Notification based S-CSCF load balancing in IMS networks

The Serving Call Session Control Function (S-CSCF) is the main node in the IP Multimedia Subsystem (IMS) signaling plane. The S-CSCF, which acts as both a SIP server and registrar, is assigned to serve end users for the duration of their connection to the IMS network. The assignment of users to an S-CSCF is performed by the Interrogating CSCF (I-CSCF) during the user SIP agent registration. The I-CSCF assigns the S-CSCF based on the capabilities required in the user profile. The 3GGP technical specification does not require the I-CSCF to consider the S-CSCF load balancing. This assignment scheme can lead to driving some of the S-CSCF nodes in the network into overload while others are still under-utilized. In this paper we present an S-CSCF assignment scheme that takes into consideration the target S-CSCF current load. The proposed mechanism is shown to evenly distribute the users between available S-CSCF in the network during simulation.