United States Patent [19J
`Ota et al.
`
`[54] CELLULAR COMMUNICATION NETWORK
`AND ITS COMMUNICATION METHOD
`
`[75]
`
`Inventors: Takeshi Ota; Kouichi Yoshimura;
`Kazunori Horikiri, all of Nakai-machi,
`Japan
`
`[73] Assignee: Fuji Xerox Co., Ltd., Tokyo, Japan
`
`[21] Appl. No.: 08/810,112
`
`[22] Filed:
`
`Feb. 25, 1997
`
`[30]
`
`Foreign Application Priority Data
`
`Feb. 26, 1996
`Feb. 10, 1997
`
`[JP]
`[JP]
`
`Japan .................................... 8-037601
`Japan .................................... 9-026263
`
`Int. Cl.7 ....................................................... H04B 7/26
`[51]
`[52] U.S. Cl. ........................... 455/553; 455/552; 455/445
`[58] Field of Search ..................................... 455/554, 555,
`455/426, 445, 432, 552, 463, 462, 437,
`440, 553; 370/338, 328; 359/118, 145
`
`[56]
`
`References Cited
`
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`5,282,257
`5,301,400
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`5,732,127
`5,812,531
`
`1/1994 Ota .
`4/1994 Sawyer et al. .......................... 455/445
`3/1995 Thompson et al. ..................... 455/440
`3/1995 Flammer et al.
`....................... 455/445
`12/1995 Israelsson ................................ 359/145
`4/1996 Emery et al. ........................... 455/445
`1/1997 Bales et al. ............................. 455/418
`6/1997 Garneurz et al. ....................... 455/437
`3/1998 Hayes ...................................... 379/115
`9/1998 Cheung et al.
`......................... 455/445
`
`FOREIGN PATENT DOCUMENTS
`
`2-162846
`2-235447
`
`6/1990
`9/1990
`
`Japan .
`Japan .
`
`I 1111111111111111 11111 111111111111111 11111 111111111111111 lll111111111111111
`US006115615A
`[11] Patent Number:
`[45] Date of Patent:
`
`6,115,615
`Sep.5,2000
`
`3-91329
`4-506294
`6-164498
`6-311083
`
`4/1991
`10/1992
`6/1994
`11/1994
`
`Japan .
`Japan .
`Japan .
`Japan .
`
`OTHER PUBLICATIONS
`
`"Dynamic Range on Fiber-Radio Microcell Radio System,"
`Proceeding of the 1994 IEICE Spring Conference B 488. H.
`Arai et al., 1994.
`Ota, Takeshi. "Coupled Star Network: A New Configuration
`for Optical Local Area Network." IEICE Trans. Commun.,
`vol. E75-B, No. 2, Feb. 1992, pp. 67-75.
`
`Primary Examiner-Salvatore Cangialosi
`Attorney, Agent, or Firm-Oliff & Berridge, PLC
`
`[57]
`
`ABSTRACT
`
`An overlay cellular communication network, which includes
`a first base station for providing a first cellular communi(cid:173)
`cation network having a first cell size, and a second base
`station for providing a second cellular communication net(cid:173)
`work which covers the first cellular communication network
`and has a second cell size, is provided to determine a proper
`transmission route immediately and to cover a broad area
`communication network with certainty.
`
`A mobile station belonging to an overlay communication
`network, which includes a micro cell having a first cell size
`and a macro cell having a second cell size, has an mobile
`station identification address in the application layer defined
`by the OSI reference model, and also has a plurality of
`addresses, each of the plurality of addresses belonging to
`one of the data link layer through the presentation layer
`defined by the OSI reference model, which represent routes
`to reach the mobile station. A transmitting route is deter(cid:173)
`mined by combining properly the mobile station identifica(cid:173)
`tion address and the address representing a route.
`
`20 Claims, 19 Drawing Sheets
`
`VZZZ2I
`
`211
`
`ROUTE-1
`
`ROUTING
`DATABASE
`,,A
`
`216
`
`--------------------
`ROUTE-2
`
`--
`
`ROUTE-1
`ROUTE-2
`
`APPLICATION LAYER
`'-'
`LEVEL ADDRESS
`Ji""
`217
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`I
`I
`I
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`~ 2 1 3
`
`APPLICATION LAYER
`LEVEL ADDRESS
`
`Ex.1015
`APPLE INC. / Page 1 of 28
`
`

