300Mb/s router only giving max 150Mb/s connection.

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300Mb/s router only giving max 150Mb/s connection.

Postby viking777 on Sun Apr 21, 2013 1:46 pm

Router is a netgear dgns 3300v2. Dual band, wireless n with router mode set to:
Up to 300Mbps at 5GHz & 54Mbps at 2.4GHz
. Wireless card is an Intel wifi link 5100 which, according to Intel is capable of up to 300 Mb/s. It has two aerials. iwconfig gives:

Code: Select all
wlan1     IEEE 802.11abgn  ESSID:"xxxxxxxxx" 
          Mode:Managed  Frequency:5.18 GHz  Access Point: xx:xx:xx:xx:xx:xx 
          Bit Rate=150 Mb/s   Tx-Power=13 dBm   
          Retry  long limit:7   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=67/70  Signal level=-43 dBm 
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:395  Invalid misc:145   Missed beacon:0


(essid and mac address hidden by me). Note the bit rate 150Mb/s.

The router is in the same room as the computer, just a few feet away, with nothing in between (except me possibly, but even when I move it makes no difference). Router firmware up to date, and using iwlwifi driver, also up to date, so why only half the maximum possible speed?

If you google this problem you will see that the answers given usually relate to 'channel bonding'. I can categorically state that there are no such options in my router configuration panel, so that is not the answer for me.

Anybody got any ideas.

BTW I get the same result on Ubuntu (150Mb/s max) but even worse on Manjaro (72Mb/s max). I cant explain the difference there.
Another note, on my old laptop (which is in another room with a wall in between) I have seen signals up to 165Mb/s which is surprising although still a long way from 300. Incidentally the old laptop is using the iwl4965 driver so maybe that makes a difference?
Fujitsu Lifebook AH532. Intel i5 processor, 6Gb ram, Intel HD3000 graphics, Intel Audio/wifi. Realtek RTL8111/8168B Ethernet.Lubuntu 13.10,Ubuntu12.10 (Unity), Mint16 (Cinnamon), Manjaro (Xfce).
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Re: 300Mb/s router only giving max 150Mb/s connection.

Postby viking777 on Mon Apr 22, 2013 2:20 pm

I've been doing quite a lot of research into this and I have come up with what looks like an explanation, although it certainly isn't an answer.

If you run the command:

Code: Select all
sudo iw dev wlan1 link


Part of the answer is:

Code: Select all
tx bitrate: 150.0 MBit/s MCS 7 40Mhz short GI


If you compare that with the wikipedia article on 802.11n https://en.wikipedia.org/wiki/IEEE_802.11n-2009 which gives this:
Selection_001.png


You see that the MCS index 7 gives exactly the bitrates that I am experiencing. 150Mb/s on Mint/Ubuntu and 72.2Mb/s on Manjaro (which is obviously only using a 20Mhz channel).

The wireless kernel.org docs http://wireless.kernel.org/en/users/Documentation/iw give a command to alter the mcs index of a wifi device but state that:

whether or not the device actually listens to your petition will vary depending on the device driver and cooperation from the firmware


I have tried it of course and it doesn't work, so I can only conclude that my driver or firmware is not cooperating with me :(

I also found this:

https://bbs.archlinux.org/viewtopic.php?id=161056

Which states there is a kernel bug in the 3.8 kernel (which is what I use on Manjaro) that is restricting wireless devices to a 20Mz channel only.

Moral is, don't be in too much of a hurry to update your kernel if you rely on wireless n!

Like I said a lot of information but no answers.
Fujitsu Lifebook AH532. Intel i5 processor, 6Gb ram, Intel HD3000 graphics, Intel Audio/wifi. Realtek RTL8111/8168B Ethernet.Lubuntu 13.10,Ubuntu12.10 (Unity), Mint16 (Cinnamon), Manjaro (Xfce).
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