ZyXEL Communications PLA-470 V2 - V3.0.5 Installationsanleitung PDF herunterladen (Seite 117)

Physical Frame Start Delimiter

The start delimiter contains two parts, the preamble and FC:

•

The preamble contains the frame sending time stamp.

•

FC (frame check) contains several fields: a contention check field, used to

check the contention level of the transmitted frames; a field indicating the

delimiter type; a variable field, which itself comprises two fields that are of

particular importance for PLC communications (the tone map, which stores

the states of the links between PLC stations and the size of the following

data frame) and a frame check sequence. A CRC (cyclic redundancy check)

is used in the latter field to check the frame integrity check sequence (see

Figure 5.13).

Physical Frame Data Body

The physical frame data body is illustrated in Figure 5.14. It comprises a MDPU

encapsulated into the PPDU. The MPDU comprises the EB (block header), PAD

(padding bits) (if the data does not completely fill the data part), and the SCB (bit

check sequence) fields. An ICV (integrity check value) is used by the SCB field to

check the integrity of the data forming the data body.

Physical Frame End Delimiter

The physical frame ends with an end delimiter, which consists of a preamble and of a

frame check field.

The frame check field consists of the four following fields (see Figure 5.15):

98 Frames

Figure 5.13 Start of frame header of physical frame

1 2 ... 112 113 114 115 116 117 118 119 120 121 122 ... 348 349

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ZyXEL Communications PLA-470 V2 - V3.0.5 Installationsanleitung Seite 117