Comment by digitallyfree | Hacker News Reader

Comment by digitallyfree | Hacker News Reader

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Yeah, the hop to the internet exchange point is the main issue with DSL or cable. I live in a major city and it takes around 10ms to hit the internet exchange point (using Ethernet the LAN latency is neglegible) and thus I get a minimum of 20ms or so just connecting to a server hosted by someone in the same neighborhood. I've actually tried this experiment with some of my nearby friends - pinging each other's public IPs on DSL or cable takes around 20ms.

With fiber, you can hit the exchange point in 1-2ms. So I suppose this tool would work well fine over fiber assuming everyone is in the same city. I've even heard of people successfully using protocols like Dante (professional audio over IP intended for LAN) over gig fiber lines as well.

From my experience, a couple milliseconds of latency is fine for keyboard or guitar processing, but anything more than that starts to mess me up. There are artists who insist on using a full analog chain for monitoring for that reason, and refuse to use digital mixers or digital wireless systems that can add several ms of latency.

Why does fiber have lower latency to the exchange than copper? That surprises me.

I thought that ISPs generally run fiber for most of the distance, and coax is only used for the last few hundred meters. The speed of signal propagation is actually faster in copper than fiber, but nobody (afaik?) does long runs over copper so it’s a moot point.

Yes the ISP runs fiber to the DSLAM or the CMTS, and copper is used for the final hop to your home. The latency comes from the buffering and processing required to get a clear signal over copper - for DSL I think you can get in a perfect scenario 7ms or so with fastpath, more if you use interleaving. For fiber you can pretty much treat it as like an Ethernet connection, with latency determined almost solely by distance.

Yup I remember fastpath, it's a choice of low latency vs higher bandwidth. I'm not sure if ISPs still actually bother offering this option to end users anymore though? I mean it's all turned into scripted tier 1 support nonsense if you call an ISP these days.

I had to specifically ask for fastpath for my DSL connection, without it I get around 35ms to the exchange. You however do need a decent connection to the DSLAM for it to work properly without packet loss. You can get the same bandwidth over fastpath as interleaving if the line is clean.

woah what is this fastpast magic ?!

Ahhhh interesting - so the latency comes from the noise in copper, which forces you to do extra work, which adds latency per bit? That makes sense - thanks!

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