Analysis and performances of the Unified Space Data Link Protocol and the Space Data Link Security Protocol specified by CCSDS.

Abstract

The purpose of this thesis is to simulate the Unified Space Data Link Protocol and analyse its performance. To do that, we first study all the recommended standards on USLP provided by the CCSDS. We choose one service, the MasterAccess Point Packet, provided by the protocol and all its properties have been studied. Firstly, the construction of a USLP frame with and without the SpaceData Link Security Protocol is analysed. An advantage of the USLP is that frames with a length of up to 65536 bits can be sent. This advantage permits to send fewer frames and, therefore, decrease the propagation delays of a communication. In each USLP frame, the mandatory information is attached to the header of the frame. The extraction of the headers is performed by the receiver. The next step is the study of the SDLS Protocol and how cryptography can be added in a USLP frame. Only the AES-128 encryption algorithm is provided in details. To be sure that the algorithm is working properly in 2021, a brute force analysis is performed. Secondly, the transmission/re-transmission process is designed following the USLP Recommended Standards. A binary symmetric channel is used to model the channel between the sender and the receiver. Furthermore, the re-transmission follows an Automatic Repeat Request algorithm: the Go-Back-N.With all these information, a model is created and implemented in Matlab. As result, we see that the AES-128 encryption can’t be analysed in Matlab because this encryption takes more time than a real sender. However, without encryption, the model simulates properly a communication with the USLP. The parameters of the communication are : the distance between the two end-points of the communication, the data rate of the channel, the binary error probability of the binary symmetric channel, the frame length and the size of the sliding window from the sender side. The model is tested on the PLATO space mission managed by the ESA. In this configuration, we obtain a throughput of up to 5Kbits/s.