Why is my Wifi link speed so slow

Discussion in 'iMac' started by steve23094, Nov 13, 2014.

  1. steve23094 macrumors 68020


    Apr 23, 2013

    Okay here is the scenario, why and how can I fix it?

    I have a mid-2012 rMBP and 2014 riMac (both running Yosemite 10.10) and Asus RT-N66U wireless router.

    On my rMBP in the same location and orientation as the iMac the Wifi link speed to my router is 450Mbps, and performance is what I would expect. Signal strength is 80%.

    On my riMac my link speed is typically around 73Mbps, very occasionally it might hit 200 or so but that is very rare. And I get the terrible performance I would expect from this speed. Signal strength is 85% (higher than the rMBP).

    All things on my router are the same between the rMBP and riMac.

    I thought it might be the bluetooth keyboard and trackpad causing interference (which would be stupid), but the rMBP in the exact same location does not suffer with reduced Wifi speed.

  2. joema2 macrumors 65816


    Sep 3, 2013
  3. WilliamG macrumors G3

    Mar 29, 2008
    I just checked my signal strength, two floors up in my house from my AC Time Capsule, and I'm at 527Mbps on my 2014 RiMac.

    Agreed with the above post. Check to make sure you're not connecting to the 2.4Ghz network. It's this sort of stuff that has had me naming my 5Ghz and 2.4Ghz networks differently for years.

    Also, routers can, unfortunately, factor into this. I know I've tried numerous routers, and none of them have performed as well as the Time Capsule. That said, your numbers are much lower than they should be with any router, so I suspect a config issue on the router/how the Mac is connecting.
  4. steve23094 thread starter macrumors 68020


    Apr 23, 2013
    Thanks for the link and I ran the network diag, it didn't find anything specific and I read the log files. And with so much information unfortunately without knowing what I am looking for it didn't really help me.


    Yeah, I'm definitely on the 5Ghz network. I name my 2.4Ghz and 5Ghz with different SSIDs.

    I was playing around with the channels on my router and I would note that typically my iMac is showing about 50dB SNR and my laptop about 31dB. With my laptop having a faster confirmed link speed that doesn't really make sense to me.

    BUT one thing I have noticed. My iMac is not dual bonding my 5Ghz wifi channel and my rMBP is. It's capping out at a 217Mbps link speed. It's like one of the iMac antennas is not active or faulty, or there is a direct compatibility issue with my router's implementation of 802.11n. Which is weird because once again my rMBP has no problems.
  5. steve23094 thread starter macrumors 68020


    Apr 23, 2013
    It's definitely the bonding. Jumping back and forth between 2.4Ghz and 5Ghz I see the link kicking up to 450 and then back down to 217Mbps five or so seconds later. So how do I fix this behaviour given it is not present in my rMBP?
  6. steve23094 thread starter macrumors 68020


    Apr 23, 2013
    I have solved my problem. So for the benefit that anybody else that may stumble across this post in the future I'll outline what happened.

    Once I had cottoned onto the fact my channels weren't bonding a lightbulb went on in my head. You can see from my earlier posts that I was confused how the iMac could have a better signal but lower link speed than my Macbook. But that was exactly the problem, because of the increased reception power of the iMac I was picking up neighbours Wifi networks in the same 5Ghz channel that my Macbook wasn't. Because of 'good neighbour' policy in the 802.11ac (and 'n'?) standard the iMac would step down from 40Mhz bonded channels to 20Mhz. My router is a 802.11n model which means a maximum of two bonded channels, if it was 802.11ac it would allow for four.

    So... how to change channels to avoid my neighbours? That was a problem.

    Router manufacturers (and specifically ASUS) typically ship out routers configured to allow EU channels, and they use the lowest common denominator in that the selectable channels are legal in all EU countries. This allows them to ship one model for the entire EU but only provides four selectable 5Ghz channels and all those were occupied by Wifi networks in the block I live in. But where I live in the UK there is a much wider choice of legal channels.

    In the United States the FCC stipulated in their wisdom to not allow users to change the country code on routers. Manufacturers implemented this policy worldwide to not fall foul of the FCC.

    I had been using RMerlin's ASUS firmware but something like 12 months ago that changed to no longer allow a country code change. So I had to install a fork of RMerlin's firmware that used an old base and still allowed the change. Here is a link to the firmware:-

    I then had to change the country code to allow the greater range of channels using these instructions:-

    And then this page told me which channels were legal in the UK:-

    So I selected a channel not used by my neighbours (and unlikely ever to be because of the amount of effort required to open them up) and voila! Bonded channels running at full speed.

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