Multiplex communications – Pathfinding or routing
Reexamination Certificate
2000-03-01
2004-03-30
Olms, Douglas (Department: 2661)
Multiplex communications
Pathfinding or routing
C370S352000, C370S397000, C370S395530
Reexamination Certificate
active
06714532
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method and an apparatus for network connection, which interconnect various networks, e.g., a Local Area Network (LAN) with a wide area network or the like. More particularly, the invention relates to a -method and an apparatus for network connection, which perform communication channel allocation for the wide area network in order to ensure communication quality.
Communications between private networks located in remote areas must be carried out through a wide area communication network. Also, data communications carried out by connecting the LAN with the wide area communication network must employ a network connecting device called a router. In this case, depending on differences in communication systems among wide area networks to be utilized, a method for providing a communication channel to the router may vary in a following manner.
A circuit switching system is available as one of the communication systems among the wide area communication networks. In this system, communication lines are linked beforehand between a user and a switching system and between switching systems. But none of the lines is closed, and no communication channels are provided between users in a normal state. To provide a communication channel for connecting specific two points, communication lines are connected to each other in the switching system by signaling process corresponding to a connection destination that a user specifies by calling before the start of communications. Such a method of transferring communication data, which is accompanied by call control processing, is called a connection-oriented transmission.
In the case of a device called a dial-up router, a connection destination is specified based on protocol control information of packet data carried on a LAN, and the packet data on the LAN is transmitted to the communication channel provided by the foregoing system. Accordingly, inter-LAN communications can be carried out by changing connection destinations when necessary. Similarly, in the circuit switching system, by using the communication channel provided by the communication line which connects the predetermined two points beforehand, the need to perform signaling process can be eliminated at each starting of communications. The communication line provided in such a manner is called a leased line. In the case of a device called a remote router, inter-LAN communications can be carried out by transmitting packet data on the LAN to the communication channel on the leased line.
There is another different communication system called a packet switching system. Also, for this system, communication lines are linked beforehand between a user and a switching system and between switching systems. In the packet switching system, however, communication lines are not so configured as to connect predetermined two points before the start of communications by signaling or a leased line like that in the circuit switching system. Instead, each switching system interprets protocol control information of the packet data on the LAN and, then, by selecting a switching system of a transfer destination and repeating transfer, transmits the packet data to a LAN of communication destination. Thus, one communication channel is always provided to the user and, by using this channel, the user can communicate with all the LANs that need to be connected. Such a method of transferring communication data, which is not accompanied by any signaling process, is called a connectionless transmission.
There is yet another system called an Asynchronous Transfer Mode (ATM) communication system. In this system, as in the case of the circuit switching system, a communication channel to connect predetermined two points is allocated corresponding to a connection destination that a user specifies by calling before the start of communications. But a communication line between switching systems is not directly connected, and only the correspondence thereof is held. A logical number for identifying the correspondence is provided to the user as a number for identifying the communication channel. The user adds this logical number to packet data, and then transmits the data. Each switching system selects a communication line to be used for transfer based on the logical number added to the packet data. Accordingly, a plurality of communication channels can be provided separately by one communication line. Also, by means of setting made beforehand as in the case of the circuit switching system, a predetermined communication channel can be used as a permanently set leased line.
In any of the above systems, it is necessary to establish correspondence between the protocol control information of the packet data on the LAN and the communication channel provided by the wide area communication network. As a method for this purpose, a Multi-Protocol over ATM (MPOA) is available, which makes a detailed description especially of the ATM communication system. In accordance with this method, a device having an address translation function and a packet switching function is provided on the communication network of the ATM system, and a communication channel for communicating with the device is permanently set. The user can transmit the data packet on the LAN to the permanently set communication channel, and can also transmit the packet data to a newly set communication channel by using the address translation function to decide a connection destination.
For data communications on the wide area communication network, if the packet switching system is used, which multiplexes all packet data on one communication channel, it is difficult to maintain, for a long time, communication quality such as assurance of a constant bandwidth keeping of constant transmission delay time or the like. On the other hand, if the circuit switching system is used, which allocates individual communication channels for respective data communications, data packets from the LAN can stay in the network connecting device during signaling process for allocating the communication channels. Therefore if the communication traffic is heavy, the data packet may be discarded, and normal communications may not be established. If the leased line is used, since a communication line connected to a specified opposite point is continuously held even when there is no data packet to be transmitted, efficiency may be reduced.
Also, in the case of logically setting communication channels by the packet switching system or the ATM communication system, similar cases may occur. This is because switching system resources are held by setting of each switching system or by. reservation for use of a buffer or the like.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to prevent data packets from staying in the network connecting device during allocation of individual communication channels for respective communications. This is achieved by selecting a connectionless transmission network such as the packet switching system or the leased line and a connection-oriented transmission network such as the circuit switching system. In this case, according to the invention, a plurality of networks operated by different subjects are used in free combination while the connectionless transmission network and the connection-oriented transmission network are kept independent of each other. Also, another object of the invention is that under an artificially specified condition one to be used for communications is selected from the plurality of networks and used.
Regarding allocation of individual communication channels for respective data communications, allocation is carried out in the starting order of communications. In this case, if a transfer capability of the network reaches saturation, no new communication channels can be allocated for subsequent new data communications. Consequently, the network may be occupied by the existing users in the circuit switching system, and new users cannot make instantaneous use of the
Antonelli Terry Stout & Kraus LLP
Hitachi , Ltd.
Olms Douglas
Pizarro Ricardo M.
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