QUIC traffic throttled on AT&T residential

Thu Feb 20 16:18:53 UTC 2020

On 2/19/2020 3:21 PM, Daniel Sterling wrote:
> On Wed, Feb 19, 2020 at 3:34 PM Blake Hudson <blake at ispn.net> wrote:
>> Yeah, that was a nice surprise to find that my tethered LTE connection
>> was out performing my wired cable modem service. Of course, I had
>> already signed up for a year of service and there were early termination
>> fees for cancelling... that and there are no other wireline providers
>> available at my home (not even ATT).
> So we're left with some questions:
>
> 1. It's clear I'm not the only one experiencing this issue. How
> widespread is this problem, really? Has it gotten rather worse over
> the past ~year?
>
> 2. Are customers of larger ISPs much more impacted than customers of
> smaller ones that (assumedly) don't have to deprioritize UDP so much?
> 2a. If users *are* impacted, as Blake notes, they may not be able to
> switch ISPs to improve their lot.. will customers complain to their
> ISP or to Google?
>
> 3. How much worse is the problem when using v4 UDP QUIC vs v6? If QUIC
> only works on v6 (and if it in fact continues to actively BREAK
> v4-only users), then is this v6's "killer app" that will drive
> adoption?
> 3a. Or will this issue hinder HTTP/3 deployment (or cause mass
> blocking of UDP on clients)?
>
> 4. Will ISPs be willing to give UDP traffic higher priority to improve
> user experience? Will that only happen once HTTP/3 is widely deployed?
>
> 5. We can only assume Google is aware of this issue; will Google work
> to improve QUIC fallback to TCP, or will they work with ISPs to get
> QUIC (esp v4 QUIC) prioritized, or will they do nothing, or will they
> actively encourage QUIC to break v4 at the expensive of current user
> experience?
> 5a. Will another company that wants HTTP/3 to succeed take the mantle
> and work with ISPs to improve the situation? I'm reminded of when
> Microsoft worked with ISPs to ensure xbox UDP traffic would transit
> properly
>
> -- Dan
Dan, my experience with Cox is that their standard cable internet 
package (advertised as 150Mbps) rate limits UDP to ~10Mbps. This appears 
to be controlled via the cable modem config file which is enforced by 
both the cable modem and the CMTS. I do not know if this is per flow or 
per circuit or affects IP4 differently than IP6. I suspect that someone 
at Cox decided that the only applications using UDP were VoIP and DNS 
and that those applications never needed more than 1Mbps so anything 
else must be "bad" and should be stopped. Whether "bad" means harmful to 
network operation, harmful to support costs, or harmful to profits, I do 
not know.

Your comments seem to differentiate IP4 vs IP6, but I don't believe that 
is relevant to the issue of an ISP throttling or breaking specific 
applications. If you have evidence that UDP on IP4 is treated 
differently than UDP on IP6 by your provider, without further 
information I would suspect that this is simply an unintentional over 
sight on their part.

Perhaps the attention you've generated on this topic, along with the 
adoption of additional UDP based applications like QUIC, will encourage 
ISPs to treat UDP in a more neutral manner and not simply see UDP as 
something that is "bad".

--Blake