ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka stáhnout pdf (Strana 76)

the destination station or is damaged when it is received, NACK (non-acknowledg-

ment) or FAIL (failure) processes are implemented between the source station and

the destination station prior to the resending of the missing or damaged segments.

Reassembly

When they are received, the segments are buffered and indexed in the reassembly

buffer of the destination station with the station address and priority. Once all the

segments of a SB are received, the data block is de-encapsulated and transmitted to

the OSI model upper layers. The SB then form IP frames with TCP or UDP headers.

The reassembly buffer can then be emptied so that the next frames can be

received. The size of the buffer is intended to favor the maximum transmission

speed over the transmission channel. However, since access to the medium (CSMA)

is not deterministic, the buffer cannot anticipate the segment transmission speed

and can find itself in a saturation situation, in which it can no longer accept addi-

tional segments. It then asks the source station to resend the segments that are not

processed at a later time.

Other Functionalities

The PLC implement other network functionalities in order to optimize the use of the

transmission channel, in particular in terms of data transmission speed.

Other Functionalities 57

Pair <SA, P>

Pair <SA, P> = Source Address, priority

Figure 3.24 Data frame fragmentation

1 2 ... 71 72 73 74 75 76 77 78 79 80 81 ... 348 349

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ZyXEL Communications PLA-470 V2 - V3.0.5 Instalační příručka Strana 76