[Starlink] It's still the starlink latency...

Sebastian Moeller moeller0 at gmx.de
Tue Sep 27 02:36:33 EDT 2022 

Hi Gene,

On 27 September 2022 05:47:48 CEST, Eugene Y Chang <eugene.chang at ieee.org> wrote:
>> [SM] I note that typically for ingress shaping a post-true-bottleneck shaper will not work unless we create an artificial bottleneck by shaping the traffic to below true bottleneck (thereby creating a new true but artificial bottleneck so the queue develops at a point where we can control it).
>> 	Also if the difference between "true structural" and artificial bottleneck is small in comparison to the traffic inrush we can see "traffic back-spill" into the typically oversized and under-managed upstream buffers, but for reasonably well behaved that happens relatively rarely. Rarely enough that ingress traffic shaping noticeably improves latency-under-load in spite of not beeing a guranteed solution.
>
>Perhaps I am overthinking this. In general, I don’t think this really works.

[SM] Yes this method's effectiveness depends on having control over the bottleneck and that in turn requires seeing all traffic traversing the bottleneck link. It turns out that for a competent ISP the relevant bottleneck is often the actual internet access link itself, that is why sqm on a home router in practice works often very well even though in theory it looks unlikely to do so.

 Consider a router with M ports from the network edge and N ports toward the network core. You are only trying to influence one of the M ports. Even if N=1, what actually happens with the buffering at N depends on all the traffic, not just the traffic you are shaping.

[SM] Not that an uncommon situation, thinking e.g. of a DSLAM, OLT or CMTS where the aggregate of access speeds exceeds the uplink capacity, and the ISP misjudged the usage and under-provided the uplink*. The more remote the bottleneck is and the less of the traversing flows we can control the more problematic the debloating exercise gets....



*) I use this phrasing because these uplinks are effectively always smaller than the aggregate marketed rates on such a device, aka the ISP oversubscribes the unit, but that is a theoretical problem as long as the actual aggregated traffic does not exceed the units uplink capacity. Dimensioning such uplinks to the worst case would likely either mean really high prices or really low contracted rates. So oversubscription per se is fine with me, as long as the ISP manages to handle the real traffic for most of the time, but I digress.



>
>> 	[SM] Well, sometimes such links are congested too for economic reasons…
>
>It is always economic. The network is always undersized because of some economic (or management) policy.

[SM] I was thinking about a specific case of a T1-ISP that notoriously let's his links to other T1 run hot during peak usage times, to incentivise content providers to buy direct access (technically they sell 'transit' but at a above market price so content providers are unlikely to use this link for traffic not intended for that ISP's AS or its single-homed customers.


>
>These days it is more and more true with the preference of taking fiber to the subscriber. It is physically possible to send more traffic to the network than the router can handle. 

[SM] That depends on the router ;), but yes with access speeds reaching close to 10 Gbps for some european ISPs home neyworking gear tends to be out of its league, with accelerators helping at least speed tests to limp along well enough.

My ISP happily markets 1Gbps service but the fine print of their contract says they don’t promise more than 700Mbps.

[SM] The question is what is the consequence/remedy if the ISP does not fulfill that promise? Over here ISPs need to publish a set of rates in a standardized format and in case of not delivering these rates customers can either opt for canceling the contract or adjusting the price they pay to the relative fulfillment of the contracted rates. The details however are being worked out ATM.


 Worst, I waited 9 months for them to resolve why I was only getting 300Mbps on my 1Gbps service (oops, sorry my 700Mbps service).

[SM] I guess mass market internet access is a low margin business, where expert debugging time is precious. I hope they at least gave you a rebate for that time.

