10-Dec-2012-cesg-1 Presentation to ESTEC Nordwijk, Netherlands 8 April 2014 CCSDS Space Link Services (SLS) Area Area Director: Gian Paolo Calzolari (ESA/ESOC) Deputy Area Director: Gilles Moury (CNES)

10-Dec-2012-cesg-2 SLS – We are the Space Link Services

10-Dec-2012-cesg-3 Communications Scenario

10-Dec-2012-cesg-4 Layering (1) CCSDS started from this layered approach. The CCSDS Data Link Layer and the Physical Layer are hosting the typical Tracking, Telemetry and Command functions; i.e. they are the historical and basic layers for CCSDS Communications.

10-Dec-2012-cesg-5 Layering (2) A more detailed view of the layered approach is shown below together with the related standards. The CCSDS Data Link Layer and the is actually split between Protocol (sub)Layer and a Synchronization and Coding (sub)Layer. NOTE: The Proximity-1 Protocol Suite is totally dedicated to Orbiter- Lander links (e.g. Mars vicinity). During the years, those basic layers revealed to be very strong, and demonstrated they could also sustain more elements built on top of them.

10-Dec-2012-cesg-6 DELTA DOR PN RANGING Prox-1TM, TC LTP DTN-BP/BSP Channel Coding and Sync IP over CCSDS CFDP AOS RANGING Encapsulation Packet SECURITY RF & Modulation SLS AREA DATA COMPRESSION SLS AREA Multispectral Hyperspectral Data Compression WG Space Data Link Security WG (SDLS Protocol Function for Authentication and Confidentiality) Space Link Protocols WG Coding & Synchronization WG RF & Modulation WG Optical Communications WG O.CC&S O.Mod&W Space Packet Protocol AOS Services Encapsulation Service SLS Area in the CCSDS Layered approach (simplified view)

10-Dec-2012-cesg-7 The Basic Communications Standards: Physical Layer The Radio Frequency and Modulation Systems standard collects most of the standards for the physical layer. It focuses upon the standardization of RF and modulation systems for Earth stations and spacecraft. Technical Recommendations are subdivided into groups representing the various subsystems. These are: Earth-to-Space Radio Frequency, Telecommand, Space-to-Earth Radio Frequency, Telemetry, Radio Metric, and Spacecraft. Policy Recommendations include: Frequency Utilization, Power Limitations, Modulation Methods, Operational Procedures, Testing Recommendations, and Spacecraft Systems. Other standards for the physical layer include Pseudo- Noise (PN) Ranging Systems and Data Transmission and PN Ranging for 2 GHz CDMA Link via Data Relay Satellite and Proximity-1.

10-Dec-2012-cesg-8 The Basic Communications Standards Synchronization and Coding (sub)layer The standards for the Synchronization and Coding (sub)layer do differentiate between Telemetry and Telecommand as they offer different types of services for those two unbalanced channels. The TM Synchronization and Channel Coding standard provides unidirectional (one way) transfer of a sequence of fixed-length TM or AOS Transfer Frames at a constant frame rate over a Physical Channel across a space link, with optional error detection/correction. The TC Synchronization and Channel Coding standard provides unidirectional (one way) transfer of a sequence of variable-length TC Transfer Frames over a Physical Channel across a space link, with optional error detection/correction. While the TC coding scheme is stable since years, many different options with different Frame/Bit Error Rate (FER/BER) performances are available for telemetry; i.e. convolutional, Reed-Solomon, concatenated RS+convolutional, Turbo Codes, Low- density Parity-check (LDPC) codes, Serially Concatenated Convolutional Codes and DVB-S2. There is also a coding standard for Proximity-1.

10-Dec-2012-cesg-9 Coding Gain Here a comparison of the Bit Error Rate curves for different coding schemes allowed by CCSDS. A given coding scheme can be good for a given scenario but cumbersome for another one (like driving to supermarket with a Rolls-Royce ) Better

10-Dec-2012-cesg-10 The Basic Communications Standards Data Link Protocol (sub)layer The most important capability of the Space Data Link Protocols (sub)layer is the Master/Virtual Channel multiplexing. The (original) standards also differentiate between Down/Up-link. The TM Space Data Link Protocol standard specifies the Data Link layer protocol, services, and procedures pertaining to the Transfer Frame for the Space-to-Earth link. It replaces the old Packet Telemetry Specification. The TC Space Data Link Protocol standard specifies the Data Link layer protocol, services, and procedures pertaining to the Transfer Frame for the Earth-to-Space link. It replaces the old Packet Telecommand Specification. The Advanced Orbiting Systems, Networks and Data Links: Architectural Specification was developed in the (late) 1980’s to provide bidirectional transmission of multiple data types (including voice and video) at high data rates targeted to manned/man-tended space stations etc. Today largely used by (ESA) EO payloads: The AOS Space Data Link Protocol standard specifies the Data Link layer protocol, services, and procedures pertaining to the CCSDS Version-2 Transfer Frame. There is also a Proximity-1 Space Data Link Protocol.

