Additional direct inward dialing connection system

An additional direct inward dialing connection system includes a determining section, announcement machines, and a connection control section. When a direct inward dialing number from a caller is received via an office line or public telephone network, the determining section determines on the basis of the state of a called station terminal whether connection to the called station terminal can be established. When an output from the determining section indicates that connection to the called station terminal is not possible, one of the announcement machines notifies the caller of the reason for connection failure based on the state of the called station terminal. The machine also announces the number of a station terminal that may additionally dialed. When the number of the station terminal is received upon additional dialing performed by the caller, the connection control section connects a call from the caller to the station terminal corresponding to the received number.

BACKGROUND OF THE INVENTION 
The present invention relates to an additional direct inward dialing 
connection system and, more particularly, to an additional direct inward 
dialing connection system using speech to prompt a caller to perform an 
additional dialing operation when connection to a station terminal cannot 
be established in a direct inward dialing function from an office line in 
an automatic private branch exchange. 
As a system for implementing an extension telephone in an automatic private 
branch exchange to terminate a call from an office line, a direct inward 
dialing connection system is generally used. In this direct inward dialing 
connection system, when the extension of a telephone is dialed after the 
user of an originating telephone set connected to an office line dials a 
direct inward dialing number, a call is made to the extension telephone in 
an idle state. To remedy the situation where a called extension telephone 
set is in a busy state, an additional direct inward dialing connection 
system for accepting additionally dialed extensions corresponding other 
telephone extensions are available. Conventional direct inward dialing 
connection systems will be described below. 
In a first conventional method, the "PBX Direct Inward Dialing Connection 
System" disclosed in Japanese Patent Laid-Open No. 3-123295, a PBX 
exchange capable of performing PBX direct inward dialing connection 
includes a means for receiving an additionally dialed PBX extension number 
which is output from an originating telephone set to designate a telephone 
set other than the telephone set which is in a busy state for which a 
connection was attempted. This first conventional method also provides a 
means for connecting the originating telephone set to the extension 
telephone set for which the additional dialing operation has been 
performed, in accordance with the received PBX extension number. When a 
telephone set or telephone set group is in a busy state, the originating 
telephone set can be connected to another extension telephone set for 
which an additional dialing operation is performed. 
In a second conventional method, the "Office Line Terminating Connection 
System" disclosed in Japanese Patent Laid-Open No. 60-84090, an automatic 
private branch exchange also accommodates an office line allowing an 
additional dialing operation. When office line connecting is attempted 
with respect to another office line while all input registers for 
receiving additionally dialed signals are in a busy state, the office line 
subscriber on the originating telephone set is notified by audible means 
that the call is being transferred to an attendant console or office line 
termination display panel. Information about the call is displayed on the 
attendant console or office line termination display panel and the office 
line subscriber is precluded from performing re-dialing operations 
including additional dialing operations. 
In the first conventional method, when a telephone set or telephone set 
group is in a busy state, a call is attempted to another extension 
telephone set on the basis of the additionally dialed number designated by 
the caller. If, therefore, this substitute extension telephone is also in 
a busy state, an additional dialing operation or re-dialing operation must 
be performed. 
The second conventional system is limited to a case wherein while all the 
input registers for receiving additional dial signals from office line 
subscribers are in a busy state, an office line subscriber is notified by 
speech that the call is being transferred to the attendant console or 
office line termination display panel. However, any description about 
application of the system to cases wherein a called extension terminal is 
in a busy state or lock-out state cannot be recognized. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an additional direct 
inward dialing connection system in which a call always is connected to a 
terminal designated by an automatic private branch exchange by only one 
additional dialing operation performed by the caller. 
