Microsoft KB Archive/841892

= PRB: You may not be able to establish an SIP session with audio between RTC clients =

Article ID: 841892

Article Last Modified on 5/20/2005

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APPLIES TO


 * Microsoft Visual Studio .NET 2003 Enterprise Architect
 * Microsoft Visual Studio .NET 2003 Enterprise Developer
 * Microsoft Visual Studio .NET 2003 Academic Edition

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SYMPTOMS
When you work with a Real-time Communications (RTC) client, you may not be able to establish a Session Initiation Protocol (SIP) session with audio, with another RTC client.



CAUSE
This behavior may occur if one of the following conditions is true:
 * The audio capture device (sound input) or the audio render device (sound output) does not support the audio format that RTC requires. Audio devices that must work with RTC should support 16 kilohertz (kHz) 8-bit mono Pulse Code Modulation (PCM), and 8 kilohertz (kHz) 8-bit mono PCM. The following list describes the RTC-supported audio formats for Microsoft Windows XP and Microsoft Windows 2000.
 * RTC on a computer that is running Windows XP and later opens the devices for 16 kilohertz (kHz) 8-bit mono PCM.
 * RTC on a computer that is running Microsoft Windows 2000 opens the devices for 8 kilohertz (kHz) 8-bit mono PCM.
 * If Acoustic Echo Cancellation (AEC) is enabled, the render device does not open if it the render device is in use. This is a limitation of Microsoft DirectSound.

Typically, multiple applications can open the render device at the same time. However, if system sounds, or an application such Microsoft Windows Media Player plays audio sounds without AEC, and RTC tries to open the device with AEC, the attempt to open the device with AEC fails. RTC then negotiates a half duplex call instead of a full duplex call.

Important Make sure that RTC applications do not intentionally cause interaction problems (such as playing &quot;ringing&quot; sounds) when calling RTC applications. Also, turn system sounds off, and temporarily pause media applications.



WORKAROUND
If the problem is caused by AEC, you can turn off the AEC in RTC applications, and instead use headset and microphone combination for audio.

Keywords: kbinfo KB841892

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