ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka stáhnout pdf (Strana 32)

PART I

PLC Theory

This part of the book is devoted to the HomePlug specification. Created by the

industrial alliance of the same name, HomePlug focuses on two principal aspects:

the physical layer, concerned with data transmission over the power line medium;

and the data link layer, which defines the architecture and mechanisms to imple-

ment, allowing this transmission to take place over the network under the best pos-

sible conditions.

Since the release of HomePlug 1.0, two more versions have appeared, bringing

improvements in transmission speed, security, and service quality.

To improve data transmission, the physical layer uses optimized techniques for

coding, modulation, and error correction, resulting in excellent connectivity

between devices and good transmission rates. The respective transmission rates for

HomePlug 1.0, Turbo, and AV are 14 Mbit/s, 85 Mbit/s, and 200 Mbit/s, placing

PLC in direct competition with Ethernet and Wi-Fi networks.

The data link layer implements a set of technologies providing excellent condi-

tions for high performance transmission of data in the form of IP packets. The net-

work access techniques that define this layer determine the network performance.

Successive releases of the HomePlug specification have improved this layer. Ser-

vice quality has been optimized using time division multiple access (TDMA) tech-

niques, and management of the network architecture of PLC devices has been

refined through a hierarchal organization of data frames. Service quality is a key ele-

ment for transmission of data in real-time applications, such as voice or video.

The difficulty of access to the physical medium under PLC provides increased

immunity to attacks, yielding a higher security level that differentiates PLC from

Wi-Fi. This immunity is further strengthened by the implementation of DES and

AES encryption of frames transmitted on the power line medium, and by network

integrity techniques that allow management of the devices authorized to participate

in the PLC network.

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ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka Strana 32