DISCO - Research Projects

Providing Optimum Capacity and Flexible Quality of Service in Packet-based Wireless Systems Using Scheduling and Soft Information

The current trend in tele- and data communications is towards integration of systems and services. Most networks, which also include wireless networks, will be based on the IP protocol. For example, it is believed that the third generation wireless systems will use IP-based core networks and that in a not too distant future all traffic will be IP-based from end-user to end-user. Thus, voice will be supported using Voice over IP (VoIP).
One major problem with this development towards transparent, general purpose IP networks is that different networks perform very differently. For instance, a fiber-based network is almost free of transmission errors whereas transmission errors are common over wireless networks due to fading and interference. The traditional solution to this problem is to make the wireless network transparent with re-spect to varying channel conditions. However, this solution has several drawbacks. Making the wireless network transparent means that much of the bandwidth need to be spent on channel cod-ing and retransmissions on the link level; a solution that reduces the throughput and increases the delay. This is problematic particularly if real-time services, such as voice communication, are to be supported.
If high speed data services are to be used also over wireless networks providing wide area coverage the capacity of the network has to increase and the cost per bit has to decrease. This means that the spectral efficiency must be improved several times. In order to provide networks with such performance we need to remove all bottlenecks and make better use of the channel properties. Moreover, applications need to be adaptive in the sense that they should be able to adjust their requirements to the current quality provided by the wireless link. Two key techniques for attaining these goals are studied in this project: the use of scheduling over several access points and the use of soft information.

In cooperation with Uppsala University and Chalmers. Supported by Vinnova.

SCTP for Soft Real-Time Applications

The Stream Control Transmission Protocol, SCTP, was originally designed as a transport mechanism for signaling information. However, its flexible design and adherence to TCP-friendly congestion control have made it a viable alternative for a wide range of applications. Several implementations of the protocol already exist and it is part of the IETF standards track. In this project the applicability and performance of SCTP for soft real-time applications, such as multimedia applications, are evaluated. The study includes an extensive performance evaluation of the protocol and also consider the suggested protocol extension for partial reliability, PR_SCTP.

Supported by Tieto Enator AB.

User Friendly Web Transport for Wireless Networks

The popularity of the Internet is increasing at a steady rate, with the WWW as the primary driving force. More and more services are becoming available on the Web and an increasing number of companies is establishing a Web presence. Designing an appropriate Web site, however, requires both artistic and technical knowledge. The pages should have an appealing and consistent look, but the design must also consider that these pages will be used in a networked environment. Pages with a large content of high-quality image data may look very appealing to the designer in his or her computer, but may provide very poor overall quality to for instance a user over a slow wireless link due to large transfer delays. Web users are typically very impatient and prefer to move on when the transfer of a page takes to long. This in turn could have important business implications since the user may then move on to the Web site of another company. Providing high overall service quality to wireless Web users requires increased knowledge of user preferences as well as flexible technical solutions that can provide the desired trade-off. The purpose of this project is thus twofold: 1) To evaluate what constitutes an appropriate Web page design from a user's perspective with a focus on how users perceive the tradeoff between image fidelity and page transfer delay. 2)To develop appropriate communication protocols that allow flexible tradeoffs between various quality-of-service parameters.

Supported by HumanIT.

Protocol Support for Mobile Environments

Historically, telecommunication and datacommunication have been two separate fields with distinct protocols and applications available in each of the fields. Today, the two fields are rapidly merging which opens up challenging new research problems and exciting new business opportunities. This project investigates how various protocols interact over a mobile wireless channel. Protocol interaction is complicated by the fact that a large number of different protocols, present at various levels of the system, interact. Further complicating the picture, several nodes are usually involved in the communication and the distance spanned by the involved protocols differ. Focus is placed on how protocols from the TCP/IP protocol suite interoperate with the underlying protocols of the wireless channel. In particular, the interaction between TCP and RLP is of high interest.

Supported by Telia Mobile AB.

Analysis and Implementation of a Partially Reliable Transport Protocol for Multimedia Applications

In the current information age, computer networks such as the Internet provide a valuable infrastructure. As with any infrastructure, a continuous development of the Internet is required to meet the demands of emerging applications in areas such as multimedia. One general approach to meet the quality of service requirements of new applications is to adapt higher layer protocols to enhance and deal with the best-effort service provided by the underlying network in new ways. To this end, we have developed a partially reliable transport protocol called PRTP. PRTP allows applications to trade reliability for latency by letting the application control the reliability level provided by the protocol. For easy integration with the current networking infrastructure, the initial version of PRTP has been designed as an extension to TCP. PRTP has been implemented both in Linux 2.2.14 and in the ns network simulator. As an example application for PRTP, an image recoding proxy system has also been developed. The proxy system is designed to provide faster web surfing over low bandwidth/high delay links such as wireless connections.

Supported by Ericsson Infotech AB.