DISCO - Research Projects
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.
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.
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
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.
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.
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.