The use of network（）,systems that effectively isolate an organization's internal network structure from an（）network, such as the INTERNET is becoming increasingly popular. These firewall systems typically act as application-layer（）between networks, usually offering controlled TELNET, FTP, and SMTP access. With the emergence of more sophisticated（）layer protocols designed to facilitate global information discovery , there exists a need to provide a general （）for these protocols to transparently and securely traverse a firewall.