`

`U.S. Patent
`U.S. Patent
`
`Sep. 5, 2000
`Sep.5,2000
`
`Sheet 1 of 19
`Sheet 1 of 19
`
`FIG.1
`
`6,115,615
`6,115,615
`
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`
`Ex.1015
`APPLEINC./ Page 2 of 28
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`Ex.1015
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`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 2 of 19
`
`6,115,615
`
`20
`
`INFORMATION
`PROCESSING
`BODY
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`INTERFACE
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`
`25
`
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`
`24
`
`21
`
`23
`
`FIG.2
`
`Ex.1015
`APPLE INC. / Page 3 of 28
`
`

`

`U.S. Patent
`
`Sep.5,2000
`
`Sheet 3 of 19
`
`6,115,615
`
`APPLICATION
`LAYER
`
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`Ex.1015
`APPLE INC. / Page 4 of 28
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`Ex.1015
`APPLE INC. / Page 5 of 28
`
`

`

`U.S. Patent
`
`Sep.5,2000
`
`Sheet 5 of 19
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`Ex.1015
`APPLE INC. / Page 6 of 28
`
`

`

`U.S. Patent
`
`Sep.5,2000
`
`Sheet 6 of 19
`
`6,115,615
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`Ex.1015
`APPLE INC. / Page 7 of 28
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 7 of 19
`
`6,115,615
`
`20
`
`41
`
`42
`
`INFORMATION
`PROCESSING
`BODY
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`INTERFACE
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`
`43
`
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`
`Ex.1015
`APPLE INC. / Page 8 of 28
`
`

`

`U.S. Patent
`
`Sep.5,2000
`
`Sheet 8 of 19
`
`6,115,615
`
`MOBILE STATION
`ADDRESS
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`
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`
`Ex.1015
`APPLE INC. / Page 9 of 28
`
`

`

`U.S. Patent
`U.S. Patent
`
`Sep. 5, 2000
`Sep.5,2000
`
`Sheet 9 of 19
`Sheet 9 of 19
`
`FIG.9
`
`6,115,615
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`Ex.1015
`APPLEINC./ Page 10 of 28
`
`Ex.1015
`APPLE INC. / Page 10 of 28
`
`

`

`U.S. Patent
`
`Sep.5,2000
`
`Sheet 10 of 19
`
`6,115,615
`
`6
`
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`
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`
`10
`
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`
`Ex.1015
`APPLE INC. / Page 11 of 28
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 11 of 19
`
`6,115,615
`
`20
`
`21
`
`23
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`
`Ex.1015
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`
`

`

`U.S. Patent
`
`Sep.5,2000
`
`Sheet 12 of 19
`
`6,115,615
`
`APPLICATION
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`Ex.1015
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`
`

`

`U.S. Patent
`
`Sep.5,2000
`
`Sheet 13 of 19
`
`6,115,615
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`APPLE INC. / Page 14 of 28
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`U.S. Patent
`U.S. Patent
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`Sep.5,2000
`Sep. 5, 2000
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`APPLE INC. / Page 17 of 28
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`

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`Ex.1015
`APPLE INC. / Page 19 of 28
`
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`Ex.1015
`APPLE INC. / Page 20 of 28
`
`

