Within each of these cells, a series of listening and calling channels must be established and the ships located within the controlled areas must operate in the specified channels following the protocol established by AVISOMEF. At the end of each grid there would be antennas that emit signals from the governing Traffic Control Centre (TCC). The vessels' identification will be conducted on medium frequency (MF). Nevertheless, the system will not be limited by a maximum distance coverage of 100 miles, typical for an MF, as the process is propagated on radio-links made from a cell to the following contiguous one and so on [7; 8; 9]. By implementing AVISOMEF, which incorporates Digital Selective Calling (DSC) as a technology already proven in GMDSS, a vessel will automatically know whether or not one of the radio packets sent by the Traffic Control Centre (TCC) is directed to it or not. When the call is directed to her, she will react by responding with a message back to the Control Centre. This message will not only include information concerning the vessel that is expected to be identified, but it will also provide information related to the environment of that vessel. This additional information will be important for the TCC to establish a relative understanding of the maritime traffic around the ship, including details about new additions to the cell from areas outside the grid. If the message is not addressed to any of the ships located in the cell, one of them will work as a repeater, thus establishing a control protocol and advancing the message to the next cell, until it reaches the ship that is expected to be identified. The calls will be launched to the various ships in the area periodically by the TCC in order to establish real-time tracking of all the vessels located there. The periodicity in which AVISOMEF must proceed to identify each vessel located in the controlled area will depend on its speed. The system, with the information received, will regulate itself. It must carry out at least one identification of each ship per cell. The messages, broadcasted from the TCC to the ships to be located, will be launched in an open collective message. The return messages from the ships to the TCC are part of a peer-to-peer system, as the initial message stores the callsigns (MMSI) of the stations acting as repeaters, therefore establishing a map of the communication path. The requirements demanded by AVISOMEF, as far as hardware is concerned, are the use of four receivers (A, B, C, and D) and a transmitter, all of them managed by a computer control [10]; a block diagram is shown in Figure 2.  
Figure 1: Subject area covered by a grid. The channels that appear underlined in each cell are used for listening. Those that appear without underlining are broadcast channels. When the message meant to identify a certain vessel starts from the TCC, it will first arrive at the vessels located in the first cells of the grid (Figure 1) and be captured by their receivers, named \"A\" (Figure 2), through channel \"1\". These receivers will be equipped with DSC technology. If said message is addressed to one of the vessels, it will be noticed thanks to the implemented DSC technology. Automatically, said ship will proceed to manifest its presence in the cell by sending a message back to the TCC on the channel that appears in Figure 1 entitled \"80\". The rest of the ships located in this first cell of the grid listen to channel \"80\" through their receiver \"C\" (Figure 2). When the ship in question is identified, there is no need for any of the vessels to rebroadcast the message to subsequent cells. As can be seen, this \"C\" receiver does not need to be equipped with DSC technology as it is only a listening channel receiver; it never needs to send a signal of self-identification. If the message sent by the TCC to the first cells of the grid is not directed to any of the ships located there, none of them would send a message back to the TCC, since none would be alerted by their receiver \"A\" (Figure 2).