ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 58)

100

101

increases when a station could not emit, making it possible to bring the use of the

network in line with this priority level.

Figure 3.5 illustrates the operation of the CSMA/CA algorithm in its entirety.

Listening to the Medium

In PLC, the medium is listened to both at the physical layer level with the PCS (phys-

ical carrier sense) and at the MAC layer level with the VCS (virtual carrier sense).

The PCS makes it possible to know the state of the medium by sensing the pres-

ence of other PLC stations and analyzing the received frames, or by listening to the

medium activity thanks to the relative power of the signal from the various stations.

The PCS relies on listening to certain received frames, preamble frames, and pri-

ority frames.

The VCS does not actually allow listening to the medium but reserves it by using

the PCS.

Transmission Channel Functionalities 39

yes

Available?

Figure 3.5 CSMA/CA operation in HomePlug 1.0

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 58

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