Overview
ISO 18440:2016 - “Space data and information transfer systems - Space link extension - Internet protocol for transfer services” - defines the Internet-based protocol (ISP1) for exchanging Space Link Extension (SLE) Protocol Data Units (PDUs) between an SLE user and an SLE provider. Published by ISO and derived from the CCSDS recommended standard, the document specifies how SLE transfer service messages are encoded, transported and managed over TCP/IP using ASN.1 encoding, while remaining implementation- and product-neutral.
Key topics and technical requirements
- Transport and encoding: Uses TCP/IP for transport and ASN.1 for data encoding to carry SLE PDUs (the ISP1 protocol).
- Association management: Procedures for establishing and releasing associations (connection setup/teardown) between SLE entities.
- Message and interface definitions: Detailed message types and primitives across layers - Authentication Layer (AL), Data Encoding Layer (DEL) and Transport Mapping Layer (TML) - including TML message and context formats.
- Connection monitoring and state machine: Mechanisms to monitor link status and a TML state table governing events, states and actions.
- Interoperability and data representation: Methods to convert PDUs between platform-specific formats to ensure cross-platform interoperability.
- Security considerations: Defines authentication and security aspects for ISP1; the 2015/2016 update replaced the recommended one-way hash from SHA‑1 to SHA‑256 and updates related references.
- Scope limits: The standard explicitly does not specify product designs, TCP/IP stack configuration, or how IP addresses and TCP port numbers are assigned or agreed.
Applications
- Enabling reliable transfer of spacecraft forward and return space-link data units - e.g., telemetry, return mission data, and other space link payloads - between ground systems and spacecraft-related service providers.
- Standardizing ground-segment communications and interfaces for multi-agency interoperability and mission-to-mission reuse.
- Guidance for middleware, protocol gateways, and ground station software that implement SLE transfer services over Internet protocols.
Who uses this standard
- Mission systems engineers and architects planning SLE-based data transfer
- Ground-segment developers implementing SLE user/provider software
- Systems integrators and interoperability teams across space agencies and commercial ground service providers
- Standards and compliance teams referencing CCSDS/ISO SLE protocols
Related standards
- CCSDS SLE Transfer Service Recommended Standards (SLE service definitions)
- Internet protocol standards: TCP and IP
- ASN.1 encoding standards
- ISO/CCSDS documents on Space Link Extension and related space-data systems
ISO 18440:2016 is available from ISO and CCSDS publications for organizations implementing ISP1 SLE transfer services and seeking interoperable, Internet-based space link transfer solutions.