TN3270 is defined by RFC 1646. TN3270E is defined by RFC 1647 and RFC 2355. 1.2 Why TN3270 is important The TN3270 protocol provides an efficient means for transporting SNA 3270 traffic over an IP network while enabling the migration of user access to TCP/IP-only connectivity, and away from native SNA networking support. For quite some time, network devices external to the mainframe have been used to provide TN3270/TN3270E server support for network clients. These outboard servers accessed the mainframe either through the SNA networking infrastructure (such as IBM 3745 Communication Controllers) or through channel connectivity (for example, a channel-attached router). They transformed the client IP connections into SNA sessions for access to the mainframe. Such outboard servers are often limited in functionality, represent an extra point of failure, and keep SNA requirements in the network, which conflicts with efforts to reduce SNA networking requirements. By implementing the TN3270 server on the mainframe, clients can access it using end-to-end native IP without requiring any SNA network support for their terminal traffic. Important functions supported by the z/OS TN3270 server are covered in the following sections: TN3270E functionality Connection security Connection mapping Connection and session management