Therefore, the technology must adapt to any cable plant quality and be
very efficient to best utilize any environment.
Figure 5.2 illustrates 64/65-octet encoding. Using this encoding, the physical layer
is partitioned into 65-octet blocks, and in each 65-octet block, up to 64-octets can hold
data and 1 octet is used for synchronization purposes. This makes the encoding very
efficient. Additionally, depending on the contents of the 64-octet block, the first byte of
Figure 5.2 64/65-octet encoding examples
Sync
Word
Octets 1-64 of data, idle, or codewords
0?—0F 64-octets of data
0?—F0 64-octets of idle
0?—F0 k-octets of data, (63-k) octets of idle Ck
Generic 65-octet block
Generic 65-octet block
Block containing all data
Block containing all idle
Block when end of frame (k-octets of data then idle)
Copper 135
the data field may contain a special codeword that provides additional information on
the contents of the block (whether it??™s the start of frame, end of frame, etc.).
Additionally, 64/65-octet encapsulation includes measures to improve the false packet
acceptance results of traditional DSL encoding. DSL physical layers generally operate
in modes that yield a bit-error rate of 10-7.
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