This ECSS handbook is intended to help implementers and users of data handling systems who are adhering to the EN 16603-50 (equivalent to ECSS-E-ST-50) series of standards. The handbook provides an overview of the EN 16603-50 standards and related CCSDS Recommended Standards and describes how the individual standards may be used together to form a coherent set of communications protocols. It also evaluates issues which could not be discussed in the Standards documents themselves, and provides guidance on option selection and implementation choices. It provides guidance to the EN 16603-50 series of standards including related CCSDS Recommendations. The information provided is informative and intended to be used as best practice; it is not binding on implementers. The information contained in this handbook is not part of the Standards. In the event of any conflict between the Standards and the material presented in this handbook, the ECSS Standards prevail.