The 3GPP IMS is a next generation network architecture aimed at bringing the features and rich services of the Internet to the telephony world. Traditionally telephony products are developed by large companies with access to the proprietary solutions required for PSTN products. However, the shift to a packet-switched architecture and open Internet protocols has increased the developer base to include the huge community of web-developers.
Consequently there are currently several open source software projects that aim to provide proof-of-concept implementations and research tools for promoting the development and adoption of IMS technologies. This work investigates the tools created by four open source IMS projects and incorporates these tools into a practical IMS test-bed framework. Evaluations are performed that demonstrate the capabilities and limitations of these tools in providing rich services to IMS users.
References
[1]
3GPP. TS 23.203 Policy and Charging Control Architecture. March 2007.
D. Vingarzan and P. Weik. IMS Signaling over Current Wireless Networks: Experiments Using the Open IMS Core. IEEE Vehicular Technology Magazine, 2(1):28--34, March 2007.
Good RVentura N(2009)End to End session based bearer control for IP multimedia subsystemsProceedings of the 11th IFIP/IEEE international conference on Symposium on Integrated Network Management10.5555/1688933.1689008(497-504)Online publication date: 1-Jun-2009
The IP Multimedia Subsystem (IMS) as defined by the 3GPP emerges as blueprint for a central architecture to provide Next Generation Network (NGN) services. As an overlay architecture for IP based access networks, it provides standardized interfaces to ...
ICFCC '09: Proceedings of the 2009 International Conference on Future Computer and Communication
There is a rapid growth and evolution in the area of telecommunications and network operators are expected to provide seamless integration of all communication applications on a single system. In these circumstances IMS has emerged out as a key player. ...
Virtual Private Networks (VPNs) are normally used for secured communications over the Internet. The VPNs have evolved significantly over the years, leading to a range of open-source and proprietary solutions. In Converged, all-IP networks terminal ...
Next-generation networks (NGNs) are the result of the evolution of traditional telephony networks. The Internet protocol (IP) multimedia subsystem (IMS) is the architectural cornerstone for NGNs, and is based on Internet Engineering Task Force (IETF) protocols (session initiation protocol (SIP), Diameter). IMS supports fixed-mobile convergence, and promises to be the docking station for new revenue-generating applications, in addition to other sound business benefits (for example, operating expense reduction).
IMS open-source projects, such as the ones presented by Waiting et al., are expected to play a key role in letting a worldwide developer community set its own IMS/NGN testbeds, thereby fostering service innovation and network research. By enabling developers worldwide to replicate standards-compliant network architectures, emerging developer community projects may finally change the course of SIP, which was meant to be for multimedia services what hypertext transfer protocol (HTTP) was for the Web.
The telecommunications industry has always been service-oriented [1], but it is being challenged by the evolution of the Internet into an over-the-top service platform that bypasses telecommunications control and converts its infrastructure into simple bit pipes. Current telecom service development frameworks and practices are unable to compete with Internet service players in terms of time to market, developer base, and potential users. This is why incumbent operators are wisely embracing newly created service development kits (for example, British Telecom (BT) Web21C, Orange Partner, Vodafone Betavine, Telefonica OPEN, and DT developer) that will need to compete as well with emerging service platforms (for example, iPhone software development kit (SDK), Google Android, and Symbian) in the NGN/Internet service arena.
The IMS is seen as one more opportunity (maybe the last one) for telecom operators to adapt to the changing world, find new business models, attract service developers, run their networks more cost efficiently, enable outsourcing of infrastructure and operations, and ultimately leverage Web 2.0 with key assets like quality of service (QoS) guarantees, security, identity management, and charging capabilities.
Once the above-mentioned motivation is established, the authors dedicate one section for each of the four open-source tools that include testbed results to demonstrate both the capabilities and limitations of the developed components. The anchoring-related work is the open-source IMS Core project by the Fraunhofer Institute, which in 2006 provided publicly available code for the core IMS elements: the SIP-based Call Session Control functions and the Diameter-based user database Home Subscriber Server (HSS).
First, the University of Cape Town (UCT) IMS client addresses showstopper number one (the client side), providing an IMS end-system implementation that seeks to be a platform for IMS enablers (reusable IMS service components). The client implementation is evaluated in terms of IMS registration and call setup times over different access networks (local area network (LAN), high-speed downlink packet access (HSDPA), and Edge), coming to the conclusion that without further optimization, a slow Edge wireless access network is not suitable for IMS communications.
Second, the UCT Internet protocol television (IPTV) server presents an IMS-ready IPTV streaming server capable of offering different video qualities depending on the access network characteristics. Rather than the selected quality of the IPTV stream determined by the media codec, the server is limited by the transcoding operations, and thus presents limitations in the number of concurrent channels offered. The authors point out that this limiting factor could be resolved by having the media files already transcoded for the different qualities, or by dedicated hardware when thinking about commercial deployments.
Third, the UCT video conferencing framework tackles another issue of conferencing in IMS, namely the diverse options (centralized, distributed, and hybrid) to distribute SIP signaling and the merging of media streams. The concluding remark is that, depending on the number of participants, the conferencing framework should adopt a centralized architectural approach for scalability reasons.
Fourth, the UCT policy control framework implements a key component in IMS-based NGNs, the policy-based resource controlling functions that arbitrate between application-driven QoS requests and the network's capabilities. A policy decision function interfaces the proxy call session control function (P-CSCF) via Diameter protocol exchange and evaluates the Extensible Markup Language (XML)-based policies that enable the operator to have control over network usage constraints and QoS classes. Policy decisions are sent to the policy enforcement point that applies the policies by gating the user traffic flows and packet-marking operations. The testbed validation of having this tight control over the SIP sessions concludes that an IMS core with QoS provisioning may suffer from unacceptable session setup delays.
In summary, the paper is a good practical overview of IMS open-source components, enabling many research opportunities. I would be more careful when extrapolating to actual commercial environments, where hardware-specific carrier-grade equipment overcomes the execution delays pointed out in some practical evaluation parts of the paper. In particular, the conclusions for the policy-based QoS part need more refinement to support the claim that per-session policy-based QoS becomes unpractical in operational settings due to the increased delay.
In any case, these tools help in understanding the detailed operations involved in delivering IMS services, and might even be key in steering the ongoing 3GPP and European Telecommunications Standards Institute (ETSI) Telecommunications and Internet Converged Services and Protocols for Advanced Networking (TISPAN) NGN standardization activities. For instance, quick proof-of-concept prototypes of new functionalities under consideration could be easily evaluated (and potentially optimized) by the consortium members, similarly to how NS2 simulations support some standardization activities.
Based on its title, readers might be disappointed with one aspect of this paper, namely one of the key points of the motivation of open-source projects: actual development community adoption experiences. I was expecting some insight and discussions on how IMS-related open-source projects have resulted in developers worldwide going beyond simple experimentation and "selfish" use of the tools to make actual code contributions to the Internet community. From my experience, I know that the mailing lists of the core IMS project create a very valuable discussion forum, however I would like to know to what extent contributions such as branches and new components are being adopted, as opposed to simple bug reports or feature suggestions to the core open-source developers.
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Good RVentura N(2009)End to End session based bearer control for IP multimedia subsystemsProceedings of the 11th IFIP/IEEE international conference on Symposium on Integrated Network Management10.5555/1688933.1689008(497-504)Online publication date: 1-Jun-2009