`

`6,115,615
`
`1
`CELLULAR COMMUNICATION NETWORK
`AND ITS COMMUNICATION METHOD
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`This invention relates to a cellular communication net(cid:173)
`work and its communication method, and more particularly
`an overlay type cellular communication network, which has
`a configuration in which cells having different cell sizes
`overlap, and its communication method. Further, this inven(cid:173)
`tion relates to a cellular communication network using both
`free space light and a radio wave as a transmission medium.
`Further this invention relates to a wide area communication
`network and a local area network (LAN). This invention also
`relates to a routing technology to switch transmission routes 15
`of a packet, which is responsible for information transmis-
`SlOn.
`2. Description of the Related Art
`Conventionally, a cellular communication network shown
`in FIG. 16 is widely known. Base stations 101a through
`101d provide services in cells 103a through 103d, respec(cid:173)
`tively. The base stations 101a through 101d are connected
`each other by a wiring network or a fixed wireless network
`(i.e. a micro wave network having directivity) 104. The base
`station 101a and a mobile station 102a communicate each
`other by means of a radio wave. Adjacent cells uses radio
`waves of different frequencies for communication between
`the base station and the mobile station, to avoid an inter(cid:173)
`ference between cells. A mobile station 102b which is near
`a boundary between cells, negotiates with the base stations
`101a and 101b in order to select a base station to be linked
`from the base stations 101a and 101b. This communication
`process is called "hand-over". This communication network
`is widely used for a mobile telephone or a personal handy 35
`phone system (PHS).
`As an extension of the above-described cellular commu(cid:173)
`nication network, a cellular communication network which
`integrates a macro cell indicating a big size cell and a micro
`cell indicating a small size cell, is proposed. For instance, 40
`Japanese Laid-Open Hei. 4-506294 proposes a system
`shown in FIG. 16, in which a communication satellite is
`employed as a macro cell 202 and base stations 101a
`through 101d built on the earth are employed as micro cells.
`In this system, a mobile station 102 is linked via a radio
`wave 204 to one of the base stations 101a through 101d in
`the area having high population, and is linked via a radio
`wave 203 to the communication satellite 201 in an area
`where it is unprofitable to build a base station because of its
`small population.
`In this specification, the structure in which the micro cell
`is overlaid with the macro cell is called an overlay cellular
`communication network. Actually, this kind of overlay cel(cid:173)
`lular communication network is spontaneously generated.
`For instance, when a PHS network whose cell size is a few
`hundred meters is built in an area where a mobile telephone
`network whose cell size is a few kilometers has been built,
`an overlay cellular communication network seems to be
`generated. These two networks are separately managed,
`however, they are not enough for a well-organized overlay
`cellular communication network. That is, a interconnection
`between the macro cell and the micro cell is not considered.
`A system in which base stations are wired by optical fibers
`and optical signals directly modulated by radio waves are
`distributed among the base stations, is proposed as the
`above-described cellular communication network (Japanese
`Patent Laid-Open No. Hei. 6-311083, and Arai et. al.,
`
`10
`
`2
`"Dynamic rage on Fiber-Radio Microcell Radio System",
`Proceeding of the 1994 IEICE Spring Conference B488
`(1994)). To form the cellular communication network, a
`system which uses free space light for communication
`5 between the base station and the mobile station, is also
`proposed (Japanese Patent Laid-Open No. Hei. 3-91329). A
`intercommunicating system rather than a cellular commu(cid:173)
`nication network, which distributes an optical signal directly
`modulated by a radio wave via an optical fiber network is
`also proposed (Japanese Patent Laid-Open No. Hei.
`6-164498).
`Meanwhile, a system which integrates light and a radio
`wave has been proposed for use in a remote control system
`(Japanese Patent Laid-Open No. Hei. 2-162846). FIG. 17
`shows a configuration of the system for remote control of a
`machine in an invisible area. A control signal from a remote
`controller 111 is transmitted to a machine 114 to be
`controlled, via interconnection devices 112 and 113. The
`control signal from the remote controller 111 is at first
`20 transmitted to an optical interface 115 of the interconnection