Regards
         Sebastian



>
>
>Gene
>----------------------------------------------
>Eugene Chang
>IEEE Senior Life Member
>eugene.chang at ieee.org
>781-799-0233 (in Honolulu)
>
>
>
>> On Sep 26, 2022, at 11:29 AM, Sebastian Moeller <moeller0 at gmx.de> wrote:
>> 
>> Hi David,
>> 
>>> On Sep 26, 2022, at 23:22, David Lang <david at lang.hm> wrote:
>>> 
>>> On Mon, 26 Sep 2022, Eugene Y Chang wrote:
>>> 
>>>>> On Sep 26, 2022, at 11:01 AM, Sebastian Moeller <moeller0 at gmx.de> wrote:
>>>>> 
>>>>> Hi Eugene,
>>>>> 
>>>>> 
>>>>>> On Sep 26, 2022, at 22:54, Eugene Y Chang via Starlink <starlink at lists.bufferbloat.net <mailto:starlink at lists.bufferbloat.net>> wrote:
>>>>>> 
>>>>>> Ok, we are getting into the details. I agree.
>>>>>> 
>>>>>> Every node in the path has to implement this to be effective.
>>>>> 
>>>>> 	Amazingly the biggest bang for the buck is gotten by fixing those nodes that actually contain a network path's bottleneck. Often these are pretty stable. So yes for fully guaranteed service quality all nodes would need to participate, but for improving things noticeably it is sufficient to improve the usual bottlenecks, e.g. for many internet access links the home gateway is a decent point to implement better buffer management. (In short the problem are over-sized and under-managed buffers, and one of the best solution is better/smarter buffer management).
>>>>> 
>>>> 
>>>> This is not completely true. Say the bottleneck is at node N. During the period of congestion, the upstream node N-1 will have to buffer. When node N recovers, the bufferbloat at N-1 will be blocking until the bufferbloat drains. Etc. etc.  Making node N better will reduce the extent of the backup at N-1, but N-1 should implement the better code.
>>> 
>>> only if node N and node N-1 handle the same traffic with the same link speeds. In practice this is almost never the case.
>> 
>> 	[SM] I note that typically for ingress shaping a post-true-bottleneck shaper will not work unless we create an artificial bottleneck by shaping the traffic to below true bottleneck (thereby creating a new true but artificial bottleneck so the queue develops at a point where we can control it).
>> 	Also if the difference between "true structural" and artificial bottleneck is small in comparison to the traffic inrush we can see "traffic back-spill" into the typically oversized and under-managed upstream buffers, but for reasonably well behaved that happens relatively rarely. Rarely enough that ingress traffic shaping noticeably improves latency-under-load in spite of not beeing a guranteed solution.
>> 
>> 
>>> Until you get to gigabit last-mile links, the last mile is almost always the bottleneck from both sides, so implementing cake on the home router makes a huge improvement (and if you can get it on the last-mile ISP router, even better). Once you get into the Internet fabric, bottlenecks are fairly rare, they do happen, but ISPs carefully watch for those and add additional paths and/or increase bandwith to avoid them.
>> 
>> 	[SM] Well, sometimes such links are congested too for economic reasons...
>> 
>> Regards
>> 	Sebastian
>> 
>> 
>>> 
>>> David Lang
>>> 
>>>>> 
>>>>>> In fact, every node in the path has to have the same prioritization or the scheme becomes ineffective.
>>>>> 
>>>>> 	Yes and no, one of the clearest winners has been flow queueing, IMHO not because it is the most optimal capacity sharing scheme, but because it is the least pessimal scheme, allowing all (or none) flows forward progress. You can interpret that as a scheme in which flows below their capacity share are prioritized, but I am not sure that is the best way to look at these things.
>>>> 
>>>> The hardest part is getting competing ISPs to implement and coordinate. Bufferbloat and handoff between ISPs will be hard. The only way to fix this is to get the unwashed public to care. Then they can say “we don’t care about the technical issues, just fix it.” Until then …..
>>>> 
>>>> 
>>>> 
>>>>> 
>>>>> Regards
>>>>> 	Sebastian
>>>>> 
>>>>> 
>>>>>> 
>>>>>> Gene
>>>>>> ----------------------------------------------
>>>>>> Eugene Chang
>>>>>> IEEE Senior Life Member
>>>>>> eugene.chang at ieee.org
>>>>>> 781-799-0233 (in Honolulu)
>>>>>> 
>>>>>> 
>>>>>> 
>>>>>>> On Sep 26, 2022, at 10:48 AM, David Lang <david at lang.hm> wrote:
>>>>>>> 
>>>>>>> software updates can do far more than just improve recovery.
>>>>>>> 
>>>>>>> In practice, large data transfers are less sensitive to latency than smaller data transfers (i.e. downloading a CD image vs a video conference), software can ensure better fairness in preventing a bulk transfer from hurting the more latency sensitive transfers.
>>>>>>> 
>>>>>>> (the example below is not completely accurate, but I think it gets the point across)
>>>>>>> 
>>>>>>> When buffers become excessivly large, you have the situation where a video call is going to generate a small amount of data at a regular interval, but a bulk data transfer is able to dump a huge amount of data into the buffer instantly.
