ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Pobierz pdf (Strona 107)

This chapter discusses the structure of the PLC frames used in HomePlug 1.0

and introduces the main characteristics of the frames in HomePlug AV.

Physical Layer Frames

If we observe the complete structure of the HomePlug 1.0 physical layer frame per-

manently exchanged between the PLC devices (see Figure 5.2), we notice that it con-

sists of a number of elements surrounding the long data frame including the data of

the higher level protocol layers from the OSI model’s point of view.

In terms of time length, the HomePlug 1.0 frame can be quantified by minimum

and maximum values, with a fixed part (header), a variable data part, and a part

used for contention periods with regard to the CSMA/CA process as indicated in

Table 5.1.

Therefore, the HomePlug 1.0 frame consists of “long” data frames, which com-

prise the data of the MAC frames, and “short” data frames, which comprise

response information from the other PLC devices.

Remember that the average time of a HomePlug 1.0 frame is 1,600 μs.

From the point of view of the physical layer modulation techniques, the

HomePlug 1.0 data frame consists of OFDM (orthogonal frequency division

multiplexing) symbols. These symbols form blocks that, in turn, constitute the com-

plete frame.

88 Frames

Figure 5.2 HomePlug 1.0 frame structure

Table 5.1 HomePlug 1.0 Frame Time Length

FIXED

(HEADER)

VARIABLE

(DATA)

CONTENTION

(CSMA/CA)

TIME

LENGTH

MIN 205.52 μs + 313.5 μs+N × 35.84 μs = 519.02 μs + (N × 35.84 μs)

MAX 205.52 μs + 1,489.5 μs+ N × 35.84 μs = 1,692.02 μs + (N × 35.84 μs)

1 2 ... 102 103 104 105 106 107 108 109 110 111 112 ... 348 349

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ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Strona 107