`device 112 by means of a free space light beam. The
`interconnection device 112 converts the free space light
`beam signal 123 into a radio wave 124, and transmits the
`produced signal to the interconnection device 113. The
`25 interconnection device 113 converts the radio wave signal
`124 into a free space light beam signal 125, and transmits the
`produced signal to the machine 114. In Fig. 17, reference
`numerals 116 and 117 are antennas. Reference numeral 119
`is an optical interface of the machine 114. A reference
`30 numeral 121 is a room where the remote controller 111 is. A
`reference numeral 122 is a room where the machine 114 is.
`A reference numeral 120 is a wall which separates the rooms
`121 and 122.
`As another example for use in a remote control system,
`Japanese Patent Laid-Open No. Hei. 2-235447 discloses a
`system which uses a radio wave to transmit a signal from a
`mobile station to a base station (interconnection device), and
`uses a free space light beam to transmit a signal from the
`base station (interconnection device) to the mobile station.
`FIG. 18 shows a network (internetwork) having a con-
`figuration which connects two networks 131 and 132 by way
`of an interconnection device 130. Types of the interconnec(cid:173)
`tion device 130 are classified into a gateway, a router, a
`bridge and a repeater in accordance with OSI (Open Systems
`45 Interconnection) reference model. FIG. 19 shows a diagram
`which associates the gateway, the router, the bridge and the
`repeater, to the layers of OSI reference model. It is known
`that the gateway, the router, the bridge and the repeater have
`interconnection features corresponding to the application
`50 layer, the network layer, the data link layer (in particular,
`MAC: the media access control layer) and the physical layer
`of OSI reference model, respectively. Conventionally, inter(cid:173)
`connection devices (interconnection device 130), such as a
`gateway, a router, a bridge or a repeater, were connected to
`55 two networks simultaneously. Meanwhile, a general termi(cid:173)
`nal (133 in FIG. 18) was not connected to two networks
`simultaneous! y.
`FIG. 20 schematically shows how a packet is encapsu(cid:173)
`lated and decomposed. At the transmission side, a packet is
`60 transmitted from the top layer to the bottom layer,
`successively, of the OSI reference model, and in each layer,
`a header of the layer (a session header, a transport header, a
`network header or a data link header) is added to the packet.
`At the reception side, a packet is transmitted from the
`65 bottom layer to the top layer of the OSI reference model, and
`in each layer, a header corresponding to the layer is removed
`from the packet. A typical gateway relays a packet after
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`6,115,615
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`3
`decomposing the packet into data entities. A router relays a
`packet after decomposing the received packet into a packet
`having a network header. A bridge and a repeater relay a
`packet without decomposing the packet itself. The repeater
`relays a packet without reference to contents of the data link 5
`header, while the bridge has a feature of packet filtering,
`which determines whether the packet is relayed or not in
`accordance with a MAC (media access control) address
`written in the data link header. A form of the packet (which
`header is attached to the packet) can be used to determine 10
`which layer of OSI reference model corresponds to a pro-
`cess.
`FIG. 20 does not show a trailer corresponding to a header,
`which is sometimes attached to the end of the packet. That
`is, a trailer (session trailer, transport trailer, network trailer
`or data link trailer), which corresponds to a header (session
`header, transport header, network header and data link
`header), can be attached to the packet. A data entity is
`sandwiched between a header and trailer to be capsulated.
`Since the header is indispensable, but the trailer is some(cid:173)
`times unnecessary, FIG. 20 does not include trailers.
`Since light is an electromagnetic wave having extremely
`high frequency, light can carry a broadband modulated
`signal. But light has a disadvantage that it is easily blocked
`by objects. Therefore, a cellular network using free space
`light has a disadvantage that a cell is small. In other words,
`more cells are required to cover a particular area.
`In the remote control system, the above-described Japa(cid:173)
`nese Patent Laid-Open Hei. 2-162846 proposes a system
`which uses both a radio wave and light, and compensates by 30
`a radio wave for a limit of distance which free space light
`can reach. Since this system simply replaces a particular
