ZyXEL Communications PLA-470 V2 - V3.0.5 Przewodnik Instalacji Pobierz pdf (Strona 272)

(guaranteed high thrughput, propagation time, jitter) are crucial for the good transmis

sion operation without data loss.

These constraints can be tolerated by implementing the following functionalities (see

Chapter 3):

•

PLC signal synchronization with 50/60 Hz in order to guarantee TDMA and

CSMA/CA time spaces with CP (contention period) and CFP (contention-free

period);

•

QMP (QoS and MAC parameters) in the CM (connection manager), CCo (central

coordinator) and STA (station) devices;

•

Propagation of the QMP between the various network devices in order to keep the

PLC network homogeneous in terms of QoS and performance.

Among the QMP parameters, Table 11.3 summarizes the most important ones for

QoS management. As a reminder, the MSDU (MAC service data unit) is the data frame at

the MAC level in the data link layer.

As we can see, the QoS management in HomePlug AV is particularly complicated and

uses many parameters permanently exchanged between the network PLC devices.

This QoS management guarantees the network constraints that are required for the

applications. HomePlug AV specifies eight application classes corresponding to various

user priority levels, as indicated in Table 11.4.

Access to the Electrical Medium

As we have seen in Chapters 7 and 10, the two main methods for gaining access to

the electrical medium are the following:

•

Capacitive coupling, which consists of connecting the PLC device (gateway or

network device) to an outlet like a home electrical device (see Figure 11.4).

•

Inductive coupling, which is more efficient to broadcast the PLC signal over

the cables and allows better performance. However, it requires access to the

electrical wirings, which is only possible at the circuit breaker panel level by

using couplers/injectors on each cable (on a single cable or several cables at

the same time).

Figure 11.5 illustrates the principle of each type of PLC signal injection over the

electrical wirings at the circuit breaker panel level. To place the PLC signal injection

systems, it is preferable to remove the case of the circuit breaker panel in order to

gain access to the various outgoing cables to the building outlets. To carry out this

operation, it is necessary to be authorized to intervene on electrical networks or to

call on an approved electrician.

Mutual induction phenomena between the electrical wirings of a network, in

particular at the circuit breaker panel level, where the cables are close to each other,

enable consideration of the system in different ways:

•

A single cable (or a single phase or the neutral cable), with induction on the

other cables.

•

Several cables at the same time, with a single injector including all the cables

and mutual induction to the neutral cable.

Choosing Network and Electrical Equipment 253

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