User Registration

Hi,

We are developing a SIP based Messenger like Skype by modifying the SIP
Communicator(Old version).

We are facing problems in the User Registration.

Here, we are using VOCAL server as the SIP Server. We connected the server
in the LAN.
The SIP Client is able to interect with the VOCAL Server.

At present, we are creating the User accounts in the server manually. we are
working on
creating the User accounts dynamically by the user.

we are unable to communicate with the VOCAL Server for registering the User
details (like User name, password,..)

My Doubts are,

1. is it possible to registering the user accounts dynamically in the VOCAL
Server..?

2. Are there any difficulties to achieve this..?

3. what are the necessary things we have to do to achieve the User
Registration..?

4. Are there any alternatives to achieve this..?

5. any related technologies to do this..?


I am waiting for your reply.

regards,
Gokulakrishnan.M