8178704
Unification of transactions and replication in three-tier architectures based on CORBA
In this paper, we describe a software infrastructure that unifies transactions and replication in three-tier architectures and provides data consistency and high availability for enterprise applications. The infrastructure uses transactions based on the CORBA object transaction service to protect the application data in databases on stable storage, using a roll-backward recovery strategy, and replication based on the fault tolerant CORBA standard to protect the middle-tier servers, using a roll-forward recovery strategy. The infrastructure replicates the middle-tier servers to protect the application business logic processing. In addition, it replicates the transaction coordinator, which renders the two-phase commit protocol nonblocking and, thus, avoids potentially long service disruptions caused by failure of the coordinator. The infrastructure handles the interactions between the replicated middle-tier servers and the database servers through replicated gateways that prevent duplicate requests from reaching the database servers. It implements automatic client-side failover mechanisms, which guarantee that clients know the outcome of the requests that they have made, and retries aborted transactions automatically on behalf of the clients.
20298520
Increasing the reliability of three-tier applications
In this paper we describe an infrastructure that provides increased reliability for three-tier applications, transparently, using commercial off-the-shelf application servers and database systems. In this infrastructure the application servers are actively replicated to protect the business logic processing. Replicating the transaction coordinator renders the two-phase commit protocol non-blocking and, thus, avoids potentially long service disruptions caused by coordinator failure. A thin interpositioning library provides client-side automatic failover, so that clients know the outcome of their requests. The interaction between the application servers and the database servers is handled through replicated gateways that prevent duplicate requests from reaching the database servers. Aborted transactions, caused by process or communication faults, are automatically retried on the client's behalf.
8961835
Design and Implementation of a Pluggable Fault-Tolerant CORBA Infrastructure
In this paper we present the design and implementation of a Pluggable Fault-Tolerant CORBA Infrastructure that provides fault tolerance for CORBA applications by utilizing the pluggable protocols framework that most CORBA ORBs provide. Our approach does not require any modification to the CORBA ORB, and requires only minimal modification to the application. Moreover, it avoids the difficulty of retrieving and assigning the ORB state by embedding the fault tolerance mechanisms into the ORB. The Pluggable Fault-Tolerant CORBA Infrastructure exhibits similar or better performance than other Fault-Tolerant CORBA systems, while providing strong replica consistency.
318699
Design and implementation of a consistent time service for fault-tolerant distributed systems
Clock-related operations are one of the many sources of replica non-determinism and of replica inconsistency in fault-tolerant distributed systems. In passive replication, if the primary server crashes, the next clock value returned by the new primary server might have actually rolled back in time, which can lead to undesirable consequences for the replicated application. The same problem can happen for active replication when the result of the first replica to respond is taken as the next clock value. In this paper we describe the design and implementation of a Consistent Time Service for faulttolerant distributed systems. The Consistent Time Service introduces a group clock that is consistent across the replicas and that ensures the determinism of the replicas with respect to clock-related operations. The groupclock is monotonicallyincreasing, is transparent to the application, and is fault-tolerant. The Consistent Time Service guaranteesthe consistency of the groupclock evenwhen faults occur, when new replicas are added into the group, and when failed replicas recover.
195350091
Design and implementation of a pluggable fault tolerant CORBA infrastructure
In this paper we present the design and implementation of a Pluggable Fault Tolerant CORBA Infrastructure that provides fault tolerance for CORBA applications by utilizing the pluggable protocols framework that is available for most CORBA ORBS. Our approach does not require modification to the CORBA ORB, and requires only minimal modifications to the application. Moreover; it avoids the difficulty of retrieving and assigning the ORB state, by incorporating the fault tolerance mechanisms into the ORB. The Pluggable Fault Tolerant CORBA Infrastructure achieves performance that is similar to, or better than, that of other Fault Tolerant CORBA systems, while providing strong replica consistency.
9212782
A reservation-based coordination protocol for Web services
Traditional transaction semantics are not appropriate for business activities that involve long-running transactions in a loosely-coupled distributed environment, in particular, for Web services that operate between different enterprises over the Internet. In this paper we describe a novel reservation-based extended transaction protocol that can be used to coordinate such business activities. The protocol avoids the use of compensating transactions, which can result in undesirable effects. In our protocol, each task within a business activity is executed as two steps. The first step involves an explicit reservation of resources. The second step involves the confirmation or cancellation of the reservation. Each step is executed as a separate traditional short-running transaction. We show how our protocol can be implemented as a reservation protocol on top of the Web services transaction specification or, alternatively, as a coordination protocol on top of the Web services coordination specification.
