Introduction to Tandem X.25 Capabilities

Flexible Call-Setup
Tandem X.25 Features and Capabilities
2–10 065307 Tandem Computers Incorporated
Transit Delay Selection and Indication
This facility permits a DTE to select a transit delay time through the packet network.
This feature is used mostly for long distance connections through a network. The
transit delay is established on a per-call basis, and the appropriate delay value is
supplied by the network at subscription time. The network must inform both DTEs
about the transit delay applied to the call by the incoming-call packet to the called
DTE, and by the call-connected packet to the calling DTE. This transit delay time
value included in the call-connected packet may be equal to, greater than, or smaller
than the value in the call request packet. The incoming-call packet to the called DTE
and the call-connected packet to the calling DTE should both contain the indication of
the transit delay for this call (Figure 2-3).
Figure 2-3. Transit Delay Indication
Network
Optimized Routing
Incoming Call
Time Delay Indication
Call Connected
Time Delay Indication
Call Accept
Call Request
Time Delay Indication
Calling
DTE
Called
DTE
021
Local
DCE
Remote
DCE
When the network receives a call request packet with the Transit Delay Indication, the
network will allocate resources to try to route the call within the requested delay time.
This facility is handled by the network routing mechanism, and may or may not have
anything to do with the priority of calls.
The TRANSITDELAY attribute can be specified for either a line or a subdevice. If both
the line and subdevice attribute are specified, the subdevice attribute is used. The user
application can also specify a dynamic value for a subdevice. The dynamic value
overrides the value set by SCF and stays in effect until the subdevice is closed.
RPOA Selection
This facility allows a calling DTE to specify one or more recognized private operating
agencies (RPOA) to handle the packet session. The RPOA is a packet-network,
value-added carrier, and acts as a transmit network within one country or between
countries.
If the RPOA selection facility is not selected, the RPOA subscription facility is used
instead for any virtual calls involving more than one RPOA and one or more