scope:

High-level Data Link Control (HDLC) procedures define the Exchange Identification (XID) command/response capability as being an optional feature for the exchange of necessary information (identification, parameters, functional capability, etc.). This International Standard specifies the parameters and procedures which may be employed for two data stations to mutually determine the data link layer addresses to be used prior to logical data link establishment. This International Standard is applicable to data stations employing HDLC balanced classes of procedures which provide the XID command/response capability with the two specific parameter fields, identified below. It is used to select a pair of operational link addresses when preassigned, system designated addresses are not known on an apriori basis; e.g. switched circuit data links. Additional XID frame functions (including the exchange of operational parameters, command/response support, higher layer information, etc.) may be accomplished in conjunction with data link layer address determination or following address determination, with additional XID frame exchanges.