Final answer:
The method used to log in directly to the z/OS UNIX shell through TCP/IP in addition to telnet is rlogin. Rlogin serves a similar purpose to telnet by providing a remote shell access but differs in authentication aspects. However, both are considered less secure than SSH.
Step-by-step explanation:
In addition to telnet, the method that can be used to log in directly to the z/OS UNIX shell through TCP/IP is rlogin (remote login).
rlogin is a protocol that allows users to connect to a remote UNIX-based system and operate within a shell environment on that system, similar to how telnet operates.
Although both telnet and rlogin allow for remote shell access, they differ in terms of authentication and security features. It's important to note that both protocols transmit data, including passwords, in plain text, which can pose a security risk.
Secure alternatives such as SSH (Secure Shell) are now commonly used in place of these older protocols for encrypted communication.