ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka Strana 67

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NACK Response
In the case a NACK type acknowledgment, the destination station resends to the
source station a response frame after a contention period in order to indicate that the
data has been damaged during the transmission. The source station resends in its
turn to the destination station a confirmation of the NACK acknowledgment and
retransmits the damaged data frame segment (see Figure 3.13).
FAIL Response
The FAIL response indicates that the destination station could not use the received
data frame due to a collision or a congestion of the data receipt buffer. The destina-
tion station cannot foresee the data rate that it will receive and can be incapable of
storing all the received data.
A 10-ms contention period specific to FAIL responses is mandatory in this case
(see Figure 3.14).
The destination station records the number of times that the FAIL status
has appeared in the segment. If this number exceeds a given threshold, the
destination station asks the source station to resend the service block from the first
segment.
48 Functionality
Figure 3.13 NACK-type acknowledgment in HomePlug 1.0
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