Unified Space Data Link Protocol

Conformance Statement for `pkg/usdl`, CCSDS 732.1-B-3

A2.1 GENERAL INFORMATION

A2.1.1 Identification of PICS

Field	Value
Date of Statement (DD/MM/YYYY)	25/08/2026
PICS Serial Number	ASTRO-USDL-PICS-003
System Conformance Statement Cross-Reference	This document

A2.1.2 Identification of Implementation Under Test (IUT)

Field	Value
Implementation Name	astro/pkg/usdl
Implementation Version	See `go.mod` / latest commit on `main`
Special Configuration	None
Other Information	Go library implementing CCSDS Unified Space Data Link Protocol. Full pipeline: PhysicalChannel (MC mux/demux) -> MasterChannel (VC mux, gap detection via the VCF Count) -> VirtualChannel (frame buffer with a per-MAP receive demultiplexer) -> MAP services (MAPP packets under rules '000'/'111', MAPA SDUs under rules '001'/'010'/'111', MAPO octet stream under rule '011'). Non-truncated and truncated (annex D) headers. Partial fixed-length packet zones completed with Encapsulation Idle Packets per clause 4.1.4.3.4; OID TFDZs filled from the mandatory clause 4.1.4.1.10 PN sequence.

A2.1.3 Identification of Supplier

Field	Value
Supplier	Ravi Suhag
Contact Point for Queries	GitHub, github.com/ravisuhag/astro
Implementation Name(s) and Version(s)	astro/pkg/usdl (Go package)
System Name(s)	Astro

A2.1.4 Identification of Specification

Field	Value
Specification	CCSDS 732.1-B-3 (Unified Space Data Link Protocol, Blue Book, Issue 3, June 2024)
Have any exceptions been required?	Yes [X] No [ ], see notes: COP-1/COP-P frame acceptance procedures are out of scope (the Bypass/Sequence Control and Protocol Control Command flags are carried but no FARM/FOP runs on them); SDLS integration is out of scope.

A2.2 TRANSFER FRAME FIELDS

Feature	Reference	Status
Truncated Transfer Frame	Annex D	O
Y: 4-octet header + 1-octet TFDF header (rule '111'); no insert zone, OCF, FECF, or pointer; length bounds enforced (6-32 octets, D1.3.2 notes 2-3, D1.4.2.4)
Spacecraft Identifier	clause 4.1.2.2.3	M
Y: 16-bit SCID
Source-or-Destination Identifier	clause 4.1.2.3	M
Y: 1-bit flag
Virtual Channel Identifier	clause 4.1.2.4	M
Y: 6-bit VCID (0-63; 63 reserved for OID)
MAP Identifier	clause 4.1.2.5	M
Y: 4-bit MAP ID (0-15)
End of Frame Primary Header Flag	clause 4.1.2.6	M
Y: selects the truncated 4-octet header
Frame Length	clause 4.1.2.7	M
Y: 16-bit, total octets - 1; cross-checked against the delivered buffer on decode
Bypass/Sequence Control Flag	clause 4.1.2.8.1	M
Y: carried and round-tripped (COP procedures out of scope)
Protocol Control Command Flag	clause 4.1.2.8.2	M
Y: carried and round-tripped
Reserve Spares	clause 4.1.2.9	M
Y: encoded '00'; validated on decode
OCF Flag	clause 4.1.2.10	M
Y: set from OCF presence; drives OCF extraction on decode
VCF Count Length	clause 4.1.2.11	M
Y: 3-bit field, 0-7 octet counts
VCF Count	clause 4.1.2.12	C
Y: 0-56 bit count, big-endian; independent sequence-controlled and expedited counters per VC (clause 4.1.2.12.4-12.5)
Insert Zone	clause 4.1.3	O
Y: configurable length via ChannelConfig
TFDF Header	clause 4.1.4.2	M
Y: 1 octet (rules + UPID) plus 16-bit pointer only for rules '000'/'001'/'010'
TFDZ Construction Rules	clause 4.1.4.2.2	M
Y: all eight values defined; services emit '000', '001', '010', '011', '111'
USLP Protocol Identifier	clause 4.1.4.2.3	M
Y: SANA registry values (0-8, 31) provided as constants; set per service
First Header / Last Valid Octet Pointer	clause 4.1.4.2.4	C
Y: FHP for rule '000', LVOP for '001'/'010'; 'all ones' specials
Only Idle Data frames	clause 4.1.4.1.5-1.9	M
Y: VCID 63, MAP 0, rule '001', UPID 'Idle Data', LVOP = last TFDZ octet
OID TFDZ fill	clause 4.1.4.1.10	M
Y: 32-cell Fibonacci LFSR PN sequence (polynomial D0+D1+D2+D22+D32, all-ones seed, never restarted), known-answer tested against annex H
Idle fill of partial fixed TFDZs	clause 4.1.4.3.4	M
Y: Encapsulation Idle Packet completes the TFDZ; discarded on extraction
Operational Control Field	clause 4.1.5	O
Y: 4 octets, presence signaled by the OCF Flag; content comes from an OCF supplier hook (SetOCFSupplier), channels with HasOCF and no supplier refuse to emit rather than fabricate an all-zero Type-1 report
Frame Error Control Field	clause 4.1.6, annex B	O
Y: 16-bit CRC-16-CCITT with known-answer tests (clause 4.1.6.2.2: the FECF, when present, is the last 16 bits; USLP defines no other FECF size)
Truncated Transfer Frame	Annex D	O
Y: 4-octet header + 1-octet TFDF header (rule '111'); no insert zone, OCF, FECF, or pointer; length bounds enforced (6-32 octets, D1.3.2 notes 2-3, D1.4.2.4)

