Point to Point Tunneling Protocol (PPTP)

Point to Point Tunneling Protocol (PPTP) is a multi-protocol virtual private network network technology, it works on the second floor. Through the agreement, the remote users through Microsoft Windows NT Workstation, Windows xp, Windows 2000 operating systems and windows2003 with Point to Point Protocol, and other secure access to corporate network systems, and can even dial into a local ISP, secure link to the company through the Internet network.
PPTP protocol assumes the PPTP client and PPTP server and available connectivity between the IP network. So if the PPTP client is already an integral part of IP network, then you can through the IP network connection with the PPTP server to obtain; and if the PPTP client has not yet connected to the network, such as in the case of Internet dial-up users, PPTP client must First call the NAS to establish IP connectivity. PPTP clients are talking about here is using the PPTP VPN protocol client, and PPTP server using the PPTP protocol which VPN server.
 PPTP can only be implemented through the PAC and PNS, the other system does not need to know PPTP. Dial-Up Networking can be connected with the PAC without needing to know PPTP. Standard PPP client software can continue to operate in the tunnel PPP link.
PPTP uses an extended version of GRE to carry user PPP packets. These enhancements allow for the PAC and the PNS of the tunnel between the user data transmission to provide low-level congestion control and flow control. This mechanism allows efficient use of available bandwidth and the tunnel to avoid unnecessary retransmission and buffer overflow. PPTP does not provide specific algorithms for low-level control, but it does define some communication parameters to support the work of such an algorithm.
 PPTP control connection packet includes an IP header, a TCP header and the PPTP control information.
Applications
When using VPN can use the PPTP protocol, you can also use the L2TP protocol, the specific setting is as follows: for example, in Windows XP, the first in the "Network Connections" window, right-click a VPN connection, select "Properties." Next, open the properties window, select "Network" tab. Then in the "VPN Type" select "PPTPVPN", click "OK" button.