10-Dec-2012-cesg-11 CCSDS Space Packet Protocol Historically, the Space Packet Protocol (SPP) has been the only method providing a flexible structure (of top of Space Data Link protocols) for transferring user/application data from Space to Earth or vice versa. Used as a common structure for TM and TC. Most innovative feature (in the early 1980s) was the APID which identified the packet contents. Previously, content was identified by data position in a repetitive frame. The APID set the data content free from the clockwork frame. Packet header also contains fields for multiplexing packets in to the link. APID subsequently (AOS and pre-Internet) proposed for reuse as networking identifier for packet routing. CCSDS packet is going to be “superseded” as network protocol with the increased networking by IP (and eventually DTN) over Encapsulation Service.

10-Dec-2012-cesg-12 Packet (CCSDS or Encapsulation) Packet Multiplexing in TM and AOS Packet End of Packet End of Packet Beginning of Packet Beginning of Packet Frame Header CCSDS Packet End of CCSDS Packet End of CCSDS Packet Frame Header Fill Packet Fill Packet Fixed Length FrameVariable Length Packet First Header Pointer in Frame Header points to First Packet header in frame Packet length in Packet Header points to next packet header in frame Packets which overrun the frame end are continued into the next frame in the VC and rejoined when demultiplexed Fill packets are used to complete a frame when a new packet is not available to complete it Frame N in Virtual ChannelFrame N+1 in Virtual Channel VC1 Frame VC3 Frame VC2 Frame VC1 Frame VC2 Frame VC3 Frame VC2 Frame VC1 Frame VC2 Frame VC3 Frame TM or AOS link consists of a stream of fixed length frames Each frame contains synchronisation, header, data (e.g. CCSDS packets) and error correction coding Any frame may be allocated to a particular Virtual Channel (VC). VCs are used share the link efficiently Link Structure Packet Multiplexing Minimum fill CCSDS packet size is 7 bytes. Incomplete minimum fill packets run into next frame End of CCSDS Packet End of CCSDS Packet Beginning of long CCSDS Packet Beginning of long CCSDS Packet Frame Header Continuation of CCSDS Packet Frame Header Fixed Length Frame First Header Pointer in Frame Header points to First Packet header in frame Packet length in Packet Header points out of frame and used to check length of reassembled packet First header pointer set to 2043d to indicate no packet header in frame Packet Segmentation End of long CCSDS Packet End of long CCSDS Packet Beginning of CCSDS Packet Beginning of CCSDS Packet Frame Header First header pointer points to end of the long packet and beginning of the next packet

10-Dec-2012-cesg-13 On top of the Data Link Layer… and below For many years, the Space Packet has been used as the main tool to carry data for whatever application including images as well as house keeping data etc. Eventually a new structure, called Encapsulation Packet, has been added to carry data in a more flexible manner as e.g. for the transfer of IP Protocol Data Units (PDUs) via CCSDS Space Data Link Layer protocols. Finally, also the basic layers for CCSDS Communications are subject to evolution and - together with new features as e.g. new powerful Uplink Codes, Variable/Adaptive Coding Modulation (VCM/ACM), enhanced space data link protocol(s). Very important is the seamless introduction of Optical Communications that aim to highly improve the Space Link Services. The related WG has just been created and will deal with Optical Coding & Modulation as well as with supporting services (e.g. weather data, etc.).

10-Dec-2012-cesg-14 Last but not least: Data Compression and Security (1 of 2) On-board data compression is needed to make full use of limited spacecraft resources like data storage and downlink capacity. The Multispectral Hyperspectral Data Compression WG takes care of this subject. They started their work with the “Lossless Data Compression” standard and eventually added standards for “Image Data Compression” and “Lossless Multispectral & Hyperspectral Image Compression” In fact multispectral & hyperspectral images can occupy enormous data volumes, and so compression algorithms specifically designed to exploit the three-dimensional structure of such images can provide tremendous benefit to space missions.

10-Dec-2012-cesg-15 Last but not least: Data Compression and Security (2 of 2) The Space Data Link Layer Security Working Group (SLS-SEA-DLS) is a joint activity between SLS and SEA Areas. The objectives of this Working Group is to develop a recommendation for a security protocol operating at the data link layer of CCSDS space links. Target missions are civilian missions (science, earth observation, telecommunications,...). This security protocol provides authentication and/or encryption both for uplink and downlink. It is compatible with CCSDS TM, TC and AOS data link protocols and independent from any specific cryptographic algorithm. This security protocol is a function within the Data Link Protocol (sub)layer.

10-Dec-2012-cesg-16 References CCSDS Web Sitehttp:// SLS Area CCSDS Publications SLS Area Publications Keep in mind the color terminology: Blue: Recommended Standards Magenta: Recommended Practices Green: Informational Reports Silver: Historical

10-Dec-2012-cesg-17 THANK YOU