Slow Download Speeds On Macbook Air

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If you find that your wireless download speeds are abysmal while youruploads speeds are pretty solid, especially with Apple devices, I’ve got apossible solution for you. I struggled with this issue for a while and decidedto write down my findings in a blog post in case I, or anyone else, runs intothis in the future.

  1. Slow Download Speeds On Macbook Air 2
  2. Macbook Air Slow
  3. Macbook Air Very Slow
  4. Slow Download Speed On Macbook Air
  5. Slow Download Speeds On Macbook Air Keyboard Cover

tldr: disable WMM QoS in your router settings.

Slow Download Speeds On Macbook Air 2

Macbook Air: OS X 10.7.1, Intel Core i7 1.8Ghz, 4GB RAM; iPhone 4S: iOS 5.0; Custom desktop: Windows 7, Intel Core 2 Duo E8400 3.0Ghz, 2GB RAM; ISP: Comcast xfinity; Whenever I used my laptop or phone, the Wi-Fi connection felt incredibly slow. Youtube videos took forever to load, Google Maps tiles filled in slowly, and even gmail felt. If you’ve been updating your Mac OS to the latest version macOS High Sierra and the download is pretty damn slow, though you have a fast internet connection. We’ve tried figuring out what is the cause of the problem or there are secret hidden settings to enable to fasten its download speed.

Symptoms

At home, I have the following setup:

  1. Macbook Air: OS X 10.7.1, Intel Core i71.8Ghz, 4GB RAM
  2. iPhone 4S: iOS 5.0
  3. Custom desktop: Windows 7, Intel Core 2 Duo E8400 3.0Ghz, 2GB RAM
  4. ISP: Comcast xfinity

Whenever I used my laptop or phone, the Wi-Fi connection felt incrediblyslow. Youtube videos took forever to load, Google Maps tiles filled in slowly,and even gmail felt unresponsive. On the other hand, my desktop, which wasconnected to the router via an ethernet cable, worked just fine.

Numbers

To confirm my observations, I decided to take some bandwidth measurementsusing bandwidthplace.com,speakeasy.net, andspeedtest.net for the laptop and the SpeedTestapp for the iPhone. The results were pretty consistent across all app anddevice pairs and looked something like this:

Desktop

  1. Download: 24 Mbps
  2. Upload: 4.5 Mbps

Laptop

  1. Download: 0.65 Mbps
  2. Upload: 4.5 Mbps

iPhone

  1. Download: 0.58 Mbps
  2. Upload: 4.4 Mbps
Download

Yikes! My laptop and iPhone download speed were more than 30 timesslower than my desktop’s download speed! On the other hand, the upload speedwas roughly the same on all devices. What the hell was going on?

Macbook Air Slow

Failed attempts

After googling for solutions, I tried a number of tweaks commonlysuggested around the web:

  1. Change DNS hosts
  2. Change wireless channel
  3. Change the wireless channel width
  4. Use a different security mode (WPA2 personal)
  5. Shut off firewalls
  6. Enable or disable IPv6 settings
  7. Reboot the router

None of these worked.

The solution

Out of desperation, I started tweaking random settings on my router andstumbled across one that finally worked. The directions for other routersmay be a little different, but here’s what I did:

  1. Go to http://192.168.1.1 and login to your router. If you’venever done this, look for instructions that came with your router or do agoogle search to find the default username and password.
  2. Find a page that has QoS settings. For the E1200, you need to click on“Applications & Gaming” and select the “QoS” sub-menu.
  3. Disable WMM Support.
  4. Click save.
Download

That’s it. The second I disabled WMM support, the download speeds for mylaptop and iPhone both jumped to 24 Mbps, perfectly matching my desktop.

What the hell is WMM?

Macbook Air Very Slow

WMM isapparently an 802.11e feature that provides higher priority for“time-dependent” traffic, such as video or voice. In theory, this should makethings like VoIP calls and video chat (e.g. Skype) perform better. Inpractice, having it enabled destroyed my Wi-Fi download speeds. Since Idisabled it, my Wi-Fi is blazing fast and I’ve seen no negativeside-effects.

Slow download speeds on macbook air pro

If anyone has more information as to why this would be the case, pleaseshare it here.

Update (April, 2014): firmware upgrades

Slow Download Speed On Macbook Air

A couple years after writing this blog post, I hit the inverse of the originalproblem: I suddenly had fast download but slow upload speeds. While lookingfor a fix, I found out that the WMM/QoS issue mentioned above may have beenfixed in newer firmware versions for my router! I once again wrote a blog postto capture all the details: Got fast download but slow upload speeds? Here’safix.

Update (Sept, 2013): some nitty-gritty details

In the last year, this post has had over 100k views and helped many people fixtheir download speeds. I’m happy I was able to help people. Other folks havebeen eager to share advice too: I got an email from a Russ Washington inAtlanta who did some impressive investigative work to uncover a potentialunderlying cause. In case it helps others, here is his email:

Yevgeniy: I ran into your blog post 'Got slow download but fastupload speeds over wireless? Here's a fix.' I have some info you may finduseful.

This happened to me too when I moved toComcast - but I had DSL running in parallel. The Comcast traffic had thisproblem but the DSL did not. Also, it affected my Linksys router when it hadstock firmware *and* after switching to DD-WRT. Clearly the traffic itself wasat issue, so I broke out the packet sniffer.

*All* inbound Comcast traffic (Internet --> client) was tagged with a DSCP valueof 8 (Class Selector 1). The DSL traffic had a DSCP value of 0. So Comcast istagging all traffic to be treated a certain way by QoS: 'Priority,' whichsounds good but is actually the second-*lowest* possible.

WMM, itself a QoS technique, apparentlyde-prioritizes (drops?) based on the Comcast-supplied value. Turning off WMMworked around it - but since WMM is part of the 802.11n spec, I wanted rootcause. Judiciously replacing that set-by-Comcast DSCP value does the trick.

So between my Linksys router and both ISPs, I had aNetscreen firewall. It lets me set DSCP values by policy - so I told it tomatch the DSL (DSCP 0). This yielded great improvement. However, I was stillnot getting full speed so even a zero value was not the best for > DSLrates. I set the DSCP value to 46 (Expedited Forwarding) and bingo, up to20Mbps, almost full provisioned speed (25Mbps).

Why only download issues? Because the only Comcast-tagged packets are the inboundones: Internet --> you, including those big data packets. When uploading,yes, you get sent ACK packets and such - but they are tiny connection-controlpackets. I imagine WWM weirds out on them too, but you (usually) wouldn'tnotice when doing multi-Mbps speed tests.

I am still trying to udnerstand WMM, but this was a big find, and I was lucky to have afirewall that let me packet-tweak. Hope you find the info useful.

Russ Washington, Atlanta, GA

Update (Sept, 2014): more nitty-gritty details

Slow Download Speeds On Macbook Air Keyboard Cover

Russ has found even more info about this issue: it turns out it’s not just aComcast DSCP bug, but also poor handling of this bug by the firmware of manyrouters. More details here: Critical DSCP bug Affecting WiFi Download Speedson Comcast.