Telephony and Conferencing

Users of H.323 or multicast conferences might encounter problems connecting with other users or receiving audio or video.

Audio problems in conferencing applications

If audio problems occur in H.323 or multicast video conferences, the microphones or sound cards on the client computers might be incorrectly configured or malfunctioning.

To diagnose sound hardware on Windows 2000 Professional computers, start the Sound Recorder application by clicking Start , pointing to Programs , Accessories , Entertainment , and then clicking SoundRecorder , or by typing sndrec32 at the command prompt. Make a recording of your own voice using Sound Recorder, and then play it back. If there is no sound, check if the microphone is properly plugged in.

If the Sound Recorder test works properly but you continue to have audio problems, verify the sound settings using Volume Control.

To verify sound settings through Volume Control

  1. Click Start , point to Programs , point to Accessories , point to Entertainment , and then select Volume Control .

  2. In the Volume Control dialog box, select Options , Properties , and then click Playback . Make sure that the Wave and Microphone check boxes are selected. You might have to scroll the window in order to see these settings.

  3. Click OK .

  4. Select the Mute check box in the Microphone column if it is not checked. This prevents speech from being echoed locally (played back on the speakers computer).

  5. If the voices of all other conference participants are too loud or too quiet, adjust the Volume Control and/or Wave sliders downward or upward as needed.

  6. Select Options,Properties , and then click Recording . Select all of the check boxes in the window at the bottom of the dialog box. (You might have to scroll the window in order to see these settings.)

  7. Click OK .

  8. Select the Mute check boxes in all of the columns except for the Microphone column if they are not already checked. Make sure that the Mute check box in the Microphone is left unchecked. This allows your speech to be sent to the conference, but prevents other sounds, including those of other conference participants, from being transmitted from your computer.

  9. If other conference participants are dissatisfied with the level of sound, adjust the Microphone slider downward or upward as needed.



A single incorrectly configured computer can cause audio problems or echoes for all other conference participants.

If you continue to encounter audio problems after adjusting the sound settings, check if the affected computers have full-duplex sound cards. Full-duplex sound cards are capable of capturing and playing audio simultaneously, while half-duplex sound cards can only do one at a time. Most modern sound cards are full-duplex, but many older sound cards are only half-duplex.

To check if the sound card on your computer supports full-duplex audio, start Sound Recorder and record a speech sample for approximately 30 seconds. After this is complete, open a second instance of Sound Recorder. Play the sample you recorded using the first instance of Sound Recorder, and while this is playing, attempt to record a sample using the second instance of Sound Recorder. If the second instance of Sound Recorder is unable to properly record a sample while the first instance is recording, the sound card does not support full-duplex audio, and thus does not work with TAPI.

If sound is distorted or otherwise continues to malfunction after you attempt the above procedures, there is most likely a problem with the microphone, sound card hardware, or sound card driver. Check with the manufacturer of your sound cards to ensure that you are using the most recent Windows 2000 drivers. Also, replace the microphones and sound cards on affected computers and attempt these tests again.

Eliminating audio echo

Audio echo is a common problem with audio conferencing systems. Echo can originate in the local audio loop-back that happens when a users microphone picks up sounds from their speakers and transmits it back to the other participants. Normal conversation can become impossible for other participants in the conference when sensitive microphones are used, speaker level is high, or the microphone and speakers are placed in close proximity to each other.

One of the easiest ways to completely eliminate audio echo is to use audio headsets. These work by eliminating the possibility of a users microphone picking up sound that is being received from other conference participants.

A more expensive solution is to use special microphones with built-in echo-canceling capabilities. These microphones detect and cancel out echo. The main advantage to these is that users do not have to wear headsets. Echo-canceling microphones are also a necessity for conference rooms because using headphones is not a practical solution.

Video problems in conferencing applications

If the video image of an H.323 conference participant cannot be seen by the other party, or if the image of a multicast conference participant cannot be see by all of the other endpoints, the computers video capture device might not be working properly. When using Phone Dialer, participants should be able to see their own video image whenever they participate in videoconferences. If this is not the case, run the camera troubleshooter included in Windows 2000 Help.

Audio and video problems in multicast conferences can also be caused by multicast issues. The following section describes how to diagnose these problems using the MCAST tool included in the Microsoft Windows 2000 Professional Resource Kit .

Verifying network is configured for multicast packets

If you are uncertain whether your network is configured to send and receive multicast packets, use the MCAST diagnostic tool. MCAST can send and receive multicast packets, helping you to determine which parts of your network are enabled for transmission of IP multicast packets. MCAST is supplied with the Microsoft Windows 2000 Professional Resource Kit . Install MCAST on the computer in question.

You can use MCAST in send mode to set up multicast sources at different locations on your network, and in receive mode to determine the locations at which multicast traffic from these sources is being received.

The following example shows MCAST being run as a multicast sender, on a Windows 2000 Professional–based computer:


MCAST will start sending multicast packets from the IP address to the multicast group IP address at the rate of 1 packet per every 1000 milliseconds. A total of 3600 packets will be sent over a one-hour period.

To run MCAST as a multicast receiver, use a command-line as follows:


MCAST will start listening for multicast packets on the IP address for the multicast group IP address Received packets are displayed on the screen:

Started.... Waiting to receive packets...

Received [1]: [GOOD] SRC- GRP- TTL- 5 Len- 256

Received [2]: [GOOD] SRC- GRP- TTL- 5 Len- 256

Received [3]: [GOOD] SRC- GRP- TTL- 5 Len- 256

Received [4]: [GOOD] SRC- GRP- TTL- 5 Len- 256

Received [5]: [GOOD] SRC- GRP- TTL- 5 Len- 256

Unable to publish multicast conference invitations

If you are unable to publish multicast conference invitations, confirm with your network administrator that the Site Server ILS Service is available at your site. The Site Server ILS Service is an essential component of TAPI IP Multicast Conferencing. This server represents the meeting place where conference creators and participants go through their client software application to find the information they need to participate in a conference.

Windows 2000 Phone Dialer cannot see ILS

The Windows 2000 Phone Dialer application must know the location of the Site Server ILS Service to provide conference creation and joining facilities.

The Phone Dialer application can locate this information in Active Directory directory service if the following conditions are fulfilled:

  • The computer running the Phone Dialer application is part of a Windows 2000 domain.

  • The user is logged on using a Windows 2000 domain account.

  • The ILS server location is published in Active Directory.

Using Active Directory in this way means that users do not need to know the location of the ILS server on their network or manually enter that information into their Phone Dialer application. This makes using IP Multicast Conferencing with Windows 2000 easier for the user.

Computer or user cannot access Active Directory

All of the components required to support TAPI Multicast Conferencing on a client computer are installed by default in Windows 2000 Professional. However, in order for a computer or a user to use TAPI Multicast Conferencing, they need to be added to a Windows 2000 domain. If computer or user accounts for Windows 2000 domain are not created, users cannot access Active Directory directory service and will need to add their ILS servers to the Phone Dialer application manually.