Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
1998-05-19
2002-05-21
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Repeater
C370S329000
Reexamination Certificate
active
06393001
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a satellite communication system for executing routing procedure to transfer data from one computer to another computer by a relay system using a satellite or satellites. The present invention also relates to a routing method for the satellite communication system, and to a storage device, for a computer, with a program of the routing.
DESCRIPTION OF THE RELATED ART
In general, a satellite relay system simultaneously utilizes the same satellite for a plurality of relay connections through the use of multiplexing technology such as the FDMA (Frequency Division Multiple Access) method, the TDMA (Time Division Multiple Access) method (synchronous time division multiplexing method) or the cell based multiplexing (asynchronous time division multiplexing) method.
This satellite relay system will provide the similar functions as that each relay connection has an individual communication line. Since no physical communication line is in fact provided for each relay connection, this communication line is called as a logical channel or a virtual channel.
Such the satellite relay system can provide communication between any computer having functions for transmitting information via satellite and any computer having functions for receiving information via satellite. To realize the communication with respect to a connection determined by the combination of the transmit computer and the receive computer, it is necessary to use a routing method for selecting one of finite number of logical channels provided by the satellite through the use of the multiplexing technology.
As for a conventional routing method for the satellite communication, there is a “static” routing method which preliminarily allocates logical channels to the respective transmit computers or the respective receive computers in a fixed manner.
Japanese Patent unexamined publication No.9(1997)-64937 describes this “static” routing method. According to this known method, when the receive computer requests to the transmit computer to transfer data, this receive computer designates an address for a satellite communication and thus the transmit computer establishes routing via the satellite communication line defined by the designated address. In fact, this publication does not clearly teach allocation of the logical channels in the satellite communication line. However, the address for the satellite communication will be apparently used for defining this logical channel because both the transmit and receive computers can use the same logical channel depending upon the address designated by the receive computer. Furthermore, in order to prevent contention between the receive computer in question and another possible receive computers with respect to the same logical channel, it is necessary to exclusively allocate the logical channels to the respective receive computers. Therefore, the publication apparently describes the “static” routing method.
However this “static” routing method will limit the number of usable connections, namely the number of combinations of the transmit and receive computers to the finite number of the logical channels which are presented by the relay system through the use of the multiplexing technology.
Since the number of the transmit and receive computers for receiving services in the communication system will increase, it will be necessary to serially use the same logical channel for different connections. A “dynamic” routing method which allocates the logical channel dynamically at every communication is served to this end.
U.S. Pat. No. 5,485,464 describes a “dynamic” routing method. According to this known method, as shown in
FIG. 1
, a transmit computer (source user) requests allocation of a logical channel to a computer (network control center) in a satellite relay system, who manages the logical channels, so that the source user is routed to a receive computer (destination user) with the aid of the network control center.
International publication W095/13681 describes another “dynamic” routing method. According to this known method, as shown in
FIG. 2
, a receive computer requests allocation of a logical channel to a connection management computer who manages the logical channels in a satellite relay system, then the connection management computer notifies it to a transmit computer or a service provider, and the transmit computer requests to the connection management computer so as to establish route from the service provider to the receive computer.
In a data communication system called as a client-server model, in general, a client computer (receive computer) always requests data transfer so that a server computer (transmit computer) transmits the data to the client computer. In the event that the same client computer continuously receives a plurality of data from the server computer, in a client-server model constructed to use the satellite relay system, it is desired to maintain the usage of the same logical channel without executing allocation procedure of logical channels at each transfer of data.
However, if the client-server model is constructed in accordance with the “dynamic” routing method described in U.S. Pat. No. 5,485,464, the client computer (receive computer) controls second or later transfer whereas it is the server computer (transmit computer) to control allocation of the logical channels executed in the network control center. Thus, when the server computer controls release of the allocation of the logical channel, some problems may occur. For example, in this model, if the same client computer requests next transfer of data to the server computer within a predetermined time period, the same logical channel will be kept to use, whereas if there is no request for next transfer within the time period, the allocation of the logical channel will be released. However, to realize this algorithm, it is necessary to introduce a timer mechanism. In addition, the logical channel cannot be utilized again for the predetermined time period after the client computer finishes its usage causing ineffective usage of the logical channel.
The above-mentioned problems can be solved by the “dynamic” routing method described in the international publication WO95/13681, in which allocation/release of the logical channel by the connection management computer is executed in response to requests from the client computer.
However, in the event of “Net-surfing” access in the Internet, wherein a client computer continuously receives data from a plurality of server computers, for example two server computers as shown in
FIG. 3
, this known routing method of WO95/13681 cannot provide that the client computer keeps the same logical channel to use. This is because since the server computer controls allocation/release of the logical channel by the connection management computer in response to the request from the client computer, if the server computer with logical channel allocation functions changes to another one, the same logical channel cannot be kept in use. Therefore, when the client computer receives data from different server computers in for example “Net-surfing” access, the routing method of WO95/13681 needs an additional procedure for switching the logical channels used causing delay in start of next transfer of data and also increase of control traffic.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a satellite communication system, a routing method for the satellite communication system, and a storage device storing a program of the routing, whereby problems due to separated location of transfer control function and logical channel allocation function in different computers can be solved.
According to the present invention, a routing method wherein a receive computer or a client computer for requesting transfer of information controls routing but a transmit computer or a server computer does not concern routing procedure is provided.
More particularly, according to the present invention, a satellite
Arent Fox Kintner & Plotkin & Kahn, PLLC
Chin Wellington
Nippon Telegraph and Telephone Corporation
Pham Brenda
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