Recording AG Sessions

... a virtual community

The Voyager multimedia server, developed at ANL, provides us with the ability to record and playback multicast audio and video streams. We would like to begin recording some of our AG sessions. In order to record them, ALL machines that contribute audio and video streams to the AG must be time synched relative to each other. The way to do this is to install and run an NTP client on each machine, which synchronizes according to Coordinated Universal Time.

Finding a Time Server

You will need to find one or more NTP servers in order to use NTP. The first place to check will be your local campus networking people. It is likely that they are already running an NTP server that you can use. They may also be able to supply you with a configuration file for unix NTP.

If your campus does not run supply NTP service, look at the configuration notes on the NTP website at http://www.eecis.udel.edu/~ntp/ntp_spool/html/notes.htm. It would be best to set up a local time server that synchronizes with one or more Stratum 2 network time servers and provides time service for the other local machines.

If you cannot find a local time server, you can use the server at ntp-1.accessgrid.org. Please send a note to ag-mcs@mcs.anl.gov to let us know you are using the server. It would be best to set up your site to have a single machine poll this server and have the other machines on site poll your local server machine.

Installing NTP on Linux

The standard AG RedHat distribution comes with the NTP client xntp3 installed. Check the configuration file /etc/ntp.conf to verify the name of the NTP server.

To ensure that NTP will start as boot, run this command as root:

/sbin/chkconfig xntpd on

To start NTP without having to reboot the machine, run this command as root:

/sbin/service xntpd start

If the xntpd service is not found, you can install it from the RedHat distribution. Mount the RedHat cdrom, and go to the directory /mnt/cdrom/RedHat/RPMS (assuming it is mounted on /mnt/cdrom). As root, run this to install xntp:

rpm -v -i xntp3*rpm

Installing NTP on Other Platforms

For those of you who are not up-to-spec, clients for other platforms available, many of which can be found at http://www.eecis.udel.edu/~ntp/software.html.

In order to accurately record media streams generated by multiple machines, all machines must have NTP clients running! Please install and run an ntp client on all video and audio machines asap! We also encourage you to install NTP clients on the display and control machines (this will become more important in the future).

If you're interested, a general explanation of network time synchronization can be found at http://www.eecis.udel.edu/~ntp/ntp_spool/html/exec.htm.