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QOS/DSCP configuration Question


Hi all,


This one is way beyond my current knowledge - I am setting up a digital audio network that utilizes Dante as the audio transport.  To do this, I am configuring a 3750X switch with 2 vlans - Data and Dante.  Data will provide audio control data, and Dante will carry the actual audio streams.


The specs say to create VLANS (did that), enable IGMP Snooping (Did that), and it also uses QOS.  I do not know past auto qos how to specify the QOS settings, and reading some of the literature out there isn't helping my AV brain much.  There's lots that I can make this Cisco switch do, but this isn't one of them lol


Here's what the spec says:


QoS: QoS stands for “Quality of Service” and in simplest of terms it is a feature that allows a network switch to prioritize data based upon its type and purpose. QoS standards were created to ensure reliability of audio on a data network in applications such as telephony, conferencing, and VOIP. Dante uses these same standards to prioritize audio, clocking info, etc. Symetrix recommends QoS be enabled in all Dante networks. Will Dante work without QoS enabled? Many times the answer is yes, but if there are Dante related issues, the first thing that should be checked is whether QoS is enabled. Dante uses standard Voice over IP (VoIP) Quality of Service (QoS) switch features to prioritize clock sync and audio traffic over other network traffic. QoS is available in both inexpensive and enterprise Ethernet switches. Any switch that supports Diffserv (DSCP) QoS with strict priority and 4 queues, and has Gigabit ports for inter-switch connections should be appropriate for use with Dante. The QoS feature must have a trust mode option, which needs to be set to DSCP (diff serve) for Dante. Trust mode refers to the type of QoS tagging of the packets which allows the network to properly prioritize the different types of packets. DSCP (Diffserv) is the layer 3 QoS tagging which Dante uses. CoS is a layer 2 Trust mode that is not compatible with Dante. Switches prioritize packets using what are called DSCP/Diffserv values. Although Dante packet priority values have been chosen to make it simple to configure QoS with many switches, some switches require special configuration to recognize and prioritize specific DSCP values.


The table in the page below details the QOS settings but set up for the SG300 series switches, which I am not using:


I know this is very broad and I am potentially asking a lot but could someone at least point me in the right direction?





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Reading the thread, I would strongly suggest you retain a consultant on QoS.

For a 3750X, I would recommend you leave QoS off until such time as you engage a consultant, because a 3750X's default QoSsettings can actually be more adverse than having QoS disabled on the device.

Or, for a 3750X, you might try it's autoQoS feature, which isn't too bad, if your traffic is like what Cisco's autoQoS model assumes it should be.  (NB: Your initial post's reference, noting usage of CS7 for some of your traffic, is NOT something Cisco's autoQoS would expect.)

Unfortunately, as Jon describes, although your question is reasonable, it requires much more information to address, and even if we could provide a perfect "do this" reply, QoS often requires monitoring and tuning to avoid degradation, over time.  The latter requires some additional understanding of the technology.

View solution in original post


Vasilii Mikhailovskii
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As it's mentioned:

>CoS is a layer 2 Trust mode that is not compatible with Dante

So you need to mls qos trust dscp

Article (by URL) says, that the solution uses CS7, EF, CS1 and BE [dscp] values. I would remark CS7 into CS3 (or into EF, but not the best solution), as CS7 is not expected for Enterprise traffic (unless you are from China).

Typical configuration for 3750 you may find  here -


sorry - how do I configure those specific QOS settings then?  I'm not familiar past auto-qos...AV guy here! lol


Have you had a chance to review the article (regarding 3750 configuration)?

If yes, what particular questions do you have on the configuration?

I'll be honest - and this might sound dumb - but that document doesn't help me, I still can't understand exactly what I need to do.  I usually run auto-qos and leave it at that, but this needs to match their spec.  I want to run the qos spec Yamaha has on certain ports (13-24), and I can't quite manage how to specify in the command line what to do.  I'm sure it isnt difficult to those who know, but I don't, and I am not a networking engineer by trade, so I am here asking for some help.  It is easy to say RTFM but when you don't understand fully the manual it's not a huge help...It sounds like I am asking for spoon feeding and I guess that's what it is - I just don't have the knowledge.  If you want me to design you a campus-wide HD Video distribution platform I'm your guy.  Networking and QOS?  Nope.

I'm sure it isnt difficult to those who know

Believe me QOS on switches isn't particularly easy for anyone :-)

The problem with that link you posted is that it says if the network has other traffic it needs to be discussed with the network administrator which is another way of saying it's quite complicated and we can't explain it all to you.

Is this network you are setting up only on this switch and purely for these devices or does it connect to other switches with other devices used for data ?

If it is multiple switches applying that suggested QOS policy to all of them may work well for Dante but could very well impact everything else.

QOS isn't something you can just apply to one switch if the traffic needs prioritising end to end across multiple devices.

