goal of the MEDIS project is a technology demonstration of several
key technologies for multimedia satellite services including Ka-Band
links, optical intersatellite links, ATM switching technology, a small
bus platform and others.
The part of Fraunhofer Fokus is the specification and realisation
of experiments showing the feasability of multimedia communication
over this platform. Fokus concentrated on the lower layers of the
communication stack from the physical layer up to the transport
Test scenarios have been specified in several steps: verification
of link characteristics, end-to-end measurements and hand-over.
The link verification step aims at measuring the characteristics
of the links (ground-satellite, satellite-ground, satellite-satellite)
that influence higher level protocols (AAL5, IP, TCP, ...). Among
the characteristics are bit error rate, error distribution, delay,
delay jitter, cell mis-insertion rate and others. These characteristics
are measured on the ATM layer.
The end-to-end measurement step measures the performance of some
critical protocols like AAL5, IP, TCP, NTP and others and compares
the theoretical performance as expected on basis of the link characteristics
with the measured performance. The interesting point in these measurements
is the time variance of the link characteristics and how the different
protocols are able to cope with this (the satellites are MEO's).
The next step is the testing of handovers from one satellite to
another one. Whether this is possible or not depends on the actual
parameters of the Ka-band channel and the ground station antennas,
so at this point it is not clear whether this will be possible or
One outcome of the work in this project is the follow-up activity