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I am using college internet. It is shared to the whole college. My problem is that i can't even browse at sometimes because the network become too busy. But I noticed something that if I download something in IDM or axel in Ubuntu it works. When I download, I can browse also. It feels like when I start a download other applications can communicate through the busy network. Is there any way to keep the connection speed constant. without a download.

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migrated from Feb 17 '13 at 14:44

This question came from our site for system and network administrators.

up vote 1 down vote accepted

By the way that standard network communication works, without QOS or similar technologies, nothing is guaranteed and it is simply down to best effort.

As for why you are seeing what you are seeing, there is no single rule and it depends on the networking equipment you use, but basically, when under load, the majority of networking equipment simply only delivers a few percentage of the total amount of traffic it should do - whilst UDP connections (voice/skype/other) will suffer, through the magic of TCP, it will keep resending and you will get the data in the end - you just see a lot of lag.

By hammering the connection, your machine will be sending a lot more packets and will get a lot more back - e.g. 2% of 1,000,000 packets is a lot more than 2% of 500 packets... (just non technical/random example).... which is why a download manager such as IDM which specifically opens multiple connections can give you higher speeds.

In addition, as for why other stuff appears to be faster - all I can think of is that the equipment they are using prioritises traffic based on where the most connections already are.

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I've seen this with wireless networks sometimes, where leaving ping or arping running can help keep the connection stable. It can also be useful because you can switch to it and see if there's a problem - high latency or dropped packets. That might be a less abusive way to get the same effect as a running download.

Are you connected by wireless or by wires?

If you haven't already, you could mention this to your technical support. They won't necessarily know about everything that happens automatically. Especially if it's only a problem at very busy times.

If you have an ssh service, it should affect that much worse than web browsing. (Some universities offer ssh shell access as an optional service to all students). That might be something useful to point out, or to use as a demonstration of the problem.

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I suggest you to read Linux Advanced Routing and Traffic Control. It exactly solved your question.

The problem you saw is caused by some applications (particularly P2P software) uploads a lot. All Internet traffic, like HTTP, will send something outside your internal network. At least, ACK packets have to be sent to confirm your computer has already received the packets sent by remote server. And those applications will block your upload link and delay the packet you sent to external network.

Also, downloading software will generate a lot of ACK packets, this also block your upload link.

So there is two ways to solve your problem:

  • Ask others in your network to lower their applications upload speed
  • Use some firewall to resort the upload traffic in your network and put small packets first

LARTC has already publish some scripts to achieve this. You can try to install them on your gateway.

BTW: Maybe you need to buy a router which run a Linux operating system. If you can access some Chinese shopping websites, try to get a DB-120. Very cheap and efficient.

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