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I recently switch from a Time Warner 10/Mbps cable connection to a Verizon 75/Mbps fiber optics connection (FIOS) and have noticed some interesting things speed-wise. I use a program called GrabIt to download items from newsgroups which basically just downloads multiple parts in parallel.

I've noticed that with my new FIOS connection when I have 50 files downloading in parallel my speed maxes out at around 10 megabyes per second, which is very fast and perfectly fine. But once it is downloading only one part the speed will drop to around 200 kilobytes per second, which is very very slow to say the least.

Previously with my cable connection the number of parts being downloaded never affected the rate at which the download was occurring. Any idea what might cause this?

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closed as off topic by ceejayoz, David Schwartz, TomTom, mulaz, Skyhawk Jan 9 '13 at 18:57

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Read the FAQ, please. ServerFault isn't for troubleshooting downloading movies off your home internet... – ceejayoz Jan 9 '13 at 18:50
up vote 2 down vote accepted

Verizon FiOS uses PPPoE which reduces the effective max transmission unit (MTU). Because of this, your TCP packets are being fragmented which has a negative impact on performance. Multiple TCP streams will maximize your throughput; however, assuming you have a simple network setup, set your MTU to 1492 to optimize your single TCP stream.

Your TCP Window settings may also be a problem.

See FiOS TCP/IP Settings.

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I'd say that the source may be throttling your connection for some reason. Also remember that the speed between two points on the internet may vary from time to time due to problems or routing.

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