Multiplex communications – Communication over free space – Repeater
Reexamination Certificate
2000-05-25
2004-05-25
Yao, Kwang Bin (Department: 2667)
Multiplex communications
Communication over free space
Repeater
C370S395520, C370S475000
Reexamination Certificate
active
06741573
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention generally relates to communication systems utilizing a satellite link and, in particular, to a method and apparatus for dynamically assigning a satellite link to a client in response to a request from the client.
2. Description of the Related Art
Because of the limited bandwidth of a network of the Internet, especially a limited bandwidth of a line to a home of an Internet user who uses a dial up, users complaints have increased due to unavailability of satisfactory service while the demand of the Internet has consistently increased. A problem for a user who has a dedicated line is inability of assuring enough bandwidth because the user may want to suppress line cost investments to a minimum.
Further, a contents provider tends to demand transmission of a larger data size than conventional information, such as an image and a voice, to make the contents fancier or to provide a new service. This causes the network bandwidth needed by users to expand more and more.
In such circumstance, a satellite network providing an advantage of a wider bandwidth and service area has been focused as a new infra-structure of network. However, a user usually prepares a receive-only device for satellite wave with no transmission function (satellite receiving antenna, antenna adapter or board, set-top-box, etc.) as a user side facility. This means the end-user having only the above receive-only device cannot use a satellite network as a part of the Internet because a bi-directional link which provides on-demand communication is its prerequisite. Therefore, some mechanism has to be implemented into a client machine to make the satellite link appear as if it is bi-directional.
When an end-user's terminal which does not have a transmitting set communicates with a satellite, the following four schemes a-d may be conventionally available.
a. In this scheme, a client machine simply receives data flowing down from a satellite. This is analogous to the morphology of a television broadcasting and has no on-demand capability which is the basic requirement of the Internet. However, the configuration is simplest. This may be referred to as a “unidirectional communication receiver”.
b. In this scheme, a client machine dials up a predetermined site using an inexpensive modem and a telephone line to request transmission of only the data residing in the site server. This is relatively easy to configure and useful, for example, when it is desired to use a satellite network as a part of an intranet. However, this can not be used in a wide area network such as the Internet. This may be referred to as a “site local receiver”.
c. In this scheme, a client machine dials up a predefined site in a manner similar to the above scheme b and requests a mediate agent server (proxy server) in that site to distribute data. The agent server receives data from a target server which may be located in other than the dialed up site and distributes it via a satellite. This makes the receiver pretend to do a bi-directional satellite communication in effect though the receiver communicates with the target server indirectly. This morphology can be used not only in a closed environment such as an intranet but also for an Internet service. However, available services are limited because the request from a client depends on service items which the agent server can process. In addition, as well as a site local receiver, the client must connect to a predefined dial-up site first. Also, a client's request packet must go through the dial-up site regardless of the target server location. This configuration may bring an unwilling state to the customer due to unneeded roundabout. This may be referred to as an “indirect receiver”.
d. This scheme emulates a perfect bi-directional communication in which a client transmits a request directly to a target server by using its surface line as a pseudo-transmitting (uploading) channel toward a satellite, while a modem, a terminal adapter (TA) and a telephone line are also required in the manner similar to the above schemes b and c. This may be referred to as a “bi-directional communication emulation receiver”. This is also used in this invention and will be described later in detail.
It is necessary to adopt the above scheme d in order to utilize a satellite link as a part of a general high bandwidth network which can be inter-operated with the Internet by making the link pretend to be a bi-directional link, i.e., to utilize a satellite communication as a perfect IP (Internet Protocol) network infra structure.
1. Prerequisite of Client:
A user prepares a client machine having a modem or TA connected with a telephone line to provide a bi-directional link interface (hereinafter called BDL-IF) for a terrestrial link and a receive-only a satellite receiver board, or a satellite receiver having a BDL-IF and an antenna connection interface (hereinafter collectively called “client machine”). To set up the client machine, not only an IP address of BDL-IF but an IP address of a unidirectional interface (hereinafter called UDL-IF), which is different from the one for BDL-IF, must be assigned. This UDL IP address is assigned from a satellite communication provider (hereinafter simply referred to as a service provider which is different from a so-called Internet service provider or ISP) such as a satellite communication enterprise or a satellite communication system integrator.
With regard to a routing table for the client machine, UDL-IF must be set to be a default interface for sending an IP packet. By doing this, a normal outgoing IP packet is hooked to be transmitted to the UDL-IF. This is for the purpose of making the TCP/IP layer above the UDL-IF driver pretend to send out its own request packet from the UDL-IF. At this time, because the receive-only UDL-IF can not send out the IP packet, the user selects a BDL-IF for sending out the IP packet instead of the UDL-IF statically or dynamically with some action. While a request packet is sent out from a selected terrestrial line to a target server, the sender address shown therein is the address of the UDL-IF.
To pretend the above mechanism is sending out a packet from UDL-IF, it is a software prerequisite for the client machine to include a function of delivering (hooking) an output IP packet to the data link layer of a preselected BDL-IF at the moment when the IP packet is delivered from the IP layer to the data link layer of the UDL-IF upon sending out the packet from that interface as shown in FIG.
1
. This mechanism is implemented in a place between the IP layer and the UDL-IF driver as a part of the function of the data link layer of the UDL-IF.
What has to be satisfied as a network prerequisite is only to assure that the client machine keeps an IP reachability to the target server through a terrestrial line, and it is not necessary to dial up to a predetermined site in the manner in which a unidirectional communication receiver or a site local receiver does.
The system described above need not modify a TCP/IP application which the user uses daily and the hardware/driver of the interface for a terrestrial line equipped in the client. Therefore, it is a substantial merit that modification of a client is minimized.
2. Data Flow:
The client machine sends out a packet which indicates the address of the UDL-IF as a sender to any target server via the BDL-IF. An addressed target server or destination server receives the IP packet and finds the route by itself or from the parent router that the sender IP address is a part of the address range managed by a service provider.
The addressed target server then transfers a reply packet toward a boundary router propagated by the service provider because the route to the sender indicates the site of the service provider, and sends it either to a router to which a satellite wave transmitting device called a “feed” is connected (hereinafter referred to “feed router”) or directly to the feed if the feed is a router itself. The feed router or the fee
Asaeda Hitoshi
Izumiyama Hidetaka
Kotani Shinya
Takei Jun
Holland & Hart LLP
International Business Machines - Corporation
Sirr, Esq. Francis A.
Yao Kwang Bin
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