InPerson sends audio and video data across the network. As a result, network traffic may increase significantly. This chapter covers:
This section includes:
In InPerson, network congestion, certain control panel settings, bandwidth, and compression are all interrelated. See Figure 2-1 for an illustrated overview of this, including the distinction between choices you can make and actions performed by InPerson
|Tip: Click on this figure to bring up an expanded, printable view of it.|
|Note: Figure 2-1 shows the Call Control Panel with the Finer Control section displayed. When you first bring up this panel from InPerson, it is not in this form. To expand it to this form, click Finer Control button.|
InPerson uses a network congestion algorithm to ensure that the video data doesn't burden the network excessively. Table 2-1 shows how the network condition is measured by packet loss. Every ten seconds, InPerson looks at the packet loss for each conference participant; it uses this information to determine the state of the network, and displays the network state on the Network Info panel (see “Monitoring Network Congestion and Compression”). If a network is congested, InPerson updates this information every second; if the network is underloaded, InPerson updates the information every 15 seconds.
< 1.0% packet loss
1.0% to 5.0% packet loss
> 5.0% packet loss
overloaded or congested
|Note: The congestion control algorithm monitors only the packet loss of people participating in a conference. If the multicast packets are forwarded to other networks, and those networks experience packet loss, InPerson will not notice. To solve this problem, change your network so that multicast packets are not forwarded needlessly. See “Adjusting the Network TTL Setting” for instructions on one technique.|
The algorithm looks at the number of packets that are lost during transmission due to network traffic. It excludes any packets that are lost on the local workstation, as a result of an overloaded system.
Periodically, InPerson transmits the congestion information to all conference participants. If any system in the conference reports a congested network, InPerson decreases the bandwidth. This can affect the frame rate, image, and sound quality. The video and audio compression algorithms may also change in response to a change in bandwidth. If network conditions don't improve, InPerson cuts bandwidth by two-thirds again. This occurs every 15 seconds. If network conditions improve, InPerson gradually increases the bandwidth—up 15 percent every 15 seconds.
There are a few different compression schemes that InPerson uses for playing video and audio. These are set to change in response to three things:
the selected performance preference
the selected bandwidth limit
network congestion, which overrides bandwidth limit settings
|Note: You can see exactly how InPerson is programmed to use compression by looking at the compression tables, located at the bottom of your /usr/lib/X11/app-defaults/InPerson file.|
At any time, you can open the Network Info panel and view a current reading of the network's congestion state and usage, frame rate, and compression schemes. See Figure 2-2.
Open this panel in either of the following ways:
Select “Network info panel...” from the Tools menu.
Click on the Network Info button in the Call Control Panel.
Check to see the congestion state: Underloaded, Nominal, or Congested. In this example, the network is underloaded. If the network becomes overloaded, InPerson automatically reduces the frame rate and degrades the image quality. See “Lessening the Network Load” to learn ways in which you can further reduce the amount of resources that InPerson consumes. See “Changing the Network Congestion Algorithm” for information about the algorithm that InPerson uses to determine whether the network is congested.
|Note: A network administrator can more closely monitor network traffic using NetVisualyzer™, an optional software product from Silicon Graphics. NetVisualyzer includes traffic monitoring, diagnostics, planning, and performance analysis tools that provide network information and statistics for Ethernet or FDDI networks.|
|Caution: You should thoroughly understand the operation of the InPerson congestion control algorithm and the behavior of your network before altering the network congestion algorithm.|
“Managing InPerson's Use of Network Bandwidth” explains how InPerson monitors network use and automatically adjusts video settings if the network becomes congested. This section describes a change you can make to the algorithm.
InPerson reports that a network is congested if a participant loses more than 5 percent of the packets. You can change the percentages to suit your network. To change these settings:
As root, edit the file /usr/lib/X11/app-defaults/InPerson
Find these two lines:
*congestionMaxUnloadedLossRate: 100 *congestionMaxLoadedLossRate: 20
The first line specifies that the network is unloaded if less than one packet out of 100 is lost; the second line specifies that the network is congested if more than one packet out of 20 is lost.
Enter different numbers; then save the file.
