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How is bandwidth allocated on my home network? (lemmy.world)
submitted 2 years ago by to c/nostupidquestions@lemmy.world
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Hi smart people,

If I have several computers on my home network and I have not set any explicit QoS rules on my router, how is bandwidth allocated? For example, if computer 1 is downloading a torrent at max speed and a second computer starts a download, how is the bandwidth allocation between the two determined? Thanks!

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[–] [S] 4 points 2 years ago (2 children)

I see. I think I understand some of that. Thank you.

Before asking this question, I experienced a situation where I had a download going on computer 1 and then started a download on computer 2. Immediately, the download speed on computer 1 plummeted and the download rate of computer 2 increased to close to the max speed. This persisted until computer 2 finished, then computer 1's speed picked back up. I was curious why the second download would have seemingly taken precedence.

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  • [–] 5 points 2 years ago

    Latency plays a big role in throughput. If one download target was 'closer', i.e. lower latency, it will be able to scale the windowsize higher, therefore allowing more data to flow through for a given connection. Imagine network packets are envelopes and data is paper. Not all envelopes can carry the same amount of paper for a given connection, and the more paper you stuff in your envelope, the faster the transfer completes.

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  • [–] 4 points 2 years ago* (1 child)

    There are a lot of variables that could cause that situation. Were both machines on the same physical link (ethernet vs wifi)? Changes to their RTT could influence it. The only thing I could really add is that you have found the reason QoS mechanisms exist, lol.

    edit: I guess I can add this: if computer 1's download was from a host that has longer total round trip latency than computer 2's download, computer 2's download will return ACKs quicker and thus get PSH packets with data quicker than computer 1. This will lead to it filling available bandwidth more easily.

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  • [–] [S] 5 points 2 years ago (1 child)

    Yes, I think this must be it. Computer 1 was wifi while computer 2 was wired.

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  • [–] 4 points 2 years ago* (last edited 2 years ago)

    Yeah. Wifi has more latency than switched ethernet on average (and really bad worst case latency since it is a shared medium, subject to neighboring RF interference that might not even be from the network, and radios try to handle retransmits on their own).

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