Kimmo E. E. Raatikainen

Optimizing World-Wide Web for weakly connected mobile workstations: An indirect approach

Modern portable computers and wireless connections over cellular telephone networks have created a new platform for distributed information processing. We have designed a communication architecture that makes it possible to exploit the existing TCP/IP communication protocols but that also takes into account specific features of cellular links. Our communication architecture is based on the concept of indirect interaction. The mediating interceptor is the bridge between the worlds of wireless and wireline communication. It also provides enhanced functionality that improves fault-tolerance and performance. In this paper we demonstrate how the architecture is used to improve the performance of the WWW information browsing. Similar solution methods can be applied to other existing applications and protocols.<<ETX>>

F-RTO: an enhanced recovery algorithm for TCP retransmission timeouts

Spurious TCP retransmission timeouts (RTOs) have been reported to be a problem on network paths involving links that are prone to sudden delays due to various reasons. Especially many wireless network technologies contain such links. Spurious retransmission timeouts often cause unnecessary retransmission of several segments, which is harmful for TCP performance. Recent proposals for avoiding unnecessary retransmissions after a spurious RTO require use of TCP options which must be implemented and enabled at both ends of teh connection. We introduce a new TCP sender algorithm for recovery after a retransmission timeout and show that unnecessary retransmissions after a spurious retransmission timeout, improving the TCP performance considerably. The algorithm is friendly towards other TCP connections, because it follows the congestion control principles and injects packets to the network at same rate as a conventional TCP sender. We implemented the algorithm and compared its performance to conventional TCP and Eifel TCP when RTOs occurred either due to sudden delays or due to packet losses. The results show that our algorithm either improves performance or gives similar througput as the other TCP variants evaluated in different test cases.

Application requirements for middleware for mobile and pervasive systems

In this paper, we examine the requirements for future middleware to support mobile and pervasive applications and identify key research areas. We illustrate the research areas with requirements identified in two specific research projects concerning pervasive healthcare and home entertainment.

Connecting Mobile Workstations to the Internet Over a Digital Cellular Telephone Network

Modern portable computers and wireless connections over a cellular telephone network have created a new platform for distributed information processing. We present a communication architecture framework which makes it possible to exploit the existing TCP/IP communication architecture but which also takes into account the specific features of wireless links. Our communication architecture is based on the principle of indirect interaction. The mediating interceptor, Mobile-Connection Host, is the bridge between the worlds of wireless and wireline communication. The interceptor also provides enhanced functionality that improves fault-tolerance and performance for applications aware of mobility. Prototypes of the architecture are implemented both for the Unix (Linux) and for the Windows (3.11) platform.

An efficient transport service for slow wireless telephone links

Modern digital cellular telephones and portable computers have created a new platform for distributed information processing. However, the characteristics of wireless telephone links are different from those of wireline links. With standard TCP/IP protocols, this can lead to severe performance problems; some are related to the control of the wireless link, some to the cooperation of the wireless link and the fixed network. One possible solution is to split the end-to-end communication path into two parts, and to establish a separate control for each part. The Mowgli communication architecture is a sophisticated elaboration of this basic idea covering several data communication layers. One of its main components is the Mowgli data channel service (MDCS), which transparently replaces the standard TCP/IP core protocols over the slow wireless link. We discuss how the Mowgli approach, using the MDCS, alleviates the problems encountered with TCP/IP protocols over slow wireless links. The results of our performance tests indicate the merits of the Mowgli approach. The transfer times and the response times become more stable, transfer times for multiple parallel bidirectional transfers are substantially reduced, and response times in interactive work can be kept at a low and predictable level, even when there is other traffic on the wireless link.

Measured performance of data transmission over cellular telephone networks

Recent developments in mobile communication and personal computer technology have laid a new foundation for mobile computing. Performance of the data communication system as seen by an application program is a fundamental factor when communication infrastructure at the application layer is designed. This paper provides results of performance measurements of data transmission over two different cellular telephone networks, a digital GSM-network and an analogue NMT-network. Since our emphasis is on performance as seen by application programs, we use the standard TCP/IP protocols in the measurements. The performance is measured using three basic operations: establishment of a wireless dial-up connection, exchange of request-reply messages, and bulk data transfer. The external conditions under which the measurements were carried out present a normal office environment when the field strength of the cellular link is good or fairly good.

Mowgli WWW software: improved usability of WWW in mobile WAN environments

Today the World-Wide Web is the most widely used distributed application. By utilising the data services of cellular telephone systems such as the digital GSM, WWW can be brought to nomadic users. However, the characteristics of cellular telephone links differ greatly from wire-line links. The narrow bandwidth, highly variable transmission delays, and sudden disconnections create problems for many Internet applications. WWW uses the HTTP and TCP/IP protocols, which exhibit a number of usability and performance problems in wide-area mobile networks. Mowgli WWW, a WWW middleware implementation, exploits several new techniques to solve these problems. Although Mowgli WWW was initially designed for a wireless WAN environment, the techniques are also profitable in fixed networks when slow or high-latency communication links are involved.

A Power-Aware Broadcasting Algorithm

Flooding is an expensive operation that is often required in the operation of mobile ad hoc networks (MANETs). In this paper, we present a novel algorithm to reduce the overhead imposed by flooding operations. The algorithm improves previous results by using a distributed function to elect the nodes that will provide the highest additional coverage to previous retransmissions. The algorithm does not require any signalling or impose special requirements on the participating devices

A Distributed Real-Time Main-Memory Database for Telecommunication

Recent developments in network and switching technologies have increased the data intensity of telecommunications systems and services. The challenges facing telecom data management are now at a point that the database research community can and should become deeply involved.

Mobility in long-term service architectures and distributed platforms

This article focuses on the convergence of two technical streams of current interest: (1) service architectures as an innovative, integrated solution to the problems addressed by intelligent networks and telecommunications management networks; and (2) mobile communications systems and related software for their control and management. Its main objectives are to: (a) introduce the state of the art in long-term service architecture (SA); (b) identify the potential benefits of using SA concepts in the design and deployment of mobile communications systems; (c) indicate principles for inclusion of personal and terminal mobility aspects in the SA; and (d) consider the implications of mobility on the distributed processing environment underlying a set of services built according to the SA. The technical content of the article partly reflects work being carried out in international cooperative fora, particularly within the global initiative TINA and selected projects of the European research program ACTS. However, most views expressed here are the result of original evaluation and synthesis carried out by the authors. The timing validity of the article is in the medium to long term, since it targets the development and deployment process of systems that may not be in operation until the turn of the century.