Vol.2 No.3 September 15, 2006
IP Multimedia Subsystem (IMS)

Editorial (pp187-188)
        A. Hafid, P. Dini, and K.H. Liu                       

Research articles:
Practical Experiences with an IMS-aware Location Service Enabler on Top of an Experimental Open Source IMS Core Implementation (pp189-224)
         P. Reichl, S. Bessler, J. Fabini, R. Pailer, A. Poropatich, N. Jordan, R. Huber, H. Weisgrab,
         C. Brandner, I. Gojmerac, M. Ries, and F. Wegscheider 
The 3GPP IP Multimedia Subsystem (IMS) is currently expected to provide the basic architecture framework for the Next Generation Network which will bridge the traditional divide between circuit-switched and packet-switched networks and consolidate both sides into one single network for all services. Therefore, the imminent commercial roll-out of IMS will have immense impact both for the migration of the core network as well as the integration of future mobile services and applications. This paper presents an OpenSER-based experimental testbed which has been designed as a minimal standard-compliant IMS core network. We discuss major practical requirements and describe our implementation of this “IMS in a bottle” approach. Furthermore, we introduce a terminal-based native IMS location service enabler. We argue that physical location data can be regarded as a type of presence information and propose an architecture which reuses a large part of the IMS presence infra-structure by applying presence mechanisms, like notification handling, access control and privacy management, to location data. We demonstrate that the realization of this service can be integrated efficiently into the IMS core environment, and pre-sent initial evaluation results for the joint demonstrator. Finally, important current and future challenges including migration, interworking, charging, Quality-of-Service, identity management, security, and regulatory aspects, are discussed in detail, thus ending up with an up-to-date research agenda.

Development of IMS Privacy & Security Framework for Open IMS Fokus Testbed (pp225-258)
         M. Sher and T. Magedanz   
Privacy, confidentiality, data integrity and intrusion detection & prevention are the security methodologies to secure communication in all fields of networking, cellular and fixed communication. With the emerging of IP Multimedia Subsystem (IMS) and Next Generation Networks (NGN), there is a great need to provide secure and trusted environment to user’s sensitive information and to provide measures to protect IMS operator’s assets. The IMS needs powerful security association between multimedia client and the network before access is granted to multimedia services because of low security dependency of PS-domain. The security features to accomplish in securing access to the IMS are to protect SIP signalling, user authentication and authorization, development of network domain security and trusted domain using policy based security associations.  In this paper we present the security and privacy management framework for IP Multimedia Subsystem (IMS) which consists of IMS Authentication & Key Agreement (AKA), Network Domain Security, and IMS Access Security for SIP-based and HTTP-based services. The presented IMS security framework is developed for Open IMS & 3Gb Testbed of Fokus, Fraunhofer with the objective to manage security across different interfaces like air contact between user and IMS core, inter and intra domains interfaces and between IMS Core and Application Servers. It also deals with security when the user is roaming or in home network and security for UMTS access networks. This independent security framework provides additional protection against security attacks to IMS domain along with the PS (Packet Switched) domain security or IP Security.

Modeling of IMS Call Flows: Load Estimation for Core Network (pp259-282)
         B. Falchuk, D. Shallgross, K.R. Krishnan, R. Morera, and S. Loeb
The support of mobile multimedia applications will require powerful control capabilities, such as those envisaged in the IP Multimedia Subsystem (IMS), which enables operators and service providers to control bearers, sessions and charging of multimedia services using Internet protocols. IMS enables operators and service providers to control bearers, sessions and charging of multimedia services using Internet protocols. IMS is seen as the main “enabler” to fixed-mobile convergence, as IMS provides services independently of the access technology and enables a smooth interoperation between different network types. Estimating the load and stress on core network components for IMS services is a requirement for the successful implementation of the IMS architecture. In this paper, we describe a formal procedure for characterizing a network service or application by means of annotated sequence diagrams, and deriving analytical models that allow us to investigate the load on different network elements imposed by the application. Our approach brings together software models that capture the semantics of the application and analytical models that describe the application in terms of states and state transitions.  Our procedure is embodied in a software component and here, as a prototypical example of its utility, we apply it to the estimation of the load on the Serving Call Session Control Function (S-CSCF) for a Voice Call Continuity (VCC) Service between a GSM network and a WLAN - to demonstrate generality, we also apply it to an IMS compliant content distribution scenario.  Such semi-automated results are critical in the planning and provisioning of IMS-compliant architectures, particularly those that support resource intensive mobile multimedia applications.