8320047
Evaluation of Transport Layer Loss Notification in Wireless Environments
Residual bit-errors in wireless environments are well known to cause difficulties for congestion controlled protocols like TCP. In this study we focus on a receiver-based loss differentiation approach to mitigating the problems, and more specifically on two different loss notification schemes. The fully receiver-based 3-dupack scheme uses additional dupacks to implicitly influence the retransmission behavior of the sender. The second TCP option scheme uses a TCP option to explicitly convey a corruption notification. Although these schemes look relatively simple at first glance, when examining the details several issues exist which are highlighted and discussed. A performance evaluation based on a FreeBSD kernel implementation show that the TCP option scheme works well in all tested cases and provides a considerable throughput improvement. The 3-dupack scheme also provide performance gains in most cases, but the improvements varies more between different test cases, with some cases showing no improvement over regular TCP.
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.
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 ...
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.
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.
16287780
Distributed object invocation in OBIWAN
The need for sharing is well-known in a large number of distributed collaborative applications. These applications are difficult to develop for an environment in which network connections are slow and not reliable.For this purpose, we developed a platform called OBIWAN that: i) allows the application programmer to decide the mechanism by which objects should be invoked, remote method invocation or invocation on a local replica, and ii) provides hooks for the application programmer to implement a set of application specific properties such as transactional support, for example.This functionality allows the application programmer to deal with situations that frequently occur in a wide-area network, such as disconnections and slow links. As a matter of fact, as long as the objects needed by an application are locally accessible, there is no need to be connected to the network. In addition, it allows the programmer to easily replace, in run-time, remote by local invocations, thus improving the performance of his application and its adaptability.The prototype is developed in Java, is very small and simple to use, the preliminary performance results are very encouraging, and existing applications can be easily modified to take advantage of the OBIWAN functionality.