The PPTP VPN solution for avoiding VOIP block

2007-7-24

The PPTP VPN will make your VOIP service non-blocking and safe.

1. The normal VoIP Usage

FIGURE 1 The normal VOIP usage

General speaking, all terminals use their real IP address to register to the SIP proxy. All your information will be transferred nakedly on the Internet, so someone can easily steal your personal information. For example someone can easily intercept your packets and decode to original voice information and there is another problem as well. In some countries providing VOIP service is not allowed so you can not use VOIP services as the network providers blocked all your VOIP packets.

2. The SIP Proxy inside the PPTP

 FIGURE 2 Put all device in a PPTP VPN

In the above diagram there is a PPTP or L2TP VPN server on the Internet. All devices connect to the VPN server and receive a virtual IP address with a certain username and password. And the VPN server has its own virtual IP.

In the diagram GIP300 A uses virtual IP 10.10.0.11 to register to SIP proxy with IP 10.10.0.12. All the packets are sent to the VPN Server and then forwarded to its destination. All devices exchange information through the VPN network and all packets are encrypted. So it is safe to use VPN providing VOIP. Everyone must login to the VPN Server and then use your VOIP service. It is easy to control the network to reject someone who wants to destroy your service.

FIGURE 3 GIP300 and SIP Server all in a PPTP VPN

Furthermore there is another advantage by using VPN. As all the packets are encrypted no one knows what you transfer on the cable. So it is not easy to block your voice packets and service.

3. The SIP Proxy outside the PPTP

FIGURE 4 The SIP Proxy Outside the PPTP

In this strategy, the PPTP server work as a NAT router between the PPTP private network and the internet. The SIP Proxy can be any normal SIP Proxy, for example, the FWD proxy.

This strategy is mainly to solve the VOIP block problem. Because usually, the packet monitoring and block is working on access network, for example, the ADSL access network or the Dial-up access network. There is no block in backbone network. So, the packet from PPTP server to SIP Proxy is safe generally.

This strategy is very useful for some ITSP who can not put all the device including SIP Proxy and Median Gateway in a PPTP VPN.

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