This Interim European telecommunications Standard (I-ETS) applies to balanced fibre branching devices to be used in single mode optical transmission networks. Unbalanced fibre branching devices should also satisfy similar mechanical and environmental requirements. The scope is to establish minimum uniform requirements for the following aspects: - optical, environmental and mechanical properties; - test conditions; - acceptance criteria. Some users may have additional specific requirements, such as a need to verify perfprmance at lower temperatures. These users should specify connectors conforming to the basic ETSI performance standard, plus additional tests or more severe test conditions. Acceptance criteria will be interpreted with respect to the condition that some of the parameters specified in this I-ETS may be affected by measurement uncertainty arising either from measurement or calibration errors. Test methods are in accordance with EN 181 000 unless otherwise specified. A fibre branching device is : A passive optical component which splits the incoming signal (M) to a number of outputs (N).