Section: New Results

QoS for Emergent Mobile Systems

Participants : Georgios Bouloukakis, Nikolaos Georgantas, Siddhartha Dutta, Valérie Issarny.

With the emergence of Future Internet applications that connect web services, sensor-actuator networks and service feeds into open, dynamic, mobile choreographies, heterogeneity support of interaction paradigms is of critical importance. Heterogeneous interactions can be abstractly represented by client-server, publish/subscribe, tuple space and data streaming middleware connectors that are interconnected via bridging mechanisms providing interoperability among the choreography peers. We make use of the eVolution Service Bus (VSB) (see § 6.2) as the connector enabling interoperability among heterogeneous choreography participants [15]. VSB models interactions among peers through generic post and get operations that represent peer behavior with varying time/space coupling.

Within this context, we study end-to-end Quality of Service (QoS) properties of choreographies, where in particular we focus on the effect of middleware interactions on QoS. We consider both homogeneous and heterogeneous (via VSB) interactions. We report in the following our results in two complementary directions:

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  Choreography peers deployed in mobile environments are typically characterized by intermittent connectivity and asynchronous sending/reception of data. In such environments, it is essential to guarantee acceptable levels of timeliness between sending and receiving mobile users. In order to provide QoS guarantees in different application scenarios and contexts, it is necessary to model the system performance by incorporating the intermittent connectivity. Queueing Network Models (QNMs) offer a simple modeling environment, which can be used to represent various application scenarios, and provide accurate analytical solutions for performance metrics, such as system response time. We provide an analytical solution regarding the end-to-end response time between users sending and receiving data by modeling the intermittent connectivity of mobile users with QNMs. We utilize the publish/subscribe middleware as the underlying communication infrastructure for the mobile users. To represent the user's connections/disconnections, we model and solve analytically an ON/OFF queueing system by applying a mean value approach. Finally, we validate our model using simulations with real-world workload traces. The deviations between the performance results foreseen by the analytical model and the ones provided by the simulator are shown to be less than 5% for a variety of scenarios [16].

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  Based on the QoS models and analyses outlined in the previous paragraph, we go one step further towards realistic QoS modeling and analysis of choreographies integrating heterogeneous interaction paradigms. We introduce QoS modeling patterns that correspond to each one of the interaction paradigms – client-server, publish/subscribe, tuple space and data streaming – and for different interaction styles – one way, two way synchronous, two way asynchronous. Our patterns rely on Queueing Network Models (QNMs) and represent the following characteristics of choreography peers and their middleware protocols: (i) reliable or unreliable interactions supported by the middleware and underlying transport layers; (ii) application-level (user) and middleware-level disconnections; (iii) application-level and middleware-level buffering of messages with finite capacity; (iv) limited lifetime of messages; and (v) timing of synchronous interactions. These QoS patterns enable the analysis and evaluation of the performance and success rates characterizing the modeled interactions. By combining several QoS patterns, we can further evaluate the end-to-end QoS of choreography interactions among heterogeneous peers. Based on our QoS models, we statistically analyze through simulations the effects on QoS when varying the parameters found in (i) to (v). We can also in this way evaluate the interconnection effectiveness, i.e., the degree of mapping of QoS semantics and expectations, when interconnecting heterogeneous choreography peers.