Introduction to Tandem X.25 Capabilities

Flexible Call-Setup
Tandem X.25 Features and Capabilities
065307 Tandem Computers Incorporated 2–5
Figure 2-2. Subaddressing
020
DTE
3110123456789
DTE Address:
Port Number:
Called Address:
3110123456789
1
31101234567891
PORT #
1
Subdevice B
PORT #
2
Subdevice A
DTE Address:
Port Number:
Called Address:
3110123456789
2
31101234567892
Subdevice C
Optional User Facilities Optional user facilities are also referred to as per-call facilities: they can be exercised or
not exercised on a per-call basis. The availability of these optional user facilities varies
somewhat from network to network. You can specify most of the optional user
facilities for X25AM per subdevice with SCF; the SCF attributes used to select the
various facilities are included in the descriptions of the facilities provided in this
subsection. A summary of attributes and SYSGEN modifiers is also provided in
Appendix B, “X25AM Parameters.”
Optional user facilities are relevant only to a subdevice configured as a switched
virtual circuit (SVC), because only SVC subdevices transmit call-setup packets.
A few optional user facilities can be defined either for a specific subdevice or for all the
subdevices related to a particular line. When optional user facilities are specified for a
line, their effect on a subdevice is subject to the following restrictions:
A subdevice specification of optional user facilities overrides the line specification
of optional user facilities.
A subdevice specification of optional user facilities has no effect on a subdevice
that is configured as a permanent virtual circuit (PVC).
Some optional user facilities can also be specified by the user application program
after a subdevice is opened. When an optional user facility is specified by an
application, it stays in effect only until the subdevice is closed.