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Transport aspects 2

12.2.4.4 FTU-O and FTU-R messages

The format of the FTU-O and FTU-R message shall be as specified in clause 12.2.1; the content of the
messages are described in detail in clauses 12.3.3 and 12.3.4.
12.2.4.5 Mapping of SOC data

All bytes of the SOC message shall be sent LSB first. An SOC message may be subdivided into fields. A field
can contain parameter values expressed in more than one byte. In this case, the field shall be split into
bytes with the byte containing the MSBs of the parameter value shall be sent first. For example, a field
carrying a 16-bit value m15,…, m0 shall be split into a first byte B0=m15…m8 and a second byte B1=m7…m0.
Some SOC messages may contain several fields. Some fields can be merged together to form a logical entity
called a macro-field, such as "PSD descriptor", which is described in clause 12.3.3.2.1.
The description of fields for specific messages is given in detail in clauses 12.3.3.2 and 12.3.4.2. All bytes of
a message that follow the currently defined bytes shall be ignored.
NOTE – If future versions of this Recommendation add extra fields to the ones already defined, for reasons of
backward compatibility, these fields will be appended to the currently defined ones.
12.2.4.6 Segmentation of SOC messages
Messages that are larger than the maximum allowed size of 1 024 bytes shall be segmented before
transmission; messages shorter than 1 024 bytes may also be segmented to improve robustness. Each
segment shall include an integer number of bytes.
Segmentation is facilitated by the segmentation index of SOC message (see Figure 12-6). The four MSBs of
this field shall indicate the number of segments, up to a maximum of 15, into which the message has been
segmented. The four LSBs of this field shall indicate the index of the current segment, starting from 0116.
For example, a segmentation index value of 9316 indicates the third segment of a total of nine. In case the
message is not segmented, the value of the field shall be 1116.

12.3 Initialization procedure

12.3.1 Overview
Initialization of an FTU-O/FTU-R pair includes the following main tasks:

• Definition of a common mode of operation (profile, TDD framing parameters, initial values of basic
modulation parameters);
• Synchronization (sample clock alignment and symbol alignment);

• Channel identification and crosstalk cancellation between the joining lines and active lines;
• Transfer from the FTU-O to the FTU-R of transmission parameters, including information on the
probe sequences, PSD masks, RFI and IAR bands to be notched and target data rates in both
transmission directions;
• Noise identification;
• Negotiation of DTU size, RS encoder and interleaver parameters, as well as the bit loading and gain
adjustment tables.

The common mode of operation shall be negotiated during the ITU-T G.994.1 handshake phase.
Information such as TDD framing parameters, limit PSD mask, locations of RFI and IAR bands to be notched,
and target data rates shall be initially available at the FTU-O through the DPU-MIB.
Figure 12-7 shows the timeline of the initialization procedure in the upstream and downstream directions,
which contains three phases:
– ITU-T G.994 handshake phase
– Channel discovery phase

– Channel analysis and exchange phase

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