Abstract A file server for continuous media must provide resource guarantees and only admit requests that do not violate the resource availability. This paper addresses the admission performance of a server that explicitly considers the variable bit rate nature of the continuous media streams. A prototype version of the server has been implemented and evaluated in several heterogeneous environments. The two system resources for which admission control is evaluated are the disk bandwidth and the network bandwidth. Performance results from both measurement and simulation are shown with respect to different admission methods and varying scenarios of stream delivery patterns. We show that the vbrSim algorithm developed specifically for the server outperforms the other options for disk admission especially with request patterns that have staggered arrivals, while the network admission control algorithm is able to utilize a large percentage of the network bandwidth available. We also show the interactions between the limits of these two resources and how a system can be configured without wasted capacity on either one of the resources. Copyright © 2004 John Wiley & Sons, Ltd.

We describe the design and implementation of a file server for variable bit rate continuous media. We address the problem of building a server where each stream may have a different bit rate and, more importantly, where the bit rate within a single stream may vary considerably. Such a server has been implemented within a high-speed network environment. The server is designed to be used in a heterogeneous environment and is linearly scalable. A significant aspect of the design of the system is the detailed consideration of the variable bit-rate profile of each data stream in performing admission control for the disk and for the network. This paper describes the system model, the user interface design, implementation details, and performance results based on initial experience with the server.

Reducing forwarding state overhead of multicast routing protocols is an important issue towards a scalable global multicast solution. We propose a new approach, dynamic tunnel multicast, which utilizes dynamically established tunnels on unbranched links of a multicast distribution tree to eliminate unnecessary multicast forwarding states. Analysis and simulation results show promising reduction in the state overhead of sparse mode multicast routing protocols.

In this paper, we address the problem of choosing a disk admission algorithm for continuous media streams where each stream may have a different bit rate, and more importantly, where the bit rate within a single stream may vary considerably.We evaluate several different Variable Bit Rate (VBR) disk admission control algorithms for continuous media.An algorithm which accepts too few streams under-utilizes the server resources, while an algorithm which accepts too many streams over-utilizes the resources resulting in inadequate service (i.e.missing or delayed data) to the clients.The evaluation process is based on a representative set of video streams encoded in MJPEG.We conclude that one particular algorithm, the VBR simulation algorithm, performs the best among realizable algorithms in terms of system utilization and delivery guarantees and performs close to an optimal algorithm, Keywords: multimedia, file servers, variable bit rate, admission control Pemhsion to mnke digitnhrd topics orall or part ofthis mnterinl for personal or clnssroom use is granted without Ike provided IIXII the copi& are not mnde or distribtltrd for prolit or coonuncrcinl advantage.11x copy-

Raven is an object-oriented programming language and system that supports distributed and multiprocessor computing. This paper describes the motivation and design of Raven's object property scheme. Raven properties are used to provide system services on a per-object basis. Raven is distinguishable from similar systems in several fundamental ways: the behavioral semantics of each system supported property is truly orthogonal to those of the others, allowing properties to be combined without side effects; and all properties can be assigned dynamically, in any combination, even after object creation. Property support is provided automatically by the system. This scheme provides a simple yet powerful and flexible system where every object can have the properties it requires.>

The task of encoding complex data structures for network transmission is more expensive is terms of processor time and memory usage than most other components of the protocol stack. This problem can be partially addressed by simplifying the network data encoding rules and streamlining their implementation. The authors examine the performance of four network data representation standards: ASN.1 Basic Encoding Rules (BER) and Packed Encoding Rules (PER), Sun Microsystems' External Data Representation (XDR), and Apollo Computer's Network Data Representation (NDR). It is found that the areas crucial to efficient encoder and decoder implementations are memory management, buffer management, and the overall simplicity of the encoding rules. It is shown that it is possible to implement ASN.1 BER and PER encoders and decoders that are as fast as their corresponding XDR versions.>

