TC Space Data Link Protocol

Conformance Statement for `pkg/tcdl`, CCSDS 232.0-B-4

A2.1 GENERAL INFORMATION

A2.1.1 Identification of PICS

Field	Value
Date of Statement (DD/MM/YYYY)	23/08/2026
PICS Serial Number	ASTRO-TCDL-PICS-001
System Conformance Statement Cross-Reference	This document

A2.1.2 Identification of Implementation Under Test (IUT)

Field	Value
Implementation Name	astro/pkg/tcdl
Implementation Version	See `go.mod` / latest commit on `main`
Special Configuration	None
Other Information	Go library implementing CCSDS TC Space Data Link Protocol. Full pipeline: PhysicalChannel (MC mux/demux) -> MasterChannel (VC mux, frame gap detection) -> VirtualChannel (frame buffer) -> Services (MAP Packet with segmentation/reassembly, MAP Access, VC Frame). Variable frame length (up to 1024 bytes). Segment Header (MAP sublayer) support for large packet segmentation. Frame Sequence Number N(S) for COP-1 integration.

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/tcdl (Go package)
System Name(s)	Astro

A2.1.4 Identification of Specification

Field	Value
Specification	CCSDS 232.0-B-4 (TC Space Data Link Protocol, Blue Book, Issue 4, October 2019)
Have any exceptions been required?	Yes [X] No [ ]

NOTE, Non-supported optional capabilities are identified in section A2.2 with explanations.

A2.2 REQUIREMENTS LIST

Table A-1: TC Service Data Units

Item	Description	Reference	Status	Support
TC-1	MAP Packet SDU	3.2.2	M	Yes
`MAPPacketService` accepts packet data via `Send()`, segments across multiple frames when data exceeds capacity, pushes frames into `VirtualChannel`, and reassembles via `Receive()`.
TC-2	MAP Access SDU	3.2.3	M	Yes
`MAPAccessService` accepts raw data via `Send()`, wraps in unsegmented frame with segment header, delivers via `Receive()`.
TC-3	VC Frame SDU	3.2.4	M	Yes
`VCFrameService` accepts pre-encoded frame bytes via `Send()`, decodes and buffers, delivers encoded bytes via `Receive()`.
TC-4	TC Transfer Frame	3.2.5	M	Yes
`TCTransferFrame` struct with `Encode()` / `DecodeTransferFrame()` round-trip support. Composed of Primary Header, optional Segment Header, Data Field, and Frame Error Control.

Table A-2: Service Parameters

Item	Description	Reference	Status	Values Allowed	Support	Notes
	MAP Packet Service Parameters
TC-5	MAP Packet	3.3.2.2	M	-	Yes	Packet data passed as `[]byte` to `MAPPacketService.Send()`. Segmented if larger than frame capacity.
TC-6	GVCID	3.3.2.3	M	-	Yes	Derived from `PrimaryHeader.GVCID()` (TFVN + SCID + VCID). VCID/SCID configured at service construction.
TC-7	MAP ID	3.3.2.4	M	0-63	Yes	`SegmentHeader.MAPID`, 6 bits. Configured per service instance.
	MAP Access Service Parameters
TC-8	MAP Access SDU	3.4.2.2	M	-	Yes	Raw data passed to `MAPAccessService.Send()`. Wrapped in single unsegmented frame.
TC-9	GVCID	3.4.2.3	M	-	Yes	Derived from `PrimaryHeader.GVCID()`.
TC-10	MAP ID	3.4.2.4	M	0-63	Yes	`SegmentHeader.MAPID`.
	VC Frame Service Parameters
TC-11	TC Frame	3.5.2.2	M	-	Yes	`VCFrameService` accepts complete `[]byte` frame data via `Send()` / `Receive()`.
TC-12	GVCID	3.5.2.3	M	-	Yes	Derived from `PrimaryHeader.GVCID()`.

