Page 1335 - 5G Basics - Core Network Aspects

Transport aspects 2

where the actual timestamps <egressTimestamp> and <ingressTimestamp> measured at the reference
plane are computed from the detected, i.e., measured, timestamps by their respective latencies. Failure to
make these corrections results in a time offset between the slave and master clocks.

The PTP timestamp is associated with the first FlexO interface (lowest PID value) of a FlexO group.

10 OTUCn mapping

10.1 Dividing and combining OTUCn
An OTUCn frame structure is specified in clause 11.3 [ITU-T G.709], and contains n synchronous instances of
OTUC frame structures. The FlexO source adaptation consists of splitting the OTUCn frame into n * OTUC
instances. Similarly, the sink adaptation combines n * OTUC instances into an OTUCn. A single or multiple
OTUC instances are then associated to a FlexO interface. Alignment and deskewing are performed on the
OTUC instances.

Figure 10-1  OTUCn divided onto n * OTUC

10.2 FlexO frame payload
The FlexO payload area is divided in 128-bit blocks. The 128-bit blocks are aligned to the start of a FlexO
payload area (following AM and OH). The FlexO frame payload consists of 5,120 blocks (frame #1-7 of the
multi-frame, with fixed stuff payload) and 5,130 blocks (frame eight of the multi-frame, without fixed
stuffing).
NOTE – This 128-bit (16-byte) word/block alignment of the 100G OTUC is analogous to the 66b block alignment of a
100G Ethernet PCS stream that is kept through the clause 91 [IEEE 802.3-2015] adaptation process.

10.3 Mapping of OTUC into FlexO frame
Groups of 128 successive bits (16 bytes) of the OTUC signal are mapped into a 128-bit block of the FlexO
frame payload area using a BMP control mechanism as specified in clause 17 of [ITU-T G.709]. The 128-bit
group of OTUC is aligned to the OTUC frame structure. The OTUC frame structure is floating in respect to
the FlexO frame.

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