In our Acronym Series, Nexum’s expert engineers define the industry’s most popular topics.

Acronym: BiDi – Bidirectional

Definition: BiDi is a type of optical transceiver that can accommodate two different directions of traffic on a single strand of fiber.

Explanation of where it’s used in the IT/IT Security Realm: 

• In non-BiDi optics, there is a 1:1 ratio for data stream to fiber. Stated another way, the data streams are unidirectional, meaning one fiber is dedicated for transmission (tx), while another fiber is dedicated for receiving (rx). Both are required to connect devices for communications. The advent of BiDi allows doubling up the tx/rx onto a single fiber using wavelength division multiplexing (WDM), which combines and separates the data on that single strand. 
• Used in this way, BiDi is a networking–specific acronym.  
• BiDi optics can be useful in areas where there are limited fiber pairs available and potential unidirectional issues in a fiber cut scenario. Since it’s an optical fiber technology, this particular type of transceiver won’t be helpful in copper (electrical) environments. 
• BiDi optics provide no physical redundancy, nor does a traditional fiber pair. A cut of one strand in a legacy pair would result in the loss of either tx or rx rendering the link unusable. Engineers need to bear in mind that using a BiDi optic on a single strand is still a single point of failure (SPoF) and BiDi optics do not remove the need for multiple links, preferably over disparate physical paths, for redundancy.