Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-09-11
2001-07-31
Ton, Dang (Department: 2732)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
Reexamination Certificate
active
06269100
ABSTRACT:
BACKGROUND
1. Field of the Invention
The present invention relates to the transfer of call legs within a telecommunication network. While the invention is applicable to many different types of networks, it particularly lends itself to use in the transfer of B channels within an integrated services digital network (ISDN) telecommunication environment. The invention is applicable to B channel transfers where the B channels are part of a primary rate interface (PRI) or ISDN user part (ISUP) based trunk network.
2. Description of the Problem Solved
Businesses and enterprises that use the public telecommunication network typically require services such as call transfer, conference calling, and call forwarding. In many cases the services are supplied by service nodes which are connected to the public network switch which serves the particular enterprise. Examples of service nodes include voicemail systems and international call-back servers. For purposes of this disclosure, we also consider a PBX or any other type of privately owned telecommunication device to be a service node. In order to supply the services required by the enterprise, the switches and service nodes often have to maintain multiple call legs for a given call. Each call leg between a given switch and a given service node is connected via a channel which is part of an interface. In an ISDN environment each channel is a B channel, and the interface is either a primary rate interface or an ISUP controlled trunk.
There are numerous situations where multiple call legs might be used. As an example, consider a user who dials into a voicemail system. Typically, a voicemail system provides an option to press a key and immediately and automatically call a party back who has left a message. When the user executes this function, the voicemail system dials the party over a separate connection and internally connects the user and the party within the voicemail system. The voicemail system stays in the call path so that the user can resume listening to messages when the call between the user and the called party is complete. This call path results in two B channels between the switch and the voicemail system being used to connect the user and the called party. Alternatively, the voicemail system could dial the party and connect the user and the party by making a transfer such as the B channel transfer described in published Bellcore Standard GR-2865-Core, Issue 2, May 1997, which is incorporated herein by reference. This transfer frees up the two B channels between the switch and the voicemail system, but at a cost to the user. When the call between the user and the called party is complete, the user must re-dial the voicemail system to resume listening to voicemail messages.
The problem created by the situation is that service nodes and their network connected switches are required to have extra active ports for the sole purpose of holding access to calls which the service node may need to recover in the future under certain conditions. The extra ports cost money because additional equipment must be purchased and maintained to supply the required capacity. If a personal computer is being used as a service node, extra adapter cards must be purchased. If long distance charges apply, the extra long distance costs can be considerable. What is needed is a way to release and conditionally retrieve a call leg which goes unused for a period of time due to a call transfer or similar event. Ideally, call retrieval should be able to be based on the occurrence of one or more of a variety of events.
SUMMARY
The present invention solves the problem discussed above by providing message extensions to the interfaces for the purpose of identifying calls legs and calls. When joined in two party or conference calls the messages exchanged between the service node and the switch also supply conditions for retrieval. Conditions such as timer expiration, in-band tones, participant release, etc. all apply. When any specific condition is satisfied, the service node signals with the call identifier and port ID if appropriate. The new message permits the service node to specify the dispensation of the remaining call legs, including retrieving them to B channels attached to the service node.
The invention operates whenever at least a first and second call leg are connected between the switch and a service node. The service node sends a transferwith-retrieve message containing retrieval conditions to the switch. The switch receives the transfer-with-retrieve message, stores the retrieval conditions, and transfers the call leg. When the retrieval conditions are satisfied, the switch notifies the service node. The specific retrieval conditions used can be selected by one of ordinary skill in the art who is designing the particular telecommunication system. Examples of possible retrieval conditions include the lapse of a specified interval of time, the receipt of specific in-band tones, and participant release. In one embodiment, the switch automatically retrieves and reconnects the call at the same time. In another embodiment, the switch waits for specific retrieval instructions from the service node. Although this method works in variety of communications systems, in the preferred embodiment the network involved is an integrated services digital network (ISDN) and the communication channels are ISDN B channels.
The invention is typically implemented using computer program products for the switches and service nodes involved. A computer program product includes a media with computer program code which causes the systems involved to perform the necessary operations. A switch which implements the invention includes a switching matrix, one or more peripheral modules connected to the switching matrix, one or more input/output devices connect the switching matrix, and a processor core which controls the operation of the switch and, during operation, contains the computer program code which implements the invention. A service node which implements the invention essentially includes similar components. However, the service node includes different computer program code. The invention operates in a communication network which includes at least one switch, one service node, and communication channels connected between.
Use of the present invention in a telecommunication network reduces the number of ports required on both switches and service nodes by using switch resources to capture mid call transfers and recover calls to the off switch system only as required. This reduction in the number of ports used to maintain calls results in significant transmission plant and port cost savings.
REFERENCES:
patent: 6081508 (2000-06-01), West et al.
Christie, IV Samuel Henry
Dagert Patrick J.
Nortel Networks Limited
Ton Dang
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