/06/2010 - 15:13

COS is only a three-bit value while DSCP is a superset extending it to a six-bit value.

You are seeing a hexadecimal representation of the byte field in Wireshark. What you are seeing elsewhere are decimal representations (e.g. 46 of the first six bits of that byte field.

This document includes a table that shows the commonly used binary, decimal, and AF values matched up: http://www.cisco.com/en/US/tech/tk543/tk757/technologies_tech_note09186a00800949f2.shtml

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