Using virtual SIP links to enable QoS for signalling

The Session Initiation Protocol (SIP) will be used on a large scale as a session signalling protocol to provide legacy as well as new services. The 3rd Generation Partnership Project (3GPP) has decided to use the SIP protocol in the IP Multimedia Subsystem of future Universal Mobile Telecommunications System (UMTS) networks. If the SIP protocol is used in carrier grade networks, Quality of Service (QoS) observations are necessary to ensure quality service provisioning. This, in particular, is important since signalling will use multiservice IP transport networks and share its resources with other services. This paper proposes the concept of Virtual SIP Links (VSLs) that connect two SIP nodes. VSLs can be used to enable QoS provisioning in SIP signalling overlay networks. Methodologies are introduced to specify, define and dimension these virtual connections. The VSL specification uses the well-known concept of leaky buckets. Simple methodologies are established that are based on known results, to calculate Message Loss Probabilities (MLPs) in leaky buckets. A simple, but efficient, queueing scheme is introduced that reduces the required network resources. Simulation results are given to validate the used models and to underline performance advantages for connections that use VSLs.