A2.3 SERVICES

Feature	Reference	Status
MAP Packet Service (MAPP)	clause 3.4, clause 4.2.2	O
Y: rule '000' with FHP on fixed-length channels (EPP idle fill, FHP resync after loss); rule '111' on variable-length channels
MAP Access Service (MAPA)	clause 3.4, clause 4.2.3	O
Y: constant-length MAPA_SDUs under rules '001'/'010' with LVOP delimiting; rule '111' on variable-length channels
MAP Octet Stream Service (MAPO)	clause 3.4, clause 4.2.4	O
Y: rule '011'; variable-length frames only (fixed-length rejected per clause 4.2.4.1)
MAP Multiplexing / Demultiplexing	clause 2.2.1, clause 3.2.4	M
Y: the VC owns a per-MAP demultiplexer: frames of other MAPs on the shared VC are queued for their own services, never discarded or misdelivered
Idle frame generation	clause 4.1.4.1	M
Y: GetNextFrameOrIdle on fixed-length channels; OID frames keep their own VC 63 count and draw from a persistent, never-restarted PN generator
COP-1 / COP-P procedures	refs [9], [10]	O
N: flags carried; FOP/FARM not implemented
SDLS	ref [15]	O
N

A2.4 CHANNEL MANAGEMENT

Feature	Reference	Status	Support
Physical Channel	clause 2.1.3	M	Y: PhysicalChannel with MC multiplexing
Master Channel	clause 2.1.3	M	Y: MasterChannel with VC multiplexing
Virtual Channel	clause 2.1.3	M	Y: VirtualChannel with frame buffering
MAP Channel	clause 2.1.3	M	Y: per-MAP service instances with Receive filtering
Frame Gap Detection	clause 4.1.2.12	M	Y: per-VC, per-QoS tracking of the VCF Count at the managed field width
VC Multiplexing	clause 4.2.6	M	Y: weighted round-robin via SDL
MC Multiplexing	clause 4.2.8	M	Y: weighted round-robin via SDL

Legend: M = Mandatory, O = Optional, C = Conditional, Y = Yes (supported), N = No (not supported)

Wire test vectors

The octets backing this statement live in the vector corpus — 20 vectors. Each vector names the clause it comes from and carries the derivation that produced it.

File
`usdl/frame.json`	12 vectors
`usdl/interop.json`	8 vectors, captured from spacepackets 0.32.0

These are data files, so any implementation can check itself against the same octets. See CONTRACT.md for how, and how this is verified for what rests on a published vector versus a reading of the clause.