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The speed of light in a fiber optic cable is slower than light in a vacuum, about 2.14e8 m/s. If you feel latency, it's probably not the one-direction or round-trip latency, but rather the MANY round trips that are typically required for an HTTP request. DNS is probably 2 round trips (CNAME then A), and that has to cross the ocean via your resolver of choice (8.8.8.8 or whatever) to get to the authoritative server if it's not already cached (or distributed; big DNS providers will serve your zone in many regions). Then you have to set up a TCP session, which is 1.5 round trips. Then you have to set up TLS, which varies, and make an HTTP request, and wait for the response. (I counted 5 total round trips until you see the response.) So basically if you calculate the speed of light between two points, multiply that by 2*(2+5) = 14 in the worst case to see your time to first byte. Doing something 14 times is always going to be slow. The underlying issue here is not so much the distance, but rather that TCP, TLS, and HTTP don't care about latency at all. (I'll ignore the application layer, which probably wants to redirect you to /verify-session-cookie and then /hey-you-logged-in for some reason. And yes, TLS1.3 has 0RTT handshakes now too, eliminating some trips.) This is the problem that HTTP/3 aims to fix; one round trip replaces the TCP handshake, TLS handshake, and HTTP request. You shoot out a packet, you get back an HTTP response. (You still have to do the DNS lookup, so we'll call this 3 round trips total.) |
To add to your post, don't forget TCP congestion window scaling, which will add some more roundtrips - this mostly depends on the size and bandwidth of the ressources, so smaller sites like HN have an advantage here. Especially if the initial ressources fit within the initcwnd (10*MSS, usually around 15kb). But this, like many of the parameters you mentioned, are highly flow- and also software specific, it becomes so hard to make meaningfull predictions.