64b/66b encoding

The 64b66b code is a line code that uniquely maps a data word of 64 bits to a code word of 66 bits. Applies this line code in the context of Gigabit Ethernet, such as 10- Gigabit Ethernet, 40 Gigabit Ethernet and 100 Gigabit Ethernet. A similar line of code is 8b10b code.

As each line code It is used to adjust a spectral Nutzdatenfolge to the physical requirements of the transmission medium, such as a conduit. By the method of implementation, in particular the direct component of freedom of the code sequence generated is guaranteed, which allows the transmission via pulse transformers, which can happen no DC component in the signal. Pulse transformers are used in the field of physical Ethernet interface for galvanic isolation. In addition, guarantees under the 64b66b encoding that the recipient of the keyword can recover the clock. This is necessary so that the receiver can detect, at which times a certain state is transferred.

Operation

The 66 bits of a codeword are preceded by a preamble of 2 bits. The four possible combinations of the preamble are each:

  • If the preamble 01, then the following 64-bit payload.
  • When the preamble is 10, immediately followed by a Type field of 8 bits in length with subsequent 56 bits of command and control information. The meaning depends on the Type field.
  • The preambles 00 and 11 are not used, and produce on receipt of an error.

The use of 01 or 10 as valid preamble guarantees on the one hand, the DC component of freedom of the preamble and on the other hand it ensures a signal edge within the preamble. Characterized the receiving end can be determined by means of a phase-locked loop of the symbol clock.

The 64 -bit user data and 56 bits of command and control data are linked by means of a self-synchronizing scrambler, so that the DC component of freedom of the data fields is statistically guaranteed. The scrambler is implemented as a linear feedback shift register. The approach using scrambler in 64b66b coding is an essential difference from the table based line code 8b10b.

Swell

  • PatentView/EP1133123 64b/66b coding for packetized serial data, (English )
  • Line code
8548
de