Multiplex communications – Pathfinding or routing – Combined circuit switching and packet switching
Reexamination Certificate
1999-03-01
2003-07-29
Yao, Kwang Bin (Department: 2662)
Multiplex communications
Pathfinding or routing
Combined circuit switching and packet switching
C370S241000, C370S401000, C370S395210
Reexamination Certificate
active
06600735
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an Internet telephone connection method for performing a call connection, etc. to a PSTN (public switched telephone network) through a gateway device for use in an Internet telephone system having a gateway device, a gate keeper, a bandwidth controller, and a router, etc.
2. Description of the Related Art
A method of implementing a protocol for servicing a telephone call from Internet to a PSTN is provided in Recommendation H.323 of ITU-T (International Telecommunication Union-Telecommunication Standardization Sector). In H.323, a gateway device for performing the interconnection processing between a PSTN and the Internet, and a gate keeper for managing/controlling plural gateway devices are used as main constituent elements. The gateway device performs conversion of a call control protocol and audio signals between the PSTN and the Internet. The gate keeper serves to manage the gateway devices in a zone under its control, and mainly performs selection of a connection destination gateway, authorization and admission control of a calling side, and allocation of a telephonic communication bandwidth in response to a call setup request from an IP (Internet Protocol) terminal or a gateway device.
In a case where a gateway device at a calling side (i.e., a call source), a gateway device at a called side (call destination) and a gate keeper are provided, the calling side gateway device which accepts a call reception from a PSTN assigns a connection condition such as the telephone number of a connection destination, etc. and inquires to the gate keeper. In response to this inquiry, the gate keeper determines the address of a called side gateway device which satisfies the request condition, and notifies it to the calling side gateway device. Subsequently, the calling side gateway device proceeds in the connection of the call to the called side gateway device. When a call setup is accepted between the gateway devices at the calling side and the called side, audio data are transmitted/received according to a protocol for transferring real-time data. In other words, the three-step procedures, that is, a procedure of determining the gateway device of a connection destination, a procedure of connecting a call to the gateway device thus determined and a procedure of transferring real-time information between the gateway devices thus connected are carried out for the call connection. The calling side gateway device may be designed in the form of an IP terminal having a telephone function.
Guidelines for the attribute information of the gateway device is specified in “a Framework for a Gateway Location Protocol” (IPTEL Working Group, Jul. 7, 1998) which has been considered by IETF (Internet Engineering Task Force). According to the guidelines, an assembly of gateway devices managed by the same gate keeper are defined as a zone, and it is assumed to extend to a form comprising plural zones. As the attribute information of the gateway device, there is provided the phone prefixes allowed, the address of a gateway device, the specification for voice coding, a signal protocol to be supported, a cost plan, a billing method, the confederation of membership, a total line capacity, an available line capacity, information concerning additive features supported, etc.
Here, the phone prefixes allowed represents an assembly of connectable telephone numbers when a connection is made from the gateway device thereof to a PSTN. Such attribute information is generally set in each gateway device by a maintainer or the like. In the following description, information causing a problem in connection such as a signal protocol supported by the phone prefixes allowed in the attribute information is referred to as “end-end attribute information”.
The standardization of IETF aims to specify means for automatically registering the above attribute information into a gate keeper and means for informing the information to other gate keepers. With these means, when a new gateway device is connected to the Internet, the attribute information to be informed is automatically distributed to all the gate keepers which are mutually connected to one another using the protocol.
According to the model provided in IETF, there are assumed not only a case where only one gateway device is selected by the gate keeper, but also a case where a destination gateway device is selected from plural choices. Accordingly, if a gateway device at a calling side is aware of any problem/congestion condition or the like at a called side, a backup mechanism to enhance the reliability could be implemented. An available line capacity and an operation/stop state of the gateway device itself may be considered as the attribute information on the problem/congestion condition.
After a gateway device at a connection destination is selected and a pair of gateway devices are determined, a call connection is carried out according to the procedure of H.323. Whether a desired bandwidth can be secured between the gateway devices becomes clear after the protocol procedure after the connection proceeds. Therefore, if the Internet is in a congested condition, a desired quality of connection may not be provided. There is proposed a gateway device having a communication bandwidth reserving procedure such as RSVP (Resource Reservation Protocol) standardized in IETF, as described in Chapter 2 of “Delivering Voice over IP Networks” (written by D. Minoli, E. Minoli). The RSVP procedure is a procedure for reserving a oneway bandwidth from a called side to a calling side. According to this procedure, bandwidths are successively ensured via routers from the application at the called side to the application at the called side. In this case, reservations requesting the same bandwidth from both the sides are needed for voice traffic which needs a symmetrical bandwidth between upward and downward directions. If each application reserves a desired bandwidth with no limitation, a bandwidth-over event would occur and it is generally known that it is impossible to implement the perfect bandwidth guarantee in RSVP.
SUMMARY OF THE INVENTION
In the above conventional technique, when an IP terminal is connected to a PSTN through a gateway device, a communication bandwidth is allocated every time a call request occurs. Therefore, a total line capacity for call connection may not be ensured if the Internet is congested although there is an available communication line between the gateway device and the PSTN. Further, when a reservation procedure of reserving a communication bandwidth is used, the reservation of the optimum bandwidth in the overall network cannot be implemented because the gateway device has no means of ascertaining the bandwidth reservation status of the other gateway devices. In addition, since the perfect guarantee cannot be implemented even for reserved bandwidth, communication quality may not be ensured even when a call is setup on a reserved bandwidth. Still further, the telephone traffic amount and the data traffic amount vary with time, and thus the network resources could not be effectively used unless control based on prediction of load can be implemented.
A first object of the present invention is, in view of the above described problem, to ensure a fixed-quality communication bandwidth matched with a traffic demand between gateway devices in the Internet, enhance reliability and flexibly support variation of a traffic condition.
In the prior art, it is necessary to use a system of setting up a call for every request between gateway devices each having a relatively small traffic amount from the viewpoint of effective use of communication bandwidths of the network. When the connection is made according to the three-step procedure as described above, there is a case where a call connection to the gateway device of a connection destination selected in the first step does not succeed. This may be caused by some problem at some intermediate point in the route, some problem of the gate
Honda Ryogo
Iwama Etsuko
Kuroyanagi Kansuke
Mori Yuichi
Sugimoto Tomohide
Hitachi , Ltd.
Nguyen Hanh
Sofer & Haroun LLP
Yao Kwang Bin
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