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ISDN Compatibility
Aspire Software Manual Features ◆ 373
Two B-Channel Transfer for PRI
Depending on your software, the system may have the ability for a keyset or single line telephone
to use the optional “Two B-Channel Transfer for PRI” service provided by some National ISDN
carriers in the U.S. (comparable to an analog centrex).
This service supports trunk-to-trunk transfer on the telco side. With this option enabled, two trunk
calls on the Aspire system can be connected together by the telco, releasing the trunks from the
Aspire and connecting the outside parties together.
The Aspire can perform a trunk-to-trunk transfer in the following cases:
● Put a PRI trunk call on hold and call/answer another PRI trunk. Press the Transfer
(Program 15-07 or SC 851: 06) or CONF key.
The status and bearer capability of the two trunks both meet the service requirements.
● Put a PRI trunk call on hold and call/answer another PRI trunk, then go on-hook
(Program 20-11-21 must be enabled "0").
The status and bearer capability of the two trunks both meet the service requirements.
To use the ISDN Two B-Channel Transfer, the system sends a Facility Message to the currently
active PRI trunk and then sets the retry timer (Program 24-02-09). The system will resend the Facil-
ity timer based on the retry timer. If there is no response after the 3rd resend, the system considers
the transfer as failed and stops resending.
When the transfer has succeeded, the telco sends the information to the system in the Facility, Dis-
connect or Release Message. When the system receives a Facility Message, it sends back Discon-
nect or Release then releases the trunks. When the system receives a Disconnect or Release, the
system simply releases the trunks (the other trunk will also receive a Disconnect or Release).
If the transfer fails, the telco sends the system Facility message with the fail information (some tel-
cos may send an Alerting, Disconnect or Release Message). In this case, the trunks are not trans-
ferred and remain in the system.
With this feature, the following conditions apply:
● Only manual transfers (such as pressing the Transfer key or going on-hook) are supported
with this feature. Aspire PRI trunks cannot perform a trunk-to-trunk transfer in the following
cases:
A. Pressing the Transfer (Program 15-07 or SC 851: 06) or CONF key while in a Conference
call with two trunks (Unsupervised Conference feature).
B. The incoming trunk call is automatically transferred to another trunk by system program-
ming (such as Call Forward Off-Premise).
● The bearer capability of the two calls must be “Speech, 3.1-kHz Audio, Unrestricted Digital
information” or compatible.
● At least one call must have been answered. The other call must:
- have already received ALERT message if it is an outgoing call
OR
- already have been answered if it is an incoming call.
● The regular Tandem Trunking programming must also be set to enable this feature.
● This feature does not support S-Bus.
● When used with Aspire Networking, this feature will work only when the two trunks are in the
same system.