Communication-oriented abstractions such as atomic multicast, group RPC, and protocols for location-independent mobile computing can simplify the development of complex applications built on distributed systems. This paper describes Coyote, a system that supports the construction of highly modular and configurable versions of such abstractions. Coyote extends the notion of protocol objects and hierarchical composition found in existing systems with support for finer-grain objects called micro-protocols that implement individual semantic properties of the target service. A customized service is constructed by selecting micro-protocols based on their semantic guarantees and configuring them together with a standard runtime system to form a composite protocol implementing the service. Micro-protocols within a composite protocol can share data and are executed using an event-driven paradigm that enhances configurability. The overall approach is described and illustrated with exampl...

We describe an evolutionary path that allows operating systems to be used in a more flexible and appropriate manner by higher-level services An inf okernel exposes key pieces of inf rmation about its algorithms and internal state; thus, its def ault policies become mechanisms, which can be controlledf rom user-level We have implemented two prototype inf okernels based on the Linux 2 4 and NetBSD 1 5 kernels, called inf Linux and inf BSD, respectively The inf okernels export key abstractions as well as basic inf ormation primitives Using inf oLinux, we have implemented f ur case studies showing that policies within Linux can be manipulated outsideof the kernel Specifically, we show that the def ault file cache replacement algorithm, file layout policy, disk scheduling algorithm, and TCP congestion control algorithm can each be turned into base mechanisms For each case study, we havef ound that inf okernel abstractions can be implemented with little code and that the overhead and accuracyof synthesizing policies at user-level is acceptable Categories a n Subject Descriptors: D.4.7 [Operatin g Systems]: Organ inE in and Desi2 Ge n ral Terms: Desi9 , Experi51 tati1 , Performance Keywords: Poli) , MechaniE) Informatir 1.

The functionality and performance innovations in file systems and storage systems have proceeded largely independently from each other over the past years. The result is an information gap: neither has information about how the other is designed or implemented, which can result in a high cost of maintenance, poor performance, duplication of features, and limitations on functionality. To bridge this gap, we introduce and evaluate a new division of labor between the storage system and the file system. We develop an enhanced storage layer known as Exposed RAID (ERAID), which reveals information to file systems built above; specifically, ERAID exports the parallelism and failure-isolation boundaries of the storage layer, and tracks performance and failure characteristics on a fine-grained basis. To take advantage of the information made available by ERAID, we develop an Informed Log-Structured File System (ILFS). ILFS is an extension of the standard logstructured file system (LFS) that has been altered to take advantage of the performance and failure information exposed by ERAID. Experiments reveal that our prototype implementation yields benefits in the management, flexibility, reliability, and performance of the storage system, with only a small increase in file system complexity. For example, ILFS/ERAID can incorporate new disks into the system on-the-fly, dynamically balance workloads across the disks of the system, allow for user control of file replication, and delay replication of files for increased performance. Much of this functionality would be difficult or impossible to implement with the traditional division of labor between file systems and storage.

The ability to configure transport protocols from collections of smaller software modules allows the characteristics of the protocol to be customized for a specific application or network technology. This paper describes an approach to building such customized protocols using Cactus, a system in which micro-protocols implementing individual attributes of transport can be combined into a composite protocol that realizes the desired overall functionality. In contrast with similar systems, Cactus supports non-hierarchical module composition and event-driven execution, both of which increase flexibility and allow finer-grain modules implementing orthogonal properties. To illustrate this approach, the design and implementation of a configurable transport protocol called CTP is presented. CTP allows customization of a number of properties including reliable transmission, congestion detection and control, jitter control, and message ordering. This suite of micro-protocols has been implemented using Cactus/C 2.0 on Red Hat Linux 6.2, with initial experimental results indicating that the ability to target the guarantees more precisely to the needs of applications can in fact result in better performance.

