I have been having this problem for a while now. Basically when I download something on the server, the download speed is very unstable. When I'm downloading something of the internet, not in local, the download speeds vary 19kb to 200kb. In lan, it starts at 11mb then goes down to 6mb gradually then just keeps fluctuating. How should I fix this problem? Is there a way to tweak the network card?

So you have used a www-browser to download? Browsers often show false downloads speeds, for example 1000MB/s which soon drops down to the real download speed.

Try this to see if you really do have inconsistent download speed:

time wget http://www.site_near_me.com/a_very_large_file.tar.gz

The "time" -command will show how many seconds it took to download that file. You can also watch wget's download speed to see if it fluctuates. Try this a couple of times and with different sites to see if you really have a problem.

I have not tumbled into any real transfer speed problems with any network card in linux.