How does data flow in a twisted-pair cable?

If I use an Ethernet cable (twisted pair cable) in what form is the data flowing - digital or analog signal?

And in pair 1, that is wire number 1 and 2, there is Transmit+ and Transmit- respectively. How is pair 1 sending data with one wire +ve voltage the other with -ve voltage?

• Did any answer help you? if so, you should accept the answer so that the question does not keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer. Commented Dec 23, 2021 at 19:29

in what form the data is flowing - digital or analog signal

That depends on your definitions. Imho, a signal in a cable is always analog but you could argue that there are distinct signal levels/symbols, making it digital.

Ethernet over twisted pair uses differential signaling. There are no absolute voltage levels but the polarity between paired wires is the signal - either pin 3 is positive to pin 6 are vice versa.

10BASE-T uses rather simple Manchester line code. Each symbol consist of a polarity change between the paired wires: `-+` signals a `1` bit and `+-` signals a `0` bit. There may be additional polarity changes in the signal, but there's always a change in the exact middle of a bit/symbol. This provides a DC-free, self-clocking signal.

100BASE-TX uses a more complex, 4b5b line code (for clock recovery) and MLT-3 signaling (stepping through `+`, `0`, `-` polarity states), increasing the bandwidth efficiency greatly. The signal is also scrambled to avoid DC bias. 100BASE-TX encoding was largely borrowed from FDDI.

1000BASE-T is pretty complex already, using four-dimensional trellis modulation plus scrambling over PAM-5 (five levels of differential voltage). The complex encoding is necessary to enable signaling over Category 5 cable with the same symbol rate as 100BASE-TX (125 MBd) and only moderately increased spectral bandwidth. This contrasts with TIA's technically simpler 1000BASE-TX which required Category 6 cable and failed to be implemented.

Note that only 10BASE-T and 100BASE-TX are using distinct transmit and receive pairs (dual simplex). 1000BASE-T and faster use four-lane full-duplex transmission across all four pairs with the help of hybrids and echo compensation.