There are a number of communication protocols that can be used in conjunction with the SpaceWire Standard (ECSS-E-ST-50-12) in order to provide a comprehensive set of services for onboard user applications. To distinguish between the various protocols a protocol identifier is used, as specified in ECSS-E-ST-50-51. This Standard specifies the CCSDS packet transfer protocol, which is one of these protocols that functions via SpaceWire. The aim of the CCSDS Packet Transfer Protocol is to transfer CCSDS Packets across a SpaceWire network. It does this by encapsulating the CCSDS Packet in a SpaceWire packet, transferring it across the SpaceWire network and then extracting the CCSDS Packet at the target. This standard may be tailored for the specific characteristics and constraints of a space project in conformance with ECSS-S-ST-00. This document (EN 16603-50-53:2015) has been prepared by Technical Committee CEN/CLC/TC 5 "Space", the secretariat of which is held by DIN (Germany). This document has been developed to specifically cover space systems and therefore has precedence over any European Standard since it covers the same scope but with a wider domain of applicability (for example aerospace). The responsible German body is Working Committee NA 131-10-01 AA "Interoperabilität von Informations-, Kommunikations- und Navigationssystemen" ("Interoperability of information, communication and navigation systems") of the Aerospace Standards Committee (NL) at DIN.