ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Pobierz pdf (Strona 106)

CHAPTER 5

Frames

To send information, the PLC stations must prepare data frames, i.e., data blocks

with a header and an area indicating the end of the frame. The block containing the

user data has a specific format that depends on the technique used in order to access

the physical medium used. As the power line medium is shared, a technique used to

circulate multiple frames coming from various machines must be determined. This

frame structure sent over the physical layer is completed by a second frame structure

encapsulated into the first one.

Figure 5.1 illustrates the transmission of data in the architecture with PLC

access via the MAC (data link) and physical (PHY) layers. The first layer corre-

sponds to the technique used to access the power line medium. The frame corre-

sponding to this protocol is called the MAC or MPDU (MAC Protocol Data Unit)

frame.

All the data coming from layers above the MAC layer is encapsulated into the

MAC frame. This MAC frame is encapsulated into a second physical layer frame in

order to convey the frame over the physical interface or electrical interface. This

frame is called PPDU (physical protocol data unit).

Figure 5.1 Data transmission in PLC access architecture

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ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Strona 106