QoS LLQ

Just revising CVOICE v8 and looking at QOS. The cisco model recommends 33% for RTP media, 5% for RTP signalling and then all the rest.

From my limited reading so far, would this be a valid config? (my router takes the config, but that does'nt mean it will work). Voice and video sharing the same PQ, but treated differently based on their DSCP value for "dropping".

class-map match-any RTP-VOICE
 match protocol rtp audio
class-map match-any RTP-VIDEO
 match protocol rtp video
class-map match-any RTP-SIGNALLING
 match protocol sip
 match protocol h323
 match protocol skinny
 match protocol mgcp

policy-map QOS-POLICY
 class RTP-VOICE
  set dscp ef
  priority percent 33
 class RTP-VIDEO
  set dscp af41
  priority percent 33
 class RTP-SIGNALLING
  set dscp cs3
  bandwidth percent 5
 class class-default
  fair-queue
  random-detect

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Comments

networker050184

This is a valid configuration. Neither traffic will be dropped by this current router on this interface (unless of course it's exceeding the alloted bandiwdth and then only in times of congestion) due to DSCP value because the priority queue will always be emptied first. If the interface is overrun thats a different story as there is a finite ammount of packet buffer space available.

azaghul

So just to confirm what I think you're saying...

Both voice and video are sharing the same 33% bandwidth in the PQ.
If the PQ is experiencing congestion, then the DSCP values come into play and video is dropped first.

networker050184

No, the PQ now has 66% of bandwidth. The DSCP values will never come into play for this traffic on this interface. The PQ is FIFO and does not perform any kind of early drop. Just plain old tail drop.

azaghul

OK, thanks for clearing that up....my misunderstanding of the QoS "lite" material in CVOICE. As always, more reading to do...

Do you know of any study material that takes a middle ground for QoS between CVOICE and the full QOS course?

pitviper

Check out the Enterprise QOS SRND guide on Cisco.com. It's a little dated but still relavent and easy enough to follow (wish that could be said for some of their other documentation).

azaghul

Thanks for that pitviper, another book to add to the reading list.

I've had a quick look at the SRND, seems my config was in the right direction as networker said, just a deeper understanding required.

drkat

+1 for the SRND