Service Discovery

The key difference between FSDLP and prior solutions is its decentralized nature. Rather than a single entity federating communications between aircraft, air traffic units, and virtual airline operations centers, the responsibility is shared between all of the aforementioned users.

To facilitate this, a method for service discovery is necessary, as an airborne client must know which provider clients are available and what capabilities they posess. A pre-determined port range of 60860—60867 is used to make port scanning easier on airborne clients.

Caution

The port range above only allows for up to eight clients on a single machine. We believe this to be a sufficient quantity, as there are typically at most two at any given moment: a network and a virtual airline.

Provider Client Identification

Provider clients shall bind to local address 127.0.0.1 on any port in the range 60860—60867, inclusive. Once bound, clients must satisfy the following exchange in order to be discoverable by airborne clients:

1. Provider client receives HTTP GET request on /id:

   GET /id HTTP/1.1

2. Provider client responds with the following JSON payload:

   {
       "protocol": "fsdlp",
       "version": 1,
       "provider": {
           "name": "",
           "type": "",
           "features": []
       }
   }

   The provider.name field shall be populated with a brief, identifiable name of the network or virtual airline. This information may be shown in virtual cockpits when prompting pilots to establush a data link connection.

   The provider.type field shall be populated with either network or other to indicate the kind of provider client. This determines the prioritization of clients in cases where multiple clients support a particular feature, as networks will take priority in such cases.

   The provider.features field shall be populated with a list of all features supported by the provider client.

Note

While not necessarily a focus of this protocol, this method does allow provider clients to discover other providers and alter their logic in reponse to the presence or absence of other clients.

Airborne Client Identification

While there are no requirements for an airborne client to be discoverable, as they are are always the first to initiate a data link connection, there are requirements on how an airborne client dicovers available provider clients.