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Old 07-03-2016, 06:42 AM   #1
Thomas Korimort
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Low data transfer rates on Debian Linux Jessie due to kernel bandwidth settings?


Hi,
i have a RaspBerry pi 2 connected to my home network as a server. Data transmission rates should be at n speeds throughout all my devices. Actually, the router-pc connections are very fast as it should be for my 30 MBit/s line. Also multiple devices at once are nicely served by our router. However, inside the home network the connection speeds from device-router-device are around 2 MBit/s, but it should be 802.11n standard speeds. What can be the reason for this. "ifconfig wlan0" gives on my RaspBerry Pi

Code:
Link encap:Ethernet  Hardware Adresse 74:da:38:33:97:3c
          inet Adresse:192.168.1.2  Bcast:192.168.1.255  Maske:255.255.255.0
          inet6-Adresse: fe80::76da:38ff:fe33:973c/64 Gültigkeitsbereich:Verbindung
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metrik:1
          RX packets:97403 errors:0 dropped:9144 overruns:0 frame:0
          TX packets:102693 errors:0 dropped:1 overruns:0 carrier:0
          Kollisionen:0 Sendewarteschlangenlänge:1000
          RX bytes:25620755 (24.4 MiB)  TX bytes:97532401 (93.0 MiB)
It shows that a large amount of the RX packages are dropped. Signal quality is good:

Code:
wlan0     IEEE 802.11bgn  ESSID:"3HuiGate_5818"  Nickname:"<WIFI@REALTEK>"
          Mode:Managed  Frequency:2.432 GHz  Access Point: C8:51:95:98:58:18
          Bit Rate:72.2 Mb/s   Sensitivity:0/0
          Retry:off   RTS thr:off   Fragment thr:off
          Power Management:off
          Link Quality=100/100  Signal level=75/100  Noise level=0/100
          Rx invalid nwid:0  Rx invalid crypt:0  Rx invalid frag:0
          Tx excessive retries:0  Invalid misc:0   Missed beacon:0
Thus my suspicion is that the kernel bandwidth managment that is included in the kernel since version 2.2 limits the connection speed. As far as i have learnt this can be adjusted by tc command, but i have not learned yet how to use that program. How can i see why those RX-packages are dropped? And how can i get finally higher home network speeds for my RaspBerry Pi 2 Linux Jessie miniDLNA server?
 
Old 07-04-2016, 02:14 AM   #2
ferrari
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Some more analysis is needed. Wireshark or tcpdump might be useful to see what actually is getting dropped (eg invalid packets?). Do you have a firewall in the mix? What does the following report?
Code:
ethtool -S wlan0
You might also conduct some useful BW testing with iperf. You'll need to set up one machine as a server and the other as client for testing.

References:
https://access.redhat.com/solutions/657483
http://www.linuxquestions.org/questi...1/#post5192737
 
Old 07-04-2016, 02:50 AM   #3
Thomas Korimort
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ethtool and iperf

I have tried ethtool, but it does not like my netwok driver it seems "ethtool -t wlan0: operation not supported", "ethtool -S wlan0: no stats available"

iperf i had used already before to determine my home network speeds of 2 MBit/s from my RasPi 2 to my Win 10 PC via the router it seems (802.11n).

Also my WLAN connection to my RasPi breaks often. Before it used to run stable after switching of power managment in wpa.conf and setting the parameter "options 8192cu rtw_power_mgnt=0 rtw_enusbss=0" in /etc/modprobe.d/8192cu.conf . Recently, again there was a lot of problems with the WLAN connection stability. I thought it was the Google DNS-servers being down often and replaced them by other DNS servers. Now again it seems to work better. For some time, the RasPi was not even useable as print server, since the WLAN connection always had to bechecked an there was more than 50% of chance that it was down when you needed it.
 
Old 07-04-2016, 05:13 AM   #4
ferrari
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Well, a quick test to eliminate wireless issues would be to connect via wired ethernet instead and conduct the same throughput tests. Interference is a likely cause of disconnections and throughput issues, so you should check for other nearby APs on same or adjacent channels.
 
Old 07-04-2016, 05:54 AM   #5
Thomas Korimort
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I used "WifiAnalyzer" on my Android Tablet to check for Wireless connectivity. Since we live in a flat there are several Wifi networks around, but they are all of weak signal through the neighbouring walls and the signal of my own network is not much disturbed. Only sometimes the channel is changed automatically. But should this really break my WLAN connection on RasPi RaspBian Jessie Linux/Win10? Already some time before in my parents home, where only one WLAN was in the environment it was same results with my RaspPi only delivering 2Mbit/s with very high signal strength (75%). And also only RX packages are dropped not TX and no errors are reported. According to my opinion this points to an issue with bandwidth policies of the kernel module responsible for bandwidth management. But i have no clue how to use the tc command and whether this is the proper thing to be adjusted in the kernel settings.

Concerning miniDLNA, it should compress my JPEG for transmission over the internet from 5 MB to approx. 200-400 KB with the option "strict_dlna" set to "yes". But it does not do that it seems and therefore slideshows in my homenetwork over miniDLNA are not possible due to loading time of one pic of around 10 secs.

Last edited by Thomas Korimort; 07-04-2016 at 05:57 AM.
 
  


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