Browsing by Author "Bhowmik, Sukanya"

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Open Access
Content-based routing in software-defined networks
(2017) Bhowmik, Sukanya; Rothermel, Kurt (Prof. Dr. rer. nat. Dr. h. c.)
Content-based routing, as provided by publish/subscribe systems, has emerged as a universal paradigm for interactions between loosely coupled application components, i.e., content publishers and subscribers, where published content is filtered and forwarded by content filters to interested subscribers. Over the past few decades, content-based publish/subscribe has been primarily implemented as an overlay network of software brokers. Even though these systems have proven to efficiently support content-based routing between a large number of distributed application components, such broker-based routing and content filtering in software results in performance (w.r.t. end-to-end latency, throughput rates, etc.) that is far behind the performance of network layer implementations of communication protocols. As a result, the goal of this thesis is to develop methods that enable content-based filtering and routing at line-rate in the network layer by exploiting the capabilities of Software-Defined Networking (SDN). In particular, this thesis focuses on realizing a high performance SDN-based publish/subscribe middleware, called PLEROMA, while addressing major obstacles raised by data (forwarding) plane and control plane limitations of software-defined networks. More specifically, the following contributions are made in this thesis. Our first contribution is to provide methods to fulfill the functional requirements of the content-based publish/subscribe paradigm on the network layer in order to enable line-rate filtering and forwarding of published content in the data plane. We propose methods to establish paths between publishers and their relevant subscribers by installing content filters directly on hardware switches in the data plane. While the developed methods result in a publish/subscribe middleware whose performance (w.r.t. end-to-end latency, throughput rates, etc.) is significantly better than state-of-the-art solutions, a network layer implementation faces some serious challenges due to inherent limitations of software-defined networks. In fact, our next three contributions focus on addressing the problems associated with expressive filtering of content in the network layer, i.e., on hardware switches in the data plane, in the presence of hardware limitations. In particular, we address limitations w.r.t. limited flow table size and limited number of bits available for filter representation in hardware switches that curtail the expressiveness of content filters. Our contributions include various methods that use the knowledge of workload in the system to mitigate the adverse effects of these data plane limitations, thus improving bandwidth efficiency in the system. Not just the data plane, but also the control plane can have its own limitations (w.r.t. scalability in the presence of dynamically changing subscription requests) which can pose as a significant bottleneck for content-based routing on software-defined networks. As a result, our final contribution is to provide methods that enable concurrent and consistent control distribution, thus paving the way for a scalable and distributed control plane solution to high dynamics in an SDN-based publish/subscribe system.
Open Access
Distributed control algorithms for adapting publish/subscribe in software defined networks
(2013) Bhowmik, Sukanya
Content-based routing has emerged as a popular paradigm in publish/subscribe systems for interactions between its system components (publishers and subscribers). Content-based routing of published information is extremely bandwidth efficient as a publication is forwarded only to subscribers which have expressed their interest in this published content. Rules or filters are applied on the content at one or more routers/brokers to determine its path through the network. Most of the state of the art solutions consist of a distributed set of brokers scaling wide-area networks. However, in each of these solutions, filtering of events takes place at the application layer at dedicated brokers. This expensive filtering phase renders the advantages of content-based pub/sub with regards to bandwidth efficiency less significant as it results in higher end-to-end latency and lower throughput rates. To overcome this problem, software-defined networking may be used to build publish/subscribe systems where filtering of events can happen directly in the Ternary Content-Addressable Memory (TCAM) of network routers. Initial work has shown that it is possible to map effectively a content-routing topology to network routers controlled by a single broker, resulting in line-rate forwarding of data packets. However, a single broker limits the performance of the system with regards to scalability and is not feasible in large networks consisting of numerous network elements. To incorporate the best of both worlds, this thesis proposes distributed control algorithms using software-defined networking that allow to build a publish/subscribe system spanning over multiple sub-networks of controllers where the controllers divide the network spatially into disjoint partitions. With respect to such an architecture, this thesis discusses the manner in which connectivity is established between sub-networks along with the costs incurred in the process. A detailed analysis of the average controller overhead and total control traffic generated in the proposed system is presented which is further supported by simulation results. It also includes an analysis on the effect of distributing control on certain performance metrics such as false positive rate of published events.