To meet the increased communication processing requirements of high-speed networks, a multiprocessing network interface is considered for processing multiple layers of a communication protocol stack. In particular, the processing of the open systems interconnection (OSI) layers 2 to 6 on the network interface are considered. OSI processing is computationally expensive because of the inclusion of the transfer syntax conversion at the presentation layer. The approach taken is to process different packets in parallel. The results obtained from simulations indicate that the approach has promise for OSI processing at higher rates.>

Group communication permits a single sender to communicate with multiple receivers. A nested group permits one or more of the receivers to be itself a group. Nested groups are particularly useful for reducing communication traffic on internetwork links and supporting subnetwork autonomy. A name graph model is used to characterize nested groups and formalize the problems of loops and duplications. The authors design and analyze a spanning shadow tree algorithm that detects potential loops and duplication. The algorithm is considered static because loops and duplicates are detected at the time of group membership modification rather than at the time a message is sent. The algorithm changes the system-level representation of the name graph in a transparent manner to avoid infinite loops and to suppress duplicated messages. The worst-case message complexity of name graph update operations is on the order of O( mod N mod /sup 2/), where mod N mod is the number of groups in the system. The complexity of updates can be justified, since run-time overhead for actual message communication is reduced.>

This paper generalizes group communications into nested groups for the internet environment. By using a name graph model, two problems in nested group name resolution are identified — resolution loops and resolution duplications. Existing approaches of solving these problems are surveyed and their shortcomings analyzed. The research contribution of this paper is the design and analysis of an algorithm which uses statically saved topology information of the name graph to detect and handle resolution and duplication loops at the time when group membership and/or group structure change. While preserving some necessary properties of loops, the algorithm transforms the name graph into one which avoids resolution loops and controls duplications. The communication complexity of the algorithm has an upper bound of Ο(|A|) in the worst case, where |A| is the number of arcs in the name graph.

Abstract syntax notation one (ASN.1) has been widely used in international standard specification: its transfer-syntax, the basic encoding rules (BER), is used as the external data representation. A BER implementation called the ED library is presented. The ED library includes a number of encoding and decoding routines that may be used as primitive functions to compose encoders and decoders for arbitrarily complicated ASN.1 data types. Based on the ED library an ASN.1-C compiler, called CASN1, is designed and implemented to free the protocol implementers from the arduous work of translating protocol-defined data-types and constructing their encoders and decoders. Given an ASN.1 protocol specification, CASN1 automatically translates the input ASN.1 modules into C and generates the BER encoders and decoders for the protocol defined data-types. The CASN1 design principles, user interface, and some example applications are discussed. The performance of the ED library and generated CASN1 code is also measured and discussed.>

This paper presents a new name form for the OSI X.500 directory system. The primary function of the directory is to provide a name-to-object look-up facility for OSI objects. The directory consists of a set of agents and a database which is distributed among the agents. The directory database is structured as a tree where each node, or entry, corresponds to an object. An entry consists of a set of attributes where one or more attributes are designated as the object name relative to the entry's immediate superior. X.500 defines a name as an ordered sequence of entry names starting from the root and terminating at the object. Therefore, a user must know the names of all the superiors of an object. In contrast, the descriptive name form is an unordered set of attributes. Only enough attributes need be given to distinguish the object from other objects. As a result, users do not have to know or understand the underlying hierarchy of the directory in order to do name look-up.

The design and implementation of a reliable group communication mechanism is presented. The mechanism guarantees a form of atomicity in that the messages are received by all operational members of the group or by none of them. Since the overhead in enforcing the order of messages is nontrivial, the mechanism provides two types of message transmission: one guarantees delivery of the messages in the same order to all members of a group, and the other guarantees only atomicity with messages delivered in some arbitrary order. The message-ordering property can be used to simplify distributed database and distributed processing algorithms. The mechanism can survive despite process, host, and communication failures.>