Page 806 - 5G Basics - Core Network Aspects

2 Transport aspects

The symbol count (CNTSYMB) shall be incremented after each symbol period passed at the U-interface
(Mds + Mus + 1 periods in total during each downstream or upstream logical frame, where the 1 represents
the combined time gaps Tg1 and Tg2, see Figure 10-26). Symbol counts are defined in upstream (CNTSYMB,us)
and downstream (CNTSYMB,ds). In a particular direction of transmission, CNTSYMB shall be set to 0 at the
symbol position which corresponds to the first RMC symbol transmitted when entering the showtime and
after reaching the value of 1 022 (modulo 1 023) while in showtime.

10.7 Normal and discontinuous operation intervals
During link state L0, when not all of the time available for data transmission is needed, a discontinuous
operation interval may be configured to facilitate transceiver power savings.
The discontinuous operation interval may be configured independently for upstream and downstream.
Symbol periods within the discontinuous operations interval of a logical frame may be filled with either
data symbols, idle symbols (see clause 10.2.1.7) or quiet symbols (see clause 10.2.1.6).
Figure 10-29 shows downstream logical frames with the identified parameters for controlling and managing
the configuration of the discontinuous operation interval in a downstream logical frame. Figure 10-30
shows upstream logical frames with the identified parameters for controlling and managing the
configuration of the discontinuous operation interval in an upstream logical frame.

A logical frame is divided into two intervals; a normal operation interval (NOI), and a discontinuous
operation interval (DOI). The NOI boundary is defined by parameter TTR (in number of symbol periods in
the NOI). The NOI starts from an RMC symbol and has TTR symbols duration. The value of TTR may be
different from one logical frame to another. The number of symbols in the NOI can be in the range from
one to Mds (including the RMC symbol, and the sync symbol if it resides within the NOI) in the downstream
direction and from 1 to Mus (including the RMC symbol, and the sync symbol if either or both reside within
the NOI) in the upstream direction. If the transmitting FTU of a particular line does not have data to send
during the NOI, it shall send one or more idle symbols or data symbols filled with dummy DTUs. In the
upstream direction, selection between transmission of idle and data symbols depends on the value of IDFus
communicated over RMC from the FTU-O to the FTU-R (see Table 9-7).
If an idle symbol is sent at a particular symbol position of the NOI, all following symbols of the NOI shall also
be idle symbols (except sync or pilot symbols, if they reside within the NOI). If the NOI ends with an idle
symbol or a data symbol filled with dummy DTUs, all symbols of the DOI of the logical frame shall be either
idle or quiet symbols (except sync symbols, if they reside within the DOI).
The DOI is configured with controlled positioning of data, idle and quiet symbols. In Figure 10-29 and Figure
10-30, the parameter TA defines the number of quiet symbol positions at the beginning of the DOI of a
logical frame and the value B' is defined as the number of symbol positions following TA that may contain
data symbols in the DOI.
Control of the discontinuous operation interval is provided by the DRA and VCE of the DPU (see Figure 5-2).
The following control parameters, separate for upstream and downstream, are communicated to the FTU-
O across the  reference point in the associated TXOP primitive (see Table 8-3):

Transmission budget (TBUDGET): parameter used to derive the index of the last symbol position that may
be used for a data symbol. This index is equal to (TBUDGET-1) if TBUDGET ≤ TTR, otherwise it is equal to
(TBUDGET+TA-1). The total number of symbol positions allocated for the RMC symbol and data symbols in
the combined NOI and DOI of a logical frame is equal to TBUDGET if the logical frame does not contain a
sync symbol, otherwise that number can be equal to TBUDGET or (TBUDGET-1), depending on the position
of the sync symbol in a logical frame.

TTR: the number of symbol positions in the NOI, including the sync symbol position if it resides within the
NOI.

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