Page 1124 - 5G Basics - Core Network Aspects

2 Transport aspects

11.2 Scrambling

The OTUk signal must have sufficient bit timing content at the ONNI. A suitable bit pattern, which prevents
a long sequence of "1"s or "0"s, is provided by using a scrambler.
The operation of the scrambler shall be functionally identical to that of a frame synchronous scrambler of
sequence length 65535 operating at the OTUk rate.
16
12
3
The generating polynomial shall be 1 + x + x + x + x . Figure 11-3 shows a functional diagram of the frame
synchronous scrambler.
Data in
  

D Q D Q D Q D Q D Q D Q D Q D Q D Q D Q D Q D Q D Q D Q D Q D Q 
S S S S S S S S S S S S S S S S
OTUk
clock
Scrambled
OTUk MSB of MFAS byte data out
G.709-Y.1331(12)_F11-3

Figure 11-3  Frame synchronous scrambler

The scrambler shall be reset to "FFFF" (HEX) on the most significant bit of the byte following the last
framing byte in the OTUk frame, i.e., the MSB of the MFAS byte. This bit, and all subsequent bits to be
16
scrambled shall be added modulo 2 to the output from the x position of the scrambler. The scrambler
shall run continuously throughout the complete OTUk frame. The framing bytes (FAS) of the OTUk
overhead shall not be scrambled.

Scrambling is performed after FEC computation and insertion into the OTUk signal.

11.3 OTUCn frame structure
The OTUCn frame structure (Figure 11-4) is based on the ODUCn frame structure and deploys the reserved
overhead bytes in row 1, columns 8 to 14 of each ODU frame structure in the ODUCn overhead for an
OTUCn specific overhead, resulting in an octet-based block frame structure with n  four rows and 3824
columns. The MSB in each octet is bit 1, the LSB is bit 8.

Interleaving of the n frame and multi-frame synchronous OTU frame structure instances within the OTUCn,
forward error correction, encoding (e.g., scrambling), deskewing and transmission order of the OTUCn are
interface specific and specified for inter-domain OTN interfaces with application codes in the interface
specific Recommendations (ITU-T G.709.x series). For OTN interfaces with vendor specific application
identifiers these specifications are vendor specific and out of scope of this Recommendation.
The bit rates of the OTUCn signals are defined in Table 7-1.

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