In order to achieve the above object, according to the present invention, 
there is provided an additional direct inward dialing connection system, 
comprising a determining means for, when a direct inward dialing number 
from a caller is received via an office line, determining on the basis of 
a state of a called station terminal whether to the called station 
terminal can be established; a notifying means for, when an output from 
the determining means indicates that the called station terminal is 
disabled, notifying the caller of a reason for the failed connection based 
on the state of the called station terminal and for notifying the caller 
of a number of a terminating station terminal to be additionally dialed; 
and a connection control means for, when the number of the station 
terminal is received upon additional dialing performed by the caller, 
connecting a call from the caller to the station terminal corresponding to 
the received number.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The present invention will be described below with reference to the 
accompanying drawings. 
FIG. 1 shows an automatic private branch exchange in an additional direct 
inward dialing connection system according to an embodiment of the present 
invention. FIG. 2 explains the operation of the embodiment. 
Referring to FIG. 1, an automatic private branch exchange 20, which 
accommodates an office line allowing an additional dialing operation, 
includes a central office line trunk (COT) 3, a push button register (PBR) 
4, announcement machines (to be AMs) 51, 52, 53, and 54, a central 
processing unit (CPU) 6, line circuits (LCs) 7, 8, and 9, a communication 
line switch (SW) 10, and a main memory unit 14. The COT 3 interfaces with 
an office line subscriber 1 via an office line 2 or a public telephone 
network (not shown). The PBR 4 receives a dial signal from the office line 
subscriber 1 via the COT 3, the office line 2, and the above public 
telephone network when direct inward dialing connection is performed. When 
a terminating connection for a called station terminal cannot be 
established, one of the AMs 51, 52, 53, and 54 outputs a terminal number 
to be additionally dialed, together with a reason for the connection 
failure. When the office line subscriber 1 additionally dials this 
additional terminal number, the CPU 6 performs control to connect the call 
to a terminal corresponding to the additionally dialed number in 
accordance with a designation from the PBR 4 which has received the 
terminal number. The LCs 7, 8, and 9 are respectively connected to station 
terminals (STAs) 11, 12, and 13 including extension telephone sets. The SW 
10 accommodates the COT 3, the PBR 4, the AMs 51, 52, 53, and 54, and the 
LCs 7, 8, and 9 and performs connection therebetween. The main memory unit 
14 stores programs and data for all sequence control operations in the 
automatic private branch exchange 20, which are performed by the CPU 6. 
The CPU 6 includes a determining section 61 and a connection control 
section 62. The determining section 61 determines, on the basis of state 
data and the like of the STAs 11 to 13 stored in the state memory area of 
the main memory unit 14, whether termination to a called station terminal 
can be performed. The connection control section 62 connects a call from a 
caller, which is generated when he/she additionally dials a destination 
terminal number provided by one of the AMs 51 to 54, to the destination 
terminal designated by the additional dialing operation via the SW 10. 
The operation of the embodiment will be described next with reference to a 
flow chart shown in FIG. 2. 
Assume that the STAs 11 and 12 belong to the same extension group, but the 
STA 13 does not belong thereto. Let XX and YY be the extension numbers of 
the STAs 11 and 12, and ZZ be the terminal number of a maintenance 
terminal (not shown). Also assume that speech communication is being 
performed between the STAs 11 and 13 via the LC 7, the SW 10, and the LC 
9. 
When the office line subscriber 1 dials a direct inward dialing number with 
respect to the automatic private branch exchange 20 in this state, this 
call is terminated to the COT 3 via the office line 2 (step S201). 
When the COT 3 notifies the CPU 6 of this office line termination, the CPU 
6 controls the SW 10 to set a link between the COT 3 and the PBR 4, and 
urges the office line subscriber 1 by a known method using a tone or 
speech to perform an additional dialing operation (step S202). 
When the office line subscriber 1 additionally dials the extension number 
XX, the PBR 4 receives the number and transfers it to the CPU 6 (step 
S203). 
When the determining section 61 of the CPU 6 recognizes, on the basis of 
state data and the like in the main memory unit 14, that the called STA 11 
is in a busy state (step S204), the determining section 61 controls the SW 
10 to set a link between the COT 3 and the AM 51 and check an available 
station terminal in the same group to which the STA 11 belongs, thereby 
transferring the extension number YY of the available STA 12 to the AM 51 
(step S205). 
