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A Survey of Application-Layer Networking Techniques for Real-time Distributed Groupware
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ABSTRACT..................................................................................................................................................................................................... 3
Adaptive Group Communication Services for Groupware Systems
- In Second International Enterprise Distributed Object Computing Workshop (EDOC’98
, 1998
"... Collaborative, multi-user applications require group multicast services that provide ordering guarantees for maintaining consistency of replicated shared context as well as provide a high degree of interactivity, even under varying load on the communication servers. While the most common view of the ..."
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Collaborative, multi-user applications require group multicast services that provide ordering guarantees for maintaining consistency of replicated shared context as well as provide a high degree of interactivity, even under varying load on the communication servers. While the most common view of the quality of service (QoS) in a distributed system is in terms of the guarantee of the network connection parameters (bandwidth, end-to-end delay) for audio and video, in this paper we investigate the various requirements placed on group communication servers for reliable data communication among diverse groups of collaborative users. We show that in the absence of such considerations in the design of a group communication service, some groups or individual users can be severely affected by bursty traffic or increase in the size of other groups. We present the design of a best-effort adaptive group communication service for supporting reliable data communication in CSCW systems, which addresses both group's requirements and individual user's requirements, balancing the needs of multiple groups of users by taking into account their priorities and needs when resources are constrained at the communication server. 1
Adaptive Forward Error Correction for Real-Time Groupware
"... Real-time distributed groupware sends several kinds of messages with varying quality-of-service requirements. However, standard network protocols do not provide the flexibility needed to support these different requirements (either providing too much reliability or too little), leading to poor perfo ..."
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Real-time distributed groupware sends several kinds of messages with varying quality-of-service requirements. However, standard network protocols do not provide the flexibility needed to support these different requirements (either providing too much reliability or too little), leading to poor performance on real-world networks. To address this problem, we investigated the use of an application-level networking technique called adaptive forward error correction (AFEC) for real-time groupware. AFEC can maintain a predefined level of reliability while avoiding the overhead of packet acknowledgement or retransmission. We analysed the requirements of typical real-time groupware systems and developed an AFEC technique to meet these needs. We tested the new technique in an experiment that measured message reliability and latency using TCP, plain UDP, UDP with nonadaptive FEC, and UDP with our AFEC scheme, under several simulated network conditions. Our results show that for awareness messages that can tolerate some loss, FEC approaches keep latency at nearly the plain-UDP level while dramatically improving reliability. In addition, adaptive FEC is the only technique that can maintain a specified level of reliability and also minimize delay as network conditions change. Our study shows that groupware AFEC can be a useful tool for improving the realworld performance and usability of real-time groupware.
Statistical Quality Of Service For Variable, Periodic, Real-Time Tasks: Scheduling And Resource Management Algorithms
, 1998
"... Scheduling algorithms for periodic tasks are crucial to many real-time systems. Traditionally, the resource requirements of tasks are assumed to be fixed ; all task deadlines must be met. Under this condition , Rate-Monotonic Scheduling (RMS), a classical algorithm, can guarantee that all deadlines ..."
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Scheduling algorithms for periodic tasks are crucial to many real-time systems. Traditionally, the resource requirements of tasks are assumed to be fixed ; all task deadlines must be met. Under this condition , Rate-Monotonic Scheduling (RMS), a classical algorithm, can guarantee that all deadlines are met. Fixed resource requirements for tasks do not match the needs of new applications, such as multimedia. For such applications, RMS must use the worst case resource requirements (WCRR) of the tasks. RMS can be extremely wasteful of system resources, due to the use of WCRR and to RMS's need to guarantee all deadlines. For such applications, we introduce algorithms to increase system utilization and system intertask fairness. This thesis answers the question of how to schedule periodic tasks with variable utilization requirements and deadlines which may be missed and still provide a statistical quality of service guarantee to bound the number of deadlines missed. We propose two technique...
