Conformance Statement for pkg/ltp, RFC 5326
Conformance is claimed against RFC 5326 only. CCSDS 734.1-B-1 profiles that RFC for space links; this implementation contains no profile-specific behavior, so no claim is made against the profile itself, see A1.5.
A1.1 GENERAL INFORMATION
A1.1.1 Identification of PICS
| Field | Value |
|---|---|
| Date of Statement (DD/MM/YYYY) | 23/08/2026 |
| PICS Serial Number | ASTRO-LTP-PICS-001 |
| System Conformance Statement Cross-Reference | This document |
A1.1.2 Identification of Implementation Under Test (IUT)
| Field | Value |
|---|---|
| Implementation Name | astro/pkg/ltp, with astro/pkg/sdnv |
| Implementation Version | See go.mod / latest commit on main |
| Special Configuration | ReceiverConfig.MaxBlockSize bounds an assembled block; serial number seeds are caller-supplied |
| Other Information | Go library implementing the LTP segment codecs and caller-pumped sender and receiver session machines. The library owns no goroutines and no clock: every timer is the caller's, matching the shape of pkg/cop's FOP-1. |
A1.1.3 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/ltp, astro/pkg/sdnv (Go packages) |
| System Name(s) | Astro |
A1.1.4 Identification of Specification
| Field | Value |
|---|---|
| Specification | RFC 5326 (Licklider Transmission Protocol, Specification, September 2008). CCSDS 734.1-B-1 profiles this RFC; no conformance to the profile's own requirements is claimed, see A1.5 |
| Have any exceptions been required? | Yes [X] No [ ], see A1.5 |
A1.2 SEGMENT STRUCTURE
| Feature | Reference | Status | Support |
|---|---|---|---|
| Segment header | clause 3.1 | M | |
Y | |||
| Version number 0 | clause 3.1 | M | |
Y: other versions rejected on decode | |||
| Segment type flags: CTRL, EXC, Flag 1, Flag 0 | clause 3.1.1 | M | |
Y | |||
| Segment type codes 0 to 15 | clause 3.1.2 | M | |
Y: codes 5, 6, 10, 11 rejected as undefined | |||
| Segment class masks: CP, EORP, EOB, RS, RA, CS, CAS, CR, CAR | clause 3.1.3 | M | |
Y: exposed as predicates on SegmentType | |||
| Session ID: engine ID and session number | clause 3.1 | M | |
Y: both SDNV | |||
| Extensions field, counts octet | clause 3.1.4 | M | |
Y: 0 to 15 header, 0 to 15 trailer | |||
| Extension TLV: tag, SDNV length, value | clause 3.1.4 | O | |
Y | |||
| Header extensions before content | clause 3.1.4 | M | |
Y | |||
| Trailer extensions after content | clause 3.1.4 | M | |
Y | |||
| Self-Delimiting Numeric Values | clause 1.6 item 20 | M | |
Y: pkg/sdnv, rejects values past 64 bits (ErrOverflow) and encodings past ten octets (ErrTooLong, RFC 6256 clause 3.2 padding included) | |||
A1.3 SEGMENT CONTENT
| Feature | Reference | Status | Support |
|---|---|---|---|
| Data segment: client service ID, offset, length | clause 3.2.1 | M | Y: all SDNV |
| Checkpoint serial number on checkpoints only | clause 3.2.1 | M | Y: non-checkpoints carry neither serial |
| Report serial number on checkpoints | clause 3.2.1 | M | Y: a checkpoint closing a retransmission cycle carries the prompting report's serial; zero when no report prompted it |
| Checkpoint serial number never zero | clause 3.2.1 | M | Y: enforced on encode and decode |
| Report segment: serials, bounds, claim count, claims | clause 3.2.2 | O | Y |
| Report serial number never zero | clause 3.2.2 | M | Y |
| Claim offsets relative to the lower bound | clause 3.2.2 | M | Y: ClaimedRanges() converts to block offsets |
| Claim length at least 1, within the bounds | clause 3.2.2 | M | Y: validated on encode and decode |
| Claims in ascending order, non-overlapping, at least one | clause 3.2.2 | M | Y: validated on encode and decode; zero-claim reports are neither emitted nor accepted |
| Report acknowledgment segment | clause 3.2.3 | O | Y |
| Cancel segment reason code | clause 3.2.4 | O | Y: codes 0 to 5; 6 to 255 rejected as reserved |
| Cancel acknowledgment has no content | clause 3.2.5 | O | Y |
