how can i connect and disconnect to internet by exist connection in the c# ?
You can't using the standard definition of the terms you are using.
By definition if you close a connection it is done. It can't be used again.
Guessing what you might really want...
If you want the client box to have a single connection then you could connect to another server, and use it as an intelligent proxy to issue commands for you. So that server does the connect/disconnect and just redirects traffic to the client. But the server MUST exist for this to work.
If you are referring to a wireless/VPN/modem 'connection' via which your client app tunnels IP traffic then normally it stays up anyways. But if you want to control it explicitly because it is closing then you would need to get the API for that specific thing (wireless/VPN/modem) and control it yourself.
Last Visit: 31-Dec-99 18:00 Last Update: 23-Apr-14 22:32