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edited Feb 18, 2023 at 21:16

No. From the table, different 10Base-T versions can use 1 or 2 pairs, and different 100Base-T versions can use 1, 2 or 4 pairs. Both 10Base-T and 100Base-TX that are extremely common use 2 pairs, 1 pair per direction.
Both MLT-3 and PAM-3 have three voltage levels. MLT-3 is a specific line code that uses 3 voltage levels in a specific way, which steps between all voltage levels in a sequence. If the bit is 1, the sequence advances, and for 0 bits, the sequence does Not advance. Basically for strings of 1, the output is a sine wave. PAM-3 just means you have 3 voltage levels, but not how they are used.
You are correct; it isn't possible to take in 4 bits and output 3 bits. But that's not what 4B3T does. The 4B3T takes in 4 bits but it does not output 3 bits. It outputs 3 ternary (PAM-3) symbols.
100Base-TX does use 4B5B, NRZ-I and MLT-3. There is really no redundancy involved. 4B5B and NRZ-I were already used on 100Base-FX. When the 100Base-TX was designed, the fiber medium dependent sublayer just was replaced with copper medium dependent sublayer which needs further tricks to fit 125 MBPS over Cat5 bandwidth of 100 MHz, and thus the MLT-3 encoding was borrowed from copper version of FDDI.

No. From the table, different 10Base-T versions can use 1 or 2 pairs, and different 100Base-T versions can use 1, or 4 pairs. Both 10Base-T and 100Base-TX that are extremely common use 2 pairs, 1 pair per direction.
Both MLT-3 and PAM-3 have three voltage levels. MLT-3 is a specific line code that uses 3 voltage levels in a specific way, which steps between all voltage levels in a sequence. If the bit is 1, the sequence advances, and for 0 bits, the sequence does Not advance. Basically for strings of 1, the output is a sine wave. PAM-3 just means you have 3 voltage levels, but not how they are used.
You are correct; it isn't possible to take in 4 bits and output 3 bits. But that's not what 4B3T does. The 4B3T takes in 4 bits but it does not output 3 bits. It outputs 3 ternary (PAM-3) symbols.
100Base-TX does use 4B5B, NRZ-I and MLT-3. There is really no redundancy involved. 4B5B and NRZ-I were already used on 100Base-FX. When the 100Base-TX was designed, the fiber medium dependent sublayer just was replaced with copper medium dependent sublayer which needs further tricks to fit 125 MBPS over Cat5 bandwidth of 100 MHz, and thus the MLT-3 encoding was borrowed from copper version of FDDI.

No. From the table, different 10Base-T versions can use 1 or 2 pairs, and different 100Base-T versions can use 1, 2 or 4 pairs. Both 10Base-T and 100Base-TX that are extremely common use 2 pairs, 1 pair per direction.
Both MLT-3 and PAM-3 have three voltage levels. MLT-3 is a specific line code that uses 3 voltage levels in a specific way, which steps between all voltage levels in a sequence. If the bit is 1, the sequence advances, and for 0 bits, the sequence does Not advance. Basically for strings of 1, the output is a sine wave. PAM-3 just means you have 3 voltage levels, but not how they are used.
You are correct; it isn't possible to take in 4 bits and output 3 bits. But that's not what 4B3T does. The 4B3T takes in 4 bits but it does not output 3 bits. It outputs 3 ternary (PAM-3) symbols.
100Base-TX does use 4B5B, NRZ-I and MLT-3. There is really no redundancy involved. 4B5B and NRZ-I were already used on 100Base-FX. When the 100Base-TX was designed, the fiber medium dependent sublayer just was replaced with copper medium dependent sublayer which needs further tricks to fit 125 MBPS over Cat5 bandwidth of 100 MHz, and thus the MLT-3 encoding was borrowed from copper version of FDDI.

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created Feb 18, 2023 at 20:55

No. From the table, different 10Base-T versions can use 1 or 2 pairs, and different 100Base-T versions can use 1, or 4 pairs. Both 10Base-T and 100Base-TX that are extremely common use 2 pairs, 1 pair per direction.
Both MLT-3 and PAM-3 have three voltage levels. MLT-3 is a specific line code that uses 3 voltage levels in a specific way, which steps between all voltage levels in a sequence. If the bit is 1, the sequence advances, and for 0 bits, the sequence does Not advance. Basically for strings of 1, the output is a sine wave. PAM-3 just means you have 3 voltage levels, but not how they are used.
You are correct; it isn't possible to take in 4 bits and output 3 bits. But that's not what 4B3T does. The 4B3T takes in 4 bits but it does not output 3 bits. It outputs 3 ternary (PAM-3) symbols.
100Base-TX does use 4B5B, NRZ-I and MLT-3. There is really no redundancy involved. 4B5B and NRZ-I were already used on 100Base-FX. When the 100Base-TX was designed, the fiber medium dependent sublayer just was replaced with copper medium dependent sublayer which needs further tricks to fit 125 MBPS over Cat5 bandwidth of 100 MHz, and thus the MLT-3 encoding was borrowed from copper version of FDDI.