Cubesat Space Protocol
CubeSat Space Protocol is a small network-layer delivery protocol designed for CubeSats. The idea was developed by a group of students from Aalborg University in 2008, and further developed for the AAUSAT3 CubeSat mission that was launched in 2013. The protocol is based on a 32-bit header containing both network and transport layer information. Its implementation is designed for embedded systems such as the 8-bit AVR microprocessor and the 32-bit ARM and AVR from Atmel. The implementation is written in C and is ported to run on FreeRTOS, Zephyr and POSIX and pthreads-based operating systems such as Linux. The three-letter acronym CSP was adopted as an abbreviation for CAN Space Protocol because the first MAC-layer driver was written for CAN-bus. The physical layer has since been extended to include several other technologies, and the name was therefore extended to the more general CubeSat Space Protocol without changing the abbreviation.
The protocol and the implementation is still actively maintained by Johan de Claville Christiansen, Space Inventor, GomSpace, and Space Cubics. The source code is available under an MIT License and hosted on GitHub.
Description
The CubeSat Space Protocol enables distributed embedded systems to deploy a service-oriented network topology. The layering of CSP corresponds to the same layers as the TCP/IP model. The implementation supports a connection-oriented transport protocol, a router-core, and several network-interfaces. A service-oriented topology eases the design of satellite subsystems, since the communication bus itself is the interface to other subsystems. This means that each subsystem developer only needs to define a service-contract, and a set of port-numbers their system will be responding on. Furthermore, subsystem inter-dependencies are reduced, and redundancy is easily added by adding multiple similar nodes to the communication bus.Key features include:
- Simple API similar to Berkeley sockets.
- Router core with static routes. Supports transparent forwarding of packets over e.g. spacelink.
- Support for both connectionless operation, and connection oriented operation.
- Service handler that implements ICMP-like requests such as ping and buffer status.
- Support for loopback traffic. This can e.g. be used for inter-process communication between subsystem tasks.
- Optional support for broadcast traffic if supported by the physical interface.
- Optional support for promiscuous mode if supported by the physical interface.
- Optional support for encrypted packets with XTEA in CTR mode.
- Optional support for HMAC authenticated packets with truncated SHA-1 HMAC.
Operating systems supported
CSP should compile on all platforms that have a recent version of the gcc compiler. CSP requires support for C99 features such as inline functions and designated initializers.- FreeRTOS – Tested on AVR8, AVR32 and ARM7.
- Linux – Tested on x86, x86-64 and Blackfin.
- Mac OS X
- Microsoft Windows
- Zephyr