ntp client creating and requesting the time.

I want to have the ntp client which can request the time.

I want to achieve some thing lik this.

I have two ntp servers say ip 172.16.1.3 and port 1043 and 2ed Ip is 172.16.1.4 port number 1044.

case 1.  i want to switch between the servers with some time out if no response from the servers.

                  which function to use for to check connection and which function to receive the time?

case 2. i have servers which uses different port numbers how specify the server port when client initiating the request to ntp server.