Wireless at dial-up speeds on 802.11b, normal in 802.11g and Windows (Ubuntu Edgy)

Xucel · 01-27-2007, 11:49 AM

I have an hp dv2000t laptop with Intel 3945 wireless chipset. Running Ubuntu 6.10 Edgy, wireless support came out of the box with the ipw3945 driver.

Problem:
Internet on 802.11b runs at worst than dial-up speeds, even though iwconfig reports a good link quality above 75% and a connection at 11 Mb/s. It seems to lag when performing a network command, pinging google gets through with pings ranging from 60-70 ms, but each ping seems to be separated by a long pause. Loading a page in firefox might require a few seconds to begin loading.

On 802.11g speeds are completely fine. In Windows (this machine has dualboot XP), speed is fine on both 802.11b and 802.11g.

Running on an open campus network with no encryption. The campus has g in the technology building and b in other areas.

Attempted Solutions:
- Tried disabling ipv6 by adding a "noipv6" in /etc/modprobe.d with the line alias net-pf-10 off.
- Ubuntu already found the correct DNS servers, which showed up under System -> Administration -> Network Settings.

Thanks for your help.

basileus · 01-28-2007, 02:03 AM

Try pinging a server for a long time and see how high your packet loss is. If there are long pauses between pings it usually means that some packets are dropped. The problem is most likely caused by some incorrect iwconfig settings. If you can't modify these from Networkmanager or some other GUI, see "man iwconfig" and "man ifconfig" and play around with different settings to see if it makes a difference.

Xucel · 01-28-2007, 07:37 PM

Hrm here are some statistics:

Quote:

eth1 Link encap:Ethernet HWaddr 00:13:02:B5:76:10
inet addr:128.237.232.107 Bcast:128.237.255.255 Mask:255.255.224.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:41687 errors:0 dropped:9339 overruns:0 frame:0
TX packets:558 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:47349446 (45.1 MiB) TX bytes:151888 (148.3 KiB)
Interrupt:193 Base address:0xe000 Memory:d6000000-d6000fff

RX packets: 41687 dropped: 9339
TX packets: 558

The transmission ratio is ridiculous here. 45.1 MiB vs. 148.3 KiB. In terms of web pages browsed during this time, it most certainly did not add up to 45.1 MiB, so that must have resulted from high packet loss. They should be closer. In windows the transmission ratio is much closer to 1 (e.g. 10,745 / 8808).

A ping to google shows:

Quote:

30 packets transmitted, 27 received, 10% packet loss, time
81729ms

Again 10% packet loss.

But what makes this most unusual is that I'm about 4 meters from the AP. And:

Quote:

IEEE 802.11b ESSID:"CMU"
Mode:Managed Frequency:2.437 GHz Access Point: 00:02:2D:29:FB

4
Bit Rate:11 Mb/s Tx-Power:15 dBm
Retry limit:15 RTS thr

ff Fragment thr

ff
Power Management

ff
Link Quality=89/100 Signal level=-46 dBm Noise level=-47 dBm
Rx invalid nwid:0 Rx invalid crypt:0 Rx invalid frag:0
Tx excessive retries:0 Invalid misc:9569 Missed beacon:0

Link Quality is at 89/100. Invalid misc seems to correspond with the number of dropped packets.

Is there a reason why the driver keeps dropping packets? I think I read that invalid misc occurs when a frame/packet fails a checksum. Is there a way to disable this?