Decentralized Environmental Notification (DEN) Service

The Decentralized Environmental Notification (DEN) Service allows vehicles and infrastructure to share environmental hazard notifications using Decentralized Environmental Notification Messages (DENM). These messages play a crucial role in cooperative intelligent transport systems (C-ITS), functioning alongside other facility-layer messages such as Cooperative Awareness Messages (CAMs) and VRU Awareness Messages (VAMs).

Required components are:

Optional (but recommended) components are:

Local Dynamic Map

Important

Logging is always an optional component but highly recommended.

A quickstart is available here, but continue reading for a detailed overview.

DENM Overview

The Decentralized Environmental Notification Message (DENM) is defined in ETSI TS 103 831 V2.2.1 (2024-04).

A DENM is composed of three core submodules within the facilities layer:

DEN Service
DEN Transmission Management
DEN Reception Management

DEN Service

The DEN Service is responsible for handling DENM messages, including their creation, management, and transmission. It interfaces with all needed submodules like the DEN Transmission Management, DEN Reception Management, and DEN Coder.

Basic usage:

from flexstack.facilities.decentralized_environmental_notification_service.den_service import DecentralizedEnvironmentalNotificationService

den_service = DecentralizedEnvironmentalNotificationService(btp_router=btp_router,
                                                            vehicle_data=vehicle_data)

The BTP Router and the Vehicle Data are required dependencies.

DEN Reception Management

The DEN Reception Management component handles incoming DENMs from other ITS stations. It processes and validates messages, ensuring they are appropriately relayed to the application layer.

This component does not require explicit instantiation, as it is automatically handled within the DEN Service.

DEN Transmission Management

The DEN Transmission Management component ensures DENM messages are transmitted correctly. It manages message triggering, periodic updates, and termination based on specific event conditions. Since this message can be addapted to cover several use cases, its implementation is strongly related with the applications layes. In this case, the DEN Transmission Management covers 2 use cases:

Emergency Vehicle Approaching Service
Longitudinal Collision Risk Warning

Application Layer: Emergency Vehicle Approaching Service

The application layer builds upon the DEN Service to implement higher-level functionalities. One example is the Emergency Vehicle Approaching Service, which is part of the Road Hazard Signalling (RHS) application described in ETSI TS 101 539-1 V1.1.1 (2013-08).

The Emergency Vehicle Approaching Service is designed to:

Alert nearby vehicles about an approaching emergency vehicle.
Use DENMs to broadcast the emergency vehicle’s position, speed, and trajectory.
Enhance road safety by allowing other vehicles to react accordingly.

It relies on the DEN Service for message management and transmission.

An example of how to use this service is provided in the Quickstart section below.

Quickstart

The following example demonstrates how to set up the Emergency Vehicle Approaching Service using the DEN Service:

import logging
import logging.config

from flexstack.applications.road_hazard_signalling_service.emergency_vehicle_approaching_service import EmergencyVehicleApproachingService
from flexstack.facilities.ca_basic_service.cam_transmission_management import VehicleData
from flexstack.utils.static_location_service import ThreadStaticLocationService as LocationService

from flexstack.btp.router import Router as BTPRouter

from flexstack.geonet.router import Router
from flexstack.geonet.mib import MIB
from flexstack.geonet.gn_address import GNAddress, M, ST, MID

from flexstack.linklayer.raw_link_layer import RawLinkLayer


logging.basicConfig(level=logging.INFO)

# Geonet
mac_address = b"\x00\x00\x00\x00\x00\x00"
mib = MIB()
gn_addr = GNAddress()
gn_addr.set_m(M.GN_MULTICAST)
gn_addr.set_st(ST.CYCLIST)
gn_addr.set_mid(MID(mac_address))
mib.itsGnLocalGnAddr = gn_addr
gn_router = Router(mib=mib, sign_service=None)

# Link-Layer
link_layer = RawLinkLayer("lo", mac_address=mac_address,
                  receive_callback=gn_router.gn_data_indicate)
gn_router.link_layer = link_layer

# BTP
btp_router = BTPRouter(gn_router)
gn_router.register_indication_callback(btp_router.btp_data_indication)

# Facility - Location Service
location_service = LocationService()
location_service.add_callback(gn_router.refresh_ego_position_vector)

# Application - Emergency Vehicle Approaching Service
vehicle_data = VehicleData()
vehicle_data.station_id = 10  # Station Id of the ITS PDU Header
vehicle_data.station_type = 5  # Station Type as specified in ETSI TS 102 894-2 V2.3.1 (2024-08)
vehicle_data.drive_direction = "forward"

denm_duration = 1000  # Each DENM is repeated for 1 second before updating
denm_service = EmergencyVehicleApproachingService(btp_router=btp_router,
                                                  vehicle_data=vehicle_data,
                                                  duration=denm_duration)

location_service.add_callback(denm_service.trigger_denm_sending)

# Start sending DENMs
location_service.location_service_thread.join()

Logging has been included to provide a way of visualizing the sent messages. View Logging to get more detailed information on how to use it.

You can explore the examples scripts avaialble, expand upon them or use them as a baseline to create your own. If you have any questions about the agents, feel free to post in the forum.