[Bloat] Updated Bufferbloat Test

[Simon Barber]

Hi Sina,

That sounds great, and I understand the desire to separate the fixed component of latency and the buffer bloat / variable part. Messaging that in a way that accurately conveys the end user impact and the impact due to unmitigated buffers while being easy to understand is tricky.

Since you are measuring buffer bloat - how much latency *can* be caused by the excessive buffering, expressing the jitter number in terms of 95%ile would be appropriate - as that’s closely related to how large the excessive buffer is. The average jitter is more related to how the competing TCP streams have some gaps due to congestion control and these gaps can temporarily lower the buffer occupancy and result in a lower average jitter number.

Really appreciate this work, and the interface and ‘latency first’ nature of this test. It’s a great contribution, and will hopefully help drive ISPs to reducing their bloat, helping everyone.

Simon


> On Feb 25, 2021, at 11:47 AM, Sina Khanifar <sina at waveform.com> wrote:
> 
>> So perhaps this can feed into the rating system, total latency < 50mS is an A, < 150mS is a B, 600mS is a C or something like that.
> 
> The "grade" we give is purely a measure of bufferbloat. If you start
> with a latency of 500 ms on your connection, it wouldn't be fair for
> us to give you an F grade even if there is no increase in latency due
> to bufferbloat.
> 
> This is why we added the "Real-World Impact" table below the grade -
> in many cases people may start with a connection that is already
> problematic for video conferencing, VoIP, and gaming.
> 
> I think we're going to change the conditions on that table to have
> high 95%ile latency trigger the degraded performance shield warnings.
> In the future it might be neat for us to move to grades on the table
> as well.
> 
> 
> On Thu, Feb 25, 2021 at 5:53 AM Simon Barber <simon at superduper.net> wrote:
>> 
>> So perhaps this can feed into the rating system, total latency < 50mS is an A, < 150mS is a B, 600mS is a C or something like that.
>> 
>> Simon
>> 
>> On February 25, 2021 5:49:26 AM Mikael Abrahamsson <swmike at swm.pp.se> wrote:
>> 
>>> On Thu, 25 Feb 2021, Simon Barber wrote:
>>> 
>>>> The ITU say voice should be <150mS, however in the real world people are
>>>> a lot more tolerant. A GSM -> GSM phone call is ~350mS, and very few
>>>> people complain about that. That said the quality of the conversation is
>>>> affected, and staying under 150mS is better for a fast free flowing
>>>> conversation. Most people won't have a problem at 600mS and will have a
>>>> problem at 1000mS. That is for a 2 party voice call. A large group
>>>> presentation over video can tolerate more, but may have issues with
>>>> talking over when switching from presenter to questioner for example.
>>> 
>>> 
>>> I worked at a phone company 10+ years ago. We had some equipment that
>>> internally was ATM based and each "hop" added 7ms. This in combination
>>> with IP based telephony at the end points that added 40ms one-way per
>>> end-point (PDV buffer) caused people to complain when RTT started creeping
>>> up to 300-400ms. This was for PSTN calls.
>>> 
>>> Yes, people might have more tolerance with mobile phone calls because they
>>> have lower expectations when out and about, but my experience is that
>>> people will definitely notice 300-400ms RTT but they might not get upset
>>> enough to open a support ticket until 600ms or more.
>>> 
>>> --
>>> Mikael Abrahamsson    email: swmike at swm.pp.se
>> 
>>