Re: [802.3ae] XSBI Bit ordering
Hello Satya (and Tom),
This bit ordering is a bit messy. Let me state the "facts" and how the
standard approached this.
1) In the SONET world, a frame is sent w/ MSB first.
2) In the Ethernet LAN world, packets are sent LSB first.
3) The XSBI was/is trying to leverage from the SONET world,
SFI-4.Allowing to
Ethernet world
to use existing OC192 parts if needed.
Given all the above ... the implementor/supplier any and all involved
should
be made aware
of these things.
The agreed 802.3ae approach to this is to have all clauses "speak" to
bit
ordering is a logical sense. Only
in clause 51 does this get highlighted (many areas). Hope this helps.
Tom,
Do you have anything to add here?
Regards,
Justin
satya wrote:
> 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
> interface
> ^ ^
>
> |
> |
> XSBI physical xsbi_tx 15 14 13 12 11 10 9 8 7
> 6 5 4 3 2 1 0
> interface
>
> Table 51 3 Receive bit mapping
>
> Name
> Bit numbers
>
> PMA service rx_data-group 0 1 2 3 4
> 5 6 7 8 9 10 11 12 13 14 15
> interface
> ^
> ^
>
> |
> |
> XSBI physical xsbi_rx 15 14 13 12 11
> 10 9 8 7 6 5 4 3 2 1 0
> interface
>
> 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.
>
> ----------
> Question
> ----------
>
> 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.
>
> Thanks
> satya
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