e created between equivalently equipped sites, regardless of the type or ownership of the public network between the sites (for example, X.25 or frame relay). Soon the effort was expanded to layer 3 devices, which would offer the same functionality on IP and/or IPX networks. These were the first true VPNs in the sense that communications were secure from leaves- droppers with access to the public network. The presence of these virtual tunnels ensured that traffic encrypted on-the-fly at the transmitting site was only going to be decrypted (again on-the-fly) by a similar piece of equipment upon arriving at the destination site. This intention for a sense of privacy, despite the fact that traffic was transmitted over the public and insecure network, was the basis for the name VPN. In the second half of the 1990s, with the IETF's help, the IP Security (IPsec) consortium estab- lished similar types of VPN communications security at the network layer (layer 3) using strong encryption, tunneling, and potential encapsulation and authentication. IPsec became a standard set of techniques that had the noble goal of allowing secure intercommunication between pieces of equip- ment of different vendors. 63,64,65,66 IPsec intercompatibility, of course, did not happen overnight, but was gaining momentum and making progress. IPsec is a computationally very demanding environ- ment, especially if longer encryption key sizes are used. If it is executed on a main CPU of available systems, it can also tax the system's performance significantly or possibly bring the system to a com- plete halt, depending on the communication applications and their frequency of use. IPsec was orig- inally implemented in software for low-speed applications or where it made business sense, such as in a first-generation firewall. It was also implemented in hardware on acceleration systems that took the forms of plug-in adapter boards. Currently, it is becoming available in special security co-proces- sor chips, as we will see in the next section and in mo