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0 pointsBugsJustFindMe1y ago0 comments

You don't need a new roundtrip for every packet. That would be devastating for throughput. One vs two vs three file packets get acked as a batch either way, not serially.

Also when you get to the end, you then see

> The actual savings here are moderate: the original is 88 KiB with gzip, and the WebP one is 83 KiB with gzip. In contrast, Brotli would provide 69 KiB.

At 69 KiB you're still over the default TCP packet max, which means both cases transmit the same number of packets, one just has a bunch of extra overhead added for the extra JavaScript fetch, load, and execute.

The time saved here is going to be negligible at best anyway, but there looks to be actually negative because we're burning time without reducing the number of needed packets at all.

0 pointsBugsJustFindMe1y ago0 comments

You don't need a new roundtrip for every packet. That would be devastating for throughput. One vs two vs three file packets get acked as a batch either way, not serially.

Also when you get to the end, you then see

> The actual savings here are moderate: the original is 88 KiB with gzip, and the WebP one is 83 KiB with gzip. In contrast, Brotli would provide 69 KiB.

The time saved here is going to be negligible at best anyway, but there looks to be actually negative because we're burning time without reducing the number of needed packets at all.

0 comments

5 comments · 1 top-level

jsnell1y ago· 4 in thread

Those numbers are for a different page. For the original page, the article quotes 44 kB with this method vs. 92 kB for gzip.

> At 69 KiB you're still over the default TCP packet max, which means both cases transmit the same number of packets,

What? No, they absolutely don't transmit the same number of packets. Did you mean some other word?

mananaysiempre1y ago

I expect what GP meant is the default TCP window size, so in a situation where bandwidth costs are dwarfed by roundtrip costs, these two cases will end up taking essentially the same time, because they will incur the same number of ACK roundtrips. Don’t know if the numbers work out, but they at least sound plausible.

jsnell1y ago

No, there is no way the numbers would work out to the same number of roundtrips. The sizes are different by a factor of 2.5x, and the congestion window will only double in a single roundtrip. The only way the number of roundtrips would be the same is if both transfers fit in the initial congestion window.

BugsJustFindMeOP1y ago

Yes, sorry

codetrotter1y ago

They were probably thinking of the max size for packets in TCP, which is 64K (65535 bytes).

However, Ethernet has a MTU (Maximum Transmission Unit) of 1500 bytes. Unless jumbo frames are used.

And so I agree with you, the number of packets that will be sent for 69 KiB vs 92 KiB will likely be different.

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