Priority transmission of SIP signaling flows in case of link failure

Signaling flow and media flow packets are mixed in transmission over a unified Internet Protocol (IP)-based infrastructure. That makes it difficult for an IP network node to identify whether the transmitted packet is signaling flow or media flow packet, and guarantee that signaling flow packets are not delayed or discarded in case of congestion caused by link failure. Exceeding standard defined values of both average transfer delay and packet loss rate of Session Initiation Protocol (SIP) signaling flow packets results in impossibility to realize reachability and quality of service. The paper aims to present an idea of marking SIP signaling flow packets with the highest priority to overcome issues regarding link failures. It is assumed that the highest priority assignment to SIP signaling flow packets guarantees upper bound of average transfer delay below 100 ms and packet loss rate below 1×10⁻³. To proof the concept, the simulation study was preformed using Network Simulator version 2 (ns-2) and independently developed SIP module. The obtained results indicate that critical performance metrics of SIP signaling flows are kept below standard upper bounds, only when the highest priority is assigned to them. Fulfilling this requirement is the major precondition to guarantee and implement reachability and quality of next generation multimedia services.