One approach to tunneling is the Point-to-Point Tunneling Protocol (PPTP) developed by Microsoft and several other companies. The PPTP keeps proprietary data reasonably secure, even though part of the path(s) between or among end users exists in public communication channels. The PPTP makes it possible for authorized users to gain access to a private network – called a virtual private network (VPN) -through an Internet service provider (ISP) or online service. Another commonly used tunneling protocol is generic routing encapsulation (GRE), developed by Cisco Systems. There are numerous, less common tunneling protocols.
Tunneling, and the use of a VPN, is not intended as a substitute for encryption/decryption. In cases where a high level of security is necessary, the strongest possible encryption should be used within the VPN itself, and tunneling should serve only as a convenience.