Envoy ACP/XF Application Programming Manual

Normal Response Mode (NRM) Protocols
EnvoyACP/XF Application Programming Manual–132179
3-5
Polling Interval
contain a two-byte control field; unnumbered frames contain the basic one-byte control
field.
So, for IBM extended control, only the following numbered frames contain a two-byte
control field:
•
Information frames (I-frames)
•
Receive Ready frames (RR-frames)
•
Receive Not Ready frames (RNR-frames)
•
Reject frames (REJ-frames)
•
Selective Reject frames (SREJ-frames)
The default setting specifies that the IBM extended control format is not enabled. (For
more information about these frames, see Appendix B, Features Common to
Bit-Synchronous Protocols.
Use SCF to specify the IBMEXTENDED/NOIBMEXTENDED modifiers either by
configuring the PROFILE in the WAN Manager subsystem database (see the
EnvoyACP/XF Configuration Manual) or directly through SCF (see the SCF Reference
Manual for EnvoyACP/XF). You cannot change these modifiers through the user
application.
Your application can indirectly enable or disable the IBMEXTENDED modifier even if
you previously specified it through SCF because IBMEXTENDED is in effect only
when EXTENDEDCONTROL is enabled. Thus, the application can indirectly
deactivate or activate the IBMEXTENDED capability by using the SETMODE 19
procedure to disable and reenable the EXTENDED capability.
Programmatically activating or deactivating EXTENDEDCONTROL is useful when an
application must communicate with stations that have different control characteristics.
However, this capability only works for a point-to-point dial (SWITCHED) environment
in which the application can programmatically determine the operating characteristics of
the remote station.
Polling Interval
In a multipoint supervisor station, the polling interval is the period that EnvoyACP/XF
waits after completing a pass through the station list and before starting the next pass
through the list. You can specify the polling interval (IDLETIMER) using SCF and the
application program can temporarily alter it by using a SETMODE 16 call. The default
poll interval is .5 seconds.
The only time when a frame other than REJ can cause the retransmission of previously
sent frames is when a primary station detects a timeout error and sends an RR frame
with the P bit set to the secondary station. (For more information about the RR frame,
see S-Frame Command/Response Codes
on page B-7.) Then the Nr in the next received
frame is interpreted as though a REJ frame had caused a retransmission. (For more
information about the REJ frame, see S-Frame Command/Response Codes on page B-
7.)