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QoS for RT Video

Most of the reference material I have seen on has RT video being marked DSCP 34 and mapped to a CBWFQ.

However, part of the Enterprise MediaNet QoS Design document refers to TelePresence traffic being in the strict priority queue which should be limited to 33% max of lin bandwidth. Being in the LLQ makes sense to me but everything else I see has it as lower priority.

Are these documents contradictory or is it me? If it's not me, what works best in practice?

Joseph W. Doherty
Hall of Fame Expert


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Often the reason different QoS documentation conflicts has much to do when it was published, as QoS recommendations are often evolving.

The reason why RT video has often been recommended not to be placed into LLQ assumes the latter has other "more critical" RT traffic such as VoIP.  As video tends to be both more bandwidth hungry and bandwidth bursty, having it in the same queue as VoIP might degrade VoIP.

BTW, a "compromise" approach, if the RT video has separate traffic flows for its voice vs. its video components, the former can be placed into LLQ with other VoIP and the latter in a "great" service video class.

When it comes to TelePresense, as Cisco markets it like "being there", and it's often marketed to upper management, recommending it being placed into LLQ helps insure it gets the very best service.  (Technically, TelePresense is really just HD video conferencing, but again, its "users" often are higher on the totem pole than those who use SD video conferencing.  Often notice "QoS" differences between calling a sales line [often no waiting] vs. calling a support line?  Sometimes QoS isn't about a technical difference but what's considered important to the business.)

Could TelePresense be adverse to other LLQ traffic?  It can, but when you're doing TelePresense deployments, considering often who the "users" will be, you insure there's ample bandwidth for it (which would also help insure there's ample bandwidth for any concurrent traffic like VoIP, otherwise the latter might be adverse to TelePresense too.)