Comment by retired

10 hours ago

What about overhead? Can you truly do 10Gb/s networking on a 10Gb/s USB port? Would having such NIC on a 20Gb/s USB port not result in higher speeds?

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retired

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adrian_b  7 hours ago

Both 10 Gb/s Ethernet and 10 Gb/s USB have bit data rates that are 3% lower than 10 Gb/s, due to encoding (64/66 bits for Ethernet, 128/132 bits for USB).

So the their maximum speed is approximately 9.7 Gb/s.

Then for Ethernet there is a protocol-dependent overhead, e.c. depending on whether TCP or UDP is used, and depending on whether standard packets or jumbo packets are used.

The TCP overhead can reach in the worst case up to close to another 3%, reducing the achievable TCP throughput to around 9.4 Gb/s.

The USB frames add some extra overhead, but it is normally not important in comparison with other factors that can reduce the throughput.

All that a 20 Gb/s USB port can do is to reduce the overhead of the USB frames, but that is a negligible improvement. Using jumbo Ethernet frames (which are 6 times bigger than standard frames), if both ends support them, is likely more useful for increasing the throughput, than using a 20 Gb/s USB port.

  • davrosthedalek  6 hours ago

    10 Gig ethernet is 10GBps usable rate (before packet overhead). The line rates are higher to accommodate this. For 10GBase-R, it's typically 10.3125 GBps, with a 64/66 encoding. For 10GBase-T, it's 4 lanes with PAM-16 at 800 MBaud -> 12.8 Gbps raw.

matt-p  9 hours ago

It uses 128b/132b encoding so 10Gb/s USB ≈ 9.69Gb/s you do then have USB framing overhead but it's probably around 2% on typical 1500B ethernet frames. So all in you are losing probably 5% or so to overhead.

I am of the opinion that 5Gbe is a much more sensible speed for a laptop adapter right now as it uses half the power and can obviously run full wack on 10Gb/s USB so you're looking at like 5Gbe vs ~9.4Gbe.

  • namibj  7 hours ago

    Stop insisting on Cat.6A (and related) copper cables for speeds beyond 1000BASE-T (maybe beyond 2.5G by now), just use dumb multi mode fiber it's way easier technology-wise and if you want power you can have that as well.

    At distances where Cat.6A is even an option the demands on the fiber are very low. And it uses less power than the BASE-T PHY. The cable at least without integrated power is very thin as well, unless you can't respect it enough to not kink it, in which case you'd want a thicker one just to prevent you from being able to break the fiber.

    • BenjiWiebe  1 hour ago

      In fact, just to for single mode fiber. Looking on fs.com, single mode cables are slightly cheaper, and the optics (for 10G) are $30 to MMF's $25.

      And you get much better future proofing with SMF. And if you do need a long fast run, SMF is what you want.