Sample applications, concerning teleconferencing and
MPEG players have been developed on the HARTIK
kernel, where robust low-level drivers are available for the
most commonly used multimedia devices, such as sound
cards, frame grabbers and network cards. We are using these
applications for testing the effectivness of our
Bandwidth Reservation strategy and its effects on the QoS of a
multimedia stream.
In particular, we realized:
A telepresence application, as an example of distributed
multimedia system. A computer samples audio and video streams
sending them to a remote host (connected by an ethernet), that
receives the streams and plays them. Using a dedicated
CBS to serve the receiver task, we solve
the receive livelock problem: using general purpouse
operating systems, processing the incoming packets is a critical
activity and all the processing time can be spent in this activity,
otherwise packets can be lost. Using CBS, we can use an
event-driven process to manage packets from the network, enuring
that this process doesn't require too much CPU bandwidth. In
this way, only the packets that the application can play are
received (it is useless to receive all the packets, if doing so
the application have not time to run!!!).
A multimedia demo composed by some MPEG players, an audio task
mixing in real-time some different audio tracks, a control task and
some background tasks concerning graphical output. Using dedicated
CBS to serve multimedia tasks, we proved
that hard (control) tasks and soft (MPEG and audio) tasks can
coexist, and multimedia tasks' unpredicatbility does not influence
the hard tasks' schedule.
We are also considering the possibility to realize adaptive
applications, that can adjust their computational requirements in order
to not require more than the reserved bandwidth.
