Cable speed between drop form 1gbps to 100mbps offen

it is due to bad cable, or connectors.

The easy fix is get a managed switch, and set up the ports to Auto-negotiation, Speed: 1000, Duplex Mode: Full

It will running as 1gbps, but due to the bad cable quality, it will only run 200mbps-Max, depends on how bad the cable is, and how much the noise it.

sample configuration on Netgear GC510P