[Bloat] Re: Vol 185, Issue 5

[David Lang <david@lang.hm>]

wifi is a very different thing than general network latency (which is what we 
were talking about before)

A large part of it is that wifi is designed or weak signals and a low number of 
users, a very different environment than most people see today.

It interprets loss as "this is a weak signal, let me do things that will help in 
the weak signal case", slowing the transmission speed, which helps in the face 
of general noise, but when the problem is interference from other wifi 
transmitters, it instead expands the window where the interference will clobber 
the retransmission.

This is why wifi doesn't degrade gracefully, it goes from "works well" to 
"doesn't work at all" in a very short time and it doesn't recover until enough 
people give up (and retries time out).

AFAIK newer protocols don't fix this, they just make it possible to cram more 
data into a given transmission

This is not a latency issue, just an airtime utilization problem.
Stations do listen and do not transmit if they hear another station talking, but 
it's very easy to be in a situation where stations A and B cannot hear each 
other, but station C can hear both (the better the antennas on the AP, the more 
likely you are to run into this problem, especially when combined with higher 
transmit levels on the AP than on the devices it's talking to)

This is why at the Scale conference, we use a LOT of APs, all turned down to 
very low power and with default or worse antennas on them to shrink the 
transmission range of the APs.

David Lang

On Sun, 20 Sep 2026, bob.mcmahon@umbernetworks.com wrote:

> Date: Sun, 20 Sep 2026 12:30:40 -0700
> From: bob.mcmahon@umbernetworks.com
> To: David Lang <david@lang.hm>
> Cc: D.Goncz-FAX-571-395-3575@replikon.net, bloat@lists.bufferbloat.net
> Subject: Re: [Bloat] Re: Vol 185, Issue 5
> 
> David is right that packets don't superpose. The useful math here is feedback 
> control.
>
> The guitar amp is a useful analogy for feedback instability. A squeal occurs 
> when the loop gain and phase satisfy the conditions for sustained 
> oscillation. The amplifier keeps supplying energy to the loop, and the 
> oscillation grows until nonlinearities and saturation bound it.
>
> Networks have feedback loops too. The delay through that loop is the RTT. 
> Tail-drop synchronization, congestion-window sawtooths, and other oscillatory 
> behaviors arise when multiple controllers react to delayed information about 
> a shared bottleneck. That is why control theory is the useful toolbox here.
>
> The key state is at the bottleneck queue. Endpoints need a timely congestion 
> signal derived from that state. Loss communicates congestion after the queue 
> has filled far enough to drop a packet. ECN lets the bottleneck communicate 
> that information earlier and more frequently, giving the senders time to 
> adjust their rates while keeping the queue shallow.
>
> The difficult segment is the wireless last hop. AQM at an AP manages its 
> queue, while contention arbitrates access to the air. Managing the air itself 
> requires scheduling: grants issued from a point with enough state to make the 
> decision, including wireless state across the relevant radios and bottleneck 
> queue state.
>
> An 802.11ax AP has detailed state about its own BSS and can use trigger 
> frames to schedule uplink transmissions within that BSS. Building-wide 
> scheduling requires a broader view: the air state across multiple radios 
> together with the forwarding and bottleneck queue state. The scheduler 
> therefore belongs at the point where those two kinds of state come together.
>
> Bob
>
>
> On 2026-09-19 02:16, David Lang wrote:
>> Explain how you think this resonance would happen? unlike sound, packets 
>> don't 'echo', they deliver messages, which can (and frequently do) trigger 
>> reply messages but unlike audio resonance, the incoming packets don't add 
>> to the outgoing packets to make a larger signal than the outgoing packets 
>> would if the timing was a little difference.
>> 
>> David Lang
>> 
>> 
>> On Sat, 19 Sep 2026, Replikon Research, D-U-N-S/FCN 77-387-4974 wrote:
>> 
>>> There are two realms of analysis where things can blow up
>>> 
>>> One is synergy and synergetics meaning the interactions between presumably
>>> interchangeable parts relevant to the interactions between presumably
>>> interchangeable routers and node points
>>> 
>>> The other is combinatorics and that's my thing I love combinatorics!!!! 
>>> The
>>> only thing that matters is what you choose to count and how much each part
>>> of what you count matters to you to put it concisely.
>>> 
>>> So while I have very little to contribute I am encouraged to hear that the
>>> bottleneck is in the latency but the causes of the latency are
>>> multi-dimensional there are at least we know where the problem is not 
>>> where
>>> that would mean we knew the causes no that's not right let me know is what
>>> the problem is yes the problem is latency
>>> 
>>> What comes to mind is it for certain latencies there may be an echo like
>>> the feedback of a guitar when the amplifiers turned up too high
>>> 
>>> Does that have any intuitional relationship to these very high level
>>> Network analyzes that you all do everyday
>>> 
>>> This question of residence no not residents got darn it in the microphone
>>> resonance like my voice yes
>>> 
>>> I think resonance and spectral radius are two characteristics of behind
>>> level network analysis which apply here to this question of latency 
>>> because
>>> when spectral radius is one resonance is nearly inevitable
>>> 
>>> Is the internet we have built evolving to an internet in which some
>>> parameterizable characteristic has a special radius of 1?
>>> 
>>> I sure as hell hope not
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