Subject: Re: [iccrg] TCP behavior across WiFi pointers ?

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:
> 
> 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
>

---

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

---

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Thu, 09 Nov 2017 09:41:03 +0900

>>> across WiFi as opposed to wired ? Especially with WiFi in the home ?

I have done a couple of measurement studies that include WiFi links, in
the course of fixing bufferbloat on WiFi. It was not specifically
focused on analysing TCP in detail, but did include TCP performance. See
[1] and [2].

>>> 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).

In most cases, the problem with link-layer retransmissions on WiFi is
that there are too many of them. For instance the Linux WiFi stack
(which is what runs on most consumer home routers) will retry each
packet up to 30 times. This causes head of line blocking for subsequent
packets, resulting in bad bufferbloat (we've improved this a lot and are
working on the rest; see [2]).

>>> issue left when running traffic over TCP over WiFi.

I assume you're talking about video streaming or other high-bandwidth
multicast traffic here, right? Just converting to unicast gets you
aggregation and link-layer retries. If that's not enough, sure, TCP will
get you reliable delivery, but you'll spend so long retransmitting that
you'll have latency problems instead of drops. Generally speaking, of
course.

On the topic of multicast in WiFi, one of the big problems on busy
networks is that there is so much multicast traffic (various forms of
service discovery, mostly) that getting DHCP traffic through is almost
impossible. This is the bane of many a busy conference network (not
including at the IETF).

-Toke

[1] http://dx.doi.org/10.1016/j.comnet.2015.07.014

[2] https://www.usenix.org/conference/atc17/technical-sessions/presentation/hoilan-jorgesen

---

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.
>
> characteristics

---

From: Simon Barber <[email-masked]>
Date: Wed, 29 Nov 2017 16:41:04 -0800

We’ve been doing some studies and work in this area at Meraki.

https://conferences.sigcomm.org/imc/2017/papers/imc17-final203.pdf

Simon

> On Nov 29, 2017, at 7:17 AM, Aaron Falk <[email-masked]> wrote:
> 
> Hey Mark-
> 
> On Wed, Nov 8, 2017 at 1:33 PM Michael Welzl <[email-masked] <mailto:[email-masked]>> wrote:
> > On Nov 8, 2017, at 6:42 PM, Toerless Eckert <[email-masked] <mailto:[email-masked]>> wrote:
> >