What could cause a network interface to intermittently drop?

Question

I bought a new computer (ASUS CG5270) last week. It would randomly shut itself off, so I returned it and got a replacement. This one doesn't have that problem, but seems to be malfunctioning.

It came with a wireless N card but I'm not using that because I don't have a wireless N router. During the initial setup, I noticed that roughly every minute or so the network activity went flat. I confirmed this by watching the "Networking" tab in task manager; I'd see the connection's utilization hover around whatever percent for a while then drop to 0 for about 10 seconds, then spike back up. This caused a lot of troubles with apps that didn't handle it well. It also makes sites that stream a lot of data like Youtube and last.fm completely unusable. For some reason, it doesn't mess with my VPN client and I'm able to access my work computers via Remote Desktop with no real troubles.

I reinstalled the driver for the device this morning. It reports itself as a Realtek RTL8168B/8111B/8112 Family PCI-E GBE NIC. Reinstalling the driver seemed to work for a couple of hours, but tonight when I watched some Youtube videos they would all lock up and refuse to start playing again after about a minute.

I feel like this is something wrong with my machine because my XBox 360 still works fine and my wife is able to watch Youtube and use last.fm from her laptop with no troubles. This seems to exclude the router and modem from suspicion.

I'm not very experienced with troubleshooting and diagnosing hardware problems. I'm going to try disabling the wireless interface to see if it's interfering. If that doesn't work then tomorrow I'm going to buy a network card, install it, and see if that solves the problem, but I'm curious if I can save myself the trouble and money. I'd love to return this one and try another PC (different brand and model this time) but I think this malfunction won't merit a return in Best Buy's eyes and honestly I'm tired of spending evenings reinstalling all of my software. Are there some settings I could mess around with that might resolve this problem? Has someone else encountered something similar and fixed it?

The only relevant system specification besides the model of network card I can think of are I'm on Vista Home Premium 64-bit.

Answer 1

It turns out the problem is Vista was trying to help. In the settings for the network card, I found a checkbox for the setting "Allow Windows to turn off this device to save power." The setting was checked. Unchecking the setting seems to have made my problems go away; today I've used Youtube and iTunes radio stations with no problems.

Answer 2

Beside checking the driver and all what you did, I would have a look at the MTU value. When set to a wrong value it causes a slowdown, in some cases I read that the ISP might also disconnect (I've never had this case thought). If you have DSL it should be 1492 or less. (maybe it is set to 1500 on Vista by default?).

To discover your current MTU value you could use the Ping technique and to set it I would advise to use the registry (the drivers are quite different for each NIC some allow the setting, some not...)

I hope it is a good advice otherwise I would try also to rollback to an older driver, that also helps sometimes...