Merlin: A Language for Provisioning Network Resources

This paper presents Merlin, a new framework for managing resources in software-defined networks. With Merlin, administrators express high-level policies using programs in a declarative language. The language includes logical predicates to identify sets of packets, regular expressions to encode forwarding paths, and arithmetic formulas to specify bandwidth constraints. The Merlin compiler uses a combination of advanced techniques to translate these policies into code that can be executed on network elements including a constraint solver that allocates bandwidth using parameterizable heuristics. To facilitate dynamic adaptation, Merlin provides mechanisms for delegating control of sub-policies and for verifying that modifications made to sub-policies do not violate global constraints. Experiments demonstrate the expressiveness and scalability of Merlin on real-world topologies and applications. Overall, Merlin simplifies network administration by providing high-level abstractions for specifying network policies and scalable infrastructure for enforcing them

An Algebraic Language for Specifying Quantum Networks

Quantum networks connect quantum capable nodes in order to achieve capabilities that are impossible only using classical information. Their fundamental unit of communication is the Bell pair, which consists of two entangled quantum bits. Unfortunately, Bell pairs are fragile and difficult to transmit directly, necessitating a network of repeaters, along with software and hardware that can ensure the desired results. Challenging intrinsic features of quantum networks, such as dealing with resource competition, motivate formal reasoning about quantum network protocols. To this end, we developed BellKAT, a novel specification language for quantum networks based upon Kleene algebra. To cater to the specific needs of quantum networks, we designed an algebraic structure, called BellSKA, which we use as the basis of BellKAT's denotational semantics. BellKAT's constructs describe entanglement distribution rules that allow for modular specification. We give BellKAT a sound and complete equational theory, allowing us to verify network protocols. We provide a prototype tool to showcase the expressiveness of BellKAT and how to optimize and verify networks in practice

Consensus protocols exploiting network programmability

Services rely on replication mechanisms to be available at all time. The service demanding high availability is replicated on a set of machines called replicas. To maintain the consistency of replicas, a consensus protocol such as Paxos or Raft is used to synchronize the replicas' state. As a result, failures of a minority of replicas will not affect the service as other non-faulty replicas continue serving requests. A consensus protocol is a procedure to achieve an agreement among processors in a distributed system involving unreliable processors. Unfortunately, achieving such an agreement involves extra processing on every request, imposing a substantial performance degradation. Consequently, performance has long been a concern for consensus protocols. Although many efforts have been made to improve consensus performance, it continues to be an important problem for researchers. This dissertation presents a novel approach to improving consensus performance. Essentially, it exploits the programmability of a new breed of network devices to accelerate consensus protocols that traditionally run on commodity servers. The benefits of using programmable network devices to run consensus protocols are twofold: The network switches process packets faster than commodity servers and consensus messages travel fewer hops in the network. It means that the system throughput is increased and the latency of requests is reduced. The evaluation of our network-accelerated consensus approach shows promising results. Individual components of our FPGA- based and switch-based consensus implementations can process 10 million and 2.5 billion consensus messages per second, respectively. Our FPGA-based system as a whole delivers 4.3 times performance of a traditional software consensus implementation. The latency is also better for our system and is only one third of the latency of the software consensus implementation when both systems are under half of their maximum throughputs. In order to drive even higher performance, we apply a partition mechanism to our switch-based system, leading to 11 times better throughput and 5 times better latency. By dynamically switching between software-based and network-based implementations, our consensus systems not only improve performance but also use energy more efficiently. Encouraged by those benefits, we developed a fault-tolerant non-volatile memory system. A prototype using software memory controller demonstrated reasonable overhead over local memory access, showing great promise as scalable main memory. Our network-based consensus approach would have a great impact in data centers. It not only improves performance of replication mechanisms which relied on consensus, but also enhances performance of services built on top of those replication mechanisms. Our approach also motivates others to move new functionalities into the network, such as, key-value store and stream processing. We expect that in the near future, applications that typically run on traditional servers will be folded into networks for performance

Partitioned Paxos via the Network Data Plane

Consensus protocols are the foundation for building fault-tolerant, distributed systems, and services. They are also widely acknowledged as performance bottlenecks. Several recent systems have proposed accelerating these protocols using the network data plane. But, while network-accelerated consensus shows great promise, current systems suffer from an important limitation: they assume that the network hardware also accelerates the application itself. Consequently, they provide a specialized replicated service, rather than providing a general-purpose high-performance consensus that fits any off-the-shelf application. To address this problem, this paper proposes Partitioned Paxos, a novel approach to network-accelerated consensus. The key insight behind Partitioned Paxos is to separate the two aspects of Paxos, agreement, and execution, and optimize them separately. First, Partitioned Paxos uses the network forwarding plane to accelerate agreement. Then, it uses state partitioning and parallelization to accelerate execution at the replicas. Our experiments show that using this combination of data plane acceleration and parallelization, Partitioned Paxos is able to provide at least x3 latency improvement and x11 throughput improvement for a replicated instance of a RocksDB key-value store

Optimizing Reserve Expansion For Disjunct Populations Of San Joaquin Kit Fox

Expanding habitat protection is a common strategy for species conservation. We present a model to optimize the expansion of reserves for disjunct populations of an endangered species. The objective is to maximize the expected number of surviving populations subject to budget and habitat constraints. The model accounts for benefits of reserve expansion in terms of likelihood of persistence of each population and monetary cost. Solving the model with incrementally higher budgets helps prioritize sites for expansion and produces a cost curve showing funds required for incremental increases in the objective. We applied the model to the problem of allocating funds among eight reserves for the endangered San Joaquin kit fox (Vulpes macrotis mutica) in California, USA. The priorities for reserve expansion were related to land cost and amount of already-protected habitat at each site. Western Kern and Ciervo-Panoche sites received highest priority because land costs were low and moderate amounts of already-protected habitat resulted in large reductions in extinction risk for small increments of habitat protection. The sensitivity analysis focused on the impacts of kit fox reproductive success and home range in non-native grassland sites. If grassland habitat is lower quality than brushland habitat resulting in higher annual variation in reproductive success or larger home ranges, then protecting habitat at the best grassland site (Ciervo-Panoche) is not cost–efficient relative to shrubland sites (Western Kern, Antelope Plain, Carrizo Plain). Finally, results suggested that lowest priority should be given to three relatively high-cost grassland sites (Camp Roberts, Contra Costa, and Western Madera) because protecting habitat at those sites would be expensive and have little effect on the expected number of surviving kit fox populations

SELNET clinical practice guidelines for bone sarcoma

Bone sarcoma are infrequent diseases, representing < 0.2% of all adult neoplasms. A multidisciplinary management within reference centers for sarcoma, with discussion of the diagnostic and therapeutic strategies within an expert multidisciplinary tumour board, is essential for these patients, given its heterogeneity and low frequency. This approach leads to an improvement in patient's outcome, as demonstrated in several studies. The Sarcoma European Latin-American Network (SELNET), aims to improve clinical outcome in sarcoma care, with a special focus in Latin-American countries. These Clinical Practice Guidelines (CPG) have been developed and agreed by a multidisciplinary expert group (including medical and radiation oncologist, surgical oncologist, orthopaedic surgeons, radiologist, pathologist, molecular biologist and representatives of patients advocacy groups) of the SELNET consortium, and are conceived to provide the standard approach to diagnosis, treatment and follow-up of bone sarcoma patients in the Latin-American context