TELNET

Description
TELNET is a Virtual Terminal protocol used by 3270 emulation software. TELNET is defined by RFC 854.

Various attributes of terminal emulation and the session with the host are done via TELNET option negotiation. Basic TELNET option negotiation consists of each side sending options preceded by one of four verbs:
 * DO option
 * The sender is requesting that the receiver turn on option. The receiver should reply with WILL option or WONT option.


 * DONT option
 * The sender is requesting that the receiver turn off option. The receiver should reply with WILL option or WONT option.


 * WILL option
 * The sender is indicating that it has turned on option.


 * WONT option
 * The sender is indicating that it has turned off option.

Note that there aren't really any replies in TELNET. One side could send a WILL independent of the other side sending a DO. Each side is obliged to operate according to the options it has sent DO for, and the options that the other side has sent WILL for. At the beginning of a session, all options are assumed to be off.

TELNET also supports sub-option negotiation, where one side requests that the other send a sub-negotiation for a particular option, and the other replies with the sub-negotiation data.

3270 emulation over TELNET uses one of two methods, both of which are supported automatically by the x3270 family.

TN3270
This a set of conventions codified in RFC 1576. It has fairly limited capabilities.

TN3270E
This is an explicit option added to TELNET, defined in RFC 2355. It is much more flexible than TN3270. For example, each message can be explicitly acknowledged by the other side.