AFDX / ARINC 664¶

Conceptual virtual-link observation surface for ARINC 664 / AFDX teaching.

Identity¶

ARINC 664 Part 7 / AFDX is represented here only as conceptual virtual-link observation evidence: virtual link, redundant network side, sequence, observed time, length, payload fingerprint, and apparent cadence.

What This Protocol Teaches¶

• AFDX constrains Ethernet with avionics timing and redundancy rules, but this page does not implement Ethernet inspection.
• Virtual links move authority from free-form packets to configured communication channels.
• Observers reason about apparent BAG/cadence, sequence, redundant A/B evidence, and missing counterparts.

Operational Context¶

ARINC 664 Part 7 / AFDX appears in commercial-aviation, avionics contexts and is modeled in the atlas at the data-link, network layer(s). The binder treats it as a passive inspection surface: what virtual-link evidence appears, what timing matters, and what outside authority is required before assigning payload meaning.

This page intentionally does not parse raw Ethernet, UDP, IP, or PCAP data. It has no switch simulation, routing, end-system scheduling, policing, or conformance behavior.

draft-core-lab: this page is in Core Lab scope but is not yet promoted to final copy. It has a source-grounded artifact and review structure; it still needs the same page-specific depth as CAN, DBC, MIL-STD-1553, UART, ARINC 429, and Modbus RTU before final-copy status.

A Concrete Artifact¶

# synthetic AFDX-like observation
VL 0x0123  seq=0x5a  network=A  len=64  t=12.000 ms
VL 0x0123  seq=0x5a  network=B  len=64  t=12.001 ms

Synthetic offline sample for explanation; not a real operational trace or live-system instruction.

Worked Decode¶

1. Both observations claim the same virtual link and sequence on redundant networks.
2. The near-identical timing suggests duplicate delivery over A/B paths, not two independent application updates.
3. The virtual link configuration and BAG assumption determine how to assess apparent cadence in this synthetic observation.
4. Payload meaning remains application-profile authority.

Field Layout / Anatomy¶

Visual Model¶

Timing And Authority¶

Authority comes from configuration: virtual-link allocation, BAG, and redundancy management. Semantic authority comes from the avionics application carried over the VL. A passive observer can compare apparent cadence, sequence continuity, A/B skew, and payload fingerprints, but cannot prove receiver acceptance, aircraft state, or application semantics.

Bytes rarely explain themselves. Name the source that defines meaning before naming engineering values: standard metadata, label table, DBC, PGN/SPN definition, object dictionary, register map, DID catalog, LDF, ARXML, channel metadata, or vendor profile.

Failure And Ambiguity¶

• Treating redundant A/B duplicates as separate state updates doubles the apparent rate.
• Seeing only A or only B is a missing counterpart in the observation, not proof of path failure.
• Duplicate sequence evidence does not prove consuming application behavior.
• Apparent BAG/cadence evidence is a teaching assumption here, not conformance checking.
• Ethernet/IP familiarity can mislead observers into assuming open network behavior.
• Application data remains opaque without interface-control authority.

Observer Lesson¶

A passive observer can infer conceptual virtual-link cadence, possible missing observations, duplicate sequence evidence, skew between redundant networks, and missing A/B counterparts. It cannot infer application semantics, receiver acceptance, physical state, or safety effect.

Python Model¶

schoolbus exposes a conceptual virtual-link observation model:

"""Runnable AFDX conceptual virtual-link observation example."""

from datetime import UTC, datetime, timedelta

from schoolbus.protocols.afdx import (
    AfdxVirtualLinkObservation,
    assess_bag_cadence,
    assess_sequence_evidence,
    compare_redundant_observations,
)

base = datetime(2026, 5, 21, 12, 0, tzinfo=UTC)

network_a = AfdxVirtualLinkObservation(
    virtual_link_id=0x123,
    network="A",
    sequence=0x5A,
    observed_at=base,
    length=64,
    payload_fingerprint="sha256:synthetic-vl-0123",
    source="samples/avionics-workbook",
)
network_b = AfdxVirtualLinkObservation(
    virtual_link_id=0x123,
    network="B",
    sequence=0x5A,
    observed_at=base + timedelta(milliseconds=1),
    length=64,
    payload_fingerprint="sha256:synthetic-vl-0123",
    source="samples/avionics-workbook",
)
network_a_next = AfdxVirtualLinkObservation(
    virtual_link_id=0x123,
    network="A",
    sequence=0x5B,
    observed_at=base + timedelta(milliseconds=4),
    length=64,
    payload_fingerprint="sha256:synthetic-vl-0123-next",
    source="samples/avionics-workbook",
)

print(network_a.explain())
print(
    compare_redundant_observations(
        network_a,
        network_b,
        max_skew=timedelta(milliseconds=2),
    ).explain()
)
successive_network_a = (network_a, network_a_next)
print(assess_sequence_evidence(successive_network_a).explain())
print(
    assess_bag_cadence(
        successive_network_a,
        expected_bag=timedelta(milliseconds=4),
    ).explain()
)

The model exposes virtual-link evidence, apparent cadence, sequence evidence, and A/B comparison. It deliberately has no raw Ethernet, no UDP, no IP, no PCAP parser, no switch simulation, and no conformance checker.

The avionics workbook includes passive synthetic conceptual virtual-link records under samples/avionics-workbook/.

Local Teaching Notes¶

The observation is synthetic and omits exact Ethernet/IP/UDP encapsulation details.

Source Confidence¶

Source confidence is high for scope and terminology, with semantic claims limited to public metadata, public source notes, and synthetic teaching artifacts.

Source Notes¶

References¶

Public Sources¶

• SAE ITC / ARINC
• ARINC 664 Part 7 Avionics Full-Duplex Switched Ethernet Network — canonical-standard.
• AIM Online
• AFDX / ARINC 664 Part 7 tutorial — vendor-tutorial.
• Tooling references
• Wireshark — public dissector/tooling context, not a binder parser surface.