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 |
4 Answers:
problem was fixed by updating the network driver which was released one day after the original post answered 25 Mar '11, 12:43 net_tech |
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 :-) answered 09 Mar '11, 07:40  Jasper ♦♦ |
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 answered 09 Mar '11, 18:14 net_tech |
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. answered 15 Mar '11, 06:31  GeonJay 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 |
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.
Thx for the additional info, I was just too lazy to calculate as precise as you did, I just did 6 times 8 :-)
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?