Modeling of SIP retransmission traffic under lossy network conditions

In this paper, we present a discrete-time fluid-flow model to characterize the behavior of an overloaded Session Initiation Protocol (SIP) server under the lossy network conditions. The model considers both redundant retransmissions due to excessive queuing delays in an overloaded server and non-redundant retransmissions due to message loss in the network and calculates the number of failed call attempts and the average response delay from sending INVITE request until receiving a 100-Trying response. The accuracy of the model is verified with the simulations. The experiments show that losses in the network reduce the amount of the offered traffic to the SIP server and decreases the severity of the overload situation.