ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 116)

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The preamble included in the SOF indicates the timestamps of the MAC type

frames.

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FC (Frame Check) is used to check the frame. The frame consists of four

OFDM symbols that are highly resistant to the noise on the transmission

channel and use a turbocode convolutional code. This code is widely used for

signal processing in HomePlug AV. These four symbols must be transmitted

over the transmission channel in order to make it possible for the destination

station to know the state of the link and the number of errors in the transmit-

ted data.

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The header contains various information concerning in particular the connec-

tion bit rate, which can vary according to the signal quality.

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The frame body contains information from the MAC layer just above. This

information is also called MPDU (MAC protocol data unit).

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The padding bits are used to fill the frame if a minimum frame size cannot be

achieved with the useful data.

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FCS (frame check sequence) is used to check the integrity of the data con-

tained in the frame body.

All the HomePlug 1.0 frame times without priority and contention headers are

estimated to be 1.5 ms, including the frame body, which includes 160 OFDM sym-

bols lasting 1.328 ms.

Figure 5.12 illustrates the constituent elements of the long frame in HomePlug

1.0 and Turbo. This long frame globally consists of three parts: the start of frame,

used to identify a long frame on the network; the data (in which the frame body with

the data of the upper layers is found); and the end of frame, used to identify end of

frame and therefore to indicate to the PLC devices that these devices can send the

next frames.

The OFDM Interface Frame 97

symbols

Figure 5.12 HomePlug 1.0 long frame structure

1 2 ... 111 112 113 114 115 116 117 118 119 120 121 ... 348 349

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 116