This update resolves several issues in the Windows Messenger Client and eliminates popping sounds coming from the speakers. It also enables users of the Voice.Net service to reach the telephony service from behind Network Address Translators (NATs).
Real-Time Communication (RTC) client communications may not work if the client is located behind a Network Address Translation (NAT) device. The hotfix that is described in this article enables NAT-aware programs to configure the RTC API to use the correct address and port when it sets up the audio or video streams. After you install this hotfix, clients that are located behind the NAT device can use audio and video communications with other clients or gateways that are located outside the NAT device. Note that this hotfix does not help clients that are located behind a NAT device to connect to the Session Initiation Protocol (SIP) server.
This hotfix does not enable Microsoft Windows Messenger clients that are located behind a NAT device to use audio and video with each other. However, the hotfix does enable Windows Messenger clients that are located behind a NAT device to communicate with phone gateways.
News source: Windows XP Patch: Windows Messenger Update (19th February 2002)
View: Windows XP Real-Time Communication Client Support (Q316397) (25th February 2002)