`signal route with a radio wave, however, it is insufficient to
`cover the whole of a relatively wide area as a cellular
`network.
`In a general cellular network, the above-described com(cid:173)
`munication process, what is called hand-over, is a control
`process carried out between plural base stations and a
`mobile station. Accordingly, there are problems that traffic
`between base stations increases and each base station must 40
`have an ability of information processing such as address
`management.
`
`35
`
`4
`to any of the free space light interface and the radio
`wave interface;
`at least one fixed first base station, each for communicat(cid:173)
`ing with the mobile station by way of a free space light
`in a first area;
`a fixed second base station for communicating with the
`mobile station by way of a radio wave in a second area.
`This configuration makes it possible to control problems
`of obstacles and to communicate surely and broadly in the
`second area formed by a radio wave, and to communicate at
`high speed in the first area formed by free space light.
`Further, when the second area covers the first area, it is
`possible to use enough high speed communication by posi(cid:173)
`tioning the first base station at the important position, and to
`15 cover a usual area by the communication via the second base
`station.
`Further, the mobile station can switch not only links to the
`first base station and the second base station, but also links
`to a plurality of base stations. Accordingly, since the mobile
`20 station can have more communication opportunities, the
`communication capacity will increase and the reliability of
`the network improves.
`To achieve the above-described objects, this invention
`also provides an overlay cellular communication network
`25 comprising: a first base station for providing a first cellular
`communication network of a first cell size;
`a second base station for providing a second cellular
`communication network of a second cell size, which
`covers the first cellular communication network, and
`a mobile station which has a mobile station identification
`address in the application layer level defined by the OSI
`reference model, and a plurality of addresses indicating
`routes to reach the mobile station from the first base
`station and the second base station, each of said plu(cid:173)
`rality of addresses belonging to one of the data link
`layer, the network layer, the transport layer, the session
`layer and the presentation layer defined by the OSI
`reference model.
`
`SUMMARY OF THE INVENTION
`The present invention has been made in view of the above
`circumstances. It is therefore an object of the invention to
`provide a new overlay type cellular communication network
`which integrates a radio wave and free space light. It is
`another object of the invention to realize efficient commu(cid:173)
`nication by providing a communication method which in a 50
`general overlay cellular communication network including a
`spontaneously generated overlay cellular communication
`network described above, make it possible to interconnect a
`macro cell and micro cell. To interconnect the macro cell and
`the micro cell in the overlay cellular communication 55
`network, there are two problems to be solved. The one is
`how to determine that a mobile station links which of the
`micro cell and the macro cell, the other is an access method
`from the fixed station to the mobile station.
`The objects and advantages of the invention may be
`realized and attained by means of the instrumentalities and
`combinations particularly pointed out in the appended
`claims. To achieve the objects and in accordance with the
`purpose of the invention, this invention provides a cellular
`communication network comprising:
`a mobile station which has a free space light interface, a
`radio wave interface and a switching unit for switching
`
`65
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic diagram illustrating a first embodi(cid:173)
`ment of the present invention;
`FIG. 2 is a schematic diagram illustrating a configuration
`45 of a mobile station 1 or 2 shown in FIG. 1;
`FIG. 3 is a schematic diagram illustrating an allotment of
`functions to each compositional element shown in FIG. 2;
`FIG. 4 is a schematic diagram illustrating encapsulation
`and decomposition of a packet in accordance with the
`present invention;
`FIG. 5 is a schematic diagram illustrating an access from
`a server to a mobile station in accordance with the present
`invention;
`FIG. 6 is a schematic diagram illustrating a second
`embodiment of the present invention;
`FIG. 7 is a schematic diagram illustrating a configuration
`of a mobile station 1 or 2 shown in FIG. 6;
