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I am hopping to get some advice on where to look for a problem with a file transfer over WiFi. This is a somewhat simple office set up. Cable Modem ->10/100 Router->10/100/1000 Switch with jumbo frames enabled. Wireless DWL-3200AP (D-Link) access point is connected to a router. Wired computer is connected to a switch over 1Gb. Wireless IBM X201 laptop has a b/g/n realtek (RTL8192SE) network card & connects to D-Link access point over G and shows 54Mb connection spped. Both computers run windows 7 and average 70MB/s file transfer speeds when they are connected to the switch. Once IBM goes wireless file transfer speeds are anywhere from 2MB/s to 2.5MB/s, I was expecting to see at least 6MB/s watching a 1GB file being copied. Wireless signal strength is not an issue. I am sitting right next to the AccessPoint.

Do I need to purchase AirPcap to troubleshoot this problem?

If I filter for tcp.analysis.flags while transferring a file over wifi I don’t get any packets displayed. None of the Wireless card settings have been changed, everything is set to factory defaults. Access point settings have not been tweaked other than security.

Thank you

asked 09 Mar '11, 07:32

net_tech's gravatar image

net_tech
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accept rate: 13%


problem was fixed by updating the network driver which was released one day after the original post

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answered 25 Mar '11, 12:43

net_tech's gravatar image

net_tech
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accept rate: 13%

If you have a problem on the "physical" wireless level and need to beacon frames etc. you might have to buy an AirPCAP adapter if you want to use Wireshark on Windows to look at things. With Linux you should be able to activate monitor mode yourself and use the internal WiFi adapter instead. That way you could find out if there are problems on the radio transmission layer.

I have to say I'm just a bit surprised that you expect 6MB/s on a 54MBit WiFi connection. 6MB/s would mean 48MBit/s, and I doubt you'd ever get that much data over a 54MBit connection. 2.5MB/s doesn't sound that unrealistic to me - WiFi isn't exactly good at getting up to maximum speeds :-)

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answered 09 Mar '11, 07:40

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Jasper ♦♦
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2

Actually, 6MB/s goodput would be 6*1024*1024*8*(1514/1460)/1000/1000 = ~52 Mbit/s... And that's on a fullduplex link and wireless is half duplex.

Apart from the maximum good-put rate on a streaming protocol, it was mentioned that the file was copied. Windows copies files per block and there is an application turn (and thus a roundtrip) between each block that can add up pretty quickly too.

(09 Mar '11, 08:45) SYN-bit ♦♦

Thx for the additional info, I was just too lazy to calculate as precise as you did, I just did 6 times 8 :-)

(09 Mar '11, 09:06) Jasper ♦♦

Jasper, I went back and tested again. With a built-in realtek adapter I am only getting 800KB/s during a file transfer, however if I insert a USB adapter and disable the built in I am getting 2.8MB/s. I did not realize that WiFi is half duplex, so I guess 2.8 – 3 Mb/s is all I can wish for.

What would you look for in the wireshark capture that may be an indication of a slow throughput using the built in adapter? At this point it does not look like the problem is signal related. Driver or Nic configuration perhaps?

(14 Mar '11, 07:04) net_tech

here is the AP's config

D-Link Access Point wlan1 -> get config

wlan1 revisions: mac 5.8 phy 4.4 analog 4.6

PCI Vendor ID: 0x168c, Device ID: 0x13

Sub Vendor ID: 0x168c, Sub Device ID: 0x13

chip is AR2312

Country Code: US

Operation Mode: Access Point

Wlan State: Enabled

Radio Frequency: 2437 MHz (IEEE 6)

Wireless LAN Mode: 802.11g

Auto Channel Select: Enabled

Extended Channel Mode: Enabled

Data Rate: best

Antenna: best

Login Username: admin

RADIUS address:

Name server IP address:

Name server domain suffix:

SSID: WL02

SSID Suppress Mode: Disabled

System Name: D-Link Access Point

Beacon Interval: 100

DTIM: 1

Fragmentation Threshold: 2346

RTS/CTS Threshold: 2346

Short Preamble: Enabled

11g Only Allowed: Disabled

CTS Mode: AUTO

CTS Rate: 11 Mbps

CTS Type: CTS-ONLY

11g Overlapping BSS Protection: Disabled

11g Beacon Rate: 1 Mbps

11g Draft 5.0 compatibility: Disabled

Short Slot Time: Enabled

Basic 11g Rate Set: (1, 2, 5.5, 11)

11g Optimization Level: 1

Burst Time: 2

Burst Sequence Threshold: 3

IP Address: 192.168.50.50

IP Mask: 255.255.255.0

Host IP Address: 0.0.0.0

Gateway IP Address: 192.168.50.1

SNTP/NTP Server IP Address: 192.168.50.5

Time Zone: 14

HW Transmit Retry Limit: 4

SW Transmit Retry Limit: 3

TransmitPower: full

Current Transmit Output Power 21.0 dBm

SuperG :Disabled

Encryption: Enabled

Cipher selection: AUTO

Authentication Type: WPA2-PSK

Default transmit key: 1

Shared Key 1, size 40, 0000000000

Access Check: Disabled

Key Entry Method: hexadecimal

Group Key Update Interval: 1800 seconds

Key Source: server

Aging Interval: 300 seconds

Telnet Access: Enabled

Telnet Timeout: 180 seconds

Minimum rate: 1 Mbps

XR Poll interval: 100 msec

XR Frame Limit: 25

XR Poll Rate String is 0.25 1 1 3 3 6 6 20

XR Fragmentation Threshold: 540

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answered 09 Mar '11, 18:14

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net_tech
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accept rate: 13%

Just to nit pick - You should consider your RF environment. How many other radios are operating in your area on the same, or neighboring frequencies? Even if you're on a different SSID you STILL share the medium (is this case medium = radio frequency). If you're in the US you really only have 3 separate frequencies or "channels": 1, 6, and 11. If you have an android or iPhone run a wifi analyzer and see how many neighboring SSIDs you can see. Note which of the above channels is LEAST used and set your AP up to use that channel. Don't set yourself up to use the other channels: 2-3 bleed over into 1; 4,5,7,8 bleed into 6; 9, 10, 12, 13 bleed into 11. It's a big ol' mess.

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answered 15 Mar '11, 06:31

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GeonJay
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accept rate: 5%

Auto Channel Select: Enabled

Access Point monitors the environment and selects the best channel. Also all neighboring APs are added to the rogue AP list.

(15 Mar '11, 06:41) net_tech

Just my 2 cents - don't let it self adjust and jump frequencies on you. I don't think there's really a standard for this, and you don't want your AP jumping frequencies in the middle of a transfer.

(15 Mar '11, 08:02) GeonJay
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question asked: 09 Mar '11, 07:32

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last updated: 25 Mar '11, 12:43

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