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Is QoS working even when not the full Bandwith is used?

Christian Reiter
Frequent Advisor

Is QoS working even when not the full Bandwith is used?


Is QoS on ProCurve Switches even working when the end of the Connection doesn't use all of the available Bandwith?

On a 100 MBit Downstream Port of a ProCurve 5308xl is a device connected which can only deal with 1 MBit/Sec.
This devices uses VoIP and Data Services on 2 VLANS:
VLAN12 for Data with 802.1p Priority of 1
VLAN13 for VoIP with 802.1p Priority of 7
QoS is enabled on the End device and on the Switch, Flow Control is also enabled on both devices

When the device downloads big amounts of Data using the Data VLAN, Voice Calls aren't working fine -> The user behing the 1 MBit device can hear the other end Speaker only with losses.

What is wrong here?

Thanks in advance,
christian reiter
Matt Hobbs
Honored Contributor

Re: Is QoS working even when not the full Bandwith is used?

Just to understand this better, the port on the 5300 is negotiating 100Mbit, but the other device is somehow limiting the amount of traffic to flow through this port to 1Mbit.

My understanding is that they way the priority queues on the 5300 work are by percentage of the bandwidth on the port.

The default allocations are:

â ¢ Queue 1 (low priority): 8%
â ¢ Queue 2 (normal or unmarked priority): 16%
â ¢ Queue 3 (medium priority): 30%
â ¢ Queue 4 (high priority): 45%

So assuming 100Mbit, your low priority queue will guarantee 8Mbit which is more than what this other device can handle - my guess is this is why you are currently having problems.

This is what I would try - either force the 5300's port to auto-10, that way that 8% will then become 0.8Mbit which should be enough left over for the VOIP traffic.

If that wasn't enough, I would change the default queue allocations - look up Guaranteed Minimum Bandwidth in the management and configuration guide. I would change the low priority queue to 5% or lower.

One last thing, I would disable flow contol - in my experience it can cause more problems that what it solves.

Let us know how you go. If still no luck, what is this other device and what can you configure on it?

Matt Hobbs
Honored Contributor

Re: Is QoS working even when not the full Bandwith is used?

On second thought, Guaranteed Minimum Bandwidth probably won't help too much as it is a minimum only. As soon as that client requests data the switch will provide as much as possible.

What you need is some kind of maximum bandwidth per queue, unfortunately the 5300 does not have this type of functionality.

I'd still be interested to find out more about this other device, maybe there is something more that can be done on it.
Christian Reiter
Frequent Advisor

Re: Is QoS working even when not the full Bandwith is used?

Hi Matt!

The other Device is a kind of Fibre-to-the-Home CPE. It is an Allied Telesis RG613-BD.

It has 1 Fibre WAN Port, 3 Copper LAN Ports and 2 FXO Phone Analog Adapters. The WAN Port is shaped to 1 Mbit Downstream an 512 Kbit Upstream.

The RG613 itself implements 802.1p also. As far as i can test QoS on the CPE side works seamless. If i place a VoIP call and do a big upload, everything works just perfect.

Troubles start when i place a phone call and do a download (IMHO in that situation the procurve has to ensure that the Voice VLAN gets priority).

I've also tried with Flowcontrol disabled, but that didn't change anything.

Now i will start another try using Guaranteed Minimum Bandwidth.