Table A-3: Service Primitives

Item	Description	Reference	Status	Support
	MAP Packet Service Primitives

TC-13	MAP_PACKET.request	3.3.3.2	M	Yes
`MAPPacketService.Send(data)` implements MAP_PACKET.request. Segments data across multiple frames using Segment Header sequence flags (First/Continuation/Last/Unsegmented). Type-A segments get N(S) from `FrameCounter.Next()`; Type-B frames always carry N(S)=0. NOTE: Send is non-blocking; a full virtual channel returns `ErrBufferFull` instead of blocking (declared simplification).
TC-14	MAP_PACKET.indication	3.3.3.3	M	Yes
`MAPPacketService.Receive()` implements MAP_PACKET.indication. Reassembles segments by buffering First/Continuation data and completing on the Last segment, then delimits packets with the configured `PacketSizer`, a frame data field carrying several packets back to back is delivered one packet at a time. Gaps in a segment sequence (First/Unsegmented interrupting a reassembly, Continuation/Last without a First, MAP ID change mid-packet) discard the partial packet and return `ErrIncompleteSegment`.
	MAP Access Service Primitives

TC-15	MAP_ACCESS.request	3.4.3.2	M	Yes
`MAPAccessService.Send(data)` implements MAP_ACCESS.request. Wraps data in frame with unsegmented segment header.
TC-16	MAP_ACCESS.indication	3.4.3.3	M	Yes
`MAPAccessService.Receive()` implements MAP_ACCESS.indication. Returns data field of next frame.
	VC Frame Service Primitives

TC-17	VCF.request	3.5.3.2	M	Yes
`VCFrameService.Send(data)` decodes frame bytes and pushes into `VirtualChannel`.
TC-18	VCF.indication	3.5.3.3	M	Yes
`VCFrameService.Receive()` pulls next frame and returns as encoded bytes.

Table A-4: TC Protocol Data Unit

Item	Description	Reference	Status	Support
TC-19	TC Transfer Frame	4.1.1	M	Yes
`TCTransferFrame` struct with `Encode()` / `DecodeTransferFrame()` round-trip. Variable length up to 1024 bytes.
TC-20	Transfer Frame Primary Header	4.1.2	M	Yes
`PrimaryHeader`, 5 octets (40 bits). All fields per CCSDS: Transfer Frame Version Number (2 bits, enforced as `00`), Bypass Flag (1 bit), Control Command Flag (1 bit), Reserved (2 bits, enforced as `00`), Spacecraft ID (10 bits), Virtual Channel ID (6 bits), Frame Length (10 bits, total-1), Frame Sequence Number (8 bits). Big-endian encoding. The invalid type Bypass=0 + Control Command=1 is rejected (`ErrInvalidFrameType`, 4.1.2.3); Type-B frames are forced to N(S)=0 on construction (4.1.2.7). Octets beyond the declared frame length are ignored on decode (CLTU fill, 4.1.2.7.2).
TC-20a	BC Frame Contents (Unlock, Set V(R))	4.1.3.3	M	Yes
`BuildUnlockCommand()` (`0x00`), `BuildSetVRCommand(vr)` (`0x82 0x00 <V(R)>`), `ParseControlCommand()`, plus frame-level builders `NewUnlockFrame()` / `NewSetVRFrame()` producing Type-BC frames (Bypass=1, CC=1, N(S)=0, no segment header). Malformed contents return `ErrInvalidControlCommand`.
TC-21	Segment Header	4.1.4.1	M	Yes
`SegmentHeader`, 1 octet: Sequence Flags (2 bits), MAP ID (6 bits). Present when MAP sublayer is used. `Encode()` / `Decode()` / `Validate()` methods. Constants: `SegUnsegmented`, `SegFirst`, `SegContinuation`, `SegLast`.
TC-22	Transfer Frame Data Field	4.1.4.2	M	Yes
`TCTransferFrame.DataField`, variable-length telecommand payload.
TC-23	Frame Error Control Field	4.1.5	M	Yes
`TCTransferFrame.FrameErrorControl`, 16-bit CRC-16-CCITT (polynomial 0x1021, init 0xFFFF). Auto-computed on construction via `NewTransferFrame()`. Verified on decode; CRC mismatch returns `ErrCRCMismatch`.

