  In emergencies such as disasters, the number of voice calls (VoIP sessions)
increases rapidly for a variety of purposes. Thus, a control server near a
disaster area may not be able to connect to VoIP sessions due to congestion. To
solve this problem, a Call Admission Control (CAC) is needed to determine
whether a VoIP session requesting a connection can be accepted or rejected. A
CAC has the purpose of guaranteeing the connection quality and communication
quality of VoIP sessions. One conventional method classifies VoIP sessions into
three classes (emergency VoIP sessions, VoIP sessions from the disaster area,
and VoIP sessions from outside the disaster area) by focusing on the outgoing
location and offers a CAC with a priority level for each. However, a
conventional CAC method cannot be applied to VoIP networks because reception
control is designed for Public Switched Telephone Networks (PSTN). When
conventional methods are applied to VoIP networks, the connection quality is
guaranteed, however the communication quality cannot be guaranteed because the
packet dropping probability is not considered. In this paper, we propose a
three-dimensional CAC that controls three classes of VoIP sessions and
guarantees both communication and connection quality in VoIP networks during
emergencies. A conventional CAC method and our proposed CAC method are
evaluated in terms of the call blocking probability, which guarantees the
connection quality, and packet dropping probability, which guarantees the
communication quality, to show the effectiveness of the proposed method.
