• AERONET System
• AERONET Configuration

Above entities include, among others: aircraft, airports, meteorological stations, telecommunication stations, communication centers.
 
1.1        Exchanged Information
Information exchanged among the entities deal with the following:

• Distress messages: sent by mobile stations and regarding some grave and imminent danger, and similar.
• Urgency messages: concerning safety of aircraft and so on.
• Flight safety messages: concerning movement of aircraft in air or about to depart.
• Meteorological messages: forecasts, observations, and so on.
• Flight regularity messages: load messages, schedules, aircraft servicing, and so on.
• Aeronautical administrative messages: regarding maintenance or operation of facilities for the aircraft operation, functional telecommunication services or messages exchanged between government civil aviation authorities.
• Reservation messages.
• General airlines messages.
• Service messages: requiring information on incorrectly transmitted messages, confirming channels' sequence numbers, and so on.

Entities involved in the transmission and reception of messages are the subscribers, the communication networks (either telegraphic or digital data networks) and the communication centers.

Main purpose of the communication centers is the switching of messages between subscribers and/or other centers.

The communication centers may be connected by means of the CIDIN data network and/ or the AFTN telegraphic network.
 
1.3        Communication Networks
1.3.1        AFTN Telegraphic Network
The AFTN (Aeronautical Fixed Telecommunication Network) telegraphic network connects communication centers and subscribers by means of point-to-point telegraphic lines. The dialogue exchanged among centers and users is performed according to three different modalities: full-duplex (the center and the user transmit and receive in the same time), half-duplex (the center and the user transmit and receive alternatively) and simplex (the center and the user can only either transmit or receive and vice versa).

The dialogue among centers and users moreover is carried on in completion with the rules of the Aeronautical Fixed Telecommunication Network protocol.
1.3.2        CIDIN Network
The Common ICAO Data Interchange Network connects communication centers by means of telephone channels, which are used for digital data transmission at medium speeds.

The communication protocols, which regulate data interchange in the network, are structured into layers.

The architecture of the network protocols partly complies with the ISO OSI reference model. The physical and data-link layers adhere to specific CCITT recommendations.

The CIDIN network has a typical mail topology, in which each single node can be connected to one or more nodes, by means of point-to-point links. In addition, CIDIN nodes can communicate through public or private packet switching networks (X.25).

Main purpose of this network is to carry messages either arriving from or destined to AFTN subscribers and/or communication centers.
 
2. System Description
AeroNet' architecture includes five main hardware and software subsystems, globally implementing the functions of the system, namely:

• The Message Switching subsystem, based on a fault-tolerant minicomputer running the Unix operating system, is the kernel of the whole system and interfaces all the other subsystems.
  It provides messages format analysis, storage, routing and output towards the transmission network interfaces as well as the automatic processing of AFTN service messages.
• The Telegraphic Subsystem is built on a set of Telegraphic Servers, based on rack-mounted i486 hardware running the Unix operating system, controlling specialized Telegraphic Multiplexers which, in turn, interface the telegraph lines. Each Telegraphic Server is connected to the Message Switching Subsystem by means of an Ethernet Local Area Network using the TCP/IP protocol suite.
  The Telegraphic Multiplexers and the Telegraphic Servers are connected by redundant serial asynchronous channels.
  The Telegraphic Multiplexer is a high-reliability, high-volume line interface device. It has a modular multiprocessor structure, suitable for minimal configurations (16 lines) as well as for massive communication centers with over 500 telegraph lines.
  
• The Data Communication Subsystem is built of a set of Data Communication Servers (DCS), based on rack-mounted i486 hardware running the Unix operating system. Each DCS houses two AT bus Protocol Processors each interfacing four synchronous lines interfacing the CIDIN network (either point-to-point links or the local X.25 switch). These boards have their own CPU and memory and run the lower layers of the CIDIN protocol (layers 2 and 3a).
  The Data Communication Servers are connected to the Message Switching subsystem by means of an Ethernet Local Area Network using the TCP/IP protocol suite.
• The Supervisory Subsystem, based on one or more graphical workstations, provides the center's supervisors with an advanced graphical user interface for system management, configuration, monitoring, etc. These workstations run the Unix operating system and the X-windows graphical user interface software.
• The Operator Subsystem, based on several graphical workstations, provides the center's operators with an advanced graphical user interface for composing AFTN messages, display messages addressed to the center, operate searches in the short and long-term archives, reconditioning incorrect messages and so on. These workstations run the Unix operating system and the X-windows graphical user interface software.

Aeronet Description