No abstract

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.

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.

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 T C P / I P 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.

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. In this paper we give an overview of the problems related to wireless mobility. We also present a new software architecture for mastering them 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. A prototype implementation of the architecture exists in an environment consisting of Linux and Windows platforms and the GSM cellular telephone network.