Encapsulation Packet Protocol

Conformance Statement for `pkg/epp`, CCSDS 133.1-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-EPP-PICS-002
System Conformance Statement Cross-Reference	This document

A2.1.2 Identification of Implementation Under Test (IUT)

Field	Value
Implementation Name	astro/pkg/epp
Implementation Version	See `go.mod` / latest commit on `main`
Special Configuration	None
Other Information	Go library implementing CCSDS Encapsulation Packet Protocol encoding, decoding, validation, and service-layer I/O for all four header sizes. Wire layout pinned by spec-derived golden vectors (e.g. 1-octet idle packet = 0xE0).

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

A2.1.4 Identification of Specification

Field	Value
Specification	CCSDS 133.1-B-3 (Encapsulation Packet Protocol, Blue Book, Issue 3, May 2020)
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: Encapsulation Packet Structure

Item	Description	Reference	Status	Support
EPP-1	Encapsulation Packet	4.1.1	M	Yes
`EncapsulationPacket` struct with `Header` and `Data` fields. `Encode()` / `Decode()` with golden wire-vector tests in addition to round-trips.
EPP-2	Packet Version Number	4.1.2.2	M	Yes
Bits 0-2 of octet 0, enforced as '111' (7) via `ErrInvalidPVN`. Distinguishes from Space Packets (PVN '000').
EPP-3	Encapsulation Protocol ID	4.1.2.3	M	Yes
Bits 3-5 of octet 0. Named constants per the SANA registry: `ProtocolIDIdle` (0), `ProtocolIDLTP` (1), `ProtocolIDIPE` (2), `ProtocolIDExtended` (6), `ProtocolIDMission` (7). Validated in `Header.Validate()`.
EPP-4	Length of Length	4.1.2.4	M	Yes
Bits 6-7 of octet 0 (2 bits). Header size derived from this field alone per table 4-1: '00'->1, '01'->2, '10'->4, '11'->8 octets (`Header.Size()`). 4.1.2.4.4 enforced: LoL '00' requires Protocol ID '000' (`ErrNonIdleOneOctetHeader`).
EPP-5	User Defined Field	4.1.2.5	M	Yes
4-bit field in octet 1 of 4- and 8-octet headers (`Header.UserDefined`, set via `WithUserDefined()`). Rejected when it cannot be encoded (`ErrFieldNeedsLongerHeader`).
EPP-6	Encapsulation Protocol ID Extension	4.1.2.6	M	Yes
4-bit field sharing octet 1 with the User Defined Field. Used for protocol identification when the Protocol ID is '110' (4.1.2.6.2); enforced as 'all zeros' otherwise (4.1.2.6.3, `ErrExtensionMustBeZero`). Protocol ID '110' requires a 4- or 8-octet header (`ErrExtendedNeedsLongHeader`).
EPP-7	CCSDS Defined Field	4.1.2.7	M	Yes
2-octet field, 8-octet header only (`Header.CCSDSDefined`, set via `WithCCSDSDefined()`). Reserved; 'all zeros' by convention (not enforced on receive, per 4.1.2.7.2 being a convention).
EPP-8	Packet Length Field	4.1.2.8	M	Yes
Total packet length in octets, header included (4.1.2.8.2). 1, 2, or 4 octets per the Length of Length field; absent in the 1-octet header. Auto-computed in `NewPacket()`; bounds checked against table 4-2 in `Header.Validate()`.
EPP-9	Encapsulated Data Field	4.1.3	M	Yes
`Data []byte`. Absent-data conditions enforced per 4.1.3.1.4/4.1.3.1.5: a packet without a data field must carry Protocol ID '000' (`ErrEmptyData` otherwise).

Table A-2: Header Sizes (figure 4-2 / table 4-1)

Item	Description	Reference	Status	Support
EPP-10	1-octet header (LoL '00')	4.1.2	M	Yes
Idle packets only; encodes as 0xE0. `NewIdlePacket()` constructor; golden vector test.
EPP-11	2-octet header (LoL '01')	4.1.2	M	Yes
1-octet Packet Length, max total 255. Default for small payloads.
EPP-12	4-octet header (LoL '10')	4.1.2	M	Yes
UDF + PIE octet, 2-octet Packet Length, max total 65,535. Selected automatically for larger payloads or via `WithLongLength()` / `WithUserDefined()` / `WithExtendedProtocolID()`.
EPP-13	8-octet header (LoL '11')	4.1.2	M	Yes
UDF + PIE octet, CCSDS Defined Field, 4-octet Packet Length, max total 4,294,967,295. Selected automatically or via `WithCCSDSDefined()`.
EPP-14	Receive fixed- or variable-length headers	4.1.2.1.2	M	Yes
`Decode()` and `Service.ReceivePacket()` accept any of the four header sizes; the sender adapts the header size to the payload per the 4.1.2.1.2 NOTE.

