Why does my computer hog so much bandwidth?
 

Hey guys, we have two macs running Tiger connecting to our Airport Express base station, one upstairs above the base station, and one on the same floor. Whenever I connect the upstairs computer to the internet, I get a really good speed, but the downstairs computer just slows to a trickle. The moment the upstairs computer switches off, the downstairs computer gets normal speeds again. I don't understand why - I've been away for 6 months and before then it was perfectly fine. The moment I came home, the problem started. Is it likely to have been a software update, or is it because the base station has been moved? Can anyone help me out?

Have you tried checked to make sure the channels are different from each other and different from any other WiFi routers in the area? You can use the free app iStumbler on your WiFi enabled Macs to check the channels.

We've changed channels to both 6 and 11, and it's made no difference whatsoever.

Run "Activity Monitor" and look at the Network tab at the bottom - it will show you how much bandwidth the Mac is using. Tell us what the numbers say.

It's almost instantaneous - I connect the upstairs computer (iMac) to the internet, and the downstairs computer (Mini) loses all the bandwidth. The funny thing is that if I switch the Airport card on the iMac off, it doesn't "release" the bandwidth - the Mini's still struggling. I have to shut the iMac down before the Mini goes back to normal.

Ok, the iMac is currently just doing nothing, and the stats read as follows:

Packets in 747, Packets out 847.
Data received 476.52 kb, Data sent 153.99
Packets in/sec 0, Packets out/sec 0
Data received/sec 0, Data sent/sec 0.

The Mini is broadcasting Airtunes (well, attempting to and failing), and the stats are:
Data received/sec 2.05 KB
Data sent/sec 186.58 KB

I switch the iMac off, Airtunes works perfectly.

That suggests that it's not really bandwidth that is the problem.
(Unless maybe your iMac has some other connection (e.g. Ethernet) to the network.)


That confirms that bandwidth is not the problem since the iMac is not using any - the last two lines say that it is not using the network at all at the moment.

Is the problem only with AirTunes? E.g. try downloading a big file (like a movie trailer from the Apple site) on the Mini to see what bandwidth it gets.

Ok, when downloading a large file, the iMac can get an average d/l speed of 450 KB per second, and with the iMac on, the Mini gets between 30-140 Kbps. When the iMac is off, the Mini can get up to 250 kbps.

The Mini uses an Airport Extreme card and the iMac is using the old Airport card. The Express is the old 2004 version.

You are using two different units in the above. Did you intend to do so? I.e. kilobytes one place, but kilobits the other places?
If you really meant kilobits in reference to the Mini's speeds, that is indeed quite slow. I'm assuming that you have a broadband Internet connection - usually at least 1 Mbps.

Sorry, those are whatever the units are in the Activity monitor. They're all the same units. I wasn't actually sure whether they were kilobytes or kilobits.

Yes, we do have a broadband connection.

I'm confused now since the Network tab of Activity Monitor does show the units - e.g. see the attached screenshot (from my Leopard machine).

We need to know the units - there is a large difference between kilobytes and kilobits

It was KB. I presume that is kilobytes?

Yes - KB (capital B) is kilobytes.
But please tell us the numbers again and supply more details this time - e.g. tell us both the "Data received/sec" and "Data sent/sec" numbers.
Even better, show us screenshots of the Network tab of the two machines at appropriate moments.

I have attached a picture from the iMac. It was getting downloading between 200-500 KB per sec typically.

And this is the screenshot from the Mini when the iMac is on.

And this is what it looks like when the iMac is off. I have to say, it almost looks like the Mini can't download more than 250 KB/s, which seems odd.

You showed us the numbers when the iMac is off - but what about when the iMac is on, but its Airport card is off?

The iMac is (you said) using the older Airport card and this is known to decrease the speed of a "mixed" network (802.11b & 802.11g) so it's not too surprising that there is some effect when the iMac's Airport card is active.

It appears that when the Airport card is switched off, the Mini still gets around 250KB/s. I find it strange to think there is such interference when the old Airport card is on because this has not been a problem until recently, and furthermore, I wouldn't have expected the newer card to be slower than the older one!

We've changed the base station to broadcast only on 802.11b instead of both b & g, and that seems to have fixed it. I wonder why the Airport Extreme card only d/l a maximum of 250 KB/s whereas the Airport card is much faster?

Maybe the Mini (with the newer Airport card) is in an area that gets more radio interference compared to the iMac.

iStumber (istumbler.net) can show you this - run it on each of the two Macs and compare.

Yeah, I ran iStumbler before, and the iMac was getting around 60-70% signal and about 50% noise, and for the Mini, that was getting more like 30% signal and 5% noise. I'm not quite sure how those particular results will affect anything.

Turns out our broadband is supposed to be "up to 2Mbps" which just begs the question "why is my iMac downloading so quickly?!" I am so confused!

Thanks for the help though, Haynes.

my initial instinct is that you have a conflict of some sort (e.g., I've seen this sort of thing happen when two computers on a lan accidentally get assigned the same address). just a thought, anyway.