Business Data Communications and Networking, 13th Edition

APPENDIX ACONNECTOR CABLES

When a message leaves a computer and begins to move onto the network, the first component it encounters is the connector cable between the computer and the circuit. When people discuss connector cables, the focus is on the standards (such as RS232 or RS449).

A.1 RS232 (DB-25)/RS449 (DB-9)

When people talk about connector cables, they frequently refer to them as a RS232, DB-25, RS449, or DB-9. This is because each connector cable is based on a specified standard. Calling the connector by its standard designation allows everyone to know precisely which connector is being discussed.

The RS232 standard is the most frequently mentioned. It was first issued in 1962, and its third revision, RS232C, was issued in 1969. The RS232D standard was issued in 1987 to expand on RS232C. The RS232D standard is also known as the EIA-232-D.

The RS232 connector cable is the standard interface for connecting data terminal equipment (DTE) to data circuit terminating equipment (DCE). The newer RS232D is specified as having 25 wires and using the DB-25 connector plug like the one used on computers. If this connector cable is attached to a computer, people may refer to it simply as DB-25; if it is not attached to a computer, they may refer to it as the RS232 interface.

DTE comprises the data source, the data sink, or both. In reality, it is any piece of equipment at which a data communications path begins or ends, such as a terminal. DCE provides all the functions required ...