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

[Michael Welzl]

> 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 of things today) is 5-10 years out of date compared to the software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  :)
But yes, whether it's worth it is questionable, of course; if TACK is good enough, it'll be easier to deploy of course.

Cheers,
Michael