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June 2004 SIW-4 - HDLC for CCSDS 1
Inc lud ing HDLC Fram ing in
CCSDS Recommendat ions
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
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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 nationaland international carriers Frame Relay and IP networks
• It supports encapsulation of IP and many other network protocols
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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
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June 2004 SIW-4 - HDLC for CCSDS 5
HDLC Frame
Link Layer Header
FR 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
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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 c onn ection identif ier (DLCI) :
A logicalidentifier used to distinguish between multiple Frame
Relay connections over a link.
Comm and/response (C/R) : This bit indicates whether
the current frame is a command frame or a response
frame.
Forward and backward expl ic i t congest ion
notif ic at ion (FECN, BECN) : The network uses these
notifications for congestion avoidance. The network sends
these notifications to the users in advance of congestion
problems.
Discard eligibi l i ty (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
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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 Insert
VCDU Framing
FEC Encode
Packet Extract
VCDU 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
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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
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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 Link
Protocols
Sync and ChannelCoding
CRC
Transfer Frame Frame Relay Frame
Bits or BytesTransfer Frames
FLG
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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, andNigeria
• Linux router used by CHIPSat ground stations
• Full operational support for IP services being developed for
TDRSS under Space Network IP Services (SNIS) project
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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
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HDLC Spacecraft
Spacecraft Launch Year Owner Organization Owner Country Status
UoSat-1 1981 University of Surrey UK decayedUoSat-2 1984 University of Surrey UK operational
AO-13 1988 AMSAT USA non-operational
SAREX 1990 AMSAT USA multiple shuttle missions
UoSat-3 1990 University of Surrey UK operational
UoSat-4 1990 University of Surrey/ESA UK non-operational
HealthSat-I 1990 SateLife USA operational
Dove 1990 AMSAT-Brazil Brazil non-operational
WeberSat 1990 Weber State University USA non-operational
LUSAT 1990 AMSAT-LU Argentina operational
PACSAT 1990 AMSAT USA semi-operational
JAS-1b 1990 JAMSAT Japan operational
UO-14 1990 University of Surrey UK operationalSARA 1991 Amateur Radio Astronomy France non-operational
S80/T 1992 Matra Espace/CNES France operational
KITSat-1 1992 Korean Advanced Institute of Science Korea operational
Arsene 1993 ENSAE/CNES France non-operational
PoSAT 1993 Portugal Portugal operational
HealthSat-II 1993 SateLife USA operational
KITSat-2 1993 Korean Advanced Institute of Science Korea operational
ITAMSAT 1993 AMSAT-I Italy semi-operational
AO-27 1993 AMRAD USA operational
Cerise 1995 Alcatel Espace/DME France operational
Fasat-A 1995 Chile Chile non-commissioned
UNAMSAT-1 1995 University Program of Space Research Mexico failed launchUNAMSAT-2 1996 University Program of Space Research Mexico non-operational
JAS-2 1996 JAMSAT Japan operational
Fasat-B 1998 Chilean Air Force (FACH) Chile operational
TechSat-1b 1998 IARC Israel unknow n
SEDSAT 1998 University of Alabama, Huntsville USA semi-operational
TMSAT-1 1998 TMSC and MUT Thailand operational
PanSat 1998 Naval Post-Graduate School USA operational
Clementine 1999 Alcatel Espace(France) France operational
SunSat 1999 Stellenbosch University South Africa non-operational
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HDLC Spacecraft (cont)
UoSat-12 1999 Surrey Satellite Technology LTD UK operational
JAWSAT 1999 USAFA/Weber State Univ. USA unknow n
SNAP-1 2000 SSTL development satellite UK operationalTsinghua-1 2000 Tsinghua University, Beijing China operational
Opal 2000 Stanford University USA operational
ASUsat-1 2000 Arizona State University USA non-operational
SaudiSat-1A 2000 King Abdulaziz City for Science & Tech Saudi Arabia unknow n
SaudiSat-1B 2000 King Abdulaziz City for Science & Tech Saudi Arabia unknow n
TIUNGSAT-1 2000 Astronautic Technology Maylasia operational
AO-40 2000 AMSAT-DL Germany operational
ARISS 2000 AMSAT USA in use on ISS
PicoSat 2000 USAF USA unknow n
FalconSat I 2000 Air Force Academy USA operational
Sapphire 2001 Stanford University USA operational
PCSat 2001 US Naval Academy USA operationalStarshine 3 2001 Project Starshine (NASA/USN/USAF) USA operational
Emerald 2002 Stanford University USA in development
ChipSat 2002 UC Berkeley USA in development
CUTE 2002 Tokyo Institute of Technology Japan in development
XI-IV 2002 University of Tokyo Japan in development
3 Corner Sat 2002 USAF/ASU USA in development
HokieSat 2002 VA Tech (University Nanosat) USA in development
AlSat (DMC) 2002 Algeria Algeria operational
TopSat 2003 UK MoD and BNSC UK in development
StenSat 2003 StenSat Group USA in development
MOST 2003 University of British Columbia Canada in development
Starshine 4 2003 Project Starshine (NASA/USN/USAF) USA in developmentStarshine 5 2003 Project Starshine (NASA/USN/USAF) USA in development
NigeriaSat (DMC) 2003 Nigeria Nigeria operational
BILSAT (DMC) 2003 Turkey Turkey operational
UK-DMC (DMC) 2003 UK UK operational
DTUsat TBD Technical University of Denmark Denmark in development
AAU Cubesat TBD Aalborg University Denmark in development
BiltenSat TBD Turkey Turkey in development
RapidEye TBD RapidEye A.G. Germany in development
PolySat TBD California Polytechnic University USA in development
Citizen-Explorer TBD University of Colorado USA in development
CESAR-1 TBD AMSAT-Chile Chile in development
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