Notification about congestion information through SIP session for call congestion control of VoIP application

The feedback algorithm in the SIP session for call congestion control is described in this paper and the performance is evaluated using OPNET. We consider the trapezoid architecture of SIP signaling. In the trapezoid architecture, the IP telephone administrative domain is defined. The INVITE message generated in the source call agent (CA) in a local SIP server or gateway flows between the local and remote dedicated SIP proxy servers and arrives at the CA in the destination node. In this control scheme, we assume that the SIP server or gateway manages SIP sessions and monitors the number of active calls. When a new request arrives and the number of active calls consequently exceeds the threshold for the maximum number of call instances that the local SIP server or gateway can process, these nodes report the call congestion status to the dedicated SIP server through this SIP session. The call congestion notification message is flooded to the other SIP servers through all the manged SIP sessions. The CA that receives the notification message starts to control the rate of sending the INVITE messages. When this CA receives the notification message that indicates that the call congestion has finished or that the defined timer has expired, the rate control is stopped. The effectiveness and the behavior are shown through the simulation study.