Table A-5: Protocol Procedures

Item	Description	Reference	Status	Support
TC-24	MAP Packet Processing Function	4.2.2	M	Yes
`MAPPacketService.Send()` segments packets into frames using Segment Header flags. Small packets produce unsegmented frames. Large packets use First/Continuation/Last segmentation. Frame Sequence Number assigned via `FrameCounter`.
TC-25	MAP Access Processing Function	4.2.3	M	Yes
`MAPAccessService.Send()` wraps raw data in unsegmented frame with MAP sublayer.
TC-26	VC Generation Function	4.2.4	M	Yes
`NewTransferFrame()` generates frames with SCID, VCID, data, optional Segment Header. CRC auto-computed. Frame Sequence Number configurable via `WithSequenceNumber()`.
TC-27	VC Multiplexing Function	4.2.5	M	Yes
`VirtualChannelMultiplexer` schedules frames from multiple Virtual Channels using weighted round-robin. Integrated into `MasterChannel`.
TC-28	MC Generation Function	4.2.6	M	Yes
`MasterChannel.AddFrame()` routes inbound frames to Virtual Channels by VCID with SCID validation.
TC-29	MC Multiplexing Function	4.2.7	M	Yes
`PhysicalChannel` implements weighted round-robin MC multiplexing across registered `MasterChannel`s via `GetNextFrame()`.
TC-30	MAP Packet Extraction Function	4.3.2	M	Yes
`MAPPacketService.Receive()` reassembles segmented packets and delimits multiple packets per frame with the `PacketSizer` (invoked on every delivery). Reports segment-sequence gaps via `ErrIncompleteSegment` instead of silently dropping them.
TC-31	MAP Access Extraction Function	4.3.3	M	Yes
`MAPAccessService.Receive()` returns data field of next frame.
TC-32	VC Reception Function	4.3.4	M	Yes
`DecodeTransferFrame()` parses raw octets into `TCTransferFrame`, verifying CRC and extracting all fields. `MasterChannel.AddFrame()` routes received frames to the appropriate `VirtualChannel` by VCID.
TC-33	VC Demultiplexing Function	4.3.5	M	Yes
`MasterChannel.AddFrame()` demultiplexes inbound frames to Virtual Channels by VCID.
TC-34	MC Reception Function	4.3.6	M	Yes
`MasterChannel.GetNextFrame()` pulls next frame from the multiplexer.
TC-35	MC Demultiplexing Function	4.3.7	M	Yes
`PhysicalChannel.AddFrame()` demultiplexes inbound frames to the correct `MasterChannel` by SCID.

Table A-6: Management Parameters

Item	Description	Reference	Status	Values Allowed	Support
	Managed Parameters for a Physical Channel

TC-36	Physical Channel Name	Table 5-1	M	Character String	Yes
`PhysicalChannel.Name`, configured at construction via `NewPhysicalChannel(name)`.
TC-37	Maximum Frame Length (octets)	Table 5-1	M	Integer (up to 1024)	Yes
`MaxFrameLength` constant = 1024. Enforced in `NewTransferFrame()` via `ErrDataTooLarge`.
TC-38	Transfer Frame Version Number (TFVN)	Table 5-1	M	'00' binary	Yes
`PrimaryHeader.VersionNumber`, enforced as `0` in `Validate()`.
TC-39	Valid Spacecraft IDs	Table 5-1	M	Integers	Yes
`PrimaryHeader.SpacecraftID`, 10 bits (0-1023). Validated in `Validate()`.
TC-40	MC Multiplexing Scheme	Table 5-1	M	Mission Specific	Yes
`PhysicalChannel` implements weighted round-robin MC multiplexing.
TC-41	Presence of Frame Error Control	Table 5-1	M	Present ('1')	Yes
Always present. CRC-16-CCITT auto-computed and verified.
	Managed Parameters for a Master Channel

