Including HDLC Framing in CCSDS Recommendations

1. Including HDLC Framing inCCSDS Recommendations James Rash - NASA/GSFC Keith Hogie, Ed Criscuolo, Ron Parise - Computer Sciences Corp SIW-4 - HDLC for CCSDS

2. Basic Concept • Add ISO HDLC frame synchronization as an option to TM/TC/AOS recommendations for data link frame synchronization • Add IETF RFC 2427 multi-protocol data link frame header as an option to TM/TC/ AOS recommendations for data link • This adds an option for spacecraft to use data link formats that are supported by all common carriers and network equipment vendors’ synchronous serial interfaces • It provides an option that separates link frame sync and FEC coding sync which allows changing FEC coding type and block length independent of data link format • It allows spacecraft data to be inserted directly into all national and international carriers Frame Relay and IP networks • It supports encapsulation of IP and many other network protocols SIW-4 - HDLC for CCSDS

3. What About IP Encapsulation in CCSDS Frames • CCSDS has defined a way to encapsulate IP packets inside CCSDS frames that uses the IP header fields for packet identification and length like CCSDS packet header fields • This doesn’t fit with the concept of providing end-to-end IP network connectivity using COTS routers • Custom CCSDS/IP gateways are required to process IP packets • These gateways need to evolve rapidly like COTS routers to incorporate new routing, traffic management, and security options • This is not feasible in a low-volume CCSDS gateway • IP packets encapsulated in CCSDS frames require more complicated data processing that IP in Frame Relay/HDLC • First header pointers and lengths require clean links to recover data • Approach results in IP packets split across link frames just like it does with CCSDS packets (with HDLC, one IP packet is in one HDLC frame) • Losing one CCSDS frame results in the loss of many IP packets • Tightly coupled to link coding and requires major hardware change whenever coding changes • Currently no definition for IP on CCSDS uplinks SIW-4 - HDLC for CCSDS

4. HDLC Space Link Data Framing • ISO/IEC 13239:2002, “Information technology -- Telecommunications and information exchange between systems -- High-level data link control (HDLC) procedures”, International Organization For Standardization (Adopted ISO/IEC 13239:2002, third edition, 2002-07-15) • HDLC FLAG bytes (01111110) between frames • no fill frames or packets • continual FLAG bit pattern when no data frames being transmitted • Bit stuffing to ensure no FLAG patterns in data or CRC • CRC-16 on end of frame for error detection • Variable length frames up to at least 4K Bytes Bit stuffing applied Flag (1B) Variable Length Frame Data CRC-16 (2B) Flag (1B) Flag (1B) Link Framing HDLC Frame SIW-4 - HDLC for CCSDS

5. Frame Relay Space Link Data Framing • IETF Multi-Protocol Encapsulation over Frame Relay (RFC 2427, STD 55) • Uses Frame Relay/HDLC - Not X.25 or LAP-B • No windowing, optional flow control - completely independent of delay • Frame Relay DLCI provides 1024 virtual channels • Standard Frame Relay processing supported by all telecom vendors • Normally one user data packet per variable length frame • No first header pointers or packet extraction processing • Any packet segmentation or fragmentation handled in upper layer protocols • Supports encapsulation of IP and many other network protocols Frame Relay/Multi-Protocol Encapsulation Header FR Hdr (2B) Encap Hdr (2B) Frame Data Link Layer Header Flag (1B) Data CRC-16 (2B) Flag (1B) Flag (1B) Link Framing HDLC Frame SIW-4 - HDLC for CCSDS

6. RFC 2427 Frame Headers • First 2 bytes of Frame Relay information • Next 2 bytes of protocol encapsulation information Address extension (EA): Used to determine the size of the header. Data link connection identifier (DLCI): A logical identifier used to distinguish between multiple Frame Relay connections over a link. Command/response (C/R): This bit indicates whether the current frame is a command frame or a response frame. Forward and backward explicit congestion notification (FECN, BECN): The network uses these notifications for congestion avoidance. The network sends these notifications to the users in advance of congestion problems. Discard eligibility (DE): DE is used to discard frames when the network experiences congestion. Frames that exceed the traffic parameters (CIR, Bc, Be) are tagged by the network with the DE bit to indicate that they are more likely to be discarded if the need arises. List of Commonly Used NLPIDs 0x00 Null Network Layer or Inactive Set (not used with Frame Relay) 0x08 Q.933 [2] 0x80 SNAP 0x81 ISO CLNP 0x82 ISO ESIS 0x83 ISO ISIS 0x8E IPv6 0xB0 FRF.9 Data Compression [14] 0xB1 FRF.12 Fragmentation [18] 0xCC IPv4 0xCF PPP in Frame Relay [17] SIW-4 - HDLC for CCSDS

