2.2 The IBM 7171 ASCII Device Attachment Control Unit - Index of

Cabling RequirementsGeneral Switched Modem SpecificationsTo attach a modem (DCE) to the IBM 7171 port (DTE), a common one-to-oneRS-232-C cable with a male connector on the DCE end and a female connector onthe DTE end is used. That cable can be built from components or can be purchasedfrom many vendors. A description of the cable is included in Appendix Bof IBM 7171 ASCII Device Attachment Control Unit Description and PlanningGuide.Modems interfacing between the IBM 7171 port and the switched telephonenetwork should be configured to automatically answer incoming calls. They shouldalso be configured (if possible) to answer incoming calls only when the DTR signalis driven active by the IBM 7171 port. When DTR is not active, the IBM 7171port is not ready to receive any calls.Modems should be configured so the RLSD signal reflects the true state of the telephonecarrier signal. If the remote modem is powered off for any reason, the IBM7171 port should be able to detect it and react accordingly.The Ring Indicator signal is expected to be driven by the modem even if it is configuredfor the auto answer mode. The IBM 7171 expects that the Ring Indicatorsignal will be driven active and then inactive at least once before the line isanswered.~,)The Data Set Ready signal is expected to be driven inactive for a period of at least200 milliseconds between sessions. In the switched network configuration (override),or autoconfiguration perceived as switched network environments, the linewill not be restarted until the DSR drop has occurred.5.9.2 Leased LineGeneral Description of the Leased Line ConfigurationCabling RequirementsA leased line is a direct connection between two modems. The lines are not routedthrough the telephone company switching equipment, but rather bypass theswitches. A leased line modem sequences its RS-232-C interface signals differentlyfrom a modem attached to the switched network. The Ring Indicator, for example,is never driven active by a modem on a leased line. Those differences are importantto the IBM 7171 as it initializes a session and as it disconnects a modem. Themodems connected to leased lines are frequently very different from those used inthe switched network. The IBM 7171 uses the differences between switched andleased line modems to determine how to sequence the RS-232-C signal lines.)To attach a modem (DCE) to the IBM 7171 port (DTE), a common one-to-oneRS-232-C cable with a male connector on the DCE end and a female connector onthe DTE end. That cable can be built from components or can be purchased frommany vendors. A description of the cable is included in Appendix B of IBM 7171ASCII Device Attachment Control Unit Description and Planning Guide.Chapter 5. IBM 7171 I/O Interface to Terminals 5-11