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.