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I have

windows 7 x64 
VoIP Modem. 
Arris Modem. 
12Mb cable internet 
ASUS P5K motherboard with built in Atheros L1 network card.

Few month ago my downloading speed started to slow down from 12mb to ~9mb and even slow as 3mb but upload speed remained high as usual.

I did:
- windows reinstall
- network drivers reinstalled
- firewall disabled
- antivirus removed and tried several same effect
- no viruses just few tracking cookies which were removed
- modem changed to a new one
- removed VoIP modem
- called ISP support they couldn't help me either
- changed LAN cable to a new one and still same effect
- deleted every software/program which may connect and download from internet

found out:
- if my computer connected to a modem, the ping on it extremely high as 400ms with 1% of packet loss but if it is not connected to my computer the ping as low as 40-20ms no packet loss. so the modem is fine - when restarted the speed return to normal and slowly goes down again.
- when I do ping test to Ping -t 8.8.8.8 it goes from 90ms up to 130ms every 4 sec.

Qs:

Can it be my Atheros Network card bad which cause high ping?

I can buy a new one for $20 TP-LINK .

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Your diagnosis seems sound to me, it's a shame you don't have a spare PCI network card lying around somewhere to eliminate the onboard LAN as the problem without paying for a new one. But, you've narrowed the problem down to that particular computer, so swapping the NIC out is the next logical step. –  Xyon Nov 12 '12 at 12:32
    
What is your response time and packet loss to local devices? for example: have you setup a ping to your router or another local PC while pinging external hosts? It might help to compare the results. –  Kyle Nov 12 '12 at 13:34
    
Can the modem connect to your USB port? –  Louis Nov 12 '12 at 14:29
    
If the network card was the culprit, ping to the router itself would get bad as well. You should test that. –  David Schwartz Jul 5 '13 at 22:13
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1 Answer

We had this exact same problem and yes it can cause what you are seeing. Changing out the card is quick and easy. Might consider a gigabit card if you have to replace it. I usually carry a spare card cause you never know where you will find a problem with one. If that is not it, at least you have a spare now but it sounds like the card is to blame.

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