When I’m living in my RV, wireless service providers are my primary source of connectivity. So when either AT&T or Verizon make major changes, I take notice.
I recently noticed that multiple websites are quite slow when browsing with my AT&T business plan, listed in AT&T Premier (business account management UI) as “Wireless Broadband Ultra for Router or Hotspt (sic)”. This is an “unlimited” 100Mbit plan with 50GB for Business Fast Track (prioritized) data. Being that I was far below the 50GB of monthly Fast Track data, my data should have had top priority, so I became suspicious. To be honest, I’ve never noticed a discernible difference between Fast Track and non-Fast Track data rates. This is all to say that I have no reason to believe that I’m being deprioritized due to usage.
Naturally, the first hing I did was conduct a speed test. I already knew from previous experience that for some reason, AT&T traffic to fast.com is throttled. Why AT&T wants bandwidth to appear lower than reality is a mystery to me, but I digress. Linode.com has speed tests that AT&T has no special treatment for, and the nearest one to me was in Fremont, CA.
The speedtest revealed 21Mbps down and 4.5Mbps up – pretty reasonable in a relatively rural area like Durango, CO. Latency was ~130ms. That speed certainly wouldn’t explain why it took anywhere between 15 seconds and 2 minutes to load
So I opened up the “Network” tab in Firefox and could clearly see that dozens of resources from
cloudfront.com were taking multiple seconds to load. The problem clearly has something to do with Cloudfront.
Is Cloudfront having problems? That’s easy enough to verify; my Sierra Wireless RV55 CAT-12 LTE-A router also contains an unlimited Verizon Business SIM card that I can use to conduct tests on Cloudfront, independent of AT&T.
web-assets.strava.com resolves to
dgpcy4fyk1eox.cloudfront.net, so rest assured, we are dealing with Cloudfront.
After switching to Verizon, I could see that Cloudfront was having no problems. Our friend
827.js downloaded in just over 1 second at 1.4MB/s. I clearly saw earlier in the Firefox network tab that this resource took nearly 1 minute to load on AT&T.
wgetis not my goto for command line HTTP fetching, it displays transfer rates in a human friendly format by default, so I used the following as my test case:
wget -O /dev/null -q --show-progress https://web-assets.strava.com/assets/federated/find-and-invite-friends/827.js
So the problem isn’t Cloudfront, because Verizon was fast enough. It wasn’t blazing fast by any means, but I also didn’t have to wait 2 minutes to learn whether Strava awarded me King of the Moutain on a local trail (I wasn’t).
Maybe this is a global AT&T problem. That’s easy to test as well – my iPhone is also on the same AT&T business account as my data-only plan, so I turned on the iPhone hotspot and made it the router’s WAN device to make sure we’re changing a single variable at a time. I conducted another speed test, revealing 23Mbps down and 3Mbps up. Nothing surprising there – normal bandwidth fluctuations for a wireless device. How about our
wget test? 1.7MB/s. The problem is clearly not all of AT&T wireless.
Let’s go back to the original configuration: connect directly to my AT&T data-only plan with my router and re-run the
wget test. Maybe I was imagining things. I’m somewhat surprised to see the
wget test with a transfer rate of ~30KB/s. I believe this rules out AT&T with a souring peering agreement somewhere between me and Cloudfront. My phone traffic to Cloudfront is unaffected; it’s only my data-only plan that is affected.
I now have a pretty clear picture of what is likely happening. Good old-fashion traffic shaping. Now that the router is connected directly to AT&T, the true test of traffic shaping is transfer rates while connected to a VPN. I’ll let the image speak for itself.
As of the time of writing, I’m unsure what is causing such a significant slowdown. It has rendered some websites effectively useless. Everything in this writeup indicates, to me, that AT&T is engaged in extremely aggressive traffic shaping for some plans, rendering many websites nearly unusable.
Do you have any ideas how to diagnose this problem further? Do you know the best way engage AT&T’s technical folks to take this seriously? Write me at
att-traffic-shaping @ this domain. I’ll add updates here if anything changes, or I get a response on https://bizcommunity.att.com.