Retransmission issue of SIP session over UDP transport protocol in IP Multimedia Subsystem - IMS

In this paper, the ability of SIP session over UDP transport protocol retransmission issue in IMS network is investigated and analysed. We described SIP session in IMS with end-to-end SIP signalling flow through the IMS entities such as P-CSCF, I-CSCF, S-CSCF and HSS, including the involvement of related SIP messages. The UDP retransmission issue, e.g., INVITE request and loss rates parameters, were conducted to determine the loss of sessions. It has been found that the gradual increase of session loss occurred after the first attempt of transmission. It is affected by the request rates and loss rates. Therefore, the deployment of RFC3261 TimerB and T1 with value of 32s and 0.5s respectively, will prevent the SIP system from the huge number of retransmission.