ARINC 664 (AFDX)¶

Overview¶

ARINC 664 Part 7 Avionics Full-Duplex Switched Ethernet (AFDX) defines a deterministic Ethernet-based network for avionics. It guarantees bounded latency through Virtual Links (VL) with pre-configured bandwidth allocation.

Key Facts

Physical: Standard IEEE 802.3 Ethernet (100 Mbps / 1 Gbps)
Topology: Switched, full-duplex
Determinism: Bandwidth Allocation Gap (BAG) per Virtual Link
Redundancy: Dual networks (A/B) with sequence numbering
Aircraft: A380, A350, B787, F-35

Virtual Link Concept¶

A Virtual Link (VL) is a unidirectional logical connection from one source to one or more destinations, with guaranteed bandwidth.

┌─────────────────────────────────────────────────────────────────┐
│                        AFDX Network                              │
│                                                                 │
│  Source ═══► VL 1024 ═══► Switch ═══► Destination A            │
│  (LRU)       (BAG=4ms)    ║          Destination B            │
│              (Lmax=512)    ╚════════► Destination C            │
│                                                                 │
│  One transmitter per VL (enforced by network configuration)     │
│  Multiple receivers (multicast addressing)                      │
└─────────────────────────────────────────────────────────────────┘

Frame Structure¶

┌──────────────────────────────────────────────────────────────────┐
│ Dst MAC │ Src MAC │ EType │ IP Header │ UDP Header │ Payload │Seq│
│  (6B)   │  (6B)   │ (2B)  │  (20B)    │   (8B)     │ (0-1471)│(1)│
└──────────────────────────────────────────────────────────────────┘

Destination MAC Format¶

Byte:  0     1     2     3        4        5
     ┌─────┬─────┬─────┬────────┬────────┬────────┐
     │0x03 │0x00 │0x00 │Net ID  │VL High │VL Low  │
     └─────┴─────┴─────┴────────┴────────┴────────┘
     Constant prefix    Network   Virtual Link ID

Sequence Number¶

1 byte appended after the UDP payload
Wraps 0→255
Used for redundancy management (duplicate elimination)

BAG (Bandwidth Allocation Gap)¶

The minimum interval between consecutive frames on a VL:

BAG Value	Min Interval	Max Bandwidth (Lmax=1518B)
1 ms	1 ms	12.1 Mbps
2 ms	2 ms	6.1 Mbps
4 ms	4 ms	3.0 Mbps
8 ms	8 ms	1.5 Mbps
16 ms	16 ms	759 kbps
32 ms	32 ms	380 kbps
64 ms	64 ms	190 kbps
128 ms	128 ms	95 kbps

Redundancy Management¶

AFDX uses dual independent networks. The receiver implements "First Valid Wins":

sequenceDiagram
    participant Source
    participant NetA as Network A
    participant NetB as Network B
    participant Sink

    Source->>NetA: Frame (seq=42)
    Source->>NetB: Frame (seq=42)
    NetA->>Sink: Frame arrives first
    Note over Sink: Accept (seq=42, new)
    NetB->>Sink: Frame arrives second
    Note over Sink: Reject (seq=42, duplicate)

API Reference¶

#include "arinc664.h"

// Initialize Virtual Link
void afdx_vl_init(afdx_vl_state_t *vl, const afdx_vl_config_t *config,
                  const uint8_t *src_mac);

// Build AFDX frame (auto-increments sequence number)
int afdx_build_frame(afdx_vl_state_t *vl, const void *payload,
                     size_t payload_len, uint8_t *frame_buf);

// Parse received frame
bool afdx_parse_frame(const uint8_t *frame, size_t frame_len,
                      uint16_t *vl_id, uint8_t *seq_num,
                      const uint8_t **payload, size_t *payload_len);

// BAG enforcement check
bool afdx_bag_check(afdx_vl_state_t *vl);

// Redundancy management
void afdx_redundancy_init(afdx_redundancy_t *rm);
bool afdx_redundancy_check(afdx_redundancy_t *rm, uint8_t seq, uint8_t network);

Build & Run¶

make -C src/aerospace/arinc664
./build/afdx_demo

References¶

ARINC Specification 664, Part 7 (2009)
ARINC Report 664P7-1