Re: [802.3ae] XSBI Bit ordering
I understand your confusion. To make it simple, think of the XSBI and
the PMA service interface as two distinct entities (for now). The PMA
service interface is described throughout the clauses in 802.3ae. The
ordering (as defined in clause 49) has bit 0 as the LSB which is the
bit in the serial stream for the fiber. Clause 49 clearly shows that the
bit ordering remains constant whether the WIS is used or not. I'll
this agian. Bit 0 on the PMA service interface is always the LSB, and
is always the first serial bit.
The XSBI is an optional physical implementation of the PMA service
interface. This means that you can use XSBI or not. The XSBI bus
is compatible with the SFI-4 bus defined by the OIF. It considers
bit 15 as the LSB which is serialized first. In other words, the bits
are reversed from the PMA service interface. Again bit 15 is the LSB
of this bus and is serialized first whether the WIS is used or not.
To connect an XSBI compatible device to a PMA service interface
it is neccessary to cross the signals as described in the clause 51
table you reference. That is bit 0 of the PMA_client maps to bit
15 of the XSBI compatible PMA. Likewise bit 1 of the PMA_client
maps to bit 14 of the XSBI compatible PMA. Up to bit 15 of the
PMA_client mapping to bit 0 of the XSBI compatible PMA. This
bit mapping exists for all cases where an XSBI compatible interface
is connected to a PMA client. It applies whether the WIS is used or
I hope that clarifies the differences between the PMA service interface
and the optional XSBI implementation.
> hi all,
> While going through the IEEE 802.3 ae Draft 3.1
> Clause 51 describes XSBI mapping as following
> For the XSBI instantiation of the PMA service interface, the mapping of
> bits between the PMA service interface and the XSBI physical interface
> is defined for transmit in Table 51 2 and for receive in Table 51 3.
> Table 51 2 Transmit bit mapping
> Name Bit numbers
> PMA service tx_data-group 0 1 2 3 4 5 6 7 8
> 9 10 11 12 13 14 15
> ^ ^
> XSBI physical xsbi_tx 15 14 13 12 11 10 9 8 7
> 6 5 4 3 2 1 0
> Table 51 3 Receive bit mapping
> Bit numbers
> PMA service rx_data-group 0 1 2 3 4
> 5 6 7 8 9 10 11 12 13 14 15
> XSBI physical xsbi_rx 15 14 13 12 11
> 10 9 8 7 6 5 4 3 2 1 0
> Clause 51 does not say bit mapping will be done
> only for LAN or WAN or for both.
> But in Clause 49
> The ordering of bits and octets for the case when no WIS is present
> between the PCS and PMA is shown in Figure 49 2
> with no bit reordering meaning that PMA LSB is mapped to LSB of PCS.
> But when WIS is present bit order change is shown in Figure 49-3.
> Do we need to change the bit ordering for both LAN and WAN application?
> If it is only for WAN i.e., with WIS only then Clause 51 has to be
> updated with this point in the XSBI description.
> Please correct if i am wrong or miss understood.
Tim Warland P. Eng.
Quake Technologies (613)270-8113 ext2311
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