# Voice Communication Systems Impact on Navigating Officers
## 4 Call Management  
A call management system could be implemented on all communication systems, which were a part of this research. However, with substantially different approaches. The call management of the UHF radio system is quite simple and differs from all other systems. In this case, the simple organization and regulation through the ship's Safety Management System could decrease the distractions of the OOW, simply by allocating different UHF channels for routine communication and for important safety related calls. In that case, the OOW should have the UHF radio on the bridge set up on the channel allocated to _important calls_. However, this system cannot prevent its own misuse. Some crew members could still call the bridge asking for non-important details. Furthermore, it cannot be used to select and reject calls automatically, or to divert a certain type of call. Consequently, the OOW decides whether they will answer the call and how fast. It is technically possible for the other three systems (satellite, mobile and internal phone system) to manage different calls before the phone starts ringing on the ship's bridge. A technical solution to the problem that is not highly complex is a call management system offering priority call selection (Figure 7). For this system to work efficiently, it is important for the caller to know how to recognize the importance of the call and thus how to select the appropriate call procedure. In that case, the caller has an option to choose whether the call is a routine one (low priority) or a high priority one (by a special number sequence or a built-in button) and, consequently, to establish the immediate connection with the bridge. Once a certain call reaches the bridge, it should be easily recognized by the OOW. High priority calls on the bridge should sound an alert (ringing tone) using a certain, easily recognizable sound pattern of higher volume that a low priority call does not have. In case the OOW does not answer within a given (rather long) ring time, the system should apply a certain rule to manage the call  
Figure 7: Call management system. e.g., redirect the call to the master's cabin (Figure 7). On the other hand, low priority calls should not ring constantly. They should use sound patterns with more silent periods and with lower volume. Another significant difference is that a low priority call should not ring as long as a high priority call. Instead, it should ring for a rather short period (e.g., 10 s), after which a certain rule (management method) should be used. The idea of such a short ringing time is to inform the OOW and provide them the opportunity to answer it, if the time is appropriate. If the OOW does not answer after the initial ringing time, the system should manage the call further by applying a certain rule. Low priority call managing methods, i.e., rules, which may be applied in case the OOW did not answer within a given time, include forwarding or rejecting the calls. Call forwarding may be used to redirect the call to another defined phone unit (backup) or even to give the choice to the caller to select and reach a certain person or a department (e.g., master, chief engineer, engine control room, etc.). Call rejection may be organized in a way that a recorded message informs the caller that the OOW is not able to answer the call and to try again later. One of the solutions to the problem of voice calls' priorities is the application of the Multilevel Precedence and Preemption (MLPP) service in the call management system. The MLPP is a priority scheme for (a) assigning one of several precedence levels to specific calls or messages so that the system handles them in a predetermined order and time frame, (b) for gaining controlled access to network resources in which calls and messages can be preempted only by higher priority calls and messages, (c) that is recognized only within a predefined domain and (d) in which the precedence level of a call outside the predefined domain is usually not recognized [21].