Networking :: Throttled Download Speeds

I have had a fairly perplexing problem with my Lubuntu Maverick installation on my laptop for the past few weeks. My laptop is connected to a DSL-based LAN via 100mbps Ethernet - pretty typical. Usually, the download speed from most websites tends to be around 340-350kb/s. However, its Ethernet connection seems to be having some strange hiccups. The speed starts out at normal ranges, but after about 5-10 minutes of internet use through any means (be it loading normal web pages, streaming video, downloading a file via a browser, or even other uses such as downloading a torrent using Transmission, or even a command line application such as apt, aptitude or wget, etc), the speed suddenly drops to around 40kb/s and will not raise again.

Once this happens, the drop is seen across the board. Again, once it happens, the speed of everything that accesses the internet is affected. Web pages load slowly, all downloads will only operate at a maximum of 40kb/s, whether it is from any browser, or wget in a terminal. The speed stayed slow until I restarted, which would give me another 5-10 minutes. My troubleshooting attempts yielded some very strange results, which I will relate here:.......