ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka stáhnout pdf (Strana 115)

The PLC Physical Frame

In HomePlug 1.0, the physical layer frames, or PHY PPDU (physical protocol data

unit) are strongly related to the MAC layer frames, as some MAC layer information

is available at the PHY layer level.

There are two PPDU types at the physical layer level: a long PPDU and a short

PPDU, as well as a number of elements delimiting these PPDU or allowing sufficient

spacing between them so that the stations have the time to transmit or receive the

frames.

The various elements of the HomePlug 1.0 physical frames are the following:

•

Three delimiters:

•

SOF (start of frame), which is used to delimit the start of the frame;

•

EOF (end of frame), which is used to delimit the end of the frame;

•

Short PPDU, which is the response frame sent back by the destination sta-

tion to indicate acknowledgment of the transmitted data.

•

Two time intervals between two frame transmissions:

•

CIFS (contention distributed interframe spacing), which is the end of frame

gap before the end of frame delimiter.

•

RIFS (response interframe spacing), which is the time interval during which

a station waits for a response from the destination station.

•

Long PPDU, which contains the data frames.

Figure 5.11 illustrates all the parts forming a PLC physical frame in HomePlug

1.0 and Turbo with the long frame containing the data of the upper layers, the

interframe gap used to delimit the frames on the physical medium, and the short

frame used to manage the responses from the PLC devices and optimize the commu-

nication times over the medium.

The physical level long frames, also called PLCP PPDU (physical level com-

mon protocol PPDU), are nothing else than blocks of bits sent over the physical

layer.

These long frames, also called long PPDU, comprise six parts: preamble, frame

check, header, frame body, padding bits, and FCS.

96 Frames

Figure 5.11 Elements of HomePlug 1.0 physical frames

1 2 ... 110 111 112 113 114 115 116 117 118 119 120 ... 348 349

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ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka Strana 115