There are three types of Telnet connection requests that dictate how Telnet chooses a name to represent the client. They are Generic requests, Specific requests, and associated printer requests. For details about associated printer requests, see Associated printer function. Most connection requests are Generic requests.
For Generic requests, Telnet has complete control over LU name assignment using the Generic mapping statements as a reference. All linemode and TN3270 connections use only Generic requests, and TN3270E terminal and printer emulators use Generic requests as their default request type. Specific mapping statements are ignored by Generic requests.
For Specific requests, the TN3270E client specifies the LU name to be used. Telnet validates the name using the Specific mapping statements as a reference. Requesting a Specific LU name allows a client to be assigned the same LU every time. This is important if the host application is LU name dependent, and the client does not have a constant Client Identifier to use for mapping an LU name. It is also important to block Telnet from assigning these LUs to Generic requests. That is why Specific mapping statements are ignored by Generic requests. If a Specific mapping does not find an LU match, Generic mapping statements are checked. Telnet confirms or denies the request during negotiation. If the LU mapping algorithms reject the client choice, Telnet sends a device type reject to the client. Most clients then notify the end user that the requested LU name is not valid or is already in use.