>>>>>>> 
>>>>>>> If you just do FIFO, then you get a small chunk of video call, then several seconds worth of CD transfer, followed by the next small chunk of the video call.
>>>>>>> 
>>>>>>> But the software can prevent the one app from hogging so much of the connection and let the chunk of video call in sooner, avoiding the impact to the real time traffic. Historically this has required the admin classify all traffic and configure equipment to implement different treatment based on the classification (and this requires trust in the classification process), the bufferbloat team has developed options (fq_codel and cake) that can ensure fairness between applications/servers with little or no configuration, and no trust in other systems to properly classify their traffic.
>>>>>>> 
>>>>>>> The one thing that Cake needs to work really well is to be able to know what the data rate available is. With Starlink, this changes frequently and cake integrated into the starlink dish/router software would be far better than anything that can be done externally as the rate changes can be fed directly into the settings (currently they are only indirectly detected)
>>>>>>> 
>>>>>>> David Lang
>>>>>>> 
>>>>>>> 
>>>>>>> On Mon, 26 Sep 2022, Eugene Y Chang via Starlink wrote:
>>>>>>> 
>>>>>>>> You already know this. Bufferbloat is a symptom and not the cause. Bufferbloat grows when there are (1) periods of low or no bandwidth or (2) periods of insufficient bandwidth (aka network congestion).
>>>>>>>> 
>>>>>>>> If I understand this correctly, just a software update cannot make bufferbloat go away. It might improve the speed of recovery (e.g. throw away all time sensitive UDP messages).
>>>>>>>> 
>>>>>>>> Gene
>>>>>>>> ----------------------------------------------
>>>>>>>> Eugene Chang
>>>>>>>> IEEE Senior Life Member
>>>>>>>> eugene.chang at ieee.org
>>>>>>>> 781-799-0233 (in Honolulu)
>>>>>>>> 
>>>>>>>> 
>>>>>>>> 
>>>>>>>>> On Sep 26, 2022, at 10:04 AM, Bruce Perens <bruce at perens.com> wrote:
>>>>>>>>> 
>>>>>>>>> Please help to explain. Here's a draft to start with:
>>>>>>>>> 
>>>>>>>>> Starlink Performance Not Sufficient for Military Applications, Say Scientists
>>>>>>>>> 
>>>>>>>>> The problem is not availability: Starlink works where nothing but another satellite network would. It's not bandwidth, although others have questions about sustaining bandwidth as the customer base grows. It's latency and jitter. As load increases, latency, the time it takes for a packet to get through, increases more than it should. The scientists who have fought bufferbloat, a major cause of latency on the internet, know why. SpaceX needs to upgrade their system to use the scientist's Open Source modifications to Linux to fight bufferbloat, and thus reduce latency. This is mostly just using a newer version, but there are some tunable parameters. Jitter is a change in the speed of getting a packet through the network during a connection, which is inevitable in satellite networks, but will be improved by making use of the bufferbloat-fighting software, and probably with the addition of more satellites.
>>>>>>>>> 
>>>>>>>>> We've done all of the work, SpaceX just needs to adopt it by upgrading their software, said scientist Dave Taht. Jim Gettys, Taht's collaborator and creator of the X Window System, chimed in: <fill in here please>
>>>>>>>>> Open Source luminary Bruce Perens said: sometimes Starlink's latency and jitter make it inadequate to remote-control my ham radio station. But the military is experimenting with remote-control of vehicles on the battlefield and other applications that can be demonstrated, but won't happen at scale without adoption of bufferbloat-fighting strategies.
>>>>>>>>> 
>>>>>>>>> On Mon, Sep 26, 2022 at 12:59 PM Eugene Chang <eugene.chang at alum.mit.edu<mailto:eugene.chang at alum.mit.edu>> wrote:
>>>>>>>>> The key issue is most people don’t understand why latency matters. They don’t see it or feel it’s impact.
>>>>>>>>> 
>>>>>>>>> First, we have to help people see the symptoms of latency and how it impacts something they care about.
>>>>>>>>> - gamers care but most people may think it is frivolous.
>>>>>>>>> - musicians care but that is mostly for a hobby.
>>>>>>>>> - business should care because of productivity but they don’t know how to “see” the impact.
>>>>>>>>> 
>>>>>>>>> Second, there needs to be a “OMG, I have been seeing the action of latency all this time and never knew it! I was being shafted.” Once you have this awakening, you can get all the press you want for free.
>>>>>>>>> 
>>>>>>>>> Most of the time when business apps are developed, “we” hide the impact of poor performance (aka latency) or they hide from the discussion because the developers don’t have a way to fix the latency. Maybe businesses don’t care because any employees affected are just considered poor performers. (In bad economic times, the poor performers are just laid off.) For employees, if they happen to be at a location with bad latency, they don’t know that latency is hurting them. Unfair but most people don’t know the issue is latency.