TC-42	SCID	Table 5-2	M	Integer	Yes
`MasterChannel.scid`, configured at construction. Enforced in `AddFrame()`.
TC-43	Valid VCIDs	Table 5-2	M	Selectable set of integers (0-63)	Yes
`PrimaryHeader.VirtualChannelID`, 6 bits (0-63). `MasterChannel.channels` maps registered VCIDs.
TC-44	VC Multiplexing Scheme	Table 5-2	M	Mission Specific	Yes
`VirtualChannelMultiplexer` implements weighted round-robin scheduling.
	Managed Parameters for a Virtual Channel

TC-45	SCID	Table 5-3	M	Integer	Yes
`PrimaryHeader.SpacecraftID`. Set via `NewTransferFrame()`.
TC-46	VCID	Table 5-3	M	0 to 63	Yes
`PrimaryHeader.VirtualChannelID`. `VirtualChannel.ID` configured at construction.
TC-47	Presence of Segment Header	Table 5-3	M	Present ('1') / Absent ('0')	Yes
Controlled via `WithSegmentHeader()` option. `SegmentHeader` struct with encode/decode.
TC-48	Service Type	Table 5-3	M	MAP Packet, MAP Access, or VC Frame	Yes
Three service implementations: `MAPPacketService`, `MAPAccessService`, `VCFrameService`. Registered via `TCServiceManager.RegisterVirtualService()`.

Table A-7: Protocol Specification with SDLS Option

Item	Description	Reference	Status	Support	Notes
TC-49	SDLS Protocol	(see ref. [8])	O	No	SDLS Option not implemented.

A2.3 CONFORMANCE SUMMARY

Overall Statistics

Category	Total Items	Supported	Not Supported
Mandatory (M)	49	49	0
Optional (O)	1	0	1
Total	50	49	1

Non-Conformances (Mandatory Items Not Supported)

None. All 49 mandatory items (including the BC frame contents, TC-20a) are supported.

Declared Simplifications

Area	Deviation
Blocking send	`Send()` never blocks; a full virtual channel buffer returns `ErrBufferFull`. The optional blocking behavior of 4.2.2 is left to the caller.

Non-Supported Optional Items

Item	Description	Reason
TC-49	SDLS Protocol	SDLS Option not implemented.

Fully Supported Mandatory Items

Key implementations:

Area	Items	Implementation
Service Data Units	TC-1-4
`TCTransferFrame` encode/decode, `MAPPacketService`, `MAPAccessService`, `VCFrameService`.
MAP Packet Service	TC-5-7, TC-13-14
`MAPPacketService` with segmentation (First/Continuation/Last/Unsegmented), `PacketSizer`-based reassembly.
MAP Access Service	TC-8-10, TC-15-16
`MAPAccessService` with unsegmented frame wrapping.
VC Frame Service	TC-11-12, TC-17-18
`VCFrameService` pass-through via `VirtualChannel`.
Protocol Data Unit	TC-19-23
`PrimaryHeader` (40-bit) with frame-type validation and Type-B N(S)=0, BC contents (TC-20a: Unlock / Set V(R)), `SegmentHeader` (8-bit), CRC-16-CCITT.
Packet Processing	TC-24-25, TC-30-31
MAP Packet segmentation/reassembly, MAP Access raw delivery.
VC Functions	TC-26-27, TC-32-33
`NewTransferFrame()`, `VirtualChannelMultiplexer` (weighted round-robin), `MasterChannel` demux by VCID.
MC Functions	TC-28-29, TC-34-35
`MasterChannel.AddFrame()` routes by VCID. `PhysicalChannel` MC mux/demux by SCID.
Management Params	TC-36-48
Physical channel name, max frame length 1024, TFVN enforced, SCID/VCID validated, segment header support, all service types.

Wire test vectors

None. pkg/tcdl has no golden wire literals to extract: its test values are inputs rather than pinned expected octets.

See how this is verified for what the corpus covers and what it does not.