Table A-3: Protocol ID Values (SANA registry)

Item	Description	Reference	Status	Support
EPP-15	Idle Packet (PID 0)	4.1.2.3 NOTE 1	M	Yes
`NewIdlePacket()` (1-octet form) and `NewIdleFillPacket(totalLength, fill)` for multi-octet idle fill packets used to fill fixed-length transfer frames. `IsIdle()` detection.
EPP-16	LTP (PID 1)	SANA registry	O	Yes
`ProtocolIDLTP` constant; `NewLTPPacket()` constructor.
EPP-17	Internet Protocol Extension (PID 2)	SANA registry	O	Yes
`ProtocolIDIPE` constant; `NewIPEPacket()` constructor.
EPP-18	Protocol ID Extension (PID 6, '110')	4.1.2.3 NOTE 2	M	Yes
`ProtocolIDExtended` constant; `WithExtendedProtocolID()` sets the 4-bit extension. Extension values are carried opaquely; the SANA extended-protocol registry is not modeled.
EPP-19	Mission-specific data (PID 7, '111')	4.1.2.3 NOTE 3	O	Yes
`ProtocolIDMission` constant; `NewMissionPacket()` constructor.
EPP-20	Reserved Protocol IDs (3, 4, 5)	SANA registry	-	Partial
Packets with reserved PIDs can be constructed and decoded (identified as "Reserved" in `Humanize()`); no named constants.

Table A-4: Service Interface

Item	Description	Reference	Status	Support
EPP-21	ENCAPSULATION.request	3.3	M	Yes
`Service.SendBytes(protocolID, data, opts...)` and `Service.SendPacket(packet)`.
EPP-22	ENCAPSULATION.indication	3.3	M	Yes
`Service.ReceiveBytes()` and `Service.ReceivePacket()` with header-size-aware streaming reads.
EPP-23	Packet Sizing	-	-	Yes
`PacketSizer(data)` implements `sdl.PacketSizer`: total length from the first octet's LoL field (1 for the idle byte). Compatible with `tmdl` and `tcdl` VCP services.

Table A-5: Management Parameters

Item	Description	Reference	Status	Values Allowed	Support
EPP-24	Maximum Packet Length	5	M	Integer	Yes
`ServiceConfig.MaxPacketLength`. Defaults to 4,294,967,295 (the protocol maximum) so no spec-valid packet is rejected unless a mission sets a lower limit.
EPP-25	Packet Multiplexing	-	O	Mission specific	No
No multiplexing or scheduling logic. Caller controls ordering of `SendPacket()` calls.

A2.3 CONFORMANCE SUMMARY

Overall Statistics

Category	Total Items	Supported	Partial	Not Supported
Mandatory (M)	17	17	0	0
Optional (O)	4	3	0	1
Unclassified (, )	2	1	1	0
Total	23	21	1	1

Non-Conformances (Optional Items Not Supported)

Item	Description	Reason
EPP-25	Packet Multiplexing	No multiplexing, scheduling, or interleaving logic.

Partial Conformances (Items Requiring Attention)

Item	Description	Reason
EPP-20	Reserved Protocol IDs	Reserved PIDs (3, 4, 5) can be constructed and decoded, but no named constants are provided.

Verification Notes

Octet 0 layout (PVN '111' | Protocol ID | 2-bit Length of Length), the pure-LoL header sizing, the octet-1 UDF/PIE split, and the total-length-including-header Packet Length semantics were verified against the fetched CCSDS 133.1-B-3 (May 2020) text and are pinned by golden wire vectors in header_test.go and packet_test.go (e.g. the 1-octet idle packet 0xE0).
Protocol ID names follow the SANA Encapsulation Protocol ID registry (1 = LTP, 2 = IPE, 6 = extension, 7 = mission-specific).

Wire test vectors

The octets backing this statement live in the vector corpus — 16 vectors. Each vector names the clause it comes from and carries the derivation that produced it.

File
`epp/header.json`	16 vectors

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.