Transmitting audio and video from one system to another makes significant use of the network. You can reduce the amount of data being sent by doing the following:
If you are in a fairly noisy environment, you should lower your audio input level so that audio data is not sent needlessly over the network. For example, if there is a fan on near your workstation, the microphone will pick up that sound during a conference. Thus, audio will be sent over the network even when you are not speaking. Lowering the audio input level will lower the audio network traffic, which could also improve the overall audio quality.
To lower the audio input level:
Pull down the Tools menu and choose “Audio control panel...”. Move the Input sliders down, which will reduce the level of audio you are sending. If you still want conference participants to hear you, don't turn it all the way down.
To prevent video data from being sent across the network, choose “Freeze Video” from the Call menu or click the Freeze Video button along the left edge of the window. (See Figure 2-3.) You stop transmitting video data; your image becomes static.
|Note: You can also choose to use a static image, instead of live video, for all of your calls. For instructions, see “Using a Static Image Instead of Video.”|
You can limit network use by telling InPerson to reduce the maximum frame rate. The frame rate specifies how many frames (images) are transmitted per second. A higher frame rate gives you a fluid image; a lower frame rate gives you less fluid (intermittent) motion. By default, InPerson sets the rate 12 to 15 frames per second. See “Managing Network Bandwidth Use Via the Application Defaults File” for information on using your app-defaults file to make this change.
This section describes how to make such a change using the InPerson control panel. See also “Managing Network Bandwidth Use Via the Application Defaults File.”
The amount of information that InPerson sends across the network (that is, the bandwidth) determines the quality of the image that other people see. In general, a higher setting produces a better image; a low setting causes the image quality to deteriorate.
|Note: The video image may look different at different points on the bandwidth scale because InPerson changes compression schemes as you move the slider up and down.|
To limit the amount of network resources that InPerson consumes:
Place the cursor over the phone; then hold down the right mouse button. A popup menu appears.
Select “Call Preferences... .” The Call Preferences window appears.
Click the small button next to the label Finer Control, to open the lower section of the window.
Use the slider above Bandwidth Limit (kbit/sec) to lower the amount of information that InPerson sends.
|Note: To return to the default setting, click on the Network Bandwidth button again.|
Click the OK button to apply the change to the next call. To use this setting as default for all future calls, click Save then click the OK button.
|Note: If you want to change the bandwidth limit during a call, select the “Call control panel...” from the conference window Tools menu. You can make the same adjustments on this panel.|
InPerson specifies a multicast time-to-live (TTL) setting of 10. This means there can be no more than 10 multicast routers or tunnels between any two participants in a conference. A network administrator might want to adjust this setting under the following conditions:
The network is large and contains more than 10 routers. Increase the number so that people are able to conference with each other.
People using InPerson are restricted to a small area of the network. Reduce the number so the multicast packets are only sent to networks that need them.
To adjust the setting:
Edit the file $HOME/.desktop-<hostname>/InPerson on each user's system.
Edit the line that beings with *multicastTTL and ends with the number of routers through which you want the packets to travel. For example, if you want to limit the packets to 8 routers, add the line:
|Note: Be careful not to set the number too high. People who are using InPerson should receive the multicast packets; people who aren't using InPerson should not receive the multicast packets unnecessarily.|
To make this change apply to all users on the system, change the line in the file /usr/lib/X11/app-defaults/InPerson instead of in your local InPerson file.
Previous sections explained how InPerson users can choose settings that lessen network use during a call. System administrators might want to specify default settings for their site; then copy these settings onto each InPerson user's system.
Edit the file /usr/lib/X11/app-defaults/InPerson on each user's system. Changes you make to this file apply to all users on the system. To make sure that the changes only apply to you, it is recommended that you make a copy this file for your own customization editing. The filename must be InPerson. You should put it in the directory ~/.desktop-<hostname> (where <hostname> is the name of the system).
Read the comments at the beginning of the file to see which settings you can customize. Here are three of the resources that you can set:
Lets you specify the maximum frame rate to capture and send.
Lets you choose from several different compression schemes with different sampling rates. Note that the audio quality deteriorates with a lower sampling rate. Table 2-2 lists the compression algorithms from which you can choose.
|Note: See the InPerson man page, inperson(1M), for more details on the resources.|