Introduction to Tandem X.25 Capabilities

Flexible Call-Setup
Tandem X.25 Features and Capabilities
2–6 065307 Tandem Computers Incorporated
The following optional user facilities are currently supported by X25AM:
Fast select
Reverse charging request and acceptance
Closed user group (CUG) selection
Bilateral closed user group (BCUG) selection
Negotiation of window size
Negotiation of packet size
Negotiation of throughput class
Call redirection with notification
Call line address modified notification
Transit delay selection and indication
RPOA selection
Note Optional user facilities can be specified only for a subdevice that is configured as SVC. PVC subdevices
do not issue call request packets; therefore, they cannot negotiate facilities (such as window size, or
packetsize) on a per-call basis.
These optional user facilities and their X25AM implementations are briefly described
below.
Fast Select
The fast-select facility eliminates the overhead and time delay of establishing and
clearing a communications session It allows the call-setup and call-disconnect calls to
include an extended Call User Data field, which can include the actual user data. The
fast-select option is desirable for applications that have either very few transactions or
short sessions on the network (such as point of sale or credit checking).
Both the local and the remote DTE must subscribe to fast select, or the network will
block the call.
Fast select allows a Call Request packet, a Call Connected packet, or a Clear Indication
packet to contain a Call User Data field of up to 128 bytes.
The fast select facility can include a restriction on response, denying authorization to
the DCE to send a Call Connected packet.
Note You cannot specify fast select by choosing an attribute for the subdevice with SCF, as you can with other
optional user facilities. To enable the fast select option, the X25AM line must be configured by SYSGEN
for extended format. (EXTFORMAT) , and the subdevice must be configured by SCF for the PTP protocol.
The application must use PTP mode 2 and specify the fast select option in the facilities field.
The fast select facility is not available with product number 5701- X25 EE (Eastern Europe/China).