June 2004 SIW-4 - HDLC for CCSDS 1

Including HDLC Framing inCCSDS Recommendations

James Rash

- NASA/GSFC

Keith Hogie, Ed Criscuolo,

Ron Parise

- Computer Sciences Corp

R/S Codeblock

Packets, Bits, etc.VC Packets, Bits, etc.DLCI

SyncMark

Data R/Ssymbols

HDLC FrameCRC

FLG

Space Data LinkProtocols

Sync and ChannelCoding

CRC

Transfer Frame Frame Relay Frame

Bits or BytesTransfer Frames

FLG

June 2004 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

June 2004 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

June 2004 SIW-4 - HDLC for CCSDS 4

HDLC Frame

Link FramingFlag(1B)

Flag(1B)

Variable Length Frame Data CRC-16(2B)

Flag(1B)

Bit stuffing applied

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

June 2004 SIW-4 - HDLC for CCSDS 5

HDLC Frame

Link Layer HeaderFR Hdr

(2B)Encap Hdr

(2B)Frame Data

Link FramingFlag(1B)

Flag(1B)

Data CRC-16(2B)

Flag(1B)

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

June 2004 SIW-4 - HDLC for CCSDS 6

RFC 2427 Frame Headers

• First 2 bytes of Frame Relay information

Upper DLCI(6 bits)

C/R EA=0

Lower DLCI(4 bits)

DE EA=1

BECN

FECN

RFC 2427 Encapsulation Header

Control (UI) 0x03(8 bits)

NLPID(8 bits)

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]

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.

• Next 2 bytes of protocol encapsulation information

June 2004 SIW-4 - HDLC for CCSDS 7

Downconvert

Receiver

Demod

Bit sync

Derandomize

Conv. Decode

Upconvert

Transmitter

Modulator

Randomize

Conv. Encode

CCSDS

Downconvert

Receiver

Demod

Bit sync

Derandomize

Conv. Decode

FEC Decode

Upconvert

Transmitter

Modulator

Randomize

Conv. Encode

FEC Encode

Antenna

HDLC FramingHDLC Framing

IPIP

101010(bits)

Frame

Net PDU

Commercial Router/Frame Relay Switch

Packet InsertVCDU Framing

FEC Encode

Packet ExtractVCDU Framing

FEC Decode

NP or IP NP or IP

CCSDS and HDLC Ground Support Comparison

• Very similar except the HDLC commercial world separates FEC and framing at a bitstream level interface

