[Make-wifi-fast] Fwd: [bbr-dev] BBR performance and optimization in cellular wireless network with high delay jitter

[Bob McMahon]

Curious to the idea of wifi providing the opposite of ECN, i.e. my rate
selection algorithm just went from one stream to two stream so TCP speed up
your feedback loop decisions with a bias to faster?

Bob

On Mon, Jul 5, 2021 at 10:20 AM Dave Taht <dave.taht at gmail.com> wrote:

> eric, I thought I'd forward this to one of the bufferbloat.net lists.
> Feel free to join. It would also be helpful to duplicate your test scripts
> here.
>
> I agree with you, bbr is way too slow here. We see it bloat massively in
> wifi also. I would like BBR to far more reactive than it is, and also for
> it to respond to RFC3168 ECN marks.
>
> You said:
>
> *" *In my opinion, in high bw jitter scenario, window based bw undaption
> method is too slow to converge to the actual bottleneck bw,  when actual bw
> imcreases, BBR needs at lease 8RTT to catch it, when it decreases, BBR then
> needs at most 10 RTT to expire the previous bw maximum, anyway it is too
> slow, causing severe buffer-bloating. "
>
> You might find the "flent" tool very useful for getting a more microscopic
> view as to what is going on.
>
> A test we would use to get a better picture of what is really going on
> would be
>
> flent -H netperf_test_server -x --socket-stats --step-size=.05 -t
> the_test_conditions --te=cc_algo=bbr --te=upload_streams=1 tcp_nup
>
> This samples a ton of tcp related stats and lets you plot them with
> flent-gui, there are 110 other tests in the suite.
>
> A more complicated invocation can get qdisc stats from the router
> involved, or iterate over CCs, or run at longer intervals. In general I
> have found running tests for 5 minutes or longer reveal interesting
> behaviors.
>
> flent -H $S --socket-stats -x --step-size=.05 -t
> 1-flow-fq_starlink_noecn-${M}-c
>
> c=${CC} --te=cpu_stats_hosts=$R --te=netstat_hosts=$R -4
> --te=qdisc_stats_hosts=
>
> $RS --te=qdisc_stats_interfaces=$RV --te=upload_streams=1 --te=cc_algo=$CC
> tcp_1
>
> up
>
>
> pic below
>
> ---------- Forwarded message ---------
> From: Eric xu <ericbin1224 at gmail.com>
> Date: Mon, Jul 5, 2021 at 12:27 AM
> Subject: Re: [bbr-dev] BBR performance and optimization in cellular
> wireless network with high delay jitter
> To: BBR Development <bbr-dev at googlegroups.com>
>
>
> Hi, Neal, thanks for your answer. I still  have two questions to discuss
> with you after having read the two links you mentioned above.
>
> 1, As mentioned in the second link, BBR's throughput on high-jitter links
> (especially in cellular) usually matches CUBIC,  as  demonstrated by the
> following figure,
> [image: 截图.PNG]
> however, what we can infer from the figure is that, the mean
> throughput(~14Mbps) is far from the available bw that is greater than
> 20Mbps as showed in the cumulative distrubution figure. Since CUBIC back
> off frequently in the LTE network with high error rate, but BBR does not
> acquire much more throughput than CUBIC, the only reason I can imagine is
> that BBR is highly affected by high delay jitter although cwnd provision is
> applied.
>
> *Is my understanding right? and is there any optimization to further
> improve thoughput in high bw and delay jitter scenario? *
>
> *2,  Is there any method to enhance BBR's adaptive ability to high bw and
> delay jitter?  *In my opinion, in high bw jitter scenario, window based
> bw undaption method is too slow to converge to the actual bottleneck bw,
> when actual bw imcreases, BBR needs at lease 8RTT to catch it, when it
> decreases, BBR then needs at most 10 RTT to expire the previous bw maximum,
> anyway it is too slow, causing severe buffer-bloating.  In high delay
> jitter scenario, BBR also will cause bw under utilizaion. *So,  what is
> your latest optimizaion to improve the performance in such a high bw and
> delay jitter network?*
>
> Thx a lot,
> Eric
> 在2021年7月4日星期日 UTC+8 下午9:59:57<Neal Cardwell> 写道：
>
>> Yes, BBR includes mechanisms to deal with this kind of jitter. Please see
>> the March 2019 thread on this topic:
>>   https://groups.google.com/g/bbr-dev/c/kBZaq98xCC4
>>
>> Our experience is that BBR's throughput on high-jitter links (cellular,
>> wifi, DOCSIS, datacenter ethernet w/ GRO/LRO) is quite good at this point
>> (usually matches CUBIC), and there are others who have documented this as
>> well, e.g.:
>>   http://web.cs.wpi.edu/~claypool/papers/driving-bbr/
>>
>> best,
>> neal
>>
>>
>> On Sun, Jul 4, 2021 at 8:53 AM Eric xu <ericb... at gmail.com> wrote:
>>
>>> Hello, dear friends. I wonder there is any optimization to BBR ,  for
>>> the reason of BBR low bandwidth utilization in wireless network with high
>>> delay jitter.  In my opinion,  High delay jitter will cause BBR to
>>> underestimate the BDP, thus limit the send rate even if  pipeline is
>>> not full. Right?
>>> So,  I wonder, *if there is any optimization to improve bw utilization
>>> in wireless network with high delay jitter, even in 5G network? *Thx a
>>> lot.
>>>
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