MLT-3 and NRZ and 4B5B Encoding

[FreshmanNewbie]

In this Ethernet PHY datasheet (https://ww1.microchip.com/downloads.../LAN8720A-LAN8720Ai-Data-Sheet-DS00002165.pdf), page 14, Figure 3-1, I see the blocks 4b5b encoding, NRZI and MLT-3.

I was reading about line coding and it's purpose.

One of the critical purpose of line coding is to have an average 0V DC level in the signal.
So, NRZI, NRZ, MLT-3 are trying to achieve this.

Also, when I went through 4b5b encoding, I noticed that this is done to ensure that there are no multiple consecutive 0s in the signal. Which I infer to be the same purpose of the NRZ etc line coding.

Also, there's a mention of Manchester encoding in the datasheet.

My question:

1. Are the blocks 4B5B encoding, NRZI & MLT-3 are present for the purpose of having an average 0V DC Level?

2. Are the above block different line coding schemes?

3. If each block has a different purpose, can someone explain me the purpose of each block?

4. Also, why is Manchester encoding not present as a block in the diagram? Doesn't it do the same line coding job?

 

[std_match]

4. Manchester encoding is only used for 10 Mbit/s (10BASE-T), and there is no block diagram for 10BASE-T in the data sheet.