Why is my Wifi link so slow?

[steve23094]

Hi,

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.

Thanks.

 

[steve23094]

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.

 

[steve23094]

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?

 

[jlake]

update to latest driver on your computer.

are you having problem with 2.4 ghz ior 5 ghz?

Use "20mhz" for 2.4 ghz. Don't use 20/40 or 40 for 2.4 ghz.

you can also try removing your wirless profile ---"forget this network"....and then reconnect.

If you're getting good (acceptable) throughput, sometimes it's best to just take what you get. Wireless can vary from device to device.

Don't worry about theoretical link speed. Just worry about getting an acceptable throughput.

Always use a wired connection when possible. I've used wireless for my main/primary desktop for the last few 15 years. I've got it wired now and it's flawless. It's hard to beat a 10/100/1000 ethernet connection.

 

[steve23094]

update to latest driver on your computer.

are you having problem with 2.4 ghz ior 5 ghz?

Use "20mhz" for 2.4 ghz. Don't use 20/40 or 40 for 2.4 ghz.

you can also try removing your wirless profile ---"forget this network"....and then reconnect.

If you're getting good (acceptable) throughput, sometimes it's best to just take what you get. Wireless can vary from device to device.

Don't worry about theoretical link speed. Just worry about getting an acceptable throughput.

Always use a wired connection when possible. I've used wireless for my main/primary desktop for the last few 15 years. I've got it wired now and it's flawless. It's hard to beat a 10/100/1000 ethernet connection.

Thanks for your reply. The problem is with 5Ghz not bonding. I have 2.4Ghz set as 20Mz.

I would like to say 'not to worry', but it is important to me as it is affecting my Time Machine backup speed and I transfer a lot of files around my network and to my NAS. Using a wired connection or Homeplug in this location is not possible. I am finding it frustrating because the problem is not present on my rMBP when it is used in the same location and orientation.

I had a thought though, maybe the point is that the wireless receiver in the iMac is too strong and it's picking up another wifi network in the area on the same channel so stepping down to 20Mhz to be a good neighbour.

So I wonder if it's possible to turn down the receive power on the Wifi card in my iMac?

Failing that does the 802.11ac standard (which is what is in my iMac, the router is 802.11n) only step down if it detects another device on the same channel, or is it any device on the 5Ghz band? Because then I need to play around with finding a new channel, which will mean I have to install the fork of Merlin's firmware because of Asus' stupid opinion that the United States is the centre of the world.

 

[steve23094]

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:-
http://forums.smallnetbuilder.com/showthread.php?t=18914

I then had to change the country code to allow the greater range of channels using these instructions:-
http://forums.smallnetbuilder.com/showthread.php?p=121385#post121385

And then this page told me which channels were legal in the UK:-
http://www.digitalairwireless.com/wireless-blog/recent/quick-guide-to-5ghz-uk-part-1.html

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.