IEEE Std 802.3ct:2021 pdf download.Amendment 13:Physical Layers and Management Parameters for 100 Gb/s Operation over DWDM Systems.
This clause specifies a staircase FEC (SC-FEC) and PMA sublayer for 100GBASE-ZR PHYs.
153.1.2 Position of SCJEC and IOOGBASE.ZR PMA in the IOOGBASE-R sublayers
Figure 153—1 shows the relationship of the SC-FEC and 100GBASE-ZR PMA to the ISO/IEC Open System Interconnection reference model.
4) The GMP mapping overhead (GMP OH) is encoded in the eight octets from columns 14 and 15 of each of the four rows of’ the SC-FEC frame.
5) The IOOGBASE-R PCS payload is GMP mapped in the area of the SC-FEC frame in the octets in columns 16 through 3815 in each of the four rows as shown in Figure 153—3.
6) The octets in the fixed stuff area of the frame are transmitted with the value zero and are ignored on receipt.
7) The SC-FEC parity area of the frame is allocated for FEC parity to be inserted as described in
153.2.3.2.5.
GMP is a generic mechanism that uses a sigma/delta distribution algorithm to accommodate an arbitrary signaling rate dit’ference between a payload and the space in which it is carried. The principles of the GMP mapper are described in ITU-T G.709 (06/2020) Annex D, with details of the encoding of the GMP overhead in ITU-T G.709 Clause 19.4.3.2.
The payload area of the SC-FEC frame is divided into 190 GMP words of 80 octets each. Each 80-octet
GMP word is either tilled with data (the logically serialized 66B encoded stream produced according to
153.2.3.2.3) or stuft which is transmitted as zero prior to scrambling and ignored on receipt.
The 66B encoded data is a logically serial stream at a rate of 103.125 Gb/s ± 100 ppm. The payload area of the SC-FEC frame has a capacity of (255/227) x (3800/4080) x 99.5328 Gb/s ± 20 ppm (—104.1367 Gb/s). The clocks for the PCS and the SC-FEC frame are independent. This results in an average number of 80-octet GMP words filled per SC-FEC frame between —188.1315 and —188.1766. Since the number of GMP words tilled in a frame is always an integer, a given SC-FEC frame will have either 188 or 189 tilled GMP words. While the GMP mechanism is generic, the particular clock rates and tolerances for this application result in a small number of cases, allowing the positions of data and stuff to be pre-computed. For either 188 or 189 GMP words filled in the SC-FEC frame, the GMP word consisting of the octets from column 16 to column 95 of row 0 will always be stuff (tilled with zero rather than 66B encoded data prior to scrambling). In the case of 188 GMP words tilled in the SC-FEC frame, the GMP word consisting of the octets from column 16 to column 95 of’ row 2 will also be stuff’. Given the range of clock rate differences that may exist between the 66B encoded data and the SC-FEC frame payload capacity, there will tend to be between 4 and 7 frames with 188 filled GMP words between every frame with 189 tilled GMP words. There is not a circumstance where there would be two consecutive frames containing 189 tilled GMP words.
The GMP overhead is illustrated in Figure 1 53—4.IEEE Std 802.3ct pdf download.