Overview
ASTERIX (All Purpose Structured EUROCONTROL Surveillance Information EXchange) is a standardized data format developed by EUROCONTROL for exchanging surveillance and related information between air traffic management systems. It operates primarily over network protocols such as UDP and TCP, with UDP commonly used for real-time surveillance data. ASTERIX defines multiple standardized categories (CAT), such as CAT001, CAT002, CAT021, and CAT048, covering different types of surveillance and aeronautical information. It enables interoperability between radar, ADS-B, multilateration, and other surveillance systems without relying on proprietary data formats.
Port 8600 is registered with IANA for ASTERIX, although the ASTERIX specification does not mandate a specific UDP port. ASTERIX data is commonly transported over UDP, including local multicast. The specific multicast address and UDP port remain implementation-dependent.
Protocol Strucutre / Field Type
ASTERIX DATA BLOCK
├── CAT (1 octet)
├── LEN (2 octets)
└── DATA RECORD(1) ... DATA RECORD(k)
└── DATA RECORD
├── FSPEC ← the bitfield table
├── DATA FIELD(1)
├── ...
└── DATA FIELD(k)
General Structure
| 0 |
12
|
3f
|
f+1N
|
| CAT | LEN | FSPEC(1) ... FSPEC(m) | DATA FIELD(1) ... DATA FIELD(k) |
FSPEC
| Bit 8 | Bit 7 | Bit 6 | Bit 5 | Bit 4 | Bit 3 | Bit 2 | Bit 1 | |
| Byte 1 | FRN 1 | FRN 2 | FRN 3 | FRN 4 | FRN 5 | FRN 6 | FRN 7 | FX |
| Byte 2 | FRN 8 | FRN 9 | FRN 10 | FRN 11 | FRN 12 | FRN 13 | FRN 14 | FX |
| Byte 3 | FRN 15 | FRN 16 | FRN 17 | FRN 18 | FRN 19 | FRN 20 | FRN 21 | FX |
FSPEC is a bitmap at the start of each Data Record where every bit (FRN 1, FRN 2, ...) flags whether a specific Data Field is present — 1 means read it, 0 means skip it, and each FRN number maps to a specific item defined by that record's ASTERIX Category (e.g. FRN 1 = I021/010 for Category 021). The last bit in each FSPEC byte is FX: 1 means another FSPEC byte follows, 0 means FSPEC ends there and the actual Data Fields begin, in the order their FRN bits were set.
Item Type
Item Type identifies the specific type of information contained within a Data Field, such as aircraft identification, position, altitude, or other surveillance data. Each item type defines how its corresponding data is structured and interpreted. Below is an example for CAT002 Item Type Category 002 Specification
CAT002 Item type
| Data Item Ref. No. | Description | System Units |
|---|---|---|
I002/000 |
Message Type | N.A. |
I002/010 |
Data Source Identifier | N.A. |
I002/020 |
Sector Number | 360°/(28) |
I002/030 |
Time of Day | 1/128 s |
I002/041 |
Antenna Rotation Period | 1/128 s |
I002/050 |
Station Configuration Status | N.A. |
I002/060 |
Station Processing Mode | N.A. |
I002/070 |
Plot Count Values | N.A. |
I002/080 |
Warning/Error Conditions | N.A. |
I002/090 |
Collimation Error | Range: 1/128 NM Azimuth: 360°/(216) |
I002/100 |
Dynamic Window - Type 1 | RHO: 1/128 NM THETA: 360°/(216) |
Multicast Address Scope
IANA reserves two IPv4 multicast ranges relevant here: 224.0.0.0/24, the Local Network Control Block, for local network control traffic that generally stays within the local subnet, and 239.0.0.0/8, the Administratively Scoped range, for multicast traffic confined to private or local networks by the administrator (IANA multicast address registry).
Example Hexdump
ASTERIX packet, Category 034
Category: 34
Length: 16
Asterix message, #01, length: 13
FSPEC
010, Data Source Identifier
000, Message Type
030, Time of Day
020, Sector Number
050, System Configuration and Status
0000 22 00 10 f4 93 19 02 37 8d 57 20 94 00 20 20 00 "......7.W .. .
ASTERIX Wireshark Dissector Github
EUROCONTROL Specification for Surveillance Data Exchange Part I