IP Phone User Manual
1.20 Integrated Services Digital Network (ISDN) Service Features
198 Feature Guide
1.20.1.11 ISDN Extension
Description
An ISDN (BRI/PRI) port can be used for either trunk or extension connection. When extension 
connection is enabled, ISDN terminal devices (e.g., ISDN telephone, G4 fax machine, personal 
computer) or a behind PBX can be connected to the port. 
If the ISDN port is in point-to-point (P-P) configuration, one terminal device can be connected 
to the port. If the ISDN port is in point-to-multipoint (P-MP) configuration, a maximum of eight 
terminal devices can be connected to the port. However, only a maximum of two devices can 
be used simultaneously. 
Individual terminal devices on a behind PBX can be addressed with Multiple Subscriber 
Number (MSN). The MSN consists of the ISDN extension number and an additional digit, 0 
through 9 or 00 through 99.
[Example]
Conditions
• Subaddressing
Subaddressing is possible between ISDN terminal devices. The subaddress goes through 
the PBX to the ISDN terminal devices directly.
• Call Transfer (PBX feature) is available only for ISDN extensions in P-MP configuration. 
(  1.11.1 Call Transfer)
(131)
Extn. No.: 13X (MSN)
Extn. No.: 14XX (MSN)
Extn. No.: 15XX 
 (MSN)
PBX
(132) (139)
...
...
Behind
PBX
(1234)
Extn. No.: 1234
ISDN Port for 
EXTN. (P-MP)
(1234) (1234)
...
...
1234:
Up to eight terminals 
can be connected to 
the port and receive 
a call simultaneously.
131–139:
Up to eight terminals 
can be connected to 
the port.
130:
All terminals receive 
a call simultaneously.
(1400) (1401) (1499)
...
...
1400–1499:
Each terminal 
receives a call. 
(Use the DDI/MSN 
feature of the 
behind PBX.)
Idle Extension 
Hunting is available.
ISDN Port for 
EXTN. (P-P/P-MP)
ISDN Port for 
EXTN. (P-P/P-MP)
ISDN Port for 
EXTN. (P-MP)










