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MX Foundation 4
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MX Foundation 4
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The ARINC 664 message format is based on the standard Ethernet frame. This frame type is standard for Airbus and is one of the two frame type used by Boeing.
This frame differs from the Ethernet standard frame only by the addition of a Sequence Number field at the end of the frame.
The frame is made up of the Ethernet Header, IP Header, UDP Header, UDP Payload, Sequence Number, and the Frame Check Sequence(FCS).
The following table shows the frame fields in order with the number of bytes for each.
| Bytes | Field | Description |
|---|---|---|
| 14 Bytes | Ethernet Header | Contains the preamble, destination address, and source address. The VL ID is encoded in the destination address. |
| 20 Bytes | IP Header | Contains the destination End System Identification. Also contains fragmentation information if a large message is being split into multiple frames. |
| 8 Bytes | UDP Header | Contains Source and destination UDP port numbers. |
| 1 - 8192 Bytes | UDP Payload | Contains the actual message being sent between Avionic systems. |
| 1 Byte | Sequence Number | Used for Integrity checking the message. The Sequence Numbers on successive frames must be in order. |
| 4 Bytes | FCS | The Frame Check Sequence (CRC32) is analyzed first to check for bit errors in the received frame. |
The Boeing EDE message format is also based on the ARINC 664 frame. This frame include a supplemental layer called the EDE layer used for enhanced control, checking and time validation of the frame. The EDE layer is added at the beginning and the end of the UDP payload.
| Bytes | Field | Description |
|---|---|---|
| 14 Bytes | Ethernet Header | Contains the preamble, destination address, and source address. The VL ID is encoded in the destination address. |
| 20 Bytes | IP Header | Contains the destination End System Identification. Also contains fragmentation information if a large message is being split into multiple frames. |
| 8 Bytes | UDP Header | Contains Source and destination UDP port numbers. |
| 8 Bytes | EDE Header | Boeing EDE layer (details below) |
| 1 - 8180 Bytes | UDP Payload | Contains the actual message being sent between Avionic systems. |
| 4 Bytes | EDE Trailer | Boeing EDE layer (details below) |
| 1 Byte | Sequence Number | Used for Integrity checking the message. The Sequence Numbers on successive frames must be in order. |
| 4 Bytes | FCS | The Frame Check Sequence is analyzed first to check for bit errors in the received frame. |
The format of a UDP payload using the EDE protocol shall be as follows:
| Bytes | Field | Description |
|---|---|---|
| 2 Bytes | EDE sequence number | Identify specifically the UDP payload |
| 6 Bytes | EDE timestamp | Timestamp (clock Reference from the source) when the frame was sent. |
| variable | User UDP payload | Identify specifically the UDP payload |
| 2 Bytes | CRC-X | CRC computed as follow; SID + EDE header + UDP payload |
| 2 Bytes | CRC-Y | CRC computed as follow; SID + EDE header + UDP payload + CRC-X |
The specification ARINC Specification 664, Part 7, Aircraft Data Network, Avionics Full Duplex Switched Ethernet (AFDX) Network defines two types of messages; Explicit and Implicit. Explicit messages contain format data to allow the receiver to interpret the data types. Implicit messages do not. This makes them more bandwidth efficient and more widely used.
UDP ports numbers allow the Avionics application to associate message structure with the port the message is received on.
A limited number of data types are defined for implicit messages and are listed below.
