Gateways and Components for Supplementary IP Telephony Services in Heterogeneous Environments
IP Telephony is a demanding interactive real-time service that already supplements the traditional telephony system to a considerable extent. It is expected to become a genuine alternative with a variety of new attractive services in the future. The recent situation and developments in the IP Teleph...
| Summary: | IP Telephony is a demanding interactive real-time service that already supplements the traditional telephony system to a considerable extent. It is expected to become a genuine alternative with a variety of new attractive services in the future. The recent situation and developments in the IP Telephony area are characterized by a variety of different usage environments, signaling approaches, protocols, devices and applications. We show that this situation, that is typically referred to as heterogeneity, has a number of inherent reasons and is not going to vanish within the near future. In many cases the different telephony components are not directly interoperable or their interaction is restricted to just a subset of the full capabilities. These circumstances make gateways that provide adequate interworking significant. Our central tenet is that gateways are appropriate and powerful means for dealing with heterogeneity. They are not restricted to the connection of legacy systems but play a significant constructive role for future setups as well. Their efficient design and realization is a challenging task. It is typically solved in a process that incorporates multiple steps. We investigate abstraction mechanisms that support this process. This investigation results in a model that facilitates the identification of general gateway structures and mechanisms that are appropriate for specific interworking requirements and scenarios. Our model fits between very high-level gateway descriptions and existing, but isolated best practice methods for particular gateway design problems. Our approach holistically covers multiple individual gateway aspects and tasks in the analysis and design process. We have chosen the interworking between the IP Telephony protocol suites H.323 and SIP for practical application of our methodology. Our efforts target large-scale IP Telephony deployment in real-world scenarios and the comprehensive and protocol-independent provisioning of supplementary services. The successful design and implementation of scalable interworking functionality for these services is the resulting practical contribution of this thesis. Our work combines the investigation of a novel signaling gateway and infrastructure components for its integration with the design and realization of end-system with unique functionality. Further, we categorize different types of media gateways and practically implement and investigate examples in this context. This activity and its outcome demonstrate the universality and power of our design and realization methodology. Additionally, we show that the combined and coordinated usage ofsignaling and media gateways is a powerful mechanism for future system designs. A practical example that uses this approach integrates low-resource decomposed wireless end-systems within our heterogeneous H.323 and SIP scenario. In the context of the presentation of general signaling gateways we show our contribution in the area of IP Telephony security. This includes the discussion of an IP Telephony enabled firewall that makes services usable in typical protected environments. The internal structure and the mechanisms of such a firewall are closely related to those of the investigated gateways. A practical IP Telephony vulnerability case study raises security problem awareness and motivates future activities with their implications on signaling gateways in this domain. Our contribution is practical as well as methodical. We have designed and realized new gateways and end-systems. These provide a novel quality for interworking in heterogeneous IP Telephony environments. It is not restricted to just basic call functionality but covers the very important and steadily extending range of supplementary services. Our gateway model and the problem analysis, design and realization methodology are general. The proof of concept implementations supplement it with instantiated templates for particular tasks. Model and templates together represent a framework that is applicable to solve various comparable interworking problems for IP-based communication systems efficiently. |
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