ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka stáhnout pdf (Strana 65)

The destination station can resend three types of acknowledgment frames:

•

ACK. The destination station has correctly received the data contained in the

frames and this data is correct.

•

NACK. The destination station has correctly received the data but some data

is damaged. This check is carried out using the CRC (cyclic redundancy check)

value. The destination station then asks the source station to resend the dam-

aged data segment.

•

FAIL. The data has not reached the destination station or the station buffer is

full and cannot receive and process the data.

Figure 3.10 illustrates, in terms of time, the various acknowledgment response

types in the HomePlug 1.0 PLC standard. This process improves the medium access

quality by allowing exchanges between the source stations and the destination sta-

tions.

The source and destination stations use one of the fields present in the data

frame to determine the response frame that will be resent to the source station. This

field, which is called FCS (frame check sequence), is used to check the integrity of the

data received by the destination station.

In the same way, the destination station resends the acknowledgment with a

part of this field, the RFCS (response FCS) field. This field is used by the source sta-

tion to know whether the data has been correctly received by comparing the trans-

mitted FCS with the received RFCS (see Figure 3.11).

46 Functionality

Figure 3.10 Acknowledgment frames in the ARQ process

1 2 ... 60 61 62 63 64 65 66 67 68 69 70 ... 348 349

Žádné komentáře

ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka Strana 65