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

Tue Jul 6 19:49:36 EDT 2021

Thanks for this. Looks interesting. Does ABC (love the acronym) try to
optimize throughput, latency or some combination, e.g. network power
(throughput/delay)?

Things like roams, seen energy over the last n milliseconds, and "I've lost
n TXOP arbitrations over time y" could also have influence on the control
feedback loop to TCP.  Not sure how TCP gets any of these stats.

None of this is end/end though. It's likely just the last/first hop which I
think is probably still useful to TCP designers - not sure.

Bob

On Tue, Jul 6, 2021 at 1:39 PM Neal Cardwell <ncardwell at google.com> wrote:

>
>
> On Tue, Jul 6, 2021 at 4:34 PM 'Bob McMahon' via BBR Development <
> bbr-dev at googlegroups.com> wrote:
>
>> 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?
>>
>
> That could make sense. That sounds a lot lot like the Accel-Brake Control
> work:
>
> https://www.usenix.org/conference/nsdi20/presentation/goyal
>
> ABC: A Simple Explicit Congestion Controller for Wireless Networks
>
> Authors:
> Prateesh Goyal, MIT CSAIL; Anup Agarwal, CMU; Ravi Netravali, UCLA;
> Mohammad Alizadeh and Hari Balakrishnan, MIT CSAIL
>
> Abstract:
> We propose Accel-Brake Control (ABC), a simple and deployable explicit
> congestion control protocol for network paths with time-varying wireless
> links. ABC routers mark each packet with an “accelerate” or “brake”, which
> causes senders to slightly increase or decrease their congestion windows.
> Routers use this feedback to quickly guide senders towards a desired target
> rate. ABC requires no changes to header formats or user devices, but
> achieves better performance than XCP. ABC is also incrementally deployable;
> it operates correctly when the bottleneck is a non-ABC router, and can
> coexist with non-ABC traffic sharing the same bottleneck link. We evaluate
> ABC using a Wi-Fi implementation and trace-driven emulation of cellular
> links. ABC achieves 30-40% higher throughput than Cubic+Codel for similar
> delays, and 2.2× lower delays than BBR on a Wi-Fi path. On cellular network
> paths, ABC achieves 50% higher throughput than Cubic+Codel.
>
> neal
>
> 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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