Comment by pas | Hacker News Reader

Comment by pas | Hacker News Reader

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So, with TCP the speed should depend on the bandwidth-delay product (which depends on the full peer to peer round-trip latency, because it needs ACKs coming in faster than it empties the window, otherwise the sending peer just waits).

Whereas most UDP applications are constant rate, with some kind of control channel.

Bufferbloat should not matter for your home connection. (Unless it is constantly in use by more than one client.)

However, when congestion occurs and the data you sent, that sits in these buffers are already stale, irrelevant, but the problem is that there's no way to invalidate the cache on the middleboxes. And it leads to worse performance because it clogs up pipes with stale data when those pipes get full. So it prevents faster unclogging. This results in a jerk in TCP, because it scales back more than it should have without the unnecessary wait for the network to transmit the stale data.

> Bufferbloat should not matter for your home connection. (Unless it is constantly in use by more than one client.)

That is wrong. A single client can saturate the connection easily (eg. while downloading a software update or uploading a photo you just took to the cloud). Once the buffers are full, all other simultaneous connections suffer from a multi-second delay.

The result is that the internet becomes unusably slow as soon as you start uploading a file.

You can see this effect by going to fast.com.

Using my smartphone, it induces and measures > 700ms latency on my cable modem connection. That’s worse than old-fashioned high-orbit satellite internet!

I'd encourage you to get a non-Intel modem

The problem with bufferbloat is not necessarily excess retransmissions or stale data (although that does happen), it is primarily that delay significantly increases in general, and that delay in competing streams or intermittently active streams is highly variable.

Traditional tcp congestion control in an environment where buffers are oversized will keep expanding the congestion window until it covers the whole buffer or the advertised receive window, even if the buffer is several seconds of packets. There may be some delay based retransmission, but traditional stacks will also adapt and assume the network changed and the peer is expected to be 8 seconds away.

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