1000BASE-T Encoding

Operating bidirectionally on twisted pairs is a challenge. The encoding used for 1000BASE-T is highly complex. It not only must achieve a balance of 0s and 1s on each cable, but it also must create a balanced electromagnetic condition across all four pairs.

The encoding method consists of several steps:

  1. Each byte is scrambled.

  2. The scrambled byte is translated to a 4-tuple of special symbols via a mapping called 8B1Q4.

  3. Each symbol is represented on the physical medium by a voltage. Five different voltage levels are used, corresponding to an alphabet of five different symbols. The physical transmission method is called 4-dimensional 5-level pulse amplitude modulation (4D-PAM5).

More details are presented in Appendix ...

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