[Rpm] [Make-wifi-fast] tack - reducing acks on wlans

[Anna Brunström]

-----Original Message-----
From: Make-wifi-fast <make-wifi-fast-bounces at lists.bufferbloat.net> On Behalf Of Toke Høiland-Jørgensen via Make-wifi-fast
Sent: den 21 oktober 2021 00:05
To: Michael Welzl <michawe at ifi.uio.no>
Cc: Rpm <rpm at lists.bufferbloat.net>; Make-Wifi-fast <make-wifi-fast at lists.bufferbloat.net>; Keith Winstein <keithw at cs.stanford.edu>
Subject: Re: [Make-wifi-fast] tack - reducing acks on wlans

Michael Welzl <michawe at ifi.uio.no> writes:

>> On 20 Oct 2021, at 17:57, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>>
>> Michael Welzl <michawe at ifi.uio.no> writes:
>>
>>>> On 20 Oct 2021, at 13:52, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>>>>
>>>> Michael Welzl <michawe at ifi.uio.no> writes:
>>>>
>>>>>> On 20 Oct 2021, at 12:44, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>>>>>>
>>>>>> Michael Welzl <michawe at ifi.uio.no> writes:
>>>>>>
>>>>>>>> On 20 Oct 2021, at 11:44, Toke Høiland-Jørgensen <toke at toke.dk> wrote:
>>>>>>>>
>>>>>>>> Michael Welzl <michawe at ifi.uio.no> writes:
>>>>>>>>
>>>>>>>>> Am I being naive? Why can't such an ARQ proxy be deployed? Is
>>>>>>>>> it just because standardizing this negotiation is too
>>>>>>>>> difficult, or would it also be too computationally heavy for an AP perhaps, at high speeds?
>>>>>>>>
>>>>>>>> Immediate thought: this won't work for QUIC
>>>>>>>
>>>>>>> .... as-is, true, though MASQUE is still being defined. Is this
>>>>>>> an argument for defining it accordingly?
>>>>>>
>>>>>> MASQUE is proxying, right? Not quite sure if it's supposed to be
>>>>>> also MITM'ing the traffic?
>>>>>
>>>>> Wellllll.... I'm not 100% sure. If I understood it correctly,
>>>>> ideas on the table would have it do this in case of tunneling
>>>>> TCP/IP over QUIC, but not in case of QUIC itself - but to me, this
>>>>> isn't necessarily good design?  Because:  =>
>>>>>
>>>>>
>>>>>> In any case, it would require clients to negotiate a proxy
>>>>>> session with the AP and trust it to do that properly?
>>>>>
>>>>> => Yes.
>>>>>
>>>>>
>>>>>> This may
>>>>>> work for a managed setup in an enterprise, but do you really
>>>>>> expect me to be OK with any random access point in a coffee shop being a MITM?
>>>>>
>>>>> MiTM is a harsh term for just being able to ACK on my behalf. Some
>>>>> capabilities could be defined, as long as they're indeed defined
>>>>> clearly. So I don't see why "yes, you can ACK my packets on my
>>>>> behalf when you get a LL-ACK from me" is MiTM'ing. I believe that
>>>>> things are now all being lumped together, which may be why the
>>>>> design may end up being too prohibitive.
>>>>
>>>> Right, okay, but even setting aside the encryption issue, you're
>>>> still delegating something that has potentially quite a significant
>>>> impact on your application's performance to an AP that (judging by
>>>> the sorry state of things today) is 5-10 years out of date compared
>>>> to the software running on your own machine. Not sure that's such
>>>> an attractive proposition?
>>>
>>> Depends - this is what explicitly signaling this capability could solve.
>>>
>>> Take TCP, for example: if I'm all hyped on L4S, I may not want to
>>> delegate ACKing to an AP that doesn't support ACKing without support
>>> for accurate ECN signaling. If I do MPTCP and see support from the
>>> peer, then perhaps I don't want this capability at all. If I don't
>>> care about these two things... well, then, ACKing hasn't changed
>>> very much for several years. I may want to include some initial
>>> option information in that signal, for the AP to relay - e.g. about
>>> window scaling and such. I suspect that QUIC / MASQUE ACKing is also
>>> going to stabilize somewhat at some point in time.
>>
>> Still a lot of complexity for something that (according to that TACK
>> paper) is only a marginal improvement over what can be achieved
>> end-to-end...
>
> It's not exactly huge complexity compared to many of the other things
> we have, and I'm not sure the improvement is marginal: this may depend
> on various things, such as the number of nodes... it's a 100%
> reduction of ACK traffic  :)

Modifying the link layer for each wireless technology to convey the information that the AP should send the TCP ACK, as done in the paper, is quite complex from a deployment perspective I think. And it is also not all ACKs that can be replaced so not sure what the reduction is in practice. Reducing the number of ACKs e2e seems preferable I think.

Anna

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