Trick to improve voice quality dramaticly on softphone/webclient

[Tom DC]

Hi,

I would like to share with the community what i did to improve the quality of the softphone dramaticly. I hope it helps you the same way, it did for me

Issue : Annoying noticable ticks in the audio, when using the softphone
Impacted : Softphone (windows) and Webclient (windows) . Don't know about Macs?

Network cards do some nifty stuff these days. The one network card more than others. For example If you have an Intel Network Card, You have a lot of chance that it has interupt coalescing enabled. It is a method to get more troughput on network interfaces. Other Network card vendors have a simular option.

It means that sometimes it can hold packets, and sends them with the next interrupt. Doing this can generate delta peaks, and these are noticable in the audio stream

I have diagnosed this in wireshark. I have Enabled and Disabled the interrupt coalescing on my wireless network card, Please see the results in 2 graphs. It is quite clear that the deltas are better when the interupt coalescing is disabled


Interupt coalescing enabled


Interupt coalescing disabled



I think as a general advice, you should disable interrupt coalescing on all devices. Servers and Clients. If it is confirmed by the community, maybe 3CX should try do someting about it. Like a check by the windows installer , or...

Please tell me if it worked for you



Kr Tom

 

[Tom DC]

Hi Mark,
Unfortunately the setting on my computer is in dutch. I think the setting in English is called Interrupt Moderation . I have taken this screenshot from google images.

If the theory is correct, this really should be disabled on the network interface when using a softphone

 

[cobaltit]

Excellent find. I'm going to have to do some testing of my own on this.

 

[BrenttG]

Here are 2 shots of the available options on a SuperMicro server which i have converted to use as a high powered workstation, its an X9DAL Board with dual gigabit server nics. Looks like the higher end nics actually have more than just on and off, the default setting is adaptive.

 

[BrenttG]

 

[Tom DC]

BrenttG,


https://01.org/linux-interrupt-moderation
To achieve lower latency, the controller usually minimizes the interval between interrupts to speed up small packet processing at the price of causing higher CPU usage and lower throughput. On the other hand, to improve throughput and minimize the overhead caused by frequent interrupts, larger interrupt intervals are desirable [1]. So an appropriate interrupt interval is critical to getting the best performance balance. The optimal interrupt interval is supposed to reduce CPU overhead when handling interrupts without adding significant packet latency or causing undue packet loss.

To balance CPU efficiency for bulk traffic with minimal latency, the Ethernet driver supports adaptive interrupt moderation, which dynamically changes the interval according to packet size and throughput. However, there are still big performance gaps compared to hand-tuned results. This article describes a new solution that sets interrupt moderation per-queue to get better network performance.




So what i (think) have learned about interrupt moderation:

Interrupt moderation disable -> low latency + low deviation
Interrupt moderation enabled -> higher latency + more deviation

Imo, if you use that workstation for VOIP. I should set the interrupt moderation to disabled or enabled + constant low rate . With this setting your network packets are sent with a constant rate. This is what voip likes.

If you think it has affected your overall network troughput speed, you could tune the interrupt moderation rate to a higher rate.

Anyhow , i think an adaptive moderation rate is to be avoided for voip. I should pick a (constant) value.


Kr

 

[YiannisH_3CX]

Hello @Tom DC

Interesting find. We will need to do some testing to see how much of a difference this setting makes to call quality and if it is network dependant. As you understand however this is a hardware option which might differ from vendor to vendor so this might be up to the network admin to test and adjust.