15278123
Taxonomy and survey of retransmission-based partially reliable transport protocols
The mismatch between the services offered by the two standard transport protocols in the Internet, TCP and UDP, and the services required by distributed multimedia applications has led to the development of a large number of partially reliable transport protocols: protocols that in terms of reliability place themselves between TCP and UDP. This paper presents taxonomy for retransmission-based, partially reliable transport protocols, i.e. the subclass of partially reliable transport protocols that makes error recovery through retransmissions. The taxonomy comprises two classification schemes: one that classifies protocols with respect to the reliability service they offer and one that classifies them with respect to their error control scheme. The objective of our taxonomy is fourfold: to introduce a unified terminology; to provide a framework in which this class of protocols can be examined, compared and contrasted; to make explicit the error control schemes used by these protocols; and, finally, to gain new insight into these protocols and thereby suggest avenues for future research. Based on our taxonomy, a survey is made of existing retransmission-based, partially reliable transport protocols. The survey shows how protocols are categorized according to our taxonomy and exemplifies the majority of reliability services and error control schemes detailed in our taxonomy.
42455029
A GSM/GPRS Testbed for TCP Performance Evaluation
Investigating the wireless Internet is a nontrivial task dueto the complexity of wireless systems and the many protocolinteractions that appear. In this paper we present a measurementtestbed that a ...
4596877
An Experimental Study on the Performance and Fairness of Loss Differentiation for TCP
The evolution of computer communications and the Internet has led to the emergence of a large number of communication technologies with widely different capabilities and characteristics. While this multitude of technologies provides a wide array of possibilities it also creates a complex and heterogeneous environment for higher-layer communication protocols. Specific link technologies, as well as overall network heterogeneity, can hamper user-perceived performance or impede end-to-end throughput. In this thesis we examine two transport layer centered approaches to improve performance. The first approach addresses the decrease in user satisfaction that occurs when web waiting times become too long. Increased transport layer flexibility with regards to reliability, together with error-resilient image coding, is used to enable a new trade-off. The user is given the possibility to reduce waiting times, at the expense of image fidelity. An experimental examination of this new functionality is provided, with a focus on image-coding aspects. The results show that reduced waiting times can be achieved, and user studies indicate the usefulness of this new trade-off. The second approach concerns the throughput degradations that can occur as a consequence of link and transport layer interactions. An experimental evaluation of the GSM environment shows that when negative interactions do occur, they are coupled to large variability in link layer round-trip times rather than simply to poor radio conditions. Another type of interaction can occur for link layers which expose higher layers to residual bit errors. Residual bit errors create an ambiguity problem for congestion controlled transport layer protocols which cannot correctly determine the cause for a loss. This ambiguity leads to an unnecessary throughput degradation. To mitigate this degradation, loss differentiation and notification mechanisms are proposed and experimentally evaluated from both performance and fairness perspectives. The results show that considerable performance improvements can be realized. However, there are also fairness implications that need to be taken into account since the same mechanisms that improve performance may also lead to unfairness towards flows that do not employ loss differentiation.
7238873
A Robust JPEG Coder for a Partially Reliable Transport Service
The usage of multimedia applications on the Internet has seen phenomenal growth in recent years. Transport protocols that provide partially reliable service have been suggested as one approach to better handle the requirements of these applications. A partially reliable service provides applications with the possibility of a flexible tradeoff between reliability and delay/throughput. Appropriately designed coders are, however, required to fully utilize a partially reliable service. In this paper we present a JPEG image coder tailored to suit the behavior of a partially reliable byte stream service. With regular JPEG, data loss typically results in severely distorted images. The robust recoder employs three major modifications to standard JPEG in order to adapt to the partially reliable transport: (1) extended resynchronization markers in order to be able to resynchronize effectively, (2) block interleaving in order to spread out the loss of a packet across the image and (3) error concealment in order to minimize the perceived quality loss. The modifications incorporate both new inventions, such as random window interleaving, as well as variations of previously known techniques.
6931993
PerDiS: Design, Implementation, and Use of a PERsistent DIstributed Store
The PerDis (Persisent Distributed Store) project addresses the issue of providing support for distributed collaborative engineering applications. We describe the design and implementation of the PerDis platform, and its support for such applications. 
 
Collaborative engineering raises system issues related to the sharing of large volumes of fine-grain, complex objects across wide-area networks and administrative boundaries. PerDiS manages all these aspects in a well defined, integrated, and automatic way. Distributed application programming is simplified because it uses the same memory abstraction as in the centralized case. Porting an existing centralized program written in C or C++ is usually a matter of a few, well-isolated changes. 
 
We present some performance results from a proof-of-concept platform that runs a number of small, but real, distributed applications on Unix and Windows NT. These confirm that the PerDiS abstraction is well adapted to the targeted application area and that the overall performance is promising compared to alternative approaches.