16064988
Enhancing Service Location Protocol for efficiency, scalability and advanced discovery
This paper presents three new mechanisms for the Service Location Protocol (SLP): mesh enhancement, preference filters and global attributes. The mesh enhancement simplifies Service Agent (SA) registrations and improves consistency among Directory Agents (DAs) by defining an interaction scheme for DAs and supporting automatic registration distribution among peer DAs. Preference filters facilitate processing of search results (e.g., finding the best match) in SLP servers (DAs and SAs) to reduce the amount of data transferred to the client for saving network bandwidth. Global attributes allow using a single query to search services across multiple types. These mechanisms can improve SLP efficiency and scalability and support advanced discovery such as discovering multi-access-point services and multi-function devices. We expect that these techniques can also be applied to other service discovery systems.
9469881
Scalable multicast routing protocol using anycast and hierarchical-trees
A novel efficient and effective Internet multicast routing protocol is presented with short delay, high throughput, resource utilization and scalability for a single multicast group g. The protocol has two features: (1) multiple shared-trees (MST) are configured to provide efficient, dynamic and quality multicast routing; (2) an anycasting approach is used to form the tree roots into an anycast group so that the multicast packets can be anycast to the nearest node at one of the shared trees to achieve the best routing service for the multicast packets. The performance of the MST protocol is analyzed through extensive simulations and compared with well-known source tree and shared-tree routing.
13980635
A Note on Dynamic Data Driven Wildfire Modeling
A proposed system for real-time modeling of wildfires is described. The system involves numerical weather and fire prediction, automated data acquisition from Internet sources, and input from aerial photographs and sensors. The system will be controlled by a non-Gaussian ensemble filter capable of assimilating out-of-order data. The computational model will run on remote supercomputers, with visualization on PDAs in the field connected to the Internet via a satellite.
45502875
DotSlash - Creating Content Distribution Networks on Demand
Traditional content distribution networks, such as Akamai, are well-suited for static web services that routinely experience large traffic volumes. They are unsuited for active content, i.e., content generated by scripts from databases, and web sites that are unlikely to receive significant number of requests. However, a few such sites will invariably experience their "fifteen minutes of fame", typically by being mentioned on a high-volume news site such as SlashDot or CNN. Such flashcrowds or "slashdot effect" will routinely cause single-server websites to collapse. We have designed and prototyped an autonomic web replication system, called DotSlash, that drafts rescue servers fully automatically, without user intervention. The system discovers suitable rescue servers via wide-area service location, either among peer servers or from a dedicated pool of rescue servers, allocates them for temporary use and redirects requests to them. The system is completely transparent to clients and does not require URL rewriting or other client modifications. We have designed two versions. The first, an Apache extension, deals only with static content, e.g., HTML pages or media objects. The second version can also replicate and execute scripts remotely. We have prototyped the system for the common LAMP (Linux, Apache, MySQL and PHP) configuration and shown that a common benchmark for bulletin boards can be replicated without code changes, yielding capacity increases bounded only by the database server. Since many such systems, including most blogs, are bottlenecked by the web server, our system can significantly increase capacity and works even for extremely rapid load increases. We are currently investigating how such systems can be further extended by increasing the database capacity of read-mostly systems with loose consistency constraints.
238897
DSSS-Based Flow Marking Technique for Invisible Traceback
Law enforcement agencies need the ability to conduct electronic surveillance to combat crime, terrorism, or other malicious activities exploiting the Internet. However, the proliferation of anonymous communication systems on the Internet has posed significant challenges to providing such traceback capability. In this paper, we develop a new class of flow marking technique for invisible traceback based on direct sequence spread spectrum (DSSS), utilizing a pseudo-noise (PN) code. By interfering with a sender's traffic and marginally varying its rate, an investigator can embed a secret spread spectrum signal into the sender's traffic. The embedded signal is carried along with the traffic from the sender to the receiver, so the investigator can recognize the corresponding communication relationship, tracing the messages despite the use of anonymous networks. The secret PN code makes it difficult for others to detect the presence of such embedded signals, so the traceback, while available to investigators is, effectively invisible. We demonstrate a practical flow marking system which requires no training, and can achieve both high detection and low false positive rates. Using a combination of analytical modeling, simulations, and experiments on Tor (a popular Internet anonymous communication system), we demonstrate the effectiveness of the DSSS-basedflow marking technique.