Android PPTP VPN connector

I need to make an Android VPN client for our VPN users to replace the default Android system settings UI. It shall be an app that provides a one click to connect to our VPN server. All network traffic is then routed through the app and the VPN tunnel. The VpnService API in Android 4.x provides the vpn tunneling. There is a good example program called ToyVpnClient from google. The work is to implement the PPTP protocol that will manage the connection to the VPN server. The following is the specification: 1. Protocal: PPTP; Android version: 4.x 2. just the function, no need to design pretty UI 3. There are 3 input fields on the UI: server IP addr, username and password; 1 checkbox "encrypt"; 1 button "connect". Once user click the button, all his internet access will go through VPN. no need root. 4. Stable surfing the internet 5. I need the complete and readable source code of java for it. To bid on the project , you need to prove you do have the skill needed for this project, especially the knowledge of PPTP protocal.