More on 40G Modules & revisiting the X40-MSA

With the new CFP MSA for 40G/100G and several companies showcasing 40G 300pin VSR modules (that actually fits the 10G 300pin MSA) I started thinking again about what form factor a 40GBase-LR4 module would take (not that it takes that much).

Currently 40G Ethernet is benefiting from demand for 40G Infiniband (or should we say riding on the Infiniband-wagon) so there are plenty of solutions out there for both copper, using devices from Gennum or Quellan, and optical in the form of QDR active cables from Avago, Finisar, Luxtera etc. With these solutions it seems that the 40GBase-KR4, CR4 and SR4 applications are pretty well covered with the CR4 and SR4 using the compact QSFP MSA module format.

However for 40GBase-LR4 the benefit from Infiniband disappears plus we have the added complexity of moving from 4×850nm VCSEL arrays to a 4×1300nm arrays and requiring the additional CWDM Mux/Demux plus female connectors, typically SC. To add to the confusion, the type of equipment that might want to use a 40GBase-LR4 module (Routers/DWDM) are the same ones using 40G 300pin VSR modules, which since they are single wavelength, are incompatible and possibly leading to the need for media converters (40GBase-LR4 to 40G VSR) finally any 4X type link does not transport native OC768 POS or OTU3(Bah!).

After some browsing on the subject I rediscovered the X40-MSA website ( which, despite the info being 3 years old, is still very applicable to today. The X40-MSA group proposes to use the XENPACK form factor and replace the XAUI with an XLAUI interface, this would reduce the investment since all the mechanics for the cages etc. already exist. Size wise it is similar in length, about half the width but a little bit higher (W=45.5mm;L=115.2mm;H=17.4mm) than both the CFP 40/100G MSA and the new 40G 300pin SFF (same size at 10G 300pin MSA). I could imagine the height being an issue so perhaps the X2 or XPACK form factor would be better as they are slightly smaller in all dimensions. The X40-MSA group also discusses about the goal of using the QSFP and leveraging work form 10G SFP+, however this would probably mean the need for an external quad EDC between the QSFP module and the ASIC/FPGA MAC/Framer – so something for the future.

The transport of OC768 POS and OTU3 is briefly touch on with the reference to the use of virtual concatenation to replace the PCS-MLD layer used by 40G Ethernet. This, for sure, would be too cumbersome but some form of byte interleaving similar to that used with the OIF TFI-5 backplane would probably suffice. Regardless of the solution it would require extra logic to be implemented into the POS framer or OTN FEC device, so its a good job there are plenty of FPGA and IP companies out there.

One alternative solution would be for the development of a new WAN orientated 40G Ethernet standard (what!! – heresy I hear you cry), something like a 40GBase-VSR which supported a SFI-5.2 interface along with XLAUI – well let’s see (but don’t hold your breath:-)

40G Ethernet Resource Center

One Response to “More on 40G Modules & revisiting the X40-MSA”

  1. 40gethernet Says:

    Since this blog was written there have been some developments in the area of using the X2 MSA format which means that although the X40-MSA is consigned to the past it was certainly on the right track.

    The first is the use of the X2 MSA form factor by Hitachi in the XL2 40Gbase-LR4 module which can be found here

    The second is the possible use ofthe X2 MSA as the basis for a new CFP2 module that would support 4xCEI-28 interfaces rather than the XAUI or XLAUI. The CFP2 is only alluded to in various presentations so we’ll have to wait a bit longer to see what the IEEE, CFP-MSA and OIF come up with.

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