Subject: TCP behavior across WiFi pointers ?

From: Toerless Eckert <[email-masked]>
Date: Wed, 8 Nov 2017 18:42:47 +0100

Any pointers to work analyzing the differences in behavior when TCP is run
across WiFi as opposed to wired ? Especially with WiFi in the home ?

I am primarily thinking that there could be a higher demand for
TCP (end-to-end) retransmissions when using WiFi because the L2/WiFi
local retransmissions are insufficient. And if so, what the characteristics
of those end-to-end retransmissions is (would assume they would be larger
than N msec, where N is whatever the L2/wifi protection window is, which
unfortunately i don't know).

Asking because we've got the poor "must-sit-in-back-of-the-bus" traffic
called IP multicast that is not protected by L2/wifi retransmissions at
all and now we're wondering if carrying it over TCP as a workaround
could help, and therefore trying to educate myself on specific known
issue left when running traffic over TCP over WiFi.

If any other TSV or other WG mailing list might be a better place to
ask. pls. let me know.

Thank!
    Toerless

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From: Michael Welzl <[email-masked]>
Date: Wed, 8 Nov 2017 19:32:47 +0100

I would think that 1) there are probably pointers, and 2) the people who have them should be on the ICCRG list, which I’m cc’ing.

I suggest for this to be the last email that includes tsvarea so that the thread entirely moves to ICCRG.

> On Nov 8, 2017, at 6:42 PM, Toerless Eckert <[email-masked]> wrote:
>

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From: Marie-Jose Montpetit <[email-masked]>
Date: Wed, 8 Nov 2017 13:37:37 -0500

I also copy the nwcrg list where a ton of people have looked at TCP over wifi.

mjm
> On Nov 8, 2017, at 1:32 PM, Michael Welzl <[email-masked]> wrote:
> 
> _______________________________________________
> iccrg mailing list
> [email-masked]
> https://www.irtf.org/mailman/listinfo/iccrg

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From: Mikael Abrahamsson <[email-masked]>
Date: Wed, 29 Nov 2017 06:17:19 +0100 (CET)

> local retransmissions are insufficient. And if so, what the characteristics

I don't know of any work you're asking for, but from my own experience 
radio networks (wifi + cellular) has the following 
(general) characteristics:

They deliver packets in-order per host.

The try very very hard to deliver all packets (true for unicast only on 
wifi), using L1/L2 retransmits.

Because of this, they sometimes "stall" shorter or longer times, so you 
might get latency spikes of hundreds of milliseconds that are gone in the 
next second. My personal record is 180 SECONDS of RTT on a 2G network.

These latency spikes might cause TCP to believe there was packet loss and 
cause retransmits, where there instead "only" was packet delay.

Radio networks have airtime schedulers, so a single packet and a train of 
packets might have very different network experience. Some network 
types send multiple packets in a single transmit opportunity, and these 
transmit opportunities might be tens of milliseconds apart.

-- 
Mikael Abrahamsson    email: [email-masked]

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From: Aaron Falk <[email-masked]>
Date: Wed, 29 Nov 2017 15:17:35 +0000

Hey Mark-

Didn't you do some work on TCP over wifi a while ago?

--aaron

On Wed, Nov 8, 2017 at 1:33 PM Michael Welzl <[email-masked]> wrote:

> I would think that 1) there are probably pointers, and 2) the people who
> have them should be on the ICCRG list, which I’m cc’ing.
>

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From: Yuchung Cheng <[email-masked]>
Date: Wed, 29 Nov 2017 13:58:28 -0800

On Tue, Nov 28, 2017 at 9:17 PM, Mikael Abrahamsson <[email-masked]>
wrote:

> radio networks (wifi + cellular) has the following (general)
> characteristics:
>
My experience is different. It is more similar to this post
https://www.ietf.org/mail-archive/web/rmcat/current/msg00815.html

> packets might have very different network experience. Some network types
> send multiple packets in a single transmit opportunity, and these transmit
> opportunities might be tens of milliseconds apart.
>
> --