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QoS on 3750E/3650E

Should I have Voice and Video in the same Queue on 3750E/3560E?  Some Cisco document recommend to have CoS 4 & 5 in Q1 (PQ) and other document recommend CoS 5 in Q1 (PQ) and CoS 4 in Q2.

1.  If I have voice and video in the same queue, video can cause problem to Voice

2.  If I have video outside PQ, this could be problem with pixilation for Video system like Telepresence

Eugene Lau
Cisco Employee

Hi Nhan,

To get started, are you able to access these links? (if unable to access, contact

Campus QoS design for TP which discuss Voice video in PQ scenarios and considerations

Also an Enterprise QoS design guide that the voice engineers use a lot.



Thanks Eugene,

I read those before.  I guess there is no standard will works for the general and TP configures.  TP configuration will combine CS5 and CS4 into PQ.  General configuration only CS5 is in PQ.

Anyhow, thanks a lot


Hey Nhan,

Great that you've checked out the documents prior. It's quite a big topic and challenging to take a simplistic view or use a standard calculation/template. The recommended practice on LAN's for TP -> Voice, Video in PQ - to guarantee the TP experience.

Essentially, the SRND's concepts are formulated as guide or starting point based on a defined tested environment (such as throughput, QoS Feature support, appropriate buffers etc) then engineers should adjust according to their constraints and priorities. You could approach through theoretical modelling or real world testing (Proof of concepts)

-> is it possible for voice traffic to be delayed if voice and video are in the PQ, from the perspective of a 3750

------>  Generally, issues occur when there is contention for bandwidth. If you have enough bandwidth and no latency issues introduced by the transport medium (such as WAN links) -> then no issues.

Simplistically, You can also think of it as - TP 30fps = 33ms a frame. A frame can be 1 or more packets. There are bursts for interactive video but there'll be other mechanisms at play at the encoding/decoding/jitter buffer etc

RTP voice - steady stream of packets 20ms apart

So there's room for both

-> If TP traffic is outside PQ, does it cause pixilation? -> again, if there is contention for bandwidth then yes. It's a matter of allocating enough. The practice of placing TP outside of PQ is typically used where real-time class circuits are expensive.