Page 1337 - 5G Basics - Core Network Aspects

Transport aspects 2

the AMs are not scrambled and the chosen values have properties of already being DC balanced. The
padding padi fields of the AMs as shown in Figure 9-3A are scrambled.

The operation of the scrambler shall be functionally equivalent to that of a frame-synchronous scrambler of
3
16
12
sequence 65535 and the generating polynomial shall be x + x + x + x + 1. (See Figure 11-3 [ITU-T G.709]
for an illustration of this scrambler.)
The scrambler resets to 0xFFFF on the most significant bit of the start of frame and the scrambler state
advances during each bit of the FlexO frame (Figure 10-3). In the source function, the AM values (ami fields)
are inserted after scrambling and before the input to the FEC encoder. In other words, the FEC encoding is
performed on unscrambled AM bits (ami fields). The FEC encoder overwrites the FEC bit fields. The sink
then receives unscrambled AM (ami fields) and FEC fields, as illustrated in Figure 10-4.

Figure 10-3  FlexO scrambler

Figure 10-4  FlexO scrambler after AM and FEC insertion

11 FOIC interface

11.1 FOIC1.4 interface
An FOIC1.4 interface is used as a system interface with 100G optical modules. A FlexO frame is adapted
over multi-channel parallel interfaces, using four ~28 Gbit/s physical lanes. No bit-multiplexing is
performed.

The alignment markers for the FlexO frame are distributed on four lanes, resulting in 240-bit of data per
lane. The alignment marker (AM) values are specified in clause 9.1. Each AM has unique UMx and UPx
values. When the four AMs distributed to lanes 0, 1, 2 and 3, the differing values are used for lane
reordering in the sink function. The CMx values are replicated on all four lanes to facilitate the searching,
alignment and deskewing process.

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