Abstractions and optimisations for model-checking software-defined networks

Software-Defined Networking introduces a new programmatic abstraction layer by shifting the distributed network functions (NFs) from silicon chips (ASICs) to a logically centralized (controller) program. And yet, controller programs are a common source of bugs that can cause performance degradation, security exploits and poor reliability in networks. Assuring that a controller program satisfies the specifications is thus most preferable, yet the size of the network and the complexity of the controller makes this a challenging effort. This thesis presents a highly expressive, optimised SDN model, (code-named MoCS), that can be reasoned about and verified formally in an acceptable timeframe. In it, we introduce reusable abstractions that (i) come with a rich semantics, for capturing subtle real-world bugs that are hard to track down, and (ii) which are formally proved correct. In addition, MoCS deals with timeouts of flow table entries, thus supporting automatic state refresh (soft state) in the network. The optimisations are achieved by (1) contextually analysing the model for possible partial order reductions in view of the concrete control program, network topology and specification property in question, (2) pre-computing packet equivalence classes and (3) indexing packets and rules that exist in the model and bit-packing (compressing) them. Each of these developments is demonstrated by a set of real-world controller programs that have been implemented in network topologies of varying size, and publicly released under an open-source license

Motivating the citizens to transact with the government through a Gamified experience

The current paper explores the implementation of gamification in the government as a way to win back trust from the citizens. The motivation of the citizens to interact with the public authorities through e-government, requires a suitable gamification framework. Octalysis framework is chosen among the available gamification frameworks due to its motivation orientated nature. Octalyis is used a tool for a pilot study to gamify the Greek taxation information system TAXIS and reveals that TAXIS requires entertaining web aspects for its long term use by the citizens.peer-reviewe

Model Checking Software-Defined Networks with Flow Entries that Time Out

179184

Online)

ABSTRACT Context Heterotopic pancreas of the gallbladder is an extremely rare entity, especially when pancreatic tissue appears histologically with an exclusively exocrine structure. Case report We report the case of a 35-year-old man who presented with symptoms of acalculous gallbladder disease with high levels of amylasuria. Immunohistochemical analysis of the surgical specimen of the cholecystectomy revealed pancreatic tissue at the gallbladder wall. Conclusions Heterotopic pancreatic tissue is a rare pathological finding in the gallbladder. It requires consideration and sensitization in the differential diagnosis of acalculous gallbladder disease, which can explain hyperamylasuria in cases of unknown origin