ccsds unified space data link (uslp) greg kazz feb. 18, 2015 scan noon time talk
TRANSCRIPT
Purpose
• The Unified Space Link Protocol (USLP) is currently a Draft CCSDS Recommended Standard at the Data Link Layer to be used over all space communications links: space-to-ground, ground-to-space, and space-to-space.
Radio Frequency and Modulation
LinkARQ
TM Space DataLink Protocol
AOS Space DataLink Protocol
TC Space DataLink Protocol
CommunicationsOperation
Procedure 1
Space DataLink Security
Protocol
TimeCodes
LosslessData
Compression
LossyData
Compression
Reed-SolomonCoding
BCH CodingConvolutional
CodingTurbo & LDPC
CodingCode & Frame
Sync.CLTU and
PLOPs
Synchronous Links Asynchronous Links
Networked CCSDS Space/Ground Communications Protocol Stack
Physical
Link
Network
Transport
Application
Internet RFCDraft CCSDS RecommendationCCSDS Recommendation CCSDS Report
OnboardNavigation
Internet IPSecSCPS-SP Space Security Protocol
Space PacketProtocol
SCPS-NP Space Network Protocol
Internet Protocol(IPv4, IPv6)
Storeand
ForwardInteractive
SCPS-FPSpace FTP
InternetFTP
InternetTCP/UDP
SCPS-TPSpaceTCP/UDP
CCSDS File
DeliveryProtocol(CFDP)
Space PacketProtocol
Space PacketProtocol
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Proximity-1 Space Data Link Protocol
CommunicationsOperation
Procedure Prox
LinkARQ
Evolving Space Communications Environment
• Development of very high rate Optical Communications• Evolution of very small low cost space vehicles• Small remote enterprises of communicating space
entities (e.g. Multi-agency Mars enterprise)• Manned missions’ utilization of Internet Protocols• Growth of Delay Tolerant Network technology for use of
selective retransmission and reliable link layer protocols.• Flight technology to support high performance Forward
Error Correcting Codes and Variable Code Modulation • What’s next?
Emerging Requirements on Link Layer• Higher Data Rates put increased pressure on current
implementations and operational data handling and routing• Larger number of space vehicles requires more spacecraft
identifiers• Inclusion of uplink security (CCSDS SDLS) will require new flight
implementations • Advances in technology provides the means to improve uplink
performance using improved codes and FPGA devices. – Support reprogramming of Flight FPGAs systems (S/W Radios)– Increased control command size due to inclusion of security
NOTE: Significant advances in technology also provides the capability to incorporate regenerative ranging for improved tracking and spacecraft clock calibration.
How USLP addresses future needs (1-2)Features Benefits
Provides a single link protocol used by flight and ground across all manned and robotic space links
• Applicable to large and diverse set of missions from ISS to Cubesats;
• Once implemented, reduces future development & testing from 4 to 1 protocol
Decouples the link framing from the channel coding
• Using S/W defined radios, missions may chose to swap in higher performing codes(~ 3 to 8 dB gain) during development or flight operations
Expands the number of Spacecraft CCSDS can identify to 8192; Makes them Transfer Frame version independent
• Existing name space is 75% full• Expectation is current ID space will
run out in the next 5-10 years due to small sat growth and slow attrition
Allows direct data delivery of other protocol data units (PDUs)
• USLP is more efficient using direct insertion requiring no encapsulation of IP Datagrams or DTN bundles
Up to 32X greater transfer frame size(64K bytes)
• Provides efficient transfer frame processing for high rate application including optical comm.
