[AG-TECH] Alternative mechanism for telco bridging

Mike Weaver - MICS/USDOE weaver at er.doe.gov
Wed Sep 4 06:04:01 CDT 2002

Hey Bob!

Thanks for writing this up so quickly.  As you (& Mary) know we've had quite
a lot of difficulties w/ telco bridging in the past and even the Gentner
(now ClearOne) techs haven't had much luck.  This setup worked really well
the other day!  Levels were easy to set and echo/feedback was almost
non-existent.  Even when we did experience a little bit of echo, it was so
negligible that it had no impact to the meeting or participants.

We'll be setting this up ASAP!

Thanks again!


----- Original Message -----
From: "Robert Olson" <olson at mcs.anl.gov>
To: <ag-tech at mcs.anl.gov>
Sent: Tuesday, September 03, 2002 17:44
Subject: [AG-TECH] Alternative mechanism for telco bridging

> See http://www-unix.mcs.anl.gov/~olson/AG/TelcoBridging.html for this
> document. I set this up in the ANL Workshop node last week for a meeting,
> and it worked quite well.
> --bob
> --------------------------------------------------
> Alternative Telephone Bridging Solution
> The standard mechanism used in the Access Grid for telephone bridging -
> using the Gentner matrix to configure a three-way link between room audio,
> network audio capture PC, and telephone interface - has some serious
> usability problems. Most serious is that obtaining an ideal balance of
> levels between the three audio realms can be quite difficult, and simple
> adjustments (say to the local microphones) can have undesired consequences
> on telephone audio levels.
> An alternative mechanism dedicates an audio card and instance of the rat
> audio capture tool to the telephone interface. In this configuration, a
> second audio capture PC (this can be the Display Machine in a standard AG
> node, if it has an audio card) is connected to the Gentner in the same way
> that the standard audio capture PC is. It can use the second audio channel
> on the Matchmaker MM100 if the node is not configured for stereo
> connections; otherwise, it is recommended that a second MM100 be
> The Gentner matrix is then set up as follows. I assume below that the
> display computer has been attached to the Gentner for telco bridging
> <Table deleted for email purposes,see the webpage>
> In other words, the telco and display computer are interconnected, and the
> audio capture and the room audio (speakers and microphones) are
> interconnected. The telco is completely independent of room audio and the
> audio capture computer. If you have the telco output routed to the echo
> cancellation reference output, remove that routing (as that audio will not
> directly appear in the room audio and this setting will likely confuse the
> echo cancellation).
> We install rat on the display computer (I did this by copying from a
> separate computer which had the PIG software installed. It is recommeded
> use the rat that comes with the PIG because the stock Windows rat will
> introduce a roughly 1-second latency). In my testing I invoked the Windows
> rat by hand with the proper address; however, it should be possible to
> install the arm-eventlistener from the PIG software suite on the display
> machine as well. I have not tested this, however. The command looks like
> rat -t 127 <ipaddress>/<port>
> You can find <ipaddress> and <port> from the arm-eventlistener window on
> the audio capture machine if you are running rat by hand.
> Once this rat is up and running, you should be able to connect to a
> telephone call as usual, and see incoming level on the display machine rat
> when there is audio coming from the telephone. When network audio comes
> you should hear this audio on the telephone line. Note that in this
> configuration, the audio from the local room is network audio from the
> point of view of the telephone interface. This makes setting telephone
> levels much easier - the telephone audio you hear in your node is exactly
> the telephone audio that others will hear. I advise turning off silence
> suppression on the telephone audio rat. Adjust the levels on that rat for
> comfortable audio levels to and from the telephone (you will likely have
> get feedback from the people on the telephone as to what an appropriate
> level is for them to listen to).

Mike Weaver
Sr. Network Administrator
SC-31/Germantown Building
US Department of Energy
1000 Independence Avenue, SW
Washington, D.C. 20585-1290
Voice: 301-903-0072
Fax: 301-528-2701
Email: weaver at er.doe.gov

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