Scalable Robust Wide-area Architecture for Unified Communications
Wang, Jiahe Helen
Technical Report Identifier: CSD-01-1169
Abstract: In a unified communication system (UCS), heterogeneous endpoints and networks are integrated over the Internet for unified and personalized human communications. Today's UCS lacks support for scalability, availability, fault tolerance, wide-area operation, and flexibility for easy novel service creation. This dissertation addresses these issues in the control architecture of such a system, including its architectural components, the signaling protocol that establishes and maintains communication sessions, and a service creation model and framework that enables powerful service customization.
Our architecture consists of orthogonal functions of name mapping, preference management, user behavior tracking, and data flow establishment and management, which are necessary to enable a wide range of personal communication services. Our architectural components run on a cluster computing platform leveraging their intra-cluster fault recovery and load-balancing mechanisms.
In our signaling protocol design, we cope with session dynamics, such as agent failure recovery, transient network partitions in the wide area, and simultaneous invitations of new participants, by using soft state and group communication over a fast-converging and bandwidth conserving application-level lightweight group membership protocol layer. Through our analysis, we find that by carefully choosing the soft state refresh periods, we can fulfill the session setup time requirement of 1.5 seconds pint and minimize the bandwidth overhead (10% of 16kbps voice stream). Our measurement-based evaluations on call handling capacity show that our cluster-based system has capacity comparable to that of an AT&T class-4 (toll) switch. Our signaling protocol supports multi-endpoint communication as the basic service, which is an important generalization of the more common two endpoint case. The primitives of multi-endpoint communication are flexible and effective building blocks in service creation. Nonetheless, the fast common-case two-endpoint communication is not sacrificed in our design.
Our service creation model and framework is network- and service endpoint-independent. Our system exposes rich primitives and parameters that enable easy and flexible user-level service creation and customization. Our framework takes a user-centric approach rather than a device-centric or service-centric one. With the user-centric approach, our model enables end users to customize the entire communication process in an integrated fashion, without being constrained to a fixed set of service features (service-centric), or being burdened by per-device configurations (device-centric). Our framework can also detect feature interactions, the undesirable interactions among user-specified preferences at the specification time.
We have implemented our designs and developed a unified communication system prototype, called ICEBERG (standing for Internet-Core nEtwork architecture BEyond the thiRd Generation). ICEBERG includes a GSM base station and a H.323 gateway that interfaces with the Public Switched Telephone Network (PSTN), and integrates the communication mechanisms such as cell phone, the PSTN phone, e-mail, and instant messaging.
Throughout our design and implementation experience, we find that localization and asynchrony are important design principles for building robust large scale, wide-area distributed systems.
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