ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 78)

The unicast mode is also possible: since the PLC stations are identified by their

MAC address, if a station knows the MAC address of another station, it can address

the MPDU directly and solely to this station.

Service Quality

The quality of service, which has become very important in IP networks, is used to

differentiate the priorities of the various traffic over the network. As we’ll see in

Chapter 6, the IP services require different constraints in terms of transmission

speed, network travel time, and jitter between the frames transmitted over the net-

work.

These constraints are decisive for applications and for the upper layers of the

OSI model to maintain a TCP connection for HTTPS traffic, an FTP connection,

and so forth.

Therefore, it is necessary to implement priority levels for MAC level and physi-

cal level frames according to the constraints of the upper layer applications. This

must be done in the frames insofar as the medium is shared as a MAC level network

hub.

The quality of service is made possible in PLC networks with the priorities of

the network devices. These priorities are indicated by the CAP parameter, which is

interpreted during the priority (PRP1 and PRP2) resolution periods just before the

contention frames.

Figure 3.25 illustrates the priority levels (CA0, CA1, CA2, and CA3) in the

PRP1 and PRP2 priority resolution periods. The contention bit included in the end

Other Functionalities 59

Figure 3.25 Quality of service management

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 78