1. What is AIS and Why It Matters for Buoys
AIS (Automatic Identification System) is a radio system that lets ships, shore stations and buoys automatically share position and identity information. When fitted to a buoy or lighthouse (called an AIS AtoN – Aid to Navigation), it broadcasts a message (Message 21) telling nearby ships: "I am here, this is my name/type, and I am on station (or off station)." Ships see this on their chart displays (ECDIS) and radar.
This works today worldwide and is governed by well-established technical standards (mainly IEC 62320-2 and ITU-R M.1371-5). Your existing certified AIS AtoN units (for example SRT Carbon/Chronos Type 1 & 3) continue to meet these standards and remain fully usable.
2. How the New Systems Fit Together
Think of the maritime digital world in three layers:
- Radio layer (how the signal travels): Classic AIS uses two VHF channels. VDES (VHF Data Exchange System, sometimes called "AIS 2.0") keeps those same AIS channels and adds extra channels for more data, two-way communication, and better security. VDES is designed to be backwards-compatible – old AIS equipment still works.
- Data-model layer (how information is organised): S-100 is the modern international framework (from the IHO) for organising all kinds of maritime digital data. S-201 is the specific "product specification" under S-100 that describes Aids to Navigation information (buoys, lights, racons, AIS AtoNs, etc.) so authorities can exchange it cleanly.
- Guidance & security layer: IALA Guidelines such as G1117 (VDES Overview) and G1192 (VDES Authentication) explain how to use VDES safely, including ways to prove that a message really came from an authorised source (authentication).
Physical AtoN (Real AtoN)
AIS AtoN unit sends Message 21 on AIS channels. Optional sensor data via AIS ASM (if Type 3). Direct broadcast.
Synthetic AtoN (Real AtoN)
Shore station transmits Message 21 with "Synthetic" flag reporting the real position (no AIS unit on buoy).
Virtual AtoN (Non physical)
Message 21 with "Virtual" flag set (created by shore). Signature follows the Virtual AtoN message (optional but recommended).
SHORE / AUTHORITY (Base station / VTS)
Receives AIS and AtoN "Synthetic" data; can relay "Synthetic" data and create & broadcast Virtual AtoN messages. Can add digital signature on VDE-TER channel (G1192 Scheme 1).
SHIP / ECDIS (Receiver)
Receives / displays Physical, Synthetic & Virtual AtoNs on ECDIS / radar. VDES-capable ships can verify the signature; legacy equipment ignores it.
PHYSICAL AtoN
(Real AtoN)
Sends Message 21 directly. Optional sensor data via ASM (Type 3).
Synthetic AtoN
(Real AtoN)
Shore transmits Message 21 with "Synthetic" flag reporting real position.
Virtual AtoN
(No physical AtoN)
Message 21 with "Virtual" flag, created by shore. Optional signature.
SHORE / AUTHORITY (Base station / VTS)
Receives AIS & Synthetic data; creates & broadcasts Virtual AtoN; can add digital signature on VDE-TER (G1192 Scheme 1).
SHIP / ECDIS (Receiver)
Displays Physical, Synthetic & Virtual AtoNs. VDES-capable ships verify signature; legacy equipment ignores it.
3. Key Standards, Guidelines & Their Current Status (as of mid-2026)
3.1. AIS (the foundation)
Still the global workhorse. Technical standard for AtoN stations is IEC 62320-2 Edition 2.0 (2016). Fully operational and required. Existing certified equipment continues to comply.
3.2. VDES (the evolution of AIS)
Defined in ITU-R M.2092. IMO has adopted amendments recognising VDES as an alternative to AIS under SOLAS, entering into force 1 January 2028. Backwards-compatible with classic AIS. Shore infrastructure is the current focus of upgrades; low-power buoy-mounted VDES AtoN units are still emerging.
3.3. S-100 & S-201 (the data language)
S-100 is the IHO Universal Hydrographic Data Model. S-201 is the IALA product specification for Aids to Navigation (AtoN) information. S-201 Edition 2.0.0, published in September 2025, is the first operational edition of S-201. It provides a common structure for the exchange of information about AtoNs, including buoys, beacons, racons, lights, sound signals and AIS. The product contains the positions, properties, operational status and general comments related to an AtoN. These are shore-side data formats – they do not change the radio signal that comes from a buoy.
3.4. G1117 – VDES Overview
IALA Guideline Edition 4.0 (Revised June 2026). Explains the whole VDES system and lists use cases, including Virtual AtoN over the higher-capacity VDE channels.
S-100 Phase 1 product specifications (S-101, S-102, S-104, S-111, S-129, plus S-124/S-128) are IHO-led and distinct from S-201, which is IALA-led.
3.5. G1192 – VDES Authentication Techniques
IALA Guideline Edition 1.0 (June 2025). First detailed, implementable method for authenticating AIS messages (especially Virtual AtoN) by sending a digital signature on a VDE-TER channel. Uses ECDSA with SHA-256. Fully backwards-compatible. TESLA protocol is mentioned as a possible future lower-overhead option for high-volume traffic.
3.6. TESLA
A cryptographic protocol that uses timed key disclosure so that many messages can be authenticated with less overhead than individual digital signatures. Referenced in G1192 for possible future use; not yet the primary scheme for AtoN.
4. Impact on Existing AIS AtoN Equipment
Current certified AIS AtoN units (Type 1 or Type 3 that meet IEC 62320-2) remain fully valid and interoperable. They continue to transmit the Message 21 that ships need. VDES is backwards-compatible, so ships and shore stations that adopt VDES still receive classic AIS AtoN messages. S-100/S-201 affect how authorities describe and exchange information about the AtoN – not the radio transmission from the buoy itself.
