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--- en:c-its:start [2026/08/06 17:54] – Initial English translation of c-its fasteiner
+++ en:c-its:start [2026/09/16 13:53] (current) – [C-ITS Messages] idahoenigmann
@@ Line 16: / Line 16: @@
 C-ITS packets are transmitted on **5.9 GHz**. The packets are unencrypted, but they can be signed.
+An overview of which vehicles and infrastructure actually send C-ITS: [[en:c-its:senders|Who is sending C-ITS?]]
 ===== C-ITS Messages =====
-Various types of messages are sent via C-ITS.
+Several standardised message types travel over C-ITS. The message contents are specified by ETSI. Machine readable message specifications are published as ASN.1 files (https://forge.etsi.org/rep/ITS/asn1).
+All messages share a common header. This header includes the messageId, which specifies the type of message.
+^ Message Id ^ Type ^ Full name ^ In one sentence ^
+| 1 | [[en_alt:c-its#denm|DENM]] | Decentralized Environmental Notification Message | Warning about an exceptional situation |
+| 2 | [[en_alt:c-its#cam|CAM]]   | Cooperative Awareness Message | Periodic status broadcast from a vehicle |
+| 4 | [[en_alt:c-its#spatem|SPATEM]] | Signal Phase and Timing Extended Message | The current state of a traffic light |
+| 5 | [[en_alt:c-its#mapem|MAPEM]] | MAP Extended Message | The geometry of an intersection |
+| 6 | [[en_alt:c-its#ivim|IVIM]] | Infrastructure to Vehicle Information Message | Road sign and infrastructure information |
+| 9 | SREM | Signal Request Extended Message | Request message for green light at intersection |
+| 10 | SSEM | Signal request Status Extended Message | Reply message to SREM |
+| 14 | CPM  | Collective Perception Message | Sensor information |
+Other, less common, message types are:
+  * VRU Awareness Message (VAM),
+  * Point of Interest Message (POIM),
+  * Parking Information Message (PIM),
+  * Interference Management Zone Message (IMZM),
+  * Service Announcement Essential Message (SAEM),
+  * Electric Vehicle Charging Spot Notification (EVCSN),
+  * Electric Vehicle Recharging Spot Reservation messages (EV-RSR),
+  * Maneuver Coordination Message (MCM),
+  * Marshalling Infrastructure Message (MIM),
+  * Marshalling Vehicle Message (MVM)
-The most important ones are: \
+While ETSI defines the structure of C-ITS messages and their permitted value ranges, some values remain open to interpretation—for example, a role may be represented as an integer without specifying what a value such as 42 actually means. ETSI can also be vague about when and how often messages should be transmitted, sometimes specifying only a broad range such as 1–100 Hz.
-| Message Type | Meaning |
-| **[[en:c-its:messages:cam|CAM]]** | Cooperative Awareness Message: periodic status message sent by vehicles |
-| **DENM** | Warning about exceptional situations, e.g. roadworks, traffic jams, stationary vehicles |
-| **MAPEM** | Description of intersections, lane geometry |
-| **SPATEM** | Signal states and timings of traffic lights |
-| **IVIM** | Road signs, infrastructure information |
+C-Roads (https://www.c-roads.eu/), an EU-funded platform for harmonising C-ITS, addresses these ambiguities. It defines concrete use cases, specifying which messages should be sent, how information should be modelled within those messages, which values to use, and under what conditions and frequency messages should be transmitted.