Feature negotiation protocol for a synchronous modem

TL;DR: In this paper, the authors propose a method for feature negotiations between two synchronous modems. But the method requires the modem to support synchronous operation, a data transfer rate of at least 4800 bits per second, and at least one non-default feature.

Abstract: A method for feature negotiations between two synchronous modems. To engage in negotiations a modem must be configured to support synchronous operation, a data transfer rate of at least 4800 bits per second, and at least one non-default feature. After the orginating modem and the answering modem have completed standard handshaking sequences the originating modem initiates the negotiations by sending a list of supported features. The answering modem responds by confirming that all the features are supported, by returning a subset of the features list, or by sending a different features list. If the answering modem did not confirm the list then the originating modem responds to the subset or to the different list by confirming the subset or different list, by returning a subset of the different list, or by sending another different list. If the originating modem does not initiate the negotiations, if the answering modem does not respond to the list sent by the originating modem, or if negotiations are not completed within a predetermined time after completion of the standard handshaking sequences, then the modems use standard (default) features.