Hi, Yes the application is using TLS when the default transport is set to UDP. The client is a Windowsce.net application. Experts, please help me understand why i can register on ser using TCP but when i use the default transport type (UDP), the application tries to send on port 5061. Is this something ser can fix or is the problem specific to the application. The client application is based on RFC2543 but i am able to register using TCP on ser. Please help. Thanks in advance. Annie