Efficient Synthesis of Network Updates

Software-defined networking (SDN) is revolutionizing the networking industry, but current SDN programming platforms do not provide automated mechanisms for updating global configurations on the fly. Implementing updates by hand is challenging for SDN programmers because networks are distributed systems with hundreds or thousands of interacting nodes. Even if initial and final configurations are correct, naively updating individual nodes can lead to incorrect transient behaviors, including loops, black holes, and access control violations. This paper presents an approach for automatically synthesizing updates that are guaranteed to preserve specified properties. We formalize network updates as a distributed programming problem and develop a synthesis algorithm based on counterexample-guided search and incremental model checking. We describe a prototype implementation, and present results from experiments on real-world topologies and properties demonstrating that our tool scales to updates involving over one-thousand nodes

Algorithms and protocols for multi-channel wireless networks

A wireless channel is shared by all devices, in the vicinity, that are tuned to the channel, and at any given time, only one of the devices can transmit information. One way to overcome this limitation, in throughput capacity, is to use multiple orthogonal channels for different devices, that want to transmit information at the same time. In this work, we consider the use of multiple orthogonal channels in wireless data networks. We explore algorithms and protocols for such multi-channel wireless networks under two broad categories of network-wide and link-level challenges. Towards handling the network-wide issues, we consider the channel assignment and routing issues in multi-channel wireless networks. We study both single radio and multi-radio multi-channel networks. For single radio multi-channel networks, we propose a new granularity for channel assignment, that we refer to as component level channel assignment. The strategy is relatively simple, and is characterized by several impressive practical advantages. For multi-radio multi-channel networks, we propose a joint routing and channel assignment protocol, known as Lattice Routing. The protocol manages channels of the radios, for the different nodes in the network, using information about current channel conditions, and adapts itself to varying traffic patterns, in order to efficiently use the multiple channels. Through ns2 based simulations, we show how both the protocols outperform other existing protocols for multi-channel networks under different network environments. Towards handling the link-level challenges, we identify the practical challenges in achieving a high data-rate wireless link across two devices using multiple off-the-shelf wireless radios. Given that the IEEE 802.11 a/g standards define 3 orthogonal wi-fi channels in the 2.4GHz band and 12 orthogonal wi-fi channels in the 5GHz band, we answer the following question: ``can a pair of devices each equipped with 15 wi-fi radios use all the available orthogonal channels to achieve a high data-rate link operating at 600Mbps?' Surprisingly, we find through experimental evaluation that the actual observed performance when using all fifteen orthogonal channels between two devices is a mere 91Mbps. We identify the reasons behind the low performance and present Glia, a software only solution that effectively exercises all available radios. We prototype Glia and show using experimental evaluations that Glia helps achieve close to 600Mbps data-rate when using all possible wi-fi channels.PhDCommittee Chair: Sivakumar, Raghupathy; Committee Member: Blough, Doug; Committee Member: Coyle, Edward; Committee Member: Eidenbenz, Stephan; Committee Member: Fekri, Faramar

A Combined Routing Method for Ad hoc Wireless Networks

To make ad hoc wireless networks adaptive to different mobility and traffic patterns, we studied in this thesis an approach to swap from one protocol to another protocol dynamically, while routing continues. By the insertion of a new layer, we were able to make each node in the ad hoc wireless network notify each other about the protocol swap. To ensure that routing works efficiently after the protocol swap, we initialized the destination routing protocol\u27s data structures and reused the previous routing information to build the new routing table. We also tested our approach under different network topologies and traffic patterns in static networks to learn whether the swap is fast and whether the swap incurs too much overload . We found that the swap latency is related to the destination protocol and the topology of the network. We also found that the control packet ratio after swap is close to the protocol running without swap, which means our method does not incur too many control packets for swap

A Combined Routing Method for Wireless Ad Hoc Networks

To make ad hoc wireless networks adaptive to different mobility and traffic patterns, this paper proposes an approach to swap from one protocol to another protocol dynamically, while routing continues. By the insertion of a thin new layer, we were able to make each node in the ad hoc wireless network notify each other about the protocol swap. To ensure that routing works efficiently after the protocol swap, we initialized the destination routing protocol\u27s data structures and reused the previous routing information to build the new routing table. We also tested our approach under different network topologies and traffic patterns in static networks to learn whether the swap was fast and whether the swap incurred too much overhead. We found that the swap latency was related to the nature of the destination protocol and the topology of the network. We also found that the control packet ratio after swap was close to that of the protocol running without swap, which indicates that our method does not incur too much overhead for the swap

Survivability Analysis of the Iridium Low Earth Orbit Satellite Network

This thesis evaluates the survivability of the proposed Iridium Low Earth Orbit (LEO) Satellite Network. In addition to the complete Iridium constellation, three degraded Iridium constellations are analyzed. This analysis occurs via the use of simulation models, which are developed to use three dynamic routing algorithms over three loading levels. The Iridium network models use a common set of operating assumptions and system environments. The constellation survivability was determined by comparing packet rejection rates, hop\u27 counts, and average end to end delay performance between the various network scenarios. It was concluded that, based on the established scenarios, the proposed Iridium constellation was highly survivable. Even with only 45 percent of its satellites functioning (modeled with 36 failed Iridium satellites), the average packet delays were never greater than 178 milliseconds (msec), well within the real time packet delivery constraint of 400 msec. As a result, while additional research is necessary, Iridium has demonstrated the network robustness that is required within the military communications environment