>>>>>>>>> 
>>>>>>>>> Talking and explaining why latency is bad is not as effective as showing why latency is bad. Showing has to be with something that has a person impact.
>>>>>>>>> 
>>>>>>>>> Gene
>>>>>>>>> -----------------------------------
>>>>>>>>> Eugene Chang
>>>>>>>>> eugene.chang at alum.mit.edu <mailto:eugene.chang at alum.mit.edu>
>>>>>>>>> +1-781-799-0233 (in Honolulu)
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>>> On Sep 26, 2022, at 6:32 AM, Bruce Perens via Starlink <starlink at lists.bufferbloat.net<mailto:starlink at lists.bufferbloat.net>> wrote:
>>>>>>>>>> 
>>>>>>>>>> If you want to get attention, you can get it for free. I can place articles with various press if there is something interesting to say. Did this all through the evangelism of Open Source. All we need to do is write, sign, and publish a statement. What they actually write is less relevant if they publish a link to our statement.
>>>>>>>>>> 
>>>>>>>>>> Right now I am concerned that the Starlink latency and jitter is going to be a problem even for remote controlling my ham station. The US Military is interested in doing much more, which they have demonstrated, but I don't see happening at scale without some technical work on the network. Being able to say this isn't ready for the government's application would be an attention-getter.
>>>>>>>>>> 
>>>>>>>>>> Thanks
>>>>>>>>>> 
>>>>>>>>>> Bruce
>>>>>>>>>> 
>>>>>>>>>> On Mon, Sep 26, 2022 at 9:21 AM Dave Taht via Starlink <starlink at lists.bufferbloat.net<mailto:starlink at lists.bufferbloat.net>> wrote:
>>>>>>>>>> These days, if you want attention, you gotta buy it. A 50k half page
>>>>>>>>>> ad in the wapo or NYT riffing off of It's the latency, Stupid!",
>>>>>>>>>> signed by the kinds of luminaries we got for the fcc wifi fight, would
>>>>>>>>>> go a long way towards shifting the tide.
>>>>>>>>>> 
>>>>>>>>>> On Mon, Sep 26, 2022 at 8:29 AM Dave Taht <dave.taht at gmail.com <mailto:dave.taht at gmail.com>> wrote:
>>>>>>>>>>> 
>>>>>>>>>>> On Mon, Sep 26, 2022 at 8:20 AM Livingood, Jason
>>>>>>>>>>> <Jason_Livingood at comcast.com <mailto:Jason_Livingood at comcast.com>> wrote:
>>>>>>>>>>>> 
>>>>>>>>>>>> The awareness & understanding of latency & impact on QoE is nearly unknown among reporters. IMO maybe there should be some kind of background briefings for reporters - maybe like a simple YouTube video explainer that is short & high level & visual? Otherwise reporters will just continue to focus on what they know...
>>>>>>>>>>> 
>>>>>>>>>>> That's a great idea. I have visions of crashing the washington
>>>>>>>>>>> correspondents dinner, but perhaps
>>>>>>>>>>> there is some set of gatherings journalists regularly attend?
>>>>>>>>>>> 
>>>>>>>>>>>> 
>>>>>>>>>>>> On 9/21/22, 14:35, "Starlink on behalf of Dave Taht via Starlink" <starlink-bounces at lists.bufferbloat.net <mailto:starlink-bounces at lists.bufferbloat.net> on behalf of starlink at lists.bufferbloat.net <mailto:starlink at lists.bufferbloat.net>> wrote:
>>>>>>>>>>>> 
>>>>>>>>>>>> I still find it remarkable that reporters are still missing the
>>>>>>>>>>>> meaning of the huge latencies for starlink, under load.
>>>>>>>>>>>> 
>>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> 
>>>>>>>>>>> --
>>>>>>>>>>> FQ World Domination pending: https://blog.cerowrt.org/post/state_of_fq_codel/<https://blog.cerowrt.org/post/state_of_fq_codel/>
>>>>>>>>>>> Dave Täht CEO, TekLibre, LLC
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> --
>>>>>>>>>> FQ World Domination pending: https://blog.cerowrt.org/post/state_of_fq_codel/<https://blog.cerowrt.org/post/state_of_fq_codel/>
>>>>>>>>>> Dave Täht CEO, TekLibre, LLC
>>>>>>>>>> _______________________________________________
>>>>>>>>>> Starlink mailing list
>>>>>>>>>> Starlink at lists.bufferbloat.net <mailto:Starlink at lists.bufferbloat.net>
>>>>>>>>>> https://lists.bufferbloat.net/listinfo/starlink <https://lists.bufferbloat.net/listinfo/starlink>
>>>>>>>>>> 
>>>>>>>>>> 
>>>>>>>>>> --
>>>>>>>>>> Bruce Perens K6BP
>>>>>>>>>> _______________________________________________
>>>>>>>>>> Starlink mailing list
>>>>>>>>>> Starlink at lists.bufferbloat.net <mailto:Starlink at lists.bufferbloat.net>
>>>>>>>>>> https://lists.bufferbloat.net/listinfo/starlink <https://lists.bufferbloat.net/listinfo/starlink>
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> 
>>>>>>>>> --
>>>>>>>>> Bruce Perens K6BP
>>>>>> 
>>>>>> _______________________________________________
>>>>>> Starlink mailing list
>>>>>> Starlink at lists.bufferbloat.net <mailto:Starlink at lists.bufferbloat.net>
>>>>>> https://lists.bufferbloat.net/listinfo/starlink <https://lists.bufferbloat.net/listinfo/starlink>
>

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