In addition there is no mention in the link of how much bandwidth needs to be allocated to each queue and this can have a big effect on how well your QOS performs.

It's not that we don't want to help and there are certainly people on here who know QOS well (I'm not one of them) but we would need to understand -

1) what else apart from Dante is going to use the switch or switches in the network

2) the bandwidth needed for Dante and it's applications

3) the end to end topology of the network

without at least that telling you do anything to your network would just be irresponsible on our part.

The only other thing I would add is that QOS is not necessarily something you can just apply and forget so any commands provided you would really need to have some understanding of what they are doing on the switch(es) because if performance for some or all of the applications was affected you would need to know what sort of things to look for.


I want to apologize as my previous answer came off a bit more flippant than I wanted. 


This is switch is for two things - Dante audio traffic which utilizes a full gig link. They claim it just about saturated the link.  And control data which is negligible. Each has its own clan. Dante does not need dhcp and an apple airport express will provide dhcp for the data vlan. 


Hope this is a tad bit more helpful. Yamaha makes this so easy by using a sg300 switch but I don't have one so I thought I could use one of our extra 3750x. 






No need to apologise totally understand where you are coming from.

Each has its own clan

Don't know what you mean by that ?

Is all the Dante traffic contained on that switch is what I was getting at.

Because if there are devices on other parts of your network that need access to it then you need to factor in the other application traffic on your network ie. you can setup QOS on the switch that the Dante devices connect to but once that traffic leaves that switch if it has to go across multiple other devices then unless you configure QOS on those as well you aren't really achieving anything.

This would also apply even if you had one of the switches used in the link.

So if that traffic does need to go across the rest of your network that link really doesn't give the full picture.

I may not be understanding how this application works so some of the above may not be relevant.



Sorry stupid iPhone. VLAN not clan. 


This switch will only have Dante devices connected to it and won't be part of our core network. It will be standalone. Does that help?

Sorry stupid iPhone. VLAN not clan. 


It will be standalone. Does that help?

Well it makes your life considerably easier because you can apply the QOS and then if it doesn't work you just change it without affecting anything else.

What I'm not sure about is if you are using a standalone switch and it is just for Dante whether you need QOS at all and your original post suggests you may not.

It may be worth trying to run it without but if you want to try and enable it then we could try to convert the link you provided to a 3750 switch.

What I'm still not sure about is what you are trying to prioritise ie. is there a server that chucks out audio and then clients are connected to the switch and they receive that audio (sorry never done this type of setup before).

If so I can't see the point of QOS on the egress queues to clients because the server port is presumably the same speed as the client ports.

Unless they are saying the control traffic needs to be prioritised between the server and clients in case it gets lost with too much data being transmitted ?


So there is the actual audio signal (what you hear), there is what we call the audio clock (this makes sure all the audio is heard at the right time - it syncs the audio timing across all Devices so they all get the same signal at the same time, then there is control data in the Dante stream. each has QOS priorities. The clock is given highest the stream uses standard VoIP priority apparently and the rest falls below those two. 

Okay, it's late where I am so i'll revisit this tomorrow if that's okay unless someone else jumps in.

The only thing missing is what bandwidth each thing takes up.

If you are assigning highest priority to the audio clock this obviously goes in the priority queue. But you don't want to allocate too much to that queue or else it restricts what other queues have.

I can't see from that link you provided any sign of what bandwidth is allocated to which queue.

I don't suppose you have those figures available even as rough estimates ?


some info:

(this states that it is optional although that is not best practice)


Dante single-link network limitations are determined by the bandwidth of the endpoints.

Network speedChannel Limitations
1000Mbps (Gigabit)512 x 512 48kHz/24bit audio channels can be sent over a single link, giving a total of 1024 bi-directional channels. For 96kHz/24bit audio the channel capacity is halved.
100Mbps (Fast Ethernet)48 x 48 48kHz/24bit audio channels can be sent over a single link, giving a total of 96 bi-directional channels. For 96kHz/24bit audio the channel capacity is halved. It is recommended that Fast Ethernet links not exceed 32 channels.

The number of channels that can traverse one link in a network is proportional to the link speed.

A link will always slow down to the lowest speed connector on that link; eg. if a Gigabit port on switch A is connected to a 100Mbps Fast Ethernet port on switch B, the link speed will be 100Mbps Fast Ethernet. This is good, because it allows you to mix link speeds in a network without having to do anything complicated.

Audio is transmitted over the network in UDP/IP Packets. A single IP packet may contain audio samples from several audio channels, and may contain multiple audio samples for each channel.

Audio packets can be transmitted using either unicast or multicast addressing. By default they are sent using unicast, but the user can change this to multicast using the Dante Controller. Multicast and unicast can be sent and / or received at the same time on a Dante device. Channels are individually selectable for multicast transmission.



Although maybe too late. Here is a document on best practices on Dante and large networks. 

I would have to try this without QoS on a down time because this is for a live 72 channel audio production system for live shows...:)

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