David E. Ott

Tuning RED for Web traffic

We study the effects of RED on the performance of Web browsing with a novel aspect of our work being the use of a user-centric measure of performance: response time for HTTP request-response pairs. We empirically evaluate RED across a range of parameter settings and offered loads. Our results show that: 1) contrary to expectations, compared to a FIFO queue, RED has a minimal effect on HTTP response times for offered loads up to 90% of link capacity; 2) response times at loads in this range are not substantially affected by RED parameters; 3) between 90% and 100% load, RED can be carefully tuned to yield performance somewhat superior to FIFO, however, response times are quite sensitive to the actual RED parameter values selected; and 4) in such heavily congested networks, RED parameters that provide the best link utilization produce power response times. We conclude that for links carrying only Web traffic, RED queue management appears to provide no clear advantage over tail-drop FIFO for end-user response times.

Coordinated multi-streaming for 3D tele-immersion

This paper looks at the problem of multi-streaming in 3D tele-immersion and describes how a protocol architecture called CP (for Coordination Protocol) can be used to coordinate video frame transport between application clusters. CP provides application endpoints with information about current network conditions, and an open architecture for implementing application-specific coordination schemes. The scheme described in this paper apportions available bandwidth among flows such that frame transport synchrony, important for 3D reconstruction performance, is significantly enhanced. Results demonstrating the effectiveness of CP in increasing multi-stream coordination, while at the same time maintaining aggregate congestion responsiveness, are obtained from a FreeBSD/Linux implementation and a live experimental network. Results underscore the importance of consistency in network information across flows for realizing dramatic improvements in frame arrival synchrony.

An open architecture for transport-level protocol coordination in distributed multimedia applications

We consider the problem of flow coordination in distributed multimedia applications. Most transport-level protocols are designed to operate independently and lack mechanisms for sharing information with other flows and coordinating data transport in various ways. This limitation becomes problematic in distributed applications that employ numerous flows between two computing clusters sharing the same intermediary forwarding path across the Internet. In this article, we propose an open architecture that supports the sharing of network state information, peer flow information, and application-specific information. Called simply the coordination protocol (CP), the scheme facilitates coordination of network resource usage across flows belonging to the same application, as well as aiding other types of coordination. The effectiveness of our approach is illustrated in the context of multistreaming in 3D tele-immersion where consistency of network information across flows both greatly improves frame transport synchrony and minimizes buffering delay.

Wait-Free Synchronization in Quantum-Based Multiprogrammed Systems

We consider wait-free synchronization in multiprogrammed uniprocessor and multiprocessor systems in which the processes bound to each processor are scheduled for execution using a scheduling quantum. We show that, in such systems, any object with consensus number P in Herlihys wait-free hierarchy is universal for any number of processes executing on P processors, provided the scheduling quantum is of a certain size. We give an asymptotically tight characterization of how large the scheduling quantum must be for this result to hold.

Transport-Level Protocol Coordination in Cluster-to-Cluster Applications

Future Internet applications will increasingly use multiple communications and computing devices in a distributed fashion. In this paper, we identify an emerging and important application class comprised of a set of processes on a cluster of devices communicating to a remote set of processes on another cluster of devices across a common intermediary Internet path. We call applications of this type cluster-to-cluster (C-to-C) applications. The networking requirements of C-to-C applications present unique challenges that current transport-level protocols fail to address. In particular, these applications require aggregate measurement of network conditions across all associated flows and coordinated transport-level protocol behavior. A Coordination Protocol (CP) is proposed which allows a C-to-C application to coordinate flow behavior in the face of changing network conditions. CP provides cluster endpoints with a consistent view of network conditions, as well as cluster membership and bandwidth usage information. An application may use CP to define and implement a coordination scheme supporting particular flow priorities and other objectives.