Fiber Rings from AFL are compact launch/receive cables designed to measure the insertion loss of the near-end and/or far-end connection of a fiber optic link using an OTDR. Both a launch and receive cable are required to measure complete link loss of a fiber with an OTDR. Launch and receive test cables can range from 150 m to 1 km (or longer) in length. AFL offers coiled lengths of multimode or single-mode fiber packaged in compact rings. Fiber Rings with 500 m of single-mode fiber are designed for broadband, long-haul fiber network test applications. (Source: AFL OTDR Fiber Rings product page and FR00-00-2000 specification sheet.)