ABSTRACT
We describe resource prioritization over the Session Initiation Protocol (SIP) network that differentiates in providing services of different types of calls. Emergency calls need to be processed with higher priority than ordinary calls, and SIP network resources that need to be allocated accordingly are explained here. The priority levels of calls that are designated with different registered Internet Assigned Numbers Authority namespaces by different authorities based on policies are described. The preemption of calls that may be needed for serving the higher-priority calls in view of limited resources is described along with behavior of SIP entities. In addition, preemption events with access and network, preemption cause codes, and semantics are articulated. The SIP quality-of-service (QOS) requirements described in the application layer by multimedia applications need to be met at the time of the session setup before completion of the session establishment. It imposes a kind of precondition for setting up the successful session should QOS requirements need to be met. The preconditions for meeting the SIP application QOS needs through using the network layer QOS signaling protocol for reservation of resources are explained with detailed examples. The SIP QOS requirements that are expressed by the Session Description Protocol (SDP) attached as the message body of SIP signaling messages are negotiated between the end points. The QOS negotiations using the SDP offer–answer model are described in addition to mapping of QOS flows on SDP media streams. We have also described SDP and SIP signaling messages compression that save bandwidth. The SIP message body in some cases may be very large. In this connection, we describe the SDP and SIP signaling compression that save bandwidth for the signaling traffic. Finally, the security aspects of SIP QOS, such as authentication and authorization, confidentiality and integrity, anonymity, and denial-of-service attacks, which are very critical for users, are elaborated.
