Over the past few months, we’ve had several customers ask about 40G/100G bi-directional (bi-di) transceivers that have recently come on the market. At first, full-duplex transmission up to 100G on a single strand of fiber sounds too good to be true. The truth, however, is a bit more complex than that. It’s important to understand what this emerging technology actually is, its intended applications, and what available alternatives may better suit your needs.

We’ve been touting the tremendous cost savings (both capital and operational) of bi-directional transceivers for years. Our portfolio includes several different form factors which offer up to 10G transmission on a single strand of fiber. Here, one laser sends and receives data on two different wavelengths:

While the terminology suggests these new 40G/100G transceivers operate the same way, that isn’t quite the case. For a single transceiver to achieve 100G bi-directional transmission, two 50G lasers are required, to offer an aggregate throughput of 100G.

Think of it as two traditional bi-dis packaged together; since two lasers are required, you don’t have the same fiber utilization advantages you get with “true” 1G and 10G bi-dis.

Additionally, these transceivers don’t perfectly interoperate with the native QSFP 4×25 channel format, which can cause interoperability issues that preclude the use of standards-based transceivers elsewhere in your network.

There are also cost considerations. This design requires additional internal components that make this particular transceiver much more expensive than a standard 100G QSFP28—namely, the SR4 and CWDM4— that would be deployed in similar applications. The cost of operating your network could rise even more due to the aforementioned interoperability issue that could force more cost-effective standards-based transceivers out of your network.

This is not to say this “bi-di” is without its uses. Despite the cost disadvantages, it could be useful for data centers looking to migrate from 10G to 40G and 100G while preserving their current fiber infrastructure.

Interested in learning more about open standards-based QSFP28s? Request a quote here.

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