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My ISP has installed a fibre based dedicated internet connection at the place where I work. In the beginning the connection terminated at one of the ISP's core routers. It resulted in a strange issue. Eventhough the assigned speed was 5mbps, when tests were done by downloading large files over http and ftp from multiple locations, the speed never went above 2mbps. But bittorrent downloads reached 5mbps. Even file download from the ISP servers were fine. So, at the ISP our link was attached directly to their edge router. After this file downloads from high bandwidth servers, like Google and MS, reached the 5 mbps limit. Sometimes the speed would fall down below 2 mbps and suddenly it will go up to the 5 mbps limit ( it keeps on happening during any single file download). But other downloads like ubuntu apt repositories still struggle to go above 2 mbps. The engineers at the ISP have not been able to sort out the issue.

After they moved us to their edge router instead of giving us 8 public ip's, they just gave 4 ip's. When we enquired about it, they told us that giving more ip's would result in arp overload at their edge router. But somehow I was able to convince them to give us the 8 ip's which we wanted. But the file download issue has remained. What might be the reason for files from different location getting downloaded with different speeds, that too with heavy fluctuation in speeds? I have downloaded files from same url's from a connection belonging to another smaller ISP, and the speeds were fine and reached full 5 mbps limit.

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Ahhhh! My eyes!!! Please re-phrase this coherently! – Ward Jun 24 '11 at 18:30
up vote 5 down vote accepted

Odds are the sites that you were downloading from had an issue, or there was some problem in between. Just because you have a 5Mbit link doesn't mean you can actually download a file from a site at 5Mbit. It means you can transfer data over the link at up to 5Mbit.

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For the past 2 years we had a connection from a different ISP. We never had this issue then. When I did a dist-upgrade on a ubuntu box, I used to get the specified speed. But with the current ISP it is much lower. – nixnotwin Jun 25 '11 at 0:29
Sounds like their upstream link is saturated. Your link to them may have 5 Megs of bandwidth available, but their link to the net may not have 5 Megs of bandwidth available. – mrdenny Jun 27 '11 at 22:28
Yes your view seems to be correct. The download url which used to give same speed with the former ISP's connection, now gives different speeds at different times. The current ISP engineers think that everything is fine on their side, so I'm looking for a way to prove that their upstream bandwidth is saturated. – nixnotwin Jun 30 '11 at 5:58
Try doing a traceroute (tracert in Windows) to see where the latency is. There's a few tools out there (or at least there used to be, but I don't remember their names) that would help show you network latency between you and the remote server you were connecting to. – mrdenny Jun 30 '11 at 20:44

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