40/100G QSFP BiDi Transceiver’s Backward Compatibility With 40G BiDi

We mentioned recently the new dual-rate 40G/100G BiDi QSFP28 pluggable optic transceiver module. Like the single-rate 40G BiDi, it lets you seamlessly upgrade short reach links from 10G without having to replace duplex LC-connectorized MMF fiber infrastructure originally meant for 10G SR. But that’s not the only reason to be excited about it.

First, let’s remind ourselves that managing and maintaining data centers can be a big job. Upgrading network gear and servers is a never-ending necessity. Often, it’s not practical to rip out all the old equipment and replace the whole thing all at once. There’s downtime to consider, refresh cycles, and of course budget limitations. If only there was a way to upgrade different portions of the data center at different times.

There is, in fact, a way with multi-rate ports. And as we described in an earlier blog post, multi-rate ports give you flexibility in your upgrade strategies. Now, with a dual-rate optic like the 40/100G BiDi, you have even more options. This is due to its backward compatibility with the original single-rate 40G BiDi. This capability, by the way, is only available from Cisco.

As shown in the figure, a dual-rate 40/100G BiDi plugged into a 40/100G switch port (green box on the left) can still link with a native 40G BiDi plugged into an older switch with a single-rate 40G port (orange box on the right). The dual-rate port on the left would be set to 40G mode in the switch software (see red outline in the figure).

Once you’re ready to upgrade the other end, you can replace the 40G switch with a new one that supports 100G QSFP28 ports, like the dual-rate 40/100G Nexus switches. Just plug in the new 40/100G BiDi, tell the switch software on both ends to run the port at 100G, and you’ve completed the upgrade.

More information can be found on the QSFP100 product family data sheet. A video on multi-rate ports can be found on the Cisco Optics playlist of the Cisco YouTube channel.

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