in optical network, what is network coding and which techniques are? is modulation a techniques of network coding?
Assuming you mean line encoding, Ethernet uses various schemes. Line code is necessary on single serial connections for clock recovery and run length limitations.
- 10BASE-F uses Manchester code
- 100BASE-X uses 4b5b (from FDDI)
- 1000BASE-X uses 8b10b
- 10GBASE-R and faster use 64b66b
- PHYs with 50G lanes use additional PAM-4 to reduce the symbol rate