In this illustration, we see a network that includes a variety of desktop computers, link-layer switches and routers. On the right edge of the network is a router labeled "Router and filter." This router connects to a server labeled "Application gateway" and also to a server placed outside of the network. A blue arrow labeled "Host-to-gateway Telnet session" points rightward from one of the computers in the network to the Application Gateway. A second blue arrow labeled "Gateway-to-remote host Telnet session" points from the Application gateway to the router outside of the network.