Mika Liljeberg

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>>

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.

Mowgli: improvements for Internet applications using slow wireless links

Modern cellular telephone systems extend the usability of portable personal computers enormously. A nomadic user can be given ubiquitous access to remote information stores and computing services. However, the behavior of wireless links creates severe inconveniences within the traditional data communication paradigm. We give an overview of the problems related to wireless mobility. We also present a new software architecture for mastering the problems and discuss a new paradigm for designing mobile distributed applications. The key idea in the architecture is to place a mediator, a distributed intelligent agent, between the mobile node and the wireline network.

Using CORBA to support terminal mobility

Nomadicity is quite a new challenge for computing and communication technologies. Some of the key issues in the field are: the impact of nomadicity on client server interaction; how to support terminal mobility, and how to cope with the unique performance characteristics of wireless access. The first issue focuses on the question of whether the computational viewpoint client server interaction mechanisms for feed environments remain valid in mobile environments. The other two issues are related to the engineering aspect of dealing with mobile routing and the unpredictable performance and reliability of wireless networks, generally orders of magnitude below those of wired networks. We show a novel way to deal with these issues in a CORBA based distributed processing environment. Object technology-CORBA, in particular-is already mature. Today CORBA provides a software execution and development environment that simplifies distributed computing and application integration. The main stream of CORBA based solutions is targeted to LAN based applications relying on (quite) fast and reliable connections. We show that the CORBA 2.0 specification also provides the means to support nomadic computing. We demonstrate how the CORBA 2.0 interoperability architecture, together with some CORBAServices (Common Object Service Specifications), can be used to provide seamless support to terminal mobility and communication through slow wireless connections. The corner stones of our solution are mediated bridges, and an Environment Specific Inter-ORE Protocol (ESIOP) tailored for wireless networks.

Introducing quality-of-service and traffic classes into wireless mobile networks

1. ~STWCT Rwent developments in wireless conummimtions have made it possible to provide mtitimedia services for mobtie users. However, mtitimedia servic~that is a m-e of different content ~es including te~ images, audio, and vide=ver wireless W require that the underlying wireless infrastructure supports some kind of Q@tyof-Service concepts and Werent trtic classes. Since many of the current wireless technologies do not support those concepts, we introduce a way of adapting mobtie wireless networks so that some aspects of Qutity-ofService and traffic classw -be supported even if the underlying infrastructure does not support them. Our Nlobfle Network Adapters can overcome most of the titations due to protocol architectures. However, they m not augment the physid characteristic of the underlying technology but they try to use the avtiable resources in the most appropriate way. Our prototype implementation indicates that priori@based mtitipletig of traffic is useti for delivering rd-time and non-rdtime data to and from a mobde terminal. Our solution is able to support both seandess and

Mobile Access to the Internet: A Mediator-Based Solution.

Nomadicity is a new challenge for computing and communication technologies. Modern cellular telephone systems extend the usability of portable personal computers enormously. A nomadic user can be given ubiquitous access to remote information stores and computing services. However, the behaviour of wireless links creates severe inconveniences within the traditional data communication paradigm. In this paper we give an overview of the problems related to wireless mobility. We also present a new software architecture for mastering the problems and discuss a new paradigm for designing mobile distributed applications. The key idea in the architecture is to place a mediator, a distributed intelligent agent, between the mobile node and the wireline network.