10BASE-T saw first light as StarLAN that made use of the already existing twisted-pair category 3 telephone cabling (instead of the dedicated coax that 10BASE5/2 required). That cabling standard carries four pairs to each wall jack. StarLAN (10) and subsequently 10BASE-T had no use for more than two pairs, so they ignored the other two. 100BASE-TX borrowed ...
If feasible, optical fiber is immune to interference.
You can use small industrial-grade switches with SFP port (to connect the fiber) in the machine.
However fiber is much more fragile then copper and you must pay attention to the bending radius.
What you're looking for is a cable tester able to certify a cable with the entire test suite. The tests must include crosstalk and detailed frequency measurement.
Basically, there are three classes of testers:
just continuity and shorts - 5-100 €
additionally wire map (proper pairings), overall length, possibly rough frequency response (cable class) - 200-...
You are correct that 10Base-T and 100Base-Tx use two pairs for communication, while 1000Base-T uses all four.
You may be confused because you're conflating different standards for different items.
10Base-T, 100Base-Tx, etc., are signaling and electrical standards from IEEE (802.3i).
The cable itself is defined by ISO/IEC 11801, and is called Category 5, 5e, ...
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 ...
"does a crossover cable decrease power consumption, increase transfer speed, or decrease load on the adapter or other components?"
No, not at all. The speed, power consumption, latency, etc. are all the same for a straight-through vs. a crossover cable. The bandwidth is the bandwidth. For 1000Base-T (1 Gbps on UTP) it is always 1 Gbps.
To answer the part of your question "Were there some cables that only had two pairs?":
I worked at a very large multi-building site that had 8wire/4pr twisted pair in the walls terminating with and split between two RJ13* jacks at each wallplate. (2 pairs going to each) One RJ13 was used for POTS phone, and the other was later used for 10baseT (...
There's nothing to stop a new twisted-pair standard using a new connector in the design, with more wires.
If a physical site had to choose between using existing 8-wire / 4-pair and recabling everything to use a new standard, then the additional costs would push most sites to stay with existing wiring for as long as it fills the need.
One half-way point ...
No this cable can carry different types of traffic other than internet traffic . Submarines cables are just physical connectivity from and to connecting two geographical locations . Further to i this cable bandwidth can be utilised for internet and point to point links for private leased lines connectivity this can be achieved by creating vlans isolating ...
How can I evaluate the stability of a connexion between two computers on the same network ?
You could run test traffic (with at least 50% of the connection's bandwidth) and analyze loss, e.g. using iperf3.
What are your advices to improve stability ? Other mean of connection ? Better ethernet cable ? More powerful router ?
Generally, shielded cable (S/FTP)...
we also see that the fiber is only used till the networking device and not the client nodes like PC or laptop.
That isn't really true. Technically, running fiber to the desktop isn't a problem. However, fiber cables are very delicate and deploying fiber when there's copper you can use is an expensive luxury.
LAN cables made up of copper wires
Generally, you don't install (copper) data and power cables like that. Power and data should be at least 5 cm apart for longer runs (do check local regulations for legal restrictions).
You should consider fiber which is practically immune to EMI. If cost is an issue check out preterminated fiber with a keystone panel.
How does the media converter know when to turn on the its Link LED?
When it sees the Tx signal from the other side of the link on its Rx. The signal must be at the correct frequency and strength for the specific ethernet standard (100Base-FX at 1300 nm in this case).
Since both network are directly connected networks . So routers are able to ping each other . Coming to clockrate when clock rate is not configured on either router it' picks default clockrate set by manufacturer.