In group communication, in order to deliver multicast messages reliably in a group, it is common practice for each member to maintain copies of all messages it sends and receives in a bu er for potential local retransmission. The storage of these messages is costly and bu ers may grow out of bound. A form of garbage collection is needed to address this issue. Garbage collection occurs once a process learns that a message in its bu er has been received by every process in the group. The message is declared stable and is released from the bu er. An important part of garbage collection is message stability detection. This dissertation presents the result of an investigation into message stability detection protocols. A number of message stability detection protocols used in popular reliable multicast protocols are studied with a focus on their performance in large scale settings. This dissertation proposes anewgossip-style protocol with improved scalability and fault tolerance. This dissertation also shows that by adding a hierarchical structure to the set of basic protocols, their performance can be signi cantly improved when the number of participants is large.

This paper presents the design and implementation of a quality of service architecture for the Internet. The architecture is based on the emerging standards for resource reservation in the Internet, namely the RSVP protocol and the associated service specifications defined by the Internet Engineering Task Force (IETF). Our architecture represents a major functional enhancement to the traditional sockets based communication subsystem, while preserving application programming interface and binary compatibility with existing applications. It is scalable and supports a wide variety of network interfaces ranging for legacy LAN interfaces, such as Token Ring and Ethernet, to high-speed ATM interfaces. The paper also describes the implementation of this architecture on the IBM AIX platform and initial our experiences with the system.

To deliver multicast messages reliably in a group, each member maintains copies of all messages it sends and receives in a buffer for potential local retransmission. The storage of these messages is costly and buffers may grow out of bound. Garbage collection is needed to address this issue. Garbage collection occurs once a process learns that a message in its buffer has been received by every process in the group. The message is declared stable and is released from the process's buffer. This paper proposes a gossip-style garbage collection scheme called GSGC for scalable reliable multicast protocols. This scheme achieves fault-tolerance and scalability without relying on the underlying multicast protocols. It collects and disseminates information in the multicast group by making each group member periodically gossip information to a random subset of the group. Extending the global gossip protocol further, this paper also investigates a local gossip scheme that achieves improved scalab...

This paper proposes to use a logical hypercube structure for detecting message stability in distributed systems. In particular, a stability detection protocol that uses such a superimposed logical structure ispresented, and its scalability is being compared with other known stability detection protocols. The main bene ts of the logical hypercube approach are scalability, faulttolerance, and refraining from overloading a single node or link in the system. These bene ts become evident by both an analytic comparison and by simulations. Another important feature ofthe logical hypercube approach is that the performance oftheprotocol is in general not sensitive to the physical topology of the underlying (physical) network. 1

Many scalable reliable multicast protocols use the local repair scheme where certain receivers retransmit packets by other receivers. Such schemes need a mechanism, called message stability, to ensure reliable delivery to all members of a multicast group and to delete those packets received by all members from the buffers of the local repairers. We propose a new protocol for message stability based on random gossiping. The protocol offers scalability and fault-tolerance by limiting each of its message transmissions only to a constant number of randomly chosen group members, hence eliminating message implosion and single point failure through the diffusion of responsibility. Both statistical analysis and simulation study indicate that our gossipstyle message stability protocol can be highly effective for large scale reliable multicast.

We examine the usefulness of component-based software-engineering for the implementation of software communication systems. We present an architecture that allows to divide protocol software into fully de-coupled components that can be plugged together using visual builder tools to rapidly prototype flexible, robust, and application-tailored communication protocols. We show the feasibility of component-based protocol engineering by demonstrating how a simple transport protocol was realized. A discussion about advantages and impacts concludes this paper. 1. Introduction While a general purpose transport protocol such as TCP has been for many years the protocol of choice for popular applications like telnet or ftp, first problems with the use of TCP arose with the success of http [25]. For new applications like audio- and video-streaming, TCP is completely unsuited. We belief that the popularity of the world wide web and new technologies like Sun's Jini (TM) [16] will produce a number ...