Assistance with QOS for Cisco Webex calling

Getting noticed

Assistance with QOS for Cisco Webex calling

Hi everyone, this is mainly for the MX but also for the MS devices as well but does anyone have any recommended settings for QOS settings for Cisco Webex voice calls please?


Currently, the Traffic Shaping Rules under SDWAN and Traffic Shaping is set to 'enable default traffic shaping rules' so SIP (Voice) has a DSCP tag of 46.


Under Swtiches and Swtich Settings, the Quality of Service for our voice vlan is set to 'Set DSCP to 46 (EF voice).

We have a single 200Mbps that could be running 30 voice calls at once plus backups between sites, etc, and internet traffic, there is no option for a second internet connection to put all the voice calls onto now.

3 Replies 3
Getting noticed

You should see AF34 for Webex already assigned in MX




Kind of a big deal
Kind of a big deal

Couple of points here.
For the MX you have 4 queue's.
Realtime: if a packet is tagged with a PHB of EF (DSCP 46) then it will be placed in this queue and be transmitted immediately.  You cannot configure traffic to go into this queue directly (you can only choose high, medium, low) but if the traffic is tagged with EF then it will be moved up into this queue.
High: This queue is a bandwith queue that is guaranteed a minimum of 4/7 of the WAN bandwidth, if the queue has bandwidth to spare it will yield this to the lower queue's.
Medium: This queue is also a bandwidth queue and is guaranteed 2/7 of the WAN bandwidth, this can also yield leftover to the low queue.

Low: This queue is the last queue with only 1/7 guarantee.  It can of course receive spare bandwidth of higher queues.
For this to work you need to accurately set your WAN bandwidth values on the top of the configuration page.


On the MS switches it is different.
There you have the ability to set VLAN and port based rules that explicitly set a DSCP value or choose to trust the incoming DSCP value from the endpoint.  There is also a link (dscp to cos queue map) which assigns a certain DSCP value to a queue.

MS switches alas don't have a priority queue but they have bandwidth queue's a bit like shared round robin.  The switches have 8 queues where the highest two are used internally and the other 6 are configurable in values from 0 to 5.  Each queue number has double the bandwidth of the queue below it.  So you could for example choose to put AF41,42,43 traffic into queue 3, AF31,32,33 into queue 2, etc...

There are no advanced systems where you can re-mark traffic depending in some policing algorithm.  So in essence you won't get the values 12,13,22,23,31,32,42,43 unless you specifically add them yourself.

Kind of a big deal
Kind of a big deal

^ This is a great write up.

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