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<TITLE>RE: [AG-TECH] Alternative mechanism for telco bridging</TITLE>
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<P><FONT SIZE=2>In case anyone would like one more option for telco bridging, we've had a lot of success with the ASPI EF2280 Vortex in conjunction with the ASPI EF200 telco unit. We haven't yet used our nodes extensively with telephone bridging yet, but in general we've found the ASPI products do a better job and easier to configure than their Gentner counterparts. The mic inputs on the Vortex also do a great job with automatic gain control, which makes it very easy to configure for appropriate line levels. Anyone out there who's looking for a better echo cancellation solution, with telco bridge or otherwise, might want to give it a look. You can find more info or sales reps on at www.polycom.com. </FONT></P>
<P><FONT SIZE=2>-Andrew </FONT>
</P>
<P><FONT SIZE=2>-----Original Message-----</FONT>
<BR><FONT SIZE=2>From: Robert Olson [<A HREF="mailto:olson@mcs.anl.gov">mailto:olson@mcs.anl.gov</A>]</FONT>
<BR><FONT SIZE=2>Sent: Tuesday, September 03, 2002 5:44 PM</FONT>
<BR><FONT SIZE=2>To: ag-tech@mcs.anl.gov</FONT>
<BR><FONT SIZE=2>Subject: [AG-TECH] Alternative mechanism for telco bridging</FONT>
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<BR>
<P><FONT SIZE=2>See <A HREF="http://www-unix.mcs.anl.gov/~olson/AG/TelcoBridging.html" TARGET="_blank">http://www-unix.mcs.anl.gov/~olson/AG/TelcoBridging.html</A> for this </FONT>
<BR><FONT SIZE=2>document. I set this up in the ANL Workshop node last week for a meeting, </FONT>
<BR><FONT SIZE=2>and it worked quite well.</FONT>
<BR><FONT SIZE=2>--bob</FONT>
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<P><FONT SIZE=2>--------------------------------------------------</FONT>
</P>
<P><FONT SIZE=2>Alternative Telephone Bridging Solution</FONT>
</P>
<P><FONT SIZE=2>The standard mechanism used in the Access Grid for telephone bridging - </FONT>
<BR><FONT SIZE=2>using the Gentner matrix to configure a three-way link between room audio, </FONT>
<BR><FONT SIZE=2>network audio capture PC, and telephone interface - has some serious </FONT>
<BR><FONT SIZE=2>usability problems. Most serious is that obtaining an ideal balance of </FONT>
<BR><FONT SIZE=2>levels between the three audio realms can be quite difficult, and simple </FONT>
<BR><FONT SIZE=2>adjustments (say to the local microphones) can have undesired consequences </FONT>
<BR><FONT SIZE=2>on telephone audio levels.</FONT>
</P>
<P><FONT SIZE=2>An alternative mechanism dedicates an audio card and instance of the rat </FONT>
<BR><FONT SIZE=2>audio capture tool to the telephone interface. In this configuration, a </FONT>
<BR><FONT SIZE=2>second audio capture PC (this can be the Display Machine in a standard AG </FONT>
<BR><FONT SIZE=2>node, if it has an audio card) is connected to the Gentner in the same way </FONT>
<BR><FONT SIZE=2>that the standard audio capture PC is. It can use the second audio channel </FONT>
<BR><FONT SIZE=2>on the Matchmaker MM100 if the node is not configured for stereo </FONT>
<BR><FONT SIZE=2>connections; otherwise, it is recommended that a second MM100 be installed.</FONT>
</P>
<P><FONT SIZE=2>The Gentner matrix is then set up as follows. I assume below that the </FONT>
<BR><FONT SIZE=2>display computer has been attached to the Gentner for telco bridging purposes.</FONT>
</P>
<P><FONT SIZE=2><Table deleted for email purposes,see the webpage></FONT>
</P>
<P><FONT SIZE=2>In other words, the telco and display computer are interconnected, and the </FONT>
<BR><FONT SIZE=2>audio capture and the room audio (speakers and microphones) are </FONT>
<BR><FONT SIZE=2>interconnected. The telco is completely independent of room audio and the </FONT>
<BR><FONT SIZE=2>audio capture computer. If you have the telco output routed to the echo </FONT>
<BR><FONT SIZE=2>cancellation reference output, remove that routing (as that audio will not </FONT>
<BR><FONT SIZE=2>directly appear in the room audio and this setting will likely confuse the </FONT>
<BR><FONT SIZE=2>echo cancellation).</FONT>
</P>
<P><FONT SIZE=2>We install rat on the display computer (I did this by copying from a </FONT>
<BR><FONT SIZE=2>separate computer which had the PIG software installed. It is recommeded to </FONT>
<BR><FONT SIZE=2>use the rat that comes with the PIG because the stock Windows rat will </FONT>
<BR><FONT SIZE=2>introduce a roughly 1-second latency). In my testing I invoked the Windows </FONT>
<BR><FONT SIZE=2>rat by hand with the proper address; however, it should be possible to </FONT>
<BR><FONT SIZE=2>install the arm-eventlistener from the PIG software suite on the display </FONT>
<BR><FONT SIZE=2>machine as well. I have not tested this, however. The command looks like this:</FONT>
</P>
<P><FONT SIZE=2>rat -t 127 <ipaddress>/<port></FONT>
</P>
<P><FONT SIZE=2>You can find <ipaddress> and <port> from the arm-eventlistener window on </FONT>
<BR><FONT SIZE=2>the audio capture machine if you are running rat by hand.</FONT>
</P>
<P><FONT SIZE=2>Once this rat is up and running, you should be able to connect to a </FONT>
<BR><FONT SIZE=2>telephone call as usual, and see incoming level on the display machine rat </FONT>
<BR><FONT SIZE=2>when there is audio coming from the telephone. When network audio comes in, </FONT>
<BR><FONT SIZE=2>you should hear this audio on the telephone line. Note that in this </FONT>
<BR><FONT SIZE=2>configuration, the audio from the local room is network audio from the </FONT>
<BR><FONT SIZE=2>point of view of the telephone interface. This makes setting telephone </FONT>
<BR><FONT SIZE=2>levels much easier - the telephone audio you hear in your node is exactly </FONT>
<BR><FONT SIZE=2>the telephone audio that others will hear. I advise turning off silence </FONT>
<BR><FONT SIZE=2>suppression on the telephone audio rat. Adjust the levels on that rat for </FONT>
<BR><FONT SIZE=2>comfortable audio levels to and from the telephone (you will likely have to </FONT>
<BR><FONT SIZE=2>get feedback from the people on the telephone as to what an appropriate </FONT>
<BR><FONT SIZE=2>level is for them to listen to).</FONT>
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