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CPDLC Server

Server Diagram

The server maintains one or more connections to upstream ACARS networks (i.e. Hoppies). Each connection simulates a single air traffic service unit (ATSU), such as Brisbane (YBBB) or Melbourne (YMMM). The server will relay CPDLC messages to the upstream ACARS network, allowing pilots to connect to a single ATS unit and communicate with all enroute controllers within that unit.

The server also allows for multiple connections upstream ACARS networks, enabling ATC to communicate with aircraft on different ACARS networks (Hoppies, FSDLP, etc.) or aggregate messages across multiple ATSUs.

Deployment​

Deploy your own CPDLC Server instance to DigitalOcean:

Deploy to DigitalOcean

After deployment, configure the following environment variables in the DigitalOcean dashboard:

  • Acars__0__StationIdentifier: Your station identifier (e.g., YBBB)
  • Acars__0__AuthenticationCode: Your Hoppie ACARS authentication code

Prerequisites​

Before running the CPDLC Server, ensure you have:

Configuration​

The server can be configured using environment variables. Copy example.env to .env and update with your settings:

# Logging
Logging__Level=Information

# ACARS Client Configuration
Acars__0__Type=Hoppie
Acars__0__FlightSimulationNetwork=VATSIM
Acars__0__StationIdentifier=YBBB
Acars__0__Url=http://www.hoppie.nl/acars/system/connect.html
Acars__0__AuthenticationCode=your-hoppie-logon-code
# Reporting interval in minutes of the ADS-C contract requested on CPDLC logon (default: 10)
Acars__0__DefaultAdscReportingInterval=10
# Minutes from the request of a selected ADS-C contract to its end. Then the default contract is requested again (default: 60)
Acars__0__SelectedAdscContractDuration=60

# Handoff Configuration
# How many minutes before the expected transfer time to send the NEXT DATA AUTHORITY message (default: 10)
Handoff__NotificationLeadTime=10

# ADS-C from VATSIM status data
# Make ADS-C reports from the VATSIM status data for aircraft that do not support ADS-C over Hoppie (default: false)
VatsimStatus__Enabled=false
# The URL of the VATSIM status data (default: https://data.vatsim.net/v3/vatsim-data.json)
VatsimStatus__Url=https://data.vatsim.net/v3/vatsim-data.json
# The time in seconds between downloads of the VATSIM status data (default: 120)
VatsimStatus__PollingIntervalSeconds=120
# Also make reports for aircraft that do not have D1 or G1 in Item 10b of the flight plan (default: false)
VatsimStatus__AllowNonEquippedAircraft=false

Multiple ACARS Connections​

You can configure multiple ACARS clients by incrementing the index (Acars__1__, Acars__2__, etc.). This is useful when serving multiple ATSUs (e.g., YBBB and YMMM)

Example configuration for multiple connections:

# Brisbane FIR
Acars__0__Type=Hoppie
Acars__0__FlightSimulationNetwork=VATSIM
Acars__0__StationIdentifier=YBBB
Acars__0__Url=http://www.hoppie.nl/acars/system/connect.html
Acars__0__AuthenticationCode=your-ybbb-hoppie-code

# Melbourne FIR
Acars__1__Type=Hoppie
Acars__1__FlightSimulationNetwork=VATSIM
Acars__1__StationIdentifier=YMMM
Acars__1__Url=http://www.hoppie.nl/acars/system/connect.html
Acars__1__AuthenticationCode=your-ymmm-hoppie-code
note

Hoppie is currently the only supported ACARS network type.

ADS-C​

When an aircraft logs on with CPDLC, the server requests the default ADS-C contract with the aircraft. When the CPDLC connection ends, the server cancels the contract.

Each ATSU has its own default reporting interval, set with Acars__<index>__DefaultAdscReportingInterval. Controllers can read this value.

A controller can select a different reporting interval for an aircraft. The selected contract ends Acars__<index>__SelectedAdscContractDuration minutes after the server sends the request. Then the server requests the default contract again. A controller can also go back to the default contract at any time.

The aircraft does not acknowledge a request. The first report after a request accepts it. If the aircraft rejects a selected contract, the server requests the default contract again. If the aircraft rejects the default contract, the server does not send it again.

The server keeps the latest report for each aircraft. When a controller connects, the plugin loads these reports, so that the controller sees the ADS-C tracks immediately.

The ADS-C page of the dashboard (/adsc) shows all the contracts and their states, and a log of all the ADS-C messages that the server sent and received.

ADS-C from VATSIM Status Data​

Not all aircraft support ADS-C over Hoppie's network. When VatsimStatus__Enabled is true, the server fakes ADS-C reports using data from the VATSIM status API.

This is only done for aircraft that have D1 or G1 in Item 10b of the flight plan, unless VatsimStatus__AllowNonEquippedAircraft is true. A report from Hoppie always has priority. If the Hoppie reports stop for more than two reporting intervals, the server uses the VATSIM status data again.

Running​

Docker​

docker-compose up

The server will be available at http://localhost:5272.

Local Development​

dotnet run --project source/CPDLCServer/CPDLCServer.csproj

The server will start on http://localhost:5261.