A1.4 SESSION PROCEDURES
| Feature | Reference | Status | Support |
|---|---|---|---|
| Red-part reliable delivery | clause 6 | M | Y |
| Green-part best-effort delivery | clause 6 | O | Y |
| Mixed red and green blocks | clause 3.1.1 | O | Y: no segment straddles the boundary |
| Checkpoint at end of red part | clause 3.1.1 | M | Y |
| End-of-block flagging | clause 3.1.3 | M | Y |
| Reception reporting on checkpoint | clause 6.13 | M | Y: report upper bound covers the checkpoint's own end even before the EORP arrives |
| Duplicate checkpoints answered with the same report | clause 6.11 | M | Y: deduplicated on checkpoint serial; the original report is resent |
| Asynchronous reception reporting | clause 6.2 | O | Y: RequestReport, checkpoint serial zero |
| Retransmission of unclaimed ranges | clause 6.13 | M | Y |
| Retransmission cycle ends with a checkpoint | clause 6.9 | M | Y: the cycle's last segment is a checkpoint wherever it sits in the block |
| Report acknowledgment | clause 6.14 | M | Y: every report acknowledged, including the final one after the sender's session closes |
| Receiver closure gated on report acknowledgment | clause 6.11, clause 6.16 | M | Y: the session stays open until every report is acknowledged; an all-green session closes on the green EOB |
| Miscolored block detection | clause 3.2.4 | M | Y: cancels with reason MISCOLORED |
| Session cancellation from either end | clause 6.19, clause 6.20 | O | Y |
| Cancel acknowledgment | clause 6.21 | M | Y: the sender acknowledges a cancel from the receiver, and the receiver one from the sender |
| Segments for other sessions ignored | clause 6 | M | Y: filtered on session ID |
A1.5 EXCEPTIONS AND UNSUPPORTED FEATURES
| Feature | Reference | Support | Rationale |
|---|---|---|---|
| CCSDS 734.1-B-1 profile requirements | 734.1-B-1 | N | |
The implementation follows RFC 5326 as written and contains no profile-specific behavior (managed parameters, profile PICS items). Conformance to the Blue Book's own requirements is therefore not claimed. | |||
| Timers: checkpoint, report, cancel retransmission | clause 6.7, clause 6.8 | N by design | |
The library owns no clock. Exposed as Resend and Request for the caller's scheduler to drive. On a light-hour link only the mission can pick a timeout. | |||
| Session multiplexing | clause 6 | N | |
One Sender and one Receiver per session; managing many is the caller's. | |||
| Authentication extension | clause 3.1.4, [LTPEXT] | P | |
The TLV encodes and decodes; no cryptographic processing. | |||
| Cookie extension | clause 3.1.4, [LTPEXT] | P | |
Same. | |||
| Random serial number generation | clause 3.2.1, clause 3.2.2 | N by design | |
The spec says the first serials must be random. The caller supplies them; a zero is rejected. A library should not pick a mission's randomness source. | |||
| Deferred transmission and link-state cues | clause 6.5 | N | |
Scheduling policy the caller owns. | |||
A1.6 IMPLEMENTATION LIMITS
| Limit | Value | Source |
|---|---|---|
| SDNV value range | 0 to 2^64 - 1 | |
pkg/sdnv, 10 octets maximum | ||
| Header extensions per segment | 15 | |
4-bit count, clause 3.1.4 | ||
| Trailer extensions per segment | 15 | |
4-bit count, clause 3.1.4 | ||
| Assembled block size | MaxBlockSize, default 64 MiB | |
Implementation choice; RFC 5326 states no ceiling, but a segment offset is an SDNV reaching 2^64 and would otherwise size an allocation | ||
| Cancel reason codes accepted | 0 to 5 | |
clause 3.2.4; 6 to 255 reserved | ||
Wire test vectors
The octets backing this statement live in the vector corpus — 19 vectors. Each vector names the clause it comes from and carries the derivation that produced it.
| File | |
|---|---|
ltp/header.json | 10 vectors |
ltp/interop.json | 5 vectors, captured from ION-DTN |
ltp/session.json | 4 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.