Evaluation of TCP retransmission delays

Many applications today (e.g., game servers and video streaming servers) deliver time-dependent data to remote users. In TCP based systems, retransmission of data might give high and varying delays. In applications with thin data streams (e.g., interactive applications like games), the interaction between game players raises stringent latency requirements, and it is therefore important to retransmit lost or corrupted data as soon as possible. In the current version of the Linux kernel (2.6.15), several variations of TCP are included. In this thesis, these variations are compared, tested and evaluated with respect to retransmission latency in different and varying RTT and loss scenarios. The variations are tested for thin and thick data streams, respectively. Thick streams transmit as much data as possible, while the thin streams only need to transfer a small amount of data every once in a while, thus potentially having considerable time intervals between the sending of a few packets. Due to poor performance experienced for the TCP variations in the thin stream part of the tests, several enhancements are proposed, implemented and tested for use in thin stream scenarios. The loss detection mechanisms of TCP do not perform adequately in a thin stream scenario, resulting in high and varying retransmission delays, something which might violate the stringent latency requirements of interactive games. The implemented enhancements provide considerable improvements in the retransmission delay, reducing both the level and the variation of the retransmission delay values

Improving latency for interactive, thin-stream applications over reliable transport

A large number of network services use IP and reliable transport protocols. For applications with constant pressure of data, loss is handled satisfactorily, even if the application is latencysensitive. For applications with data streams consisting of intermittently sent small packets, users experience extreme latencies more frequently. Due to the fact that such thin-stream applications are commonly interactive and time-dependent, increased delay may severely reduce the experienced quality of the application. When TCP is used for thin-stream applications, events of highly increased latency are common, caused by the way retransmissions are handled. Other transport protocols that are deployed in the Internet, like SCTP, model their congestion control and reliability on TCP, as do many frameworks that provide reliability on top of unreliable transport. We have tested several application- and transport layer solutions, and based on our findings, we propose sender-side enhancements that reduce the application-layer latency in a manner that is compatible with unmodified receivers. We have implemented the mechanisms as modifications to the Linux kernel, both for TCP and SCTP. The mechanisms are dynamically triggered so that they are only active when the kernel identifies the stream as thin. To evaluate the performance of our modifications, we have conducted a wide range of experiments using replayed thin-stream traces captured from real applications as well as artificially generated thin-stream data patterns. From the experiments, effects on latency, redundancy and fairness were evaluated. The analysis of the performed experiments shows great improvements in latency for thin streams when applying the modifications. Surveys where users evaluate their experience of several applications’ quality using the modified transport mechanisms confirmed the improvements seen in the statistical analysis. The positive effects of our modifications were shown to be possible without notable effects on fairness for competing streams. We therefore conclude that it is advisable to handle thin streams separately, using our modifications, when transmitting over reliable protocols to reduce retransmission latency

Layered multicast with forward error correction (FEC) for Internet video

In this paper, we propose RALF, a new FEC-based error control protocol for layered multicast video. RALF embodies two design principles: decoupling transport layer error control from upper layer mechanisms and decoupling error control and congestion control at the transport layer. RALF works with our previously proposed protocol RALM - a layered multicast congestion control protocol with router assistance. RALF provides tunable error control services for upper layers. It requires no additional complexities in the network beyond those for RALM. Its performance is evaluated through simulations in NS2.published_or_final_versio

Application of Advanced Early Warning Systems with Adaptive Protection

This project developed and field-tested two methods of Adaptive Protection systems utilizing synchrophasor data. One method detects conditions of system stress that can lead to unintended relay operation, and initiates a supervisory signal to modify relay response in real time to avoid false trips. The second method detects the possibility of false trips of impedance relays as stable system swings “encroach” on the relays’ impedance zones, and produces an early warning so that relay engineers can re-evaluate relay settings. In addition, real-time synchrophasor data produced by this project was used to develop advanced visualization techniques for display of synchrophasor data to utility operators and engineers

Performance evaluation of TCP-based applications over DVB-RCS DAMA schemes

Transmission Control Protocol (TCP) performance over Digital Video Broadcasting-Return Channel via Satellite (DVB-RCS) standard is greatly affected by the total delay, which is mainly clue to two components, propagation delay and access delay. Both are significant because they are dependent oil the long propagation path of the satellite link. I-lie former is intrinsic and due to radio wave propagation over the satellite channel for both TCP packets and acknowledgements. It is regulated by the control loop that governs TCP. The latter is due to the control loop that governs the demand assignment Multiple access (DAMA) signalling exchange between satellite terminals and the network control center. necessary to manage return link resources. DAMA is adopted in DVB-RCS standard to achieve flexible and efficient use of the shared resources. Therefore, performance of TCP over DVB-RCS may degrade due to the exploitation of two nested control loops also depending oil both file selected DAMA algorithm and the traffic profile. This paper analyses the impact of basic DAMA implementation oil TCP-based applications over a DVB-RCS link for a large Set Of study Cases. To provide a detailed overview of TCP performance in DVB-RCS environment, the analysis includes both theoretical approach and simulation campaign. Copyright (C) 2009 John Wiley & Sons, Ltd

Virtualisation and Thin Client : A Survey of Virtual Desktop environments

This survey examines some of the leading commercial Virtualisation and Thin Client technologies. Reference is made to a number of academic research sources and to prominent industry specialists and commentators. A basic virtualisation Laboratory model is assembled to demonstrate fundamental Thin Client operations and to clarify potential problem areas

Proceedings of the NSSDC Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications

The proceedings of the National Space Science Data Center Conference on Mass Storage Systems and Technologies for Space and Earth Science Applications held July 23 through 25, 1991 at the NASA/Goddard Space Flight Center are presented. The program includes a keynote address, invited technical papers, and selected technical presentations to provide a broad forum for the discussion of a number of important issues in the field of mass storage systems. Topics include magnetic disk and tape technologies, optical disk and tape, software storage and file management systems, and experiences with the use of a large, distributed storage system. The technical presentations describe integrated mass storage systems that are expected to be available commercially. Also included is a series of presentations from Federal Government organizations and research institutions covering their mass storage requirements for the 1990's