According to the <59/2002/EC Directive Bulgaria has to fulfil the EU requirements for vessel tracking in the VTS zones, as well as to exchange AIS data with the other EU member states. Bulgaria has had a 100% AIS coverage of the A1 zone since 2004. The AIS data exchange was realized in 2007 with the set up of a National AIS Server.

The National AIS server was developed by Astra Paging Ltd. under contract with the Bulgarian Maritime Administration. The server provides the necessary features for integration of the Bulgarian VTMIS (Vessel Traffic Management and Information System) and the European SafeSeaNet ship traffic monitoring system. In mid-2007, the National AIS server was also integrated into the Mediterranean AIS network, which is based in Italy.


  1. Collecting, checking and merging of AIS NMEA data received from:
    • Bulgarian VTMIS base stations
    • External AIS receivers / base stations
    • EU SRIT system
    • Mediterranean AIS server
    • Other National AIS servers
  2. Processing, analysis and storage of the AIS information in raw (NMEA) and decoded format into an SQL relational database engine
  3. Filtering of the data stream based on different sets of parameters (AIS source number, message number, geographic area)
  4. Data stream downsampling
  5. Dispatching of AIS data to the following external systems:
    • EU level
    • EU SRIT system
    • Mediterranean AIS server
    • Other National AIS servers
    • National level
    • Border police
    • Bulgarian Navy
    • Customs
    • Port community



Input interfaces

  • Outgoing TCP connection to the data source and incoming TCP data
  • Incoming TCP connection from the data source and incoming TCP data
  • Incoming UDP stream from the data source
  • Serial connection (RS232)
  • Console input (for testing and further development)

NMEA processing

  • Processed messages – 1,2,3,4,5,9,18,19,24a/b
  • CRC check
  • Timestamp check
  • Duplicated message filter
  • Performance – up to 20000 messages/minute

Database features

  • Raw (NMEA) archive – 30 days
  • Statistics archive – 5 years
  • “Snapshot” feature
  • Vessels database
  • “Last seen” feature
  • Tracking – 72 hours


  • By message number
  • By source number
  • By geographic area


  • Interval – from 0 to 7200 seconds
  • Message 9 (SAR aircraft) is not subject to downsampling

Output network interfaces

  • Incoming TCP connection to the server and outgoing TCP data
  • Outgoing TCP connection to the client and outgoing TCP data
  • Outgoing UDP stream to the client
  • VPN encapsulation (PPTP RFC2637)

Output application level protocols

  • NMEA (IEC 61993-2, 61162-1) real time streaming
  • XML output at client’s request
  • VT Explorer protocol

Archive recovery

  • Extraction of data for a selected time interval from the database
  • Replay of the extracted data by means of the “VT Explorer replay” utility

Administration and monitoring

  • Web based administration of the users and filter parameters
  • Web based monitoring of the data sources
  • Web based monitoring of the hardware and system integrity
  • Web based direct access to the database
  • SQL interface