7. NP or IP NP or IP Packet Insert VCDU Framing FEC Encode Packet Extract VCDU Framing FEC Decode CCSDS and HDLC Ground Support Comparison • Very similar except the HDLC commercial world separates FEC and framing at a bitstream level interface Commercial Router/ Frame Relay Switch CCSDS Net PDU IP IP HDLC Framing HDLC Framing Frame FEC Encode FEC Decode 101010 (bits) Randomize Derandomize Randomize Derandomize Conv. Encode Conv. Decode Conv. Encode Conv. Decode Bit sync Bit sync Modulator Demod Modulator Demod Transmitter Receiver Transmitter Receiver Upconvert Downconvert Upconvert Downconvert Antenna SIW-4 - HDLC for CCSDS

8. Fixed Length FEC Coding Blocks and HDLC • Question - How do you put variable bit length HDLC frames in fixed byte length code blocks (e.g. Reed-Solomon, TPC, LDPC) ? • Answer - Separate data link framing and FEC coding • Different approach from traditional CCSDS framing where transfer frame and R-S code block use the same attached sync mark (ASM) • HDLC inserts into fixed length R/S, TPC, LDPC codeblock as a bitstream and is extracted as a bitstream on the other end of link • In the commercial network world R/S, TPC, LDPC and convolutional coding are performed at the physical layer independent of HDLC data link framing • FEC has no relation to any framing present in the bit stream • HDLC provides its own sync independent of any optional coding sync marks • Separation of coding allows changing coding type and block length with no changes to HDLC framing Variable Bit Length HDLC Frames HDLC Frame Data Codeblock Size number of Bits ••• Coding R/S Sym ASM ASM Fixed Length FEC Codeblock SIW-4 - HDLC for CCSDS

9. Adding HDLC to CCSDS Recommendations • IP packets similar to CCSDS packets • RFC 2427 encapsulation similar to CCSDS encapsulation header • HDLC framing appears as a bitstream service directly into CCSDS forward-error-correction code blocks • HDLC framing can be radiated directly without R/S coding added SIW-4 - HDLC for CCSDS

10. Ground Support for HDLC • HDLC is widely used by the amateur radio community • HDLC has been used by NASA’s South Pole TDRSS Relay (SPTR) since 1997 • TDRSS relay satellites don’t see frames of CCDSDS or HDLC they just relay RF signals • Routers installed at White Sands in a special configuration for SPTR • HDLC was installed in a few months to support the STS-107 shuttle flight and the Communication and Navigation Demonstration on Shuttle (CANDOS) experiment • Routers and convolutional decoders at NASA Ground Network (GN) sites at Wallops and Merritt Island • Routers at NASA Space Network (SN) sites at White Sands Ground Terminal (WSGT) and Second TDRSS Ground Terminal (STGT) • Routers used by SSTL DMC stations in UK, Turkey, Algeria, and Nigeria • Linux router used by CHIPSat ground stations • Full operational support for IP services being developed for TDRSS under Space Network IP Services (SNIS) project SIW-4 - HDLC for CCSDS

11. Current HDLC in Space Status • Used for over 20 years in small educational and experimental spacecraft. • Over 80 past, present, or planned missions used or will use HDLC • Developed and operated by 23 universities, 8 amateur groups, and 7 commercial space entities in 24 countries • Also represented are NASA, the US Air Force, the US Navy, and the Chilean Air Force. • Earth resources satellites by Germany and Turkey, are currently in development and will use HDLC. • A Disaster Monitoring Constellation (DMC) by UK, Algeria, Nigeria, and Turkey is currently operational and uses HDLC with 8Mbps downlinks. • NASA’s CHIPSat is currently operational and uses HDLC • Future missions (e.g. GPM, MMS, LRO) are selecting HDLC/Frame Relay for its flexibility, simple implementation, low-cost, and wide availability SIW-4 - HDLC for CCSDS

12. HDLC Spacecraft SIW-4 - HDLC for CCSDS

13. HDLC Spacecraft (cont) SIW-4 - HDLC for CCSDS