Cgr overbooking management

Nel CGR lo stesso cammino può essere assegnato ad una quantità di bundle tale da superare la capacità di uno o più contatti che lo compongono. Lo scopo del mio lavoro di tesi è stato quello di implementare una funzionalità aggiuntiva nel CGR, chiamata Overbooking Management, in grado, se attivata, di rilevare e gestire tale problematica, migliorando dove possibile l’efficienza in termini di tempi di consegna dei dati e di sfruttamento delle risorse.

DTN discovery and routing: from space applications to terrestrial networks.

L'argomento di questa tesi è l'architettura di rete Delay-/Disruption-Tolerant Networking (DTN), progettata per operare nelle reti “challenged”, dove la suite di protocolli TCP/IP risulta inefficace a causa di lunghi ritardi di propagazione del segnale, interruzioni e disturbi di canale, ecc. Esempi di reti “challenged” variano dalle reti interplanetarie alle Mobile Ad-Hoc Networks (MANETs). Le principali implementazioni dell'architettura DTN sono DTN2, implementazione di riferimento, e ION, sviluppata da NASA JPL per applicazioni spaziali. Una grande differenza tra reti spaziali e terrestri è che nello spazio i movimenti dei nodi sono deterministici, mentre non lo sono per i nodi mobili terrestri, i quali generalmente non conoscono la topologia della rete. Questo ha portato allo sviluppo di diversi algoritmi di routing: deterministici per le reti spaziali e opportunistici per quelle terrestri. NASA JPL ha recentemente deciso di estendere l'ambito di applicazione di ION per supportare anche scenari non deterministici. Durante la tesi, svolta presso NASA JPL, mi sono occupato di argomenti diversi, tutti finalizzati a questo obiettivo. Inizialmente ho testato la nuova implementazione dell'algoritmo IP Neighbor Discovery (IPND) di ION, corretti i bug e prodotta la documentazione ufficiale. Quindi ho contribuito ad integrare il Contact Graph Routing (CGR) di ION nel simulatore DTN “ONE” utilizzando la Java Native Interface (JNI) come ponte tra il codice Java di ONE e il codice C di ION. In particolare ho adattato tutte le librerie di ION necessarie per far funzionare CGR all'interno dell'ambiente di ONE. Infine, dopo aver analizzato un dataset di tracce reali di nodi mobili, ho contribuito a progettare e a sviluppare OCGR, estensione opportunistica del CGR, quindi ne ho curato l'integrazione in ONE. I risultati preliminari sembrano confermare la validità di OCGR che, una volta messo a punto, può diventare un valido concorrente ai più rinomati algoritmi opportunistici.

Energy–aware forwarding strategies for delay tolerant networking (DTN) routing protocols

This research addresses efficient use of the available energy in resource constrained mobile sensor nodes to prevent early depletion of the battery and maximize the packet delivery rate. This research contributes two energy-aware enhancement strategies to improve the network lifetime and delivery probability for energy constrained applications in the delay-tolerant networking environment.

Efficient QR Decomposition Using Low Complexity Column-wise Givens Rotation (CGR)

QR decomposition (QRD) is a widely used Numerical Linear Algebra (NLA) kernel with applications ranging from SONAR beamforming to wireless MIMO receivers. In this paper, we propose a novel Givens Rotation (GR) based QRD (GR QRD) where we reduce the computational complexity of GR and exploit higher degree of parallelism. This low complexity Column-wise GR (CGR) can annihilate multiple elements of a column of a matrix simultaneously. The algorithm is first realized on a Two-Dimensional (2 D) systolic array and then implemented on REDEFINE which is a Coarse Grained run-time Reconfigurable Architecture (CGRA). We benchmark the proposed implementation against state-of-the-art implementations to report better throughput, convergence and scalability.

Supporting Predicate Routing in DTN over MANET

We consider a Delay Tolerant Network (DTN) whose users (nodes) are connected by an underlying Mobile Ad hoc Network (MANET) substrate. Users can declaratively express high-level policy constraints on how "content" should be routed. For example, content may be diverted through an intermediary DTN node for the purposes of preprocessing, authentication, etc. To support such capability, we implement Predicate Routing [7] where high-level constraints of DTN nodes are mapped into low-level routing predicates at the MANET level. Our testbed uses a Linux system architecture and leverages User Mode Linux [2] to emulate every node running a DTN Reference Implementation code [5]. In our initial prototype, we use the On Demand Distance Vector (AODV) MANET routing protocol. We use the network simulator ns-2 (ns-emulation version) to simulate the mobility and wireless connectivity of both DTN and MANET nodes. We show preliminary throughput results showing the efficient and correct operation of propagating routing predicates, and as a side effect, the performance benefit of content re-routing that dynamically (on-demand) breaks the underlying end-to-end TCP connection into shorter-length TCP connections.

PreDA: Predicate Routing for DTN Architectures over MANET

We consider a Delay Tolerant Network (DTN) whose users (nodes) are connected by an underlying Mobile Ad hoc Network (MANET) substrate. Users can declaratively express high-level policy constraints on how “content” should be routed. For example, content can be directed through an intermediary DTN node for the purposes of preprocessing, authentication, etc., or content from a malicious MANET node can be dropped. To support such content routing at the DTN level, we implement Predicate Routing [1] where high-level constraints of DTN nodes are mapped into low-level routing predicates within the MANET nodes. Our testbed [2] uses a Linux system architecture with User Mode Linux [3] to emulate every DTN node with a DTN Reference Implementation code [4]. In our initial architecture prototype, we use the On Demand Distance Vector (AODV) routing protocol at the MANET level. We use the network simulator ns-2 (ns-emulation version) to simulate the wireless connectivity of both DTN and MANET nodes. Preliminary results show the efficient and correct operation of propagating routing predicates. For the application of content re-routing through an intermediary, as a side effect, results demonstrate the performance benefit of content re-routing that dynamically (on-demand) breaks the underlying end-to-end TCP connections into shorter-length TCP connections.

Erasure error correcting codes applied to DTN communications.

The space environment has always been one of the most challenging for communications, both at physical and network layer. Concerning the latter, the most common challenges are the lack of continuous network connectivity, very long delays and relatively frequent losses. Because of these problems, the normal TCP/IP suite protocols are hardly applicable. Moreover, in space scenarios reliability is fundamental. In fact, it is usually not tolerable to lose important information or to receive it with a very large delay because of a challenging transmission channel. In terrestrial protocols, such as TCP, reliability is obtained by means of an ARQ (Automatic Retransmission reQuest) method, which, however, has not good performance when there are long delays on the transmission channel. At physical layer, Forward Error Correction Codes (FECs), based on the insertion of redundant information, are an alternative way to assure reliability. On binary channels, when single bits are flipped because of channel noise, redundancy bits can be exploited to recover the original information. In the presence of binary erasure channels, where bits are not flipped but lost, redundancy can still be used to recover the original information. FECs codes, designed for this purpose, are usually called Erasure Codes (ECs). It is worth noting that ECs, primarily studied for binary channels, can also be used at upper layers, i.e. applied on packets instead of bits, offering a very interesting alternative to the usual ARQ methods, especially in the presence of long delays. A protocol created to add reliability to DTN networks is the Licklider Transmission Protocol (LTP), created to obtain better performance on long delay links. The aim of this thesis is the application of ECs to LTP.