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The main difference between an
application and an applet form, apart from the obvious fact that
the applet might be run from a web browser, is that with the
applet an end user cannot take advantage of a built-in video
player to view films. Such a constraint comes from the security
restrictions introduced into Java VM: an applet cannot receive
any data that comes from the host different to the one the
applet has been dowloaded. In the SVDA system it is common that
a video server that streams data is not the computer that hosts
an applet bytecode - and so the constraint is in force. Security
limitations for an application form of Java programs are much
weaker. That is why it is possible to make use of the whole
functionality of the system without running any other
externals.
In the case of the applet it is
necessary to start additional application - Java Media Framework (JMF)
Player. The player can be specified with an IP address that
video is distributed to (the one ordered using the client
application). It is capable to play MPEG-1 video streams at
Solaris 2.5, 2.6 and 2.7 operating system. The version for
Microsoft Windows is being developed.
All the clients reported below are useful only when a user has an access to an already working SVDA system. It is possible to use the implementation that is working on the local (in the cs.agh.edu.pl domain) servers either through the applet start page or by downloading a proper piece of software. In order to connect to the local servers a user has to specify as login parameters:
player netdoc://address:port/mpg
where:
address - local or multicast address where a movie is being received
port - the port number for receiving data
In order to run the Media Stream Manager server we must run msm_server application. The command line arguments, written on the standard output when msm_server is started without any arguments given, must be specified.
There is a helper script named msm_run that makes it easier to start a server. The script contains thorough description for each of the parameters that must be present in the command line.
In order to run the Content Manager server we must run vfs_server application. The command line arguments, written on the standard output when vfs_server is started without any arguments, must be specified.
There is a helper script named vfs_run that makes it easier to start a server. The script contains thorough description for each of the parameters that must be present in the command line.
In order to run the Archive server we must run as_server application. The command line arguments, written on the standard output when as_server is started without any arguments, must be specified.
There is a helper script named as_run that makes it easier to start a server. The script contains thorough description for each of the parameters that must be present in the command line.
The archive server requires that a configuration file name is specified in the command line. The configuration file is a text file so it can be created with a simple text editor, like vi. Each line of the file must contain the following information:
In order to run the main SVDA server we must run svda_server
application. The command line arguments, written on the standard
output when svda_server is started without any arguments,
must be specified.
Moreover, the program takes an advantage of the environment and
the configuration file.
Two environment variables must be set:
VFS_HOME - must point to the directory that contains the
configuration file.
NS_IOR_FILE - must point to the file that contains the IOR of
a OrbixNames daemon that all the servers registers with.
The configuration file contains information that allow to tune
the way the system work. It is a text file. It must be named
main_server.conf and be placed in $VFS_HOME
directory. The file contains the following information (each
parameter per one line):
lock_interval - the system uses this value to determine
when it has to lock a film instance which is about to be
played. That means if it is lock_interval or less seconds to the
play time, the film is locked.
request_timeout - requests stays in a queue for this
number of seconds after its time passed.
time_function_type - the function calculating time
priority of files. Possible values are GAP, ARCTG and
LINEAR.
gap_height, gap_position - two parameters used by GAP
function. Otherwise they have no meaning. They have to range
from 0 to 1 (non-inclusive).
threshold - this value determines what is the minimum
difference between a file already stored on a video server and
the new one, which is to be stored, to actually remove the first
one. It also has to be between 0 and 1.
already_stored_bonus - a video server on which a
requested film is already downloaded increases its priority
(when searching for the best server to download this film) by
this value. It has to range from 0 to 1.
maximum_lock_time - this value determines what is the
maximum time (in seconds) during which a file can remain
locked. After that time lock is removed.
All parameter listed above have their default values. They are used when the configuration file is missing or corrupted. The file must be changed with caution because it is not very error proof.
The etc/main_server.conf file is an example of the configuration file.
There is a helper script named svda_run that makes it easier to start a server. The script contains thorough description for each of the parameters that must be set up.
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