The direct-buried fiber optic cables allow underground laying without usage of additional pipes. The cables stand up with added mechanical protection, moisture resistance, and environmental and biological hazards to rodents, termites, and fire. These include, but are not limited to:. Recommendation ITU-T L. First, in order to demonstrate sufficient performance of an. Installing fiber underground is one of the most durable ways to protect a network's backbone — when it's done right. Below is a breakdown of the key categories, product.