How USLP addresses future needs (2-2)
Features Benefits
Provides a variable length transfer frame for all links including AOS and TM applications
• Provides optional Insert Zone service for low latency commanding/ARQ without forcing every frame to carry it
• More efficient AOS type ops by eliminating Fill frame insertion
Utilizes Virtual Channels as addressable unit in all protocols
• Replaces MAPs in TC; Port IDs in Proximity-1
• Replaces TC and Prox-1 Segmentation
Master Channel Services are signaled (OCF, FECF, Insert Zone, TF length)
• MC Services no longer managed• Data driven approach allows for
more spacecraft control
Can support Variable Code Modulation
• Physical layer parameters (modulation type, etc) can be commanded via USLP much like Proximity-1
Comparison of USLP to AOS
Structural Elements AOS USLPFrame and Code block Alignment Fixed Fixed/Variable
Spacecraft Ids 256 8192
Sequence Counter Size Fixed (2.7e8) Variable (0-7e16)Virtual Channels 64 maximum 64 or
32 independent/32 dependent
Structural Aspects AOS USLPMaximum Frame Size (in Octets) 2048 65536Frame Size constraint Managed/Fixed Variable/SignaledVC-OCF Presence in VC Managed SignaledInsert Zone Presence Managed SignaledInsert Zone Size Fixed SignaledFrame Error Control Field Fixed Signaled
USLP
AOS6-8 OctetsMandatory
OptionalFixed
2 OctetsOptional
Variable
8 bits
Frame
USLP
AOS
FrameHeader
USLP AOS
Transfer Frame Data Field
USLP vs AOS Structures
USLP Transfer Frame Structures
VersionID
3 bits 3 bits
SpacecraftID
13 bits 6 Bits
Virtual Channel
ID
SequenceCounter
Value
0-56 Bits16 Bits
Frame Length
1 bit
Destinationor
SourceID
OCFFlag
1 bit
FECFSize
2 bits
SequenceCounterLength
1 bit 1 bit
InsertZone
IncludedFlag
Sequence CounterBehavior
Flag
1 bit
Unspecified
TransferFrameHeader
VirtualChannelSecurityHeader
Transfer FrameData Field
(TFDF_SDU)
VirtualChannelSecurityTrailer
VirtualChannel
OperationalControl Field
TransferFrame
Error ControlField
6-13 Octets 4 Octets VariableVariableVariable VariableMandatory Optional Optional OptionalOptional Optional
VC Group MC Group Trailer Group
TransferFrameInsert Zone
Optional
Transfer frame Data Field Header
VC Data Structure and Protocol fields Identifier Mandatory ! Optional
Structuring Rules
Contained Protocol ID
Optional (only required for Stream Data)
Optional• First Header Pointer For packets• Last valid octet for user defined data
3 bits 5 bits 8 bits 16 bits Variable
• CCSDS Space Packets• Internet Datagrams• DTN Bundles/Fragments • User Octets
TFDF Data Zone
TransferFrameHeader
TransferFrame
TransferFrame
Data FieldExtended
Contained Protocol ID
• Version ID- is extended to 3 bits to accommodate an additional frame version after this one (110) is codified
• Spacecraft ID - allows for 8192 names
• Destination/Source - Identifies the Spacecraft ID as either the source of the data or the intended recipient
• Unspecified – A spare bit
• Virtual Channel ID – provides for 64 VC that can be divided into 4 groups
• Frame Length –(N+1) allows for frame to be as large as 65536 octets
• Transfer Frame Inset Zone Flag
• Frame Error Control Field – signals if a FECF is contained and its size in octets
• Operation Control Field Flag –signals the presence if an operational control field is present
• VC Counter Behavior Flag indicates whether there is a separate VC counter for each VC or only VCs 0-31
while VCs 32-63 share a single counter
• VC Counter Size – the contained value identifies the size of the VC count field– (size can be 0 to 7 octets)
• VC Counter Value –VC counter value field has a minimum size of 0 octet and a maximum size of 7 octets;• This counter will increment for each VC or VC “Group” based on the VC Counter Behavior Flag value
USLP Transfer Frame Header
VersionID
3 bits 3 bits
SpacecraftID
13 bits 6 Bits
Virtual Channel
ID
VCCounter
Value
0-56 Bits16 Bits
Frame Length
1 bit
Destinationor
SourceID
OCFFlag
1 bit
FECFSize
2 bits
VCCounterLength
1 bit 1 bit
InsertZone
IncludedFlag
VC CounterBehavior
Flag
1 bit
Unspecified
The organization of data within a VC is signaled within a VC header. Header identifies both the type of data unit contained and the data delimiting rules that apply.
