The global deployment of IP multicast has been slow due to the difficulties related to heterogeneity, scalability, manageability, and lack of a robust interdomain multicast routing protocol. Application-level multicast becomes a promising alternative. Many overlay multicast systems have been proposed in recent years. However, they are insufficient in supporting applications that require any-source multicast with varied host capacities and dynamic membership. In this paper, we propose two capacity-aware multicast systems that focus on host heterogeneity, any source multicast, dynamic membership, and scalability. We extend Chord and Koorde to be capacity-aware. We then embed implicit degree-varying multicast trees on top of the overlay network and develop multicast routines that automatically follow the trees to disseminate multicast messages. The implicit trees are well balanced with the workload evenly spread across the network. We rigorously analyze the expected performance of multisource capacity-aware multicasting, which was not thoroughly addressed in any previous work. We also perform extensive simulations to evaluate the proposed multicast systems.

The global deployment of IP multicast has been slow due to the difficulties related to heterogeneity, scalability, manageability, and lack of a robust inter-domain multicast routing protocol. Application-level multicast becomes a promising alternative. Many overlay multicast systems have been proposed in recent years. However, they are insufficient in supporting applications that require large-scale any-source multicast with highly varied host capacities and highly dynamic membership. In this paper, we propose two capacity-aware multicast systems that focus on host heterogeneity, dynamic membership, scalability, and any source multicast. We extend Chord and Koorde to be capacity-aware. We then embed implicit degree-varying multicast trees on top of the overlay network and develop multicast routines that automatically follow the trees to disseminate multicast messages. The implicit trees are well balanced with workload evenly spread across the network. We also perform extensive simulations to evaluate the proposed multicast systems

Effective use of limited network resources is crucial in supporting network-based multimedia applications. A K-metric altruistic Qos routing algorithm is proposed to tackle the issue of network resource overcommitmnent. based on this algorithm, a multimedia dispersion scheme is developed to alleviate the high blocking ratio problem caused by high bandwidth requirement. Our evaluation shows that the proposed scheme is capable of achieving at 30% improvement in terms of reducing the average blocking ratio.

Capability has been widely used as a fundamental mechanism for access control in distributed systems. When an object manager receives a capability from a user process for accessing an object, it verifies the genuineness of the capability and checks whether the access request is allowed with the access rights placed on the capability. Capabilities have been recognized to be more suitable than centralized access control lists for object protection in a distributed system because of several obvious reasons. However, most existing capability based systems can only enforce static access control policies, which means all the access privileges a user possesses for an object are fully represented by a capability and will not change due to object access. These capability systems cannot be used to enforce dynamic access control policies, required by many complex applications, in which each authorization may depend upon a user's access history and/or an object's history of being accessed. The paper proposes an extended capability architecture to enforce dynamic access control policies both effectively and efficiently. The key issue is how to capture the dynamic access information in both capabilities and object managers while avoiding main disadvantages of centralized access control lists. A number of frequently desired security policies are used to demonstrate the power and flexibility of the proposed architecture. The problems regarding capability management including propagation, revocation, and distribution of capabilities are also discussed.

Commercial applications often require complex access control policies which are hardly enforced by mechanisms based on a multilevel security model due to the properties of a lattice. Nor can they be enforced by discretionary access control like the access control matrix described by Harrison, Ruzzo, and Ullman without extra constraints since their enforcement still demands some degree of mandatory control. Frequently-desired multilevel exceptions are systematically categorized and it is shown that many security policies required by commercial sectors are actually examples of these multilevel exceptions. A new access control model based on Boolean expressions of classified categories is developed to enforce these policies in a uniform and elegant way.

In this paper, we investigate a scheduling algorithm, called circular window control (CWC) scheme, for packet switch fabrics. The scheme is simple and efficient. It uses a fixed length window with circular transmission sequences to minimize possible switch and output contentions. The scheme can attain a maximal throughput of 100%; in nonblocking switches as well as banyan-based blocking switches. The performance analyses and simulation results of the CWC scheme an also presented.

Autonomous servers are introduced as a mechanism for solving many online problems, such as dispatching elevators in an office building, taxis in a city, or disk heads in a system with multiple copies of a file. The difference between autonomous servers and conventional online algorithms is that no centralized controller coordinates the servers. In essence, distributed online algorithms are studied under the assumption of limited knowledge: each server is independent of the others and has limited knowledge of the positioning of the other servers. The performance of such servers is examined using analytical and experimental methods. Applications and open problems are discussed.>