Private branch exchange

Details Private branch exchange Private branch exchange

1998-11-12

2004-03-16

Bui, Bing (Department: 2642)

Telephonic communications

Call or terminal access alarm or control

C379S198000, C379S229000, C379S231000, C379S234000

Reexamination Certificate

active

06707897

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a private branch exchange having a caller number informing function and a caller number information restricting function or having a connected party number informing function and a connected party number information restricting function.
BACKGROUND ART
In an integrated services digital network (ISDN), a caller number informing function and a called number information restricting function are defined, and a private branch exchange having a function of informing a caller number has already been developed. The caller number informing function is provided so that a called party can identify the calling party and, if necessary, can call back with use of the informed caller number. In the public integrated services digital network (ISDN), too, the caller number provided along with a call setting signal at the time of calling is verified on condition that a callback can be made. If the caller number is determined to be improper in the verification by the network, the improper caller number is replaced with a proper caller number and transmitted to the destination apparatus. In the network, caller numbers are managed in units of an interface (i.e., an office line or a plurality of office lines capable of being controlled by one control channel).
In order to carry out the caller number informing function, a data structure, for example, as shown in
FIG. 1
, is adopted. In
FIG. 1
, whether or not the caller number is informed is determined as follows. A caller number information element identifier in OCTET1 (8-bit data) is referred to in order to determine whether there is data on the caller number. If there is the caller number data, the caller number data is read from OCTET4. In this manner, the caller number is informed to the called party. The caller number data in OCTET4 is character-string data.
The caller number informing function will be further described.
FIG. 2
schematically shows a process
40
for the caller number in the conventional private branch exchange. A call signal
41
from an extension may be an analog signal or a digital signal, depending on the type of the extension. On the basis of a caller number
42
associated with the extension held within the private branch exchange, a process
43
for associating the caller number
42
with the call signal is performed. A call signal
44
to the network is termed “call setting” in the integrated services digital network and it includes the caller number
45
. The counter-side terminal
46
receives a call via the integrated services digital network and includes a display
47
.
In
FIG. 2
, if the private branch exchange has received the call signal
41
from the extension, it associates the call signal
41
with the caller number
42
stored therein and corresponding to the extension. When the private branch exchange sends the call signal
44
, it incorporates the caller number
45
into the call signal
44
. The destination apparatus
46
which has received the call displays the caller number on the display
47
and identifies the caller. Using this number, a callback is made. In a case where the extension is one matching the integrated services digital network, the caller number may be contained in the call signal
41
and informed from the extension.
According to standards or recommendations specifying the protocols of the integrated services digital network, it is verified by the network, from a standpoint of security, whether the caller number
45
coincides with a contractual number. If the caller number does not coincide, it may be replaced with the contractual number on the network.
On the other hand, a service called “direct dial-in” is provided, wherein if a callback is made or a general call is received from the network, the extension for the call reception is determined on the basis of the content of the called number information element included in the call setting signal for the call reception.
FIG. 3
schematically shows a direct dial-in process
50
in the conventional private branch exchange. A called number conversion table
51
converts the called number to the extension number in order to carry out the direct dial-in. The called number conversion table
51
is provided for each interface (an office line or office lines controllable by one control channel). The call reception signal
52
from the network is termed “call setting” in the integrated services digital network and includes the called number
53
. The called number conversion table
51
is searched on the basis of the called number
53
, and the extension number
54
of the called party is obtained. The call reception signal
55
to the extension number
54
may be an analog signal or a digital signal, depending on the kind of the extension.
In
FIG. 3
, if the call reception signal
52
is received from the network, the private branch exchange obtains the extension number
54
of the called party on the basis of the called number
53
included in the private exchange, with use of the called number conversion table
51
provided within the exchange. Then the private branch exchange sends out the call reception signal
55
. Thereby, the call is connected to the extension corresponding to the called number.
In general, the private branch exchange accommodates more extension terminals than called numbers which can be received from the network. Thus, all extensions are not assigned called numbers, nor can automatically receive calls. There are many extension terminals which cannot directly receive calls from the integrated services digital network.
When such an extension transmits a call with use of the integrated services digital network, a callback cannot be made. Thus, the caller number information element which can identify the extension cannot be sent to the network. In such a case, the caller number is supplemented by the network. In the case of the private branch exchange, however, no callback can be made to the extension, which actually transmitted the call, with the supplemented number. In this case, a caller number presentation restriction should have been sent to the network to prevent the counter-side terminal from being provided with the caller number, but this is not done.
Moreover, in general, in the private branch exchange having the function of informing the caller number, the caller numbers permitting callback are preset in the extension terminal or in the private branch exchange. In the private branch exchange, in a case where the extension always selects a specified office line to make a call, if the caller number is properly set, the call passes the network verification and reaches the counter-side terminal. It is usual, however, in the private branch exchange that use is made of an office line selection function for selecting a most inexpensive office line or selecting a non-busy office line when a certain office line is busy. In this case, if the extension issues a call by selecting an office line different from an ordinary one, the caller number which is proper in the ordinarily selected office line is determined to be improper in the different office line by the network verification. As a result, a default number in the network is supplemented and transmitted to the counter-side terminal.
As stated above, in the conventional private branch exchange, it is difficult to easily inform the caller number with which a callback can actually be made. If the office line selection function is used, the number, which is proper in ordinary cases, may become improper. It is very difficult to take such flexible measures as informing the caller number with which a callback can actually be made, or sending a caller number presentation restriction to the network in a case where the proper caller number cannot be informed.
In the conventional private branch exchange, as described above, services have not been informed from the standpoint as to whether or not a callback can be made, when the caller number is informed or the presentation restriction is sent. There is a concern that a caller

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