ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación descargar pdf (Pagina 55)

HomePlug 1.0 PLC Network Hierarchy by Means of Priorities

Within IEEE 802.3 Ethernet frames, a VLAN field may be placed described in the IEEE

802.1Q standard. Within the framework of PLC networks in peer-to-peer mode, this field is

used to create almost a hierarchy between the PLC devices of the same network. The field is

encoded on 3 bits and therefore can have eight values.

Table 3.3 lists the four available PLC priorities according to the value of the VLAN field.

It may be useful to implement a higher priority on a PLC device used as a gateway to

another IP network or being connected to a device of the server type liable to receive much

traffic from the other network PLC devices connected to the PC in the client mode of said

server. Several PLC devices connected to IP telephones over the network and having prior-

ity 4 to provide the best transmission time for real-time audio communications may also be

possible.

This priority is one of the most important PLC network configuration parameters in the

peer-to-peer mode, even though it is only a logical parameter that has no influence on the

PLC links at a physical level. We’ll cover this parameter again in Chapter 9.

The peer-to-peer mode is widely used in PLC networks complying with the

HomePlug 1.0 standard, since PLC networks in which each device creates PLC links

with devices connected to the other sockets of the electrical network can be quickly

created with it. This mode is thus used to create a PLC ad hoc network over the elec-

trical architecture of the building for the application requirements of the local area

network.

The configuration and the optimization of the PLC network depend on the

functionalities anticipated on the local area network and on the requirements in

terms of client-server architecture in order to achieve a realistic architecture with

regard to the performance of the PLC technologies.

Figure 3.3 illustrates the various steps in the organization of a PLC network in

the peer-to-peer mode from the functionality requirements to the technical

solutions.

Centralized Mode

The architecture of the HomePlug AV PLC technology is actually neither in the

peer-to-peer mode nor in the master-slave mode. It involves two device types:

devices with a similar hierarchical level and a centralizing device, as illustrated in

Figure 3.4.

The CCo (central) device manages medium access allocations for the various

PLC devices that want to communicate between themselves.

36 Functionality

Table 3.3 PLC Priorities of VLAN Field

PRIORITY

VLAN FIELD

VALUE

APPLICATION CLASS

Priority 3 7,6 VoIP (less than 10 ms transmission time)

Priority 2 4,5 Video over IP (less than 100 ms transmission time)

Priority 1 2,3 Raw data transfer and control traffic

Priority 0 0,1 Limited data communication

1 2 ... 50 51 52 53 54 55 56 57 58 59 60 ... 348 349

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ZyXEL Communications PLA-470 V2 - V3.0.5 Guía de instalación Pagina 55

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