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2 Transport aspects
The serial bit stream of an OTUC signal is inserted into the FlexO frame payload so that the bits will be
transmitted on the FlexO interface in the same order that they were received at the input of the mapper
function.
In clause 8.3, the shown bit rate ratio between FlexO frame and payload is 256/241.
10.3.1 Mapping of OTUC into 100G FlexO frame
There exists a one-to-one relationship between an OTUC and a 100G FlexO interface. The FlexO payload
area is segmented in 128-bit blocks. The OTUC is mapped in contiguous 128-bit segments.
There are (5,140*128*8 – 1,280*15) / (239*16*8*4) = 42.85 OTUC frames per FlexO multi-frame. This
results in ~5 OTUC frames per FlexO frame, or a new OTUC frame every ~24 FlexO frame rows, as shown in
Figure 10-2A.
Figure 10-2A OTUC mapped into 100G FlexO frame payload
The FlexO frame payload does not divide elegantly into 128-bit blocks in a single row. The block will spill
over and cross row boundaries as shown in Figure 10-2A. The 128-bit alignment is always consistent across
FlexO frames and the first 128-bit block starts immediately following the overhead area.
The AVAIL field indicates whether an OTUC is mapped into the FlexO frame payload (set to ''1'') or if the
FlexO payload is empty (set to ''0''). Other AVAIL values are not valid for 100G FlexO interfaces.
10.4 FlexO group alignment and deskewing
FlexO members are identified within a group and reordered using GID, MAP and PID FlexO OH field. The PID
sequence is used to recreate an OTUCn in proper sequence order. For example OTUC#1 is mapped into a
FlexO frame with the minimum PID number, and so on.
Deskewing in the sink process is performed between OTUC frames within the group, using OTUC FAS as
specified in [ITU-T G.709].
The skew requirements are intended to account for variations due to digital mapping and cable lengths.
The skew tolerance requirement is 300 ns.
NOTE – These requirements are in line with [OIF FlexE IA] Low Skew applications.
10.5 Scrambling
The FlexO frame payload, AM padding, fixed stuffing and overhead must be scrambled prior to
transmission, in order to provide DC balance and proper running disparity on the interface. The ami fields in
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