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I want to run a 90m cable from my main router to a host. It will work, as 90m does not exceed the maximum length allowed.

Router --(50m)--> Switch --(40m)--> Host A

If the cable is long or has a lot of interference, a switch in the middle is definitely required as a booster/repeater. However, is it better to put one in the middle in my case?

I could also run 2 separate wires like this. It is more expensive and harder to maintain I must admit:

Wire 1: Router --(50m)--> Switch
wire 2: Router -----------(90m)-----------> Host A

I am not asking how to design my network. My question is: which is better in term of signal quality (bandwidth and latency)?

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    "90m does not exceed the maximum length allowed." That depends. If it is a horizontal cable run using solid-core cable, then that works for wall plate to wall plate, then you are allowed up to 10 meters of stranded cable patch cords that you can use to connect the devices to the wall plates. What does not work is a 90 meter stranded cable patch cord. If properly installed and tested (using an expensive, professional cable tester) to the cable category specification, you should have no problems.
    – Ron Maupin ♦
    Commented Apr 21, 2020 at 4:11

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which is better in term of signal quality (bandwidth and latency)?

Bandwidth, latency, and signal quality are all different things.

Provided your cable actually meets the specifications (as Ron M. has pointed out in his comment, stranded patch cable at that length doesn't), the signal quality will be fine.

A switch in the middle will add a tiny amount of latency (in the order of 1-10 microseconds).

Bandwidth depends on the hardware. If you put a 100 Mbit/s switch in the middle of an otherwise 1 Gbit/s link, it'll slow the link to 100 Mbit/s. If the switch can link with the intended speed there's no impact on bandwidth (switches usually support forwarding at wire speed [non-blocking]).

If you're concerned about signal integrity in a difficult environment and need to pull cable anyway you should consider fiber. Preterminated multi-mode fiber isn't really expensive.

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  • By "bandwidth", I actually meant signal degradation in 2 of my wiring situations -- signal loss will translate into packet resent and bandwidth loss. Personally, I think that the switch helps a little to reduce signal loss on the wire. I have optical fiber converters, but want to avoid putting 2 extra devices on both ends. And the switch at the middle is a plan to expand Wi-Fi network (some extra APs will be connected to it).
    – Livy
    Commented Apr 21, 2020 at 7:39
  • Corrupted frames don't necessarily cause retransmissions - only for (transport) protocols that confirm data delivery, like TCP. Note that the Ethernet standards limit stranded cable to 20 m per link, so a switch in the middle wouldn't really solve that problem.
    – Zac67 ♦
    Commented Apr 21, 2020 at 12:40
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Assuming the cables meet specifications, the signal quality will be fine. The switch adds a trivial amount of latency.

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