Telephonic communications – Plural exchange network or interconnection – Interexchange signalling
Reexamination Certificate
2002-02-19
2003-12-23
Hong, Harry S. (Department: 2642)
Telephonic communications
Plural exchange network or interconnection
Interexchange signalling
C370S426000, C370S522000, C379S231000, C379S234000, C379S901000
Reexamination Certificate
active
06668052
ABSTRACT:
BACKGROUND OF THE SYSTEM
The present invention relates to telecommunication systems. In particular, the invention concerns a method and system for signaling used in call setup.
A Centrex subscriber group is a subscriber group so implemented in a public exchange that, without being connected to a private automatic branch exchange, it can use functions typical of extensions connected to a PABX. A Centrex subscriber group is so implemented in the exchange that the exchange will provide a service resembling a PABX or a PABX network without employing separate branch exchanges. A feature typical of the functions of a Centrex exchange is a private numbering plan. It is a telecommunication service that allows the subscriber to use subscriber numbers deviating from the public numbering plan for communication between certain subscriptions within the area of one or more networks. The numbering plan can be implemented e.g. by reserving subscriber numbers beginning with a given sequence of digits for the use of an enterprise or a corresponding community.
A telephone exchange supporting the Centrex service is provided with a special database in which are stored all the numbers included in the public numbering plan that correspond to the private numbering plan. The Centrex service can be extended so as to allow it to be used between several telephone exchanges, in which case all the exchange have corresponding databases. In the signaling between two Centrex exchanges, a number included in a private numbering plan is converted into a number included in the public numbering plan. The subscriber, which may be e.g. an analog subscriber, an ISDN subscriber or a branch exchange, dials the numbers and the public network exchange performs the number conversion. If the subscriber dials a number included in a private numbering plan, then the public network exchange converts the number into a number consistent with the public numbering plan. In other words, the public telephone network uses numbers consistent with the public numbering plan, which are converted in Centrex exchanges so that the users of terminal equipment will see the numbers consistent with the private numbering plan. Therefore, for the operation of the Centrex system, a heavy database needs to be maintained, which means a waste of resources of the telecommunication system.
FIG. 1
a
is a diagrammatic representation of a prior-art system. Connected to a first exchange SW A is a Centrex subscription A. The Centrex subscription A implements a Centrex service that uses a private numbering plan in conjunction with the first exchange SW A. In the example, the Centrex service is implemented in the first exchange SW A, so the first exchange is a Centrex exchange. A corresponding service can also be implemented using an intelligent network.
A first telecommunication terminal TE
1
is connected to the Centrex subscription A in the first exchange SW A using DSS1 signaling (DSS1, Digital Subscriber Signaling No. 1) or equivalent. The first exchange SW A is connected via a public telephone network ISDN to a second exchange SW B. For communication between the first and second exchanges, ISUP signaling (ISUP, ISDN User Part) is used.
In a corresponding manner, a second Centrex subscription B is connected to the second exchange SW B, which likewise is a Centrex exchange. Connected to the Centrex subscription B in the second exchange SW B is a second telecommunication terminal TE
2
using DSS1 signaling. In the example, the subscriber lines of both terminals TE
1
, TE
2
are comprised in a private numbering plan implemented via a Centrex service. The first and second telecommunication terminals TE
1
, TE
2
may be ISDN subscribers, analog subscribers or branch exchanges.
In this prior-art solution, the first exchange SW A comprises a Centrex subscriber database, which contains all A-subscriber and B-subscriber numbers both in a long form and in a short form, i.e. in forms consistent with the public and the private numbering plans. Thus, e.g. a short B-subscriber number 123 corresponds to a long number 456 789. The first exchange SW A and the second exchange SW B have identical databases. When an A-subscriber calls a B-subscriber by dialing the number 123, this number is converted into 456 789 and the call is routed using the long number in the public telephone network ISDN.
When the second exchange B receives an A-subscriber number, e.g. 456 789, it checks the number received against the numbers in the Centrex database. If a corresponding number is found in the database, then the long number 456 789 is again converted into the short number 123, which is transmitted to the display
10
of the second terminal TE
2
, and the second terminal TE
2
generates a ringing tone as used for internal calls. Thus, the user of the second terminal TE
2
can recognize the incoming call as an internal call.
A private numbering plan and/or special group functions can also be implemented in a virtual private network VPN which uses signaling consistent with the QSIG standard. The virtual private network VPN is gaining ground in network solutions in which an economic network protected against outsiders is needed. QSIG is an ISDN common channel signaling system designed for use in private networks. The QSIG signaling was developed by an open group of enterprises including all of the largest European PABX manufacturers. The designation QSIG refers to signaling transmitted over an ISDN Q-point. QSIG defines a number of protocols which can be used for interaction between a plurality of PINX's (PINX, Private Integrated services Network eXchange). A PINX is connected to the nearest telephone exchange e.g. via a 2 Mbit/s link carrying QSIG signaling. A QSIG protocol largely resembles the ITU-T (International Telecommunication Union) Q.931 protocol. The essential difference between these is that Q.931 is an asymmetric protocol while QSIG is symmetric.
A virtual private network can also be utilized in an IP environment (IP, Internet Protocol), in which case it is possible to implement e.g. remote operation of a protected intranet used by an organization, i.e. an extranet. Extranet means a data network which is implemented between organizations using the Internet as a data transmission means and which can be used to interconnect the intranets of the organizations included in the system.
Using a virtual private network, it is possible to interconnect Centrex subscriber groups, Public Branch Exchanges (PBX) and individual subscribers. A VPN system can also be implemented using a public telephone network for data transmission. In the VPN system, a private numbering plan is identified by a special Corporate Network Identifier CNID. Subscriber identification is performed using a CNID parameter packed in the APP parameter (APP, Application Transport Parameter). The APP parameter additionally contains the A-subscriber and B-subscriber numbers in the private numbering plan, e.g. in the internal numbering used in an enterprise. However, matching VPN and Centrex systems is a problematic task because the prior art Centrex system does not understand the APP parameter used in QSIG signaling.
The object of the invention is to eliminate the problems referred to above. A specific object of the invention is to disclose a new type of method and system for signaling used for call setup in a situation where at least one of the telecommunication terminals belongs to a Centrex subscriber group. The present invention enables cooperation between a QSIG VPN network and a Centrex subscriber group in a manner transparent to the user, i.e. so that the user will perceive it as consistent cooperation regardless of the system to which the terminal equipment is connected.
SUMMARY OF THE INVENTION
The basic idea of the invention is to use in the Centrex exchange the same APP parameter as is used by a QSIG VPN network in VPN ISUP signaling, both for communication with another Centrex exchange and for communication with a VPN exchange.
The invention concerns a method for signaling used for call setup in a telec
Antonelli Terry Stout & Kraus LLP
Hong Harry S.
Nokia Corporation
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