A client that is behind a UPnP certified NAT device cannot log on to a to a server if your computer has only one SIP port specified (826284)

SYMPTOMS

If your computer is behind a network address translation (NAT) device such as a router or an Internet Connection Sharing computer that uses the UPnP service, and the static port range on your computer is set to use only one Session Initiation Protocol (SIP) port, you cannot log on to a server (such as a Microsoft Live Communications Server server) by using a real-time communications client (such as Microsoft Windows Messenger).

CAUSE

This issue occurs because two SIP ports are required when your computer is behind a UPnP certified NAT device.

SIP is a signaling protocol that is used to establish real-time communications sessions. To permit communication (sending and receiving data) between two computers, a port has to be opened on each computer. One of these ports is reserved for SIP traffic.

RESOLUTION

To resolve this issue, configure the computer that is operating behind the NAT device to grant a minimum of two SIP ports for signaling.

For more information about how to configure how the real-time communications client listens for incoming sessions, visit the following MSDN Platform SDK Web sites:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rtcclnt/rtc/irtcclient2_put_allowedports.asp
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rtcclnt/rtc/irtcclient_initialize.asp
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/rtcclnt/rtc/irtcclient2_initializeex.asp

For more information about using the Microsoft Real-Time Communications (RTC) Client API for Scalable Applications, visit the following MSDN Web site:

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnrtcclnt/html/use_rtcapi.asp