Data link control procedures: What they are and what they mean to the user

The United States of America Standards Institute (USASI) formerly known as the American Standards Association) is the national standards body in the United States. From its modest beginning in 1918, USASI has grown into a national federation of more than 138 technical societies and trade associations that are either member bodies or associate members. In addition, USASI has some 2200 company members. Within USASI, there are three sectional committees that work in the broad area of data processing standards. These are X3 (Computers and Information Processing), X4 (Office Machines), and X6 (Computers and Related Equipment). Each sectional committee usually has several subcommittees operating under its direction. For example, as shown in Figure 1, Sectional Committee, X3, has eight subcommittees which are X3.1 (Optical Character Recognition), X3.2 (Codes and Input/Output), X3.3 (Data Transmission), X3.4 (Common Programming Languages), X3.5 (Vocabulary), X3.6 (Problem Definition and Analysis), X3.7 (Magnetic Ink Character Recognition), and X3.8 (Data Elements and their Coded Representation). Subcommittee X3.3 (Data Transmission) has the following work scope: “Determine and define the operational characteristics governing the performance of digital data generating and receiving systems combined with communications systems.” To accomplish this work scope, X3.3 has six task groups operating under its direction (see Figure 2). One of these task groups, X3.3.4 (Control Procedures) is developing what are known as Data Link Control (DLC) procedures. These procedures will specify how data communications can be controlled by using the communications control characters provided in the coded character set known as the United States of America Standard Code for Information Interchange (USASCII).