Flexible network management requires explicit control of the exact paths taken by different network flows. Whatever the way this endeavour is achieved (e.g. Multiprotocol Label Switching, Virtual Local Area Networks and OpenFlow), this need may lead to an explosion of entries in the forwarding tables of network equipment. In this article, we present an algorithm that aggregates many network paths in a reduced number of trees, thus allowing shrinking the forwarding state in switching devices. Path aggregation algorithms are often deployed to reduce data-plane state with different routing approaches and the presented algorithm achieves better results than existent algorithms with similar goals. Additionally, we show that most types of popular routing and switching equipment, even using off-the-shelf routing software, may be used to implement multi-path routing with trees. This highlights the applicability of the proposed algorithm and its significance in light of the current trend of separating the data- and the control-planes in modern networks.

It is common that, in a long-term asynchronous collaborative activity, groups of users engage in occasional synchronous sessions. In this paper, we analyze the data management requirements for supporting this common work practice in typical collaborative activities and applications. We call the applications that support such work practice multi-synchronous applications. This analysis shows that, as users interact in different ways in each setting, some applications have different requirements and need to rely on different data sharing techniques in synchronous and asynchronous settings. We present a data management system that allows to integrate a synchronous session in the context of a long-term asynchronous interaction, using the suitable data sharing techniques in each setting and an automatic mechanism to convert the long sequence of small updates produced in a synchronous session into a large asynchronous contribution. We exemplify the use of our approach with two multi-synchronous applications.

Mobile computing characteristics demand data management systems to support independent operation. However, the execution of updates in a mobile client usually need to be considered tentative because uncoordinated updates that conflict need to be reconciled. In this paper we present a mechanism to independently guarantee that updates can be executed in the server without conflicts. To this end, clients obtain leased reservations upon the database state. Updates are specified as common small PL/SQL programs, dubbed mobile transactions, that execute both in the mobile client and in the server. Using the available reservations, the client transparently verifies that a transaction can be executed in the same way both in the mobile client and in the server, thus leading to the same final result. Mobile transactions may specify conflict detection and resolution rules to be used when transactions cannot be locally guaranteed.

The increasing popularity of portable computers opens the possibility of collaboration among multiple distributed and disconnected users. In such environments, collaboration is often achieved through the concurrent modification of shared data. DOORS is a distributed object store to support asynchronous collaboration in distributed systems that may contain disconnected computers. In this summary we focus on the mechanisms to support disconnected operation. The DOORS architecture is composed by servers that replicate objects using an epidemic propagation model. Clients cache key objects to support disconnected operation. Users run applications to read and modify the shared data (independently from other users)-a read any/write any model of data access is used. Modifications are propagated from clients to servers and among servers as sequences of operations-the system is log-based. Objects are structured according to an object framework that decomposes object operation in several components. Each component manages a different aspect of object execution. Each object represents a data type (e.g. a structured document) and it is composed by a set of sub-objects. Each sub-object represents a subpart of the data type (e.g. sections). A new object is created composing the set of subobjects that store the type-specific data with the adequate implementations of the other components. The following main characteristics are the base to support disconnected operation in DOORS.

In distributed systems, it is often necessary to provide coordination among the multiple concurrent processes. Quorum systems provide a decentralized approach to provide such coordination that is resilient to node and communication link failures. Quorum systems are highly available and may be used to balance the load among the elements of the system. In this paper, we propose a modification to the hierarchical grid quorum system that leads to a smaller quorum size and better availability and load. We also propose a new hierarchical quorum construction based on the organization of elements in a triangular shape that presents better average quorum size, availability and load than other highly-available systems with almost optimal load.

In asynchronous collaborative applications, users usually collaborate accessing and modifying shared information independently. We have designed and implemented a replicated object store to support such applications in distributed environments that include mobile computers. Unlike most data management systems, awareness support is integrated in the system. To improve the chance for new contributions, the system provides high data availability. The development of applications is supported by an object framework that decomposes objects in several components, each one managing a different aspect of object "execution". New data types may be created relying on pre-defined components to handle concurrent updates, awareness information, etc.