Envoy ACP/XF Application Programming Manual

EnvoyACP/XF Application Programming Manual–132179
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Normal Response Mode (NRM)
Protocols
This section describes application considerations for the Normal Response Mode
(NRM) protocols supported by EnvoyACP/XF. The protocols described here are
Synchronous Data Link Control (SDLC) and Advanced Data Communications Control
Procedures Normal Response Mode (ADCCP-NRM).
NRM Features
EnvoyACP/XF allows you to use SDLC or ADCCP-NRM to establish an NRM data link
for point-to-point or multipoint configurations.
The distinctive features of ADCCP-NRM and SDLC are:
•
Point-to-point (primary and secondary) station types
•
Multipoint (supervisor and tributary) station types
NRM is an operating mode in which one station connected to the data link controls all
line activity. In a point-to-point environment, the controlling station is the primary
station and the other station is the secondary. In a centralized, multipoint environment,
the controlling station sometimes is called the supervisor and all other stations the
tributaries (although the terms primary and secondary also are used to refer to multipoint
configurations).
To activate the data link, the supervisor station issues the SNRM (Set Normal Response
Mode) or the SNRME (Set Normal Response Mode Extended) command to all tributary
stations; to close the link, the supervisor station issues a DISC (disconnect) command.
Secondary or tributary stations only respond to commands; they never issue them. Once
the link is activated, the supervisor can transmit data to any tributary station. However,
tributary stations can transmit data only when the supervisor specifically permits them to
do so (by polling them).
SDLC is a line protocol developed by IBM that has become a de facto standard in
bit-synchronous data communications. The EnvoyACP/XF version of SDLC conforms to
the standard described in the IBM Synchronous Data Link Control General Information
Manual.
ADCCP is a bit-synchronous, data-communications, line protocol developed by the
American National Standards Institute (ANSI). The EnvoyACP/XF version of ADCCP-
Normal Response Mode (NRM) corresponds to the ANSI Unbalanced, Normal
Response Mode class of procedures with optional functions 1, 2, 3, 4, 5, 6, 7, and 10, as
described in the X3.66-1979 document.