The AM 51 outputs instruction such as "Please dial the number YY because 
the telephone set of the extension number XX is busy" in accordance with 
the above information from the CPU 6 (step S206). 
This instruction is delivered to the office line subscriber 1 via the SW 
10, COT 3, and the office line 2. The office line subscriber 1 then 
additionally dials the number YY (step S213). 
This number YY is received by the PBR 4 via the COT 3 and the SW 10 (step 
S214). The number is transferred from the PBR 4 to the CPU 6. The 
connection control section 62 of the CPU 6 performs connection control 
with respect to the STA 12 corresponding to the number YY by a known 
method like the one disclosed in Japanese Patent Laid-Open No. 3-123295 
described above (step S215). 
When a direct inward dialing connection request is generated with respect 
to the STA 11 which in a lock-out state, the determining section 61 of the 
CPU 6 recognizes the lock-out state of the called STA 11 in step S204 on 
the basis of state data and the like in the main memory unit 14, and 
instructs the AM 52 to instruct the office line subscriber 1 by speech 
(steps S207 and S208). The instruction in this case is, for example, 
"Please dial the number YY because the extension telephone set of the 
extension number XX is in an off-hook state." 
When a direct inward dialing connection request is generated with respect 
to the STA 11 while termination thereto is regulated, the determining 
section 61 of the CPU 6 recognizes the termination regulation imposed on 
the called STA 11 in step S204 on the basis of state data and the like in 
the main memory unit 14, and instructs the AM 53 to instruct the office 
line subscriber 1 by speech (steps S209 and S210). The instruction in this 
case is, for example, "Please dial the number ZZ because connection to the 
telephone set of the extension number XX is being regulated." When the 
office line subscriber 1 additionally dials the number ZZ, this call is 
terminated/connected to the maintenance terminal by the connection control 
section 62. 
When a direct inward dialing connection request is generated with respect 
to the STA 13 corresponding to a dead number, the determining section 61 
of the CPU 6 recognizes in step S204, on the basis of state data and the 
like in the main memory unit 14, that the called STA 13 corresponds to a 
dead number, and instructs the AM 54 to instruct the office line 
subscriber 1 by speech (steps S211 and S212). The instruction speech in 
this case, is, for example, "Please dial the number ZZ because the dialed 
number is a dead number." 
As described above, according to the present invention, when connection to 
a called station terminal designated by a direct inward dialing number 
from an originating office line subscriber is disabled, the automatic 
private branch exchange notifies the caller of the reason for the failed 
connection and a number to be additionally dialed. Therefore, a call from 
the caller is connected to a terminating terminal designated by the 
automatic private branch exchange without fail by performing only one 
additional dialing operation. 
In this embodiment, connection to a called station terminal is disabled 
because of the busy or lock-out state of the called station terminal, 
terminating connection regulation, or a dead number. However, the present 
invention is not limited to these reasons for connection failure. 
For example, when the present invention is to be applied to a case wherein 
a transfer service is registered in a called station terminal, only the 
information about transfer may be given to the caller, and the call may be 
connected to the transfer destination without notifying the caller of an 
additional number to dial. When an additional number different from the 
one given by the notifying means is received, a termination transfer 
destination may be determined in accordance with the received additional 
dial number, or only the given additional number may be received. 
Furthermore, in this embodiment, the announcement machines 51 to 54 each 
execute speech notification for each cause of terminating connection 
failure. Each are activated by a particular form of traffic. However, one 
speech instruction unit may have the functions of the above plurality of 
announcement machines. Such a speech guide unit may be activated by 
different forms of traffic. 
As has been described above, according to the present invention, since a 
call is connected to a terminal designated by the automatic private branch 
exchange without fail by only one additional dialing operation performed 
by the caller, the caller will not need to redial a direct inward dialing 
number or perform an additional dialing operation again. 
Therefore, considerable improvement in service, can be achieved, and the 
incomplete connection traffic can be reduced.