Page 1249 - 5G Basics - Core Network Aspects

Transport aspects 2

Annex B

Adapting 64B/66B encoded clients via transcoding into 513B code blocks
(This annex forms an integral part of this Recommendation.)

Clients using 64B/66B coding can be adapted in a codeword and timing transparent mapping via
transcoding into 513B code blocks to reduce the bit rate that is required to transport the signal. The
resulting 513B blocks can be mapped in one of several ways depending on the requirements of the client
and the available bandwidth of the container into which the client is mapped. This mapping can be applied
to serial or parallel client interfaces.

B.1 Transmission order

The order of transmission of information in all the diagrams in this annex is first from left to right and then
from top to bottom.

B.2 Client frame recovery
For 40GBASE-R and 100GBASE-R clients, framing recovery consists of the recovering 64B/66B block lock per
the state diagram in Figure 82-10 of [IEEE 802.3]. For other 64B/66B encoded clients, block lock is achieved
as per the state diagram in Figure 49-12 of [IEEE 802.3]. Descrambling is performed as per the process
shown in Figure 49-10 of [IEEE 802.3].

Each 66B codeword (after block lock) is one of the following:
 a set of eight data bytes with a sync header of "01";
 a control block (possibly including seven or fewer data octets) beginning with a sync header of
"10".
The 64 bits following the sync header are scrambled as a continuous bit-stream (skipping sync headers and
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PCS lane markers) according to the polynomial G(x) = 1 + x +x . The 64B/66B PCS receive process will
descramble the bits other than (1) the sync header of 66B data and control blocks, and (2) the PCS lane
markers.
Figure B.1 illustrates the ordering of 64B/66B code blocks after the completion of the recovering process
for an interface.

Transmissi
Transmission orderon order
66B Block
66B Block
1 1 66B Block
66B Block
66B Block
66B Block
2 2 66B Block
3 3 66B Block
66B Block
66B Block
66B Block
: : : : :
x x 66B Block
66B Block
66B Block
Transmissi
1….…………….........66….…………….........66 Transmission orderon order
1
Figure B.1 – Stream of 64B/66B code blocks for transcoding
B.3 Transcoding from 66B blocks to 513B blocks
The transcoding process at the encoder operates on an input sequence of 66B code blocks.
66B control blocks (after descrambling) follow the format shown in Figure B.2.
A group of eight 66B blocks is encoded into a single 513B block. The format is illustrated in Figure B.3.

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