ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 316)

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Management of hybrid accesses between FDMA (frequency division multiple

access) and TDMA (time division multiple access);

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Management of the QoS by a TDMA time space system, like in HomePlug AV for

HD video applications.

As illustrated by Figure 13.2, these two principles should make it possible to avoid

mutual interference and optimize the use of the common communication medium.

The main problem relating to the coexistence of PLC technologies comes from

the fact that the use of the frequency band is not standardized. This results in a

reduced available bandwidth for each technology. Data communications are still

operational but in degraded, even highly degraded, modes that are detrimental to

the routing of the provided services to the upper layers (IP, TCP, and so forth) and

prevent the good operation of the applications.

In the same way as the presence of too many PLC devices on the same electrical

network must be avoided (limited to 16 devices in the HomePlug 1.0 and Turbo

specifications), it is necessary to avoid the implementation of several PLC technolo-

gies on the same electrical network (HomePlug, DS2, Spidcom, and so forth).

The CEPCA alliance proposals are close to those implemented in HomePlug

AV, which provides a mechanism for the coexistence of HomePlug 1.0, Turbo, and

AV networks with a TDMA time space allocation scheme (see Chapters 3 and 5).

Figure 13.3 diagrammatically illustrates this coexistence system, in which some

time periods are allocated to data exchanges between HomePlug 1.0 devices and

other periods to exchanges between the devices of other HomePlug specifications.

This type of intelligent management of the coexistence of devices from various

HomePlug technologies should be extended to other technologies with the expected

development of an IEEE standard.

As indicated in Table 13.1, the various HomePlug specification developments

always attempted to promote interoperability and therefore open-endedness of PLC

networks. On the other hand, the other PLC technologies are neither interoperable

with HomePlug nor between themselves, which highly restricts the open-endedness

of these networks.

Coexistence of Multiple Networks 297

Figure 13.2 Proposal for the management of mutual interference between PLC technologies

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 316