Eratic network speed

Question

Having erratic network speeds and have come to the end of ideas for troubleshooting. Basically I have a wired connection that when downloading files starts off slow and slowly builds speed then will suddenly die at that point it will start to speed up again and then die. This just keeps happening until the connection gives up (goes to zero and stays) or the file is downloaded. Watching the network graph looks almost like a heart monitor with its rises and drops.

The system is an MSI P6N NForce board with built in NVidia gigabyte ethernet card. The problem happens on Windows Vista and Windows 7 (RC1) but works fine when XP is used. I also have tried installing a different network card (DLINK PCI 10/100) and see the same problem.

Things I have tried...
- Turning off receive side scaling, flow control, congestion providers and a few other tcp stack settings available via "netsh"
- different cable
- different router
- reinstall both Win7 and Vista
- Microsoft provided drivers and supplied drivers both for the (Dlink and Nvidia cards)

Has anyone seen this sort of thing before? Is there anything else to try before I pull my hair out? The only thing that works is installing XP then everything runs like a champ at full speed with a solid connection.

Answer 1

Since everything works fine with XP and you've tried multiple routers we can probably rule out problems on the network.

Again, since it works fine with XP and you've tried two different network cards it's not going to be hardware problem.

Assuming you're installing the same firewall on XP, Vista and Windows 7 it has to be something about the OS itself.

Vista and Windows 7 do have a new IP stack. The only thing I can't think of to try to make them more like XP is to disable IPv6.

You can disable IPv6 either on each adapter or do it system-wide. The latter is probably the choice here. Here's a Microsoft Knowledge Base entry telling you how to do it.

Answer 2

I can suggest 3 things:

1) Disable vista's auto-tuning
netsh interface tcp set global autotuninglevel=disabled

2) Disable windows outbound firewall.
Goto control Panel->Administrator tools->Local Security Policy->firewall).
Setup your profile with a new outbound allow all rule.

3) Disable "outbound filtering" on your Anti-virus and try. If it does not work, disable AV altogether.

Answer 3

If the advice given by Dave Webb doesn't work, the problem is probably on the side of your ISP.

I would suggest in that case to call your ISP's support. They have the tools to test your line from the other side.

Answer 4

What you are seeing is the normal behavior of a TCP/IP network with only one flow travelling across it. Look at this PDF for an example of TCP's sawtooth behavior. There may not be a whole lot that you can do about this because it indicates congestion in the network which is what triggers the downswings.

For more information on TCP behavior try Googling with TCP sawtooth and you will find lots of material about it.