Project specifications / tenders could request "compatibility with the migration to the S-100 standard – specifically regarding VDES." This is a forward-looking procurement preference rather than a direct international mandatory requirement that every physical buoy must already transmit on VDES channels. Traditional AIS AtoN continues to satisfy the core safety function.
5. Bottom-Line Takeaway
✓ Your existing certified AIS AtoN equipment continues to work and remains fully interoperable.
✓ VDES and S-100 mainly improve shore-side data exchange, capacity and future security (especially for Virtual AtoNs).
✓ VDES carriage is currently a voluntary alternative to AIS under SOLAS V (not a replacement mandate), and AIS remains the baseline carriage requirement. They do not make current AIS AtoN units obsolete.
✓ SRT will develop VDES ready products as part of an ongoing growth strategy, although this will take some time.
Reference Table – Standards, Guidelines, Protocols & Abbreviations
| Name / Abbreviation | Type & Current Status | Basic Description |
|---|---|---|
| AIS | System – Fully operational | Automatic Identification System. Radio system for ships, shore and AtoN to share position/identity. Core technology for buoy-mounted and shore-based transponders. |
| AIS AtoN | Application – Operational | AIS fitted to an Aid to Navigation (buoy, beacon, etc.). Transmits Message 21. Can be Physical (on the aid), Synthetic or Virtual. Type 1/3 units may also be shore-mounted to transmit Virtual targets over a wide area. |
| IEC 62320-2 | Standard – Ed. 2.0 (2016) current | International performance & test standard for AIS AtoN stations. Existing certified units meet this. |
| ITU-R M.1371-5 | Recommendation – Current | Technical characteristics of the AIS system (messages, timing, etc.). |
| VDES | System – SOLAS alternative from 2028 | VHF Data Exchange System ("AIS 2.0"). Keeps AIS channels + adds capacity, two-way and satellite capability. Backwards-compatible with AIS. |
| ITU-R M.2092 | Recommendation – Current | Technical characteristics of VDES. |
| IEC 63514 | Standard – Draft | Maritime navigation and radiocommunication equipment and systems – VHF Data Exchange System (VDES) – Shipborne mobile station – Operational and performance requirements, methods of test and required test results. Advanced through multiple Committee Draft (CD) stages, with a Committee Draft for Voting (CDV) anticipated. Final International Standard publication is targeted around 2027, aligning closely with the January 1, 2028 effective date for IMO/SOLAS VDES framework updates. |
| S-100 | Framework – Phase 1 operational 2026 | IHO Universal Hydrographic Data Model. Modern way to structure and exchange maritime digital data (charts, AtoN info, etc.). |
| S-201 | Product Specification Ed. 2.0.0 first operational edition Published September 2025 |
IALA product specification under S-100 for exchanging AtoN information. It provides a common structure for exchanging information about AtoNs, including their positions, properties, operational status and general comments. It is a shore-side data product. |
| S-125 | Product Spec – Under development | Related S-100 product for certain AtoN notices and changes. |
| G1117 | IALA Guideline – Ed 4.0 (Revised June 2026) | VDES Overview. Explains the system and use cases, including Virtual AtoN over VDE channels. |
| G1192 | IALA Guideline – Ed 1.0 (June 2025) | VDES Authentication Techniques. First detailed method for authenticating AIS/Virtual AtoN messages using digital signatures on VDE-TER. |
| R0126 (A-126) | IALA Recommendation – Current | Use of AIS in Marine Aids to Navigation Services. |
| TESLA | Protocol – Referenced for future use | Timed Efficient Stream Loss-tolerant Authentication. Lower-overhead way to authenticate many broadcast messages; mentioned in G1192. |
| ECDSA / SHA-256 | Cryptographic algorithms | Digital signature method used in G1192 Scheme 1 (secp256r1 curve, 128-bit security). |
| Physical AtoN | Concept | Real buoy/beacon with an AIS (or future VDES) transmitter on it. |
| Synthetic AtoN | Concept | Real physical aid (buoy/beacon) that has no AIS transmitter. A shore station transmits Message 21 on its behalf, reporting the aid's actual position. |
| Virtual AtoN | Concept | Digital-only marker created by a shore station (or by a configured Type 1/3 unit); appears on ship displays but no physical structure exists at the reported position. |
| Message 21 | AIS message type | The standard AIS report for an Aid to Navigation (name, position, type, on/off station, virtual flag, etc.). |
| VDE-TER | VDES component | VHF Data Exchange – Terrestrial. Higher-capacity terrestrial data channels within VDES used for additional information and authentication signatures. |
| ASM | VDES / AIS component | Application Specific Messages. Specialised AIS/VDES messages that carry additional data (e.g. sensor readings from a Type 3 AtoN) beyond the basic position report. |
| VDE-SAT | VDES component | VHF Data Exchange – Satellite. Satellite component of VDES providing global coverage beyond terrestrial range. |
| Type 1 / Type 3 | AIS AtoN station types | Type 1: basic transmit-only AtoN station. Type 3: more capable station that can also receive and support additional functions (including sensor data via ASM). Both can be configured for Virtual AtoN transmission, including from shore sites. |
| IALA | Organization | International Organization for Marine Aids to Navigation (formerly the International Association of Marine Aids to Navigation and Lighthouse Authorities). |
| IEC | Organization | International Electrotechnical Commission. |
| IHO | Organization | International Hydrographic Organization. |
Certified AIS AtoN Equipment, Ready Today
Maritec Solutions supplies internationally certified AIS AtoN transponders — including SRT Carbon and Chronos Type 1 & 3 — that meet IEC 62320-2 and remain fully interoperable as VDES and S-100 evolve. Speak to us about current equipment and future-ready procurement requirements.
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