1. Identifies Protocol of User’s data (i.e. CCSDS Space Packets, Internet Datagrams, DTN Bundles or bundle segments, user octets)
2. Streaming requires added header information for the VC service data unit. I. First header pointerII. Last valid user octet
Data Inclusion Rules Streaming Pointer Field(Optional based on Data Rules)
‘000’ Complete User Data units Not Required
‘001’ Streaming packets First Header Pointer
‘010’ Streaming User Octets Last Valid Octet in VC Data Field
‘011-111’ To be defined via SANA To be defined per defined rules
TFDF HeaderVC Data Structure and Protocol fields Identifier Mandatory
Data Inclusion Rules
Protocol ID
Optional (only required for Stream Data)Streaming Data Pointer
• First Header Pointer For packets• Last valid octet for user defined data
3 bits 5 bits 8 bits 16 bits Variable
• CCSDS Space Packets• Internet Datagrams• DTN Bundles/Fragments • User Octets
TFDF Data Zone
Transfer Frame Data Field
ExtendedProtocol ID
Protocol ID
‘00000’ CCSDS Packets
‘00001’ IP Datagrams
‘00010’ DTN Bundle
‘00011’ User Octets
‘11111’ Field Extension
USLP Summary• Greater number of Spacecraft require a larger Spacecraft ID field• Longer Frames reduce handling processing complexities at
higher rates• Higher rates require longer frame sequence counters for
accounting • Unifying the Link Layer Protocols would reduce development &
maintenance costs• Running the data link layer protocol unaligned to the channel
code allows more independence between layers • Uses data driven (Frame Header Signaled) Master Channel
Services instead of control via management
Structural Aspects USLP AOS TC
Maximum Frame Size (in Octets) 2048 65536 1024Frame Size Constraint Variable/Signaled Managed/Fixed Variable/Signaled
VC-OCF Presence in VC Signaled Managed Not Included
Control Data Flag Presence Signaled in TFDF Managed Signaled
Insert Zone Size Managed/Fixed Variable/Signaled Not Included
Frame Error Control Field Managed/Optional Managed/Fixed Managed/OptionalFrame and Codeblock Aligned Managed/Optional Fixed Variable Codeblock
Spacecraft Ids 8192 256 1024
Sequence Counter Size Variable (0->7e16) Fixed (2.7e8) 256Virtual Channels 64* 64 64
Segmentation Signaled in TFDF No (uses Streaming) Separate FormatSegmentation (pseudo VCs) Signaled (32 VCs) No 16 Identifies Frame Contents Signaled in TFDF Managed by VC Managed by VC
Comparison of USLP, AOS and TC for Command
Transfer Frame Assembly
TransferFrameHeader
TransferFrame
SecurityHeader
VC Frame Data Field
(TFDF_SDU)
TransferFrame
SecurityTrailer
VCOperationalControl Field
TransferFrame
Error CheckField
Transfer Frame
6-10 Octets 4 Octets VariableVariableVariable VariableMandatory Optional Optional OptionalOptional Optional
VC Contents
Received from SAPand inserted into frame
Received from OCF
Calculated and entered into frame
Computed and entered in frame
Generated and entered into frame 1
4
3
2
5
Note: The number within the circles identifies the order of inclusion in the frame formation process
TransferFrameInsertZone
VariableOptional
LDPCRate ½ Block size 16 384 bitsRate ½ Block size 1024 1/2, 1024 LDPC with BCH TEDLDPC Rate 4/5 Block size 16384
GSFC-LDPC (8176,7156)
BCH SEC TED
Coding Performance (not including short LDPC codes) (provided by JPL Coding Group)
Packet SAP VC_OCFService
Data Unit
VCA_SDUs
VCF_SDUsOCF_SDUs
Virtual Channel
Processing
Virtual Channel Creation
Virtual Channel Data Unit (VCDU)
Master Channel Process (Virtual Channel Multiplexing)
Master Channel Data Unit (MCDU)
All Channel Multiplexing
Physical Channel
Coding and Sync Sub-Layer
Packets
PacketProcessingFunction
VCAProcessingFunction
VirtualChannel
Processing
Master ChannelProcess
VCA-SAP
OptionalProcess
Multiplexer
ReplicatedProcesses
Process
Legend
Security Process
CRC Creation
OCF
-SAP
Note: -Packet SAP can support multiple users-VCA SAP can only support a single user
TSDF-SAP
TSDF_SDUs
VCF-SDU = VC Data Field
Insert ZoneService
Data Unit