June 2004 SIW-4 - HDLC for CCSDS 8

ASM R/S SymCoding

HDLC Frame Data

•••ASM

Fixed Length FEC Codeblock

Variable Bit Length HDLC Frames

Codeblock Size number of Bits

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

June 2004 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

R/S Codeblock

Packets, Bits, etc.VC Packets, Bits, etc.DLCI

SyncMark

Data R/Ssymbols

HDLC FrameCRC

FLG

Space Data LinkProtocols

Sync and ChannelCoding

CRC

Transfer Frame Frame Relay Frame

Bits or BytesTransfer Frames

FLG

June 2004 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

June 2004 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

June 2004 SIW-4 - HDLC for CCSDS 12

HDLC Spacecraft

Spacecraft Launch Year Owner Organization Owner Country Status

UoSat-1 1981 University of Surrey UK decayedUoSat-2 1984 University of Surrey UK operationalAO-13 1988 AMSAT USA non-operationalSAREX 1990 AMSAT USA multiple shuttle missionsUoSat-3 1990 University of Surrey UK operationalUoSat-4 1990 University of Surrey/ESA UK non-operationalHealthSat-I 1990 SateLife USA operationalDove 1990 AMSAT-Brazil Brazil non-operationalWeberSat 1990 Weber State University USA non-operationalLUSAT 1990 AMSAT-LU Argentina operationalPACSAT 1990 AMSAT USA semi-operationalJAS-1b 1990 JAMSAT Japan operationalUO-14 1990 University of Surrey UK operationalSARA 1991 Amateur Radio Astronomy France non-operationalS80/T 1992 Matra Espace/CNES France operationalKITSat-1 1992 Korean Advanced Institute of Science Korea operationalArsene 1993 ENSAE/CNES France non-operationalPoSAT 1993 Portugal Portugal operationalHealthSat-II 1993 SateLife USA operationalKITSat-2 1993 Korean Advanced Institute of Science Korea operationalITAMSAT 1993 AMSAT-I Italy semi-operationalAO-27 1993 AMRAD USA operationalCerise 1995 Alcatel Espace/DME France operationalFasat-A 1995 Chile Chile non-commissionedUNAMSAT-1 1995 University Program of Space Research Mexico failed launchUNAMSAT-2 1996 University Program of Space Research Mexico non-operationalJAS-2 1996 JAMSAT Japan operationalFasat-B 1998 Chilean Air Force (FACH) Chile operationalTechSat-1b 1998 IARC Israel unknownSEDSAT 1998 University of Alabama, Huntsville USA semi-operationalTMSAT-1 1998 TMSC and MUT Thailand operationalPanSat 1998 Naval Post-Graduate School USA operationalClementine 1999 Alcatel Espace(France) France operationalSunSat 1999 Stellenbosch University South Africa non-operational

June 2004 SIW-4 - HDLC for CCSDS 13

HDLC Spacecraft (cont)

UoSat-12 1999 Surrey Satellite Technology LTD UK operationalJAWSAT 1999 USAFA/Weber State Univ. USA unknownSNAP-1 2000 SSTL development satellite UK operationalTsinghua-1 2000 Tsinghua University, Beijing China operationalOpal 2000 Stanford University USA operationalASUsat-1 2000 Arizona State University USA non-operationalSaudiSat-1A 2000 King Abdulaziz City for Science & Tech Saudi Arabia unknownSaudiSat-1B 2000 King Abdulaziz City for Science & Tech Saudi Arabia unknownTIUNGSAT-1 2000 Astronautic Technology Maylasia operationalAO-40 2000 AMSAT-DL Germany operationalARISS 2000 AMSAT USA in use on ISSPicoSat 2000 USAF USA unknownFalconSat I 2000 Air Force Academy USA operationalSapphire 2001 Stanford University USA operationalPCSat 2001 US Naval Academy USA operationalStarshine 3 2001 Project Starshine (NASA/USN/USAF) USA operationalEmerald 2002 Stanford University USA in developmentChipSat 2002 UC Berkeley USA in developmentCUTE 2002 Tokyo Institute of Technology Japan in developmentXI-IV 2002 University of Tokyo Japan in development3 Corner Sat 2002 USAF/ASU USA in developmentHokieSat 2002 VA Tech (University Nanosat) USA in developmentAlSat (DMC) 2002 Algeria Algeria operationalTopSat 2003 UK MoD and BNSC UK in developmentStenSat 2003 StenSat Group USA in developmentMOST 2003 University of British Columbia Canada in developmentStarshine 4 2003 Project Starshine (NASA/USN/USAF) USA in developmentStarshine 5 2003 Project Starshine (NASA/USN/USAF) USA in developmentNigeriaSat (DMC) 2003 Nigeria Nigeria operationalBILSAT (DMC) 2003 Turkey Turkey operationalUK-DMC (DMC) 2003 UK UK operationalDTUsat TBD Technical University of Denmark Denmark in developmentAAU Cubesat TBD Aalborg University Denmark in developmentBiltenSat TBD Turkey Turkey in developmentRapidEye TBD RapidEye A.G. Germany in developmentPolySat TBD California Polytechnic University USA in developmentCitizen-Explorer TBD University of Colorado USA in developmentCESAR-1 TBD AMSAT-Chile Chile in development