how a network interface card identifies if the ethernet cable is plugged? [closed]

I want to write a program to find whether the ethernet media is up or not which is connected to the ethernet adapter (language is not decided yet). I want to know about the algorithms and protocols which are used by an ethernet adapter, to identify whether the media is connected or not. I know ethernet adapter contains a solid LED to identify whether the connection is up or not. I want know what is the mechanism behind it. It will be really helpful if you can answer this and provide some references to the information about those algorithms.

Solution 1:

Ethernet over twisted pair uses Fast Link Pulses to (auto) negotiate a link: each port advertises its link capabilities, e.g. 1000BASE-T full duplex, 100BASE-TX full duplex, 100BASE-TX half duplex, 10BASE-T full duplex, 10BASE-T half duplex, and when a link partner is detected, the best mutual protocol is selected and the link is established (depending on its subtleties).

Accordingly, its not the media that is detected (e.g. by a mechanical switch in the jack) but the link partner.

FLPs are defined in IEEE 802.3 Clause 28, the actual link process is detailed in each physical-layer variant, e.g. 1000BASE-T in Clause 40.5. You can download the IEEE 802.3 specifications free after registration.