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QOS question?!!!


when i read the RFC-Recommended Values for Marking, which is in Cisco QOS design Guide docments...

i noticed that COS 4, IPP 4 and DSCP AF41  recommended for Video payload

and Cos 3, IPP 3 and DSCP CS3 recommended for Voice/video signaling

my question is, why we don't use AF31, AF32, or AF33 for those type of traffic instead of CS3, in other words why it used CS for that traffic and not AF as for the others that are mentioned in the table.



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QOS question?!!!


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Well Cisco says (in


The  QoS Baseline recommends marking Call-Signaling to CS3. However,  currently most Cisco IP Telephony products mark Call-Signaling to AF31. A  marking migration from AF31 to CS3 is under way within Cisco, but in  the interim it is recommended that both AF31 and CS3 be reserved for  Call-Signaling and that Locally-Defined Mission-Critical Data  applications be marked to a temporary placeholder non-standard DSCP,  such as 25. Upon completion of the migration, the QoS Baseline marking  recommendations of CS3 for Call-Signaling and AF31 for Locally-Defined  Mission-Critical Data applications should be used. These marking  recommendations are more in line with RFC 2474 and RFC 2597.

So, AF31 will be used for Locally-Defined Mission-Critical Data.  NB: I have not looked at the two RFCs, but I would guess AF32 and AF33 would be used for different drop priorities for such traffic.  Signaling you want to avoid dropping at all.

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