`FIG. 8 is a schematic diagram illustrating an allotment of
`60 functions to each compositional element shown in FIG. 7;
`FIG. 9 is a schematic diagram illustrating a third embodi(cid:173)
`ment of the present invention;
`FIG. 10 is a schematic diagram illustrating a route of a
`usual data communication in FIG. 9;
`FIG. 11 is a schematic diagram illustrating a route of a
`signal which requires real time communication (such as
`sound or image);
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`6,115,615
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`5
`FIG. 12 a schematic diagram illustrating a configuration
`of a mobile station 1 shown in FIG. 9;
`FIG. 13 is a schematic diagram illustrating an assignment
`of functions to each compositional element shown in FIG.
`12;
`FIG. 14 is a schematic diagram illustrating a fourth
`embodiment of the present invention;
`FIG. 15 is a schematic diagram illustrating a conventional
`cellular communication network;
`FIG. 16 is a schematic diagram illustrating a conventional 10
`overlay type cellular;
`FIG. 17 is a schematic diagram illustrating a conventional
`art (Japanese Patent Laid-Open Hei. 2-162846);
`FIG. 18 is a schematic diagram illustrating a configuration
`which connects two networks via relay device;
`FIG. 19 is a diagram which corresponds a gateway, a
`router, a bridge and a repeater to the layers defined by OSI
`reference model;
`FIG. 20 is a schematic diagram illustrating a construction
`and decomposition of a packet in accordance with OSI 20
`reference model.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`In the following, embodiments of the present invention
`are explained.
`[Embodiment 1]
`FIG. 1 shows a configuration according to a first embodi(cid:173)
`ment of the present invention. This cellular network com(cid:173)
`pensates by a macro cell 10 formed by using a radio wave
`for a blank among micro cells 4a through 4d formed by
`using free space light. This embodiment uses an infrared
`wireless LAN for the micro cell. The infrared wireless LAN
`employs a CSMA group protocol (i.e. CSMNCA, CSMN
`CD), which is categorized as a contention protocol, as a
`protocol in the data link layer. PHS-PBX (personal handy
`phone system private branch exchange) is employed as a
`macro cell 10. PHS is a well-known virtual circuit switching
`communication system. Base stations 3a through 3d covers
`the micro cells 4a through 4d, respectively. The base stations
`3a through 3d are connected each other by a wiring network
`5. lOBASE-T is used for the wiring network 5, which
`interconnects the micro cells 4a through 4d. Instead of
`lOBASE-T, any Ethernet group networks can be used for the
`wiring network 5,. Servers 9a and 9b are also connected to
`the wiring network 5. A base station 6 covers the macro cell
`10. The base station 6 sends out a radio wave 12 from an
`antenna 8.
`Since both the infrared wireless LAN and the PHS-PBX
`have been commercially available, it is easy to get them. As
`described above, an overlay cellular communication
`network, which uses an infrared wireless LAN for the micro
`cell and uses PHS-PBX for the macro cell, is spontaneously
`generated, when both the infrared wireless LAN and PHS(cid:173)
`PBX are simply built. A hardware construction of both the
`infrared wireless LAN and the PHS-PBX is not enough for
`a well-organized overlay cellular communication network.
`Each of mobile stations 1 and 2 has both an interface for
`a radio wave (PHS) and an interface for free space light
`(infrared wireless LAN), and uses one of these two inter- 60
`faces by switching them in accordance with circumstances.
`For instance, since the mobile station 1 is in a service area
`of the micro cell 4c, it is linked to the micro cell base station
`3c by using a free space light interface. On the other hand,
`since the mobile station 2 is not in service areas of micro 65
`cells, it is linked to the macro cell base station 6 by using a
`radio wave.
`
`6
`The macro cell base station 6 is connected to the wiring
`network 5 via a gateway 7. Therefore, a network of the
`macro cell 10 using radio waves is logically separated from
`a network consisting of micro cells 4a through 4d using free
`5 space light. This separation is caused by the large difference
`of a transmission rate or a medium control protocol between
`the PHS used for the macro cell 10 and the infrared wireless
`LAN used for the micro cell, that is, impossibility of direct
`connection near the physical layer between them. The PHS
`has a transmission rate around 32 Kbps and employs a
`protocol of a virtual circuit switching system in the data link
`layer, while the infrared wireless LAN has a transmission
`rate around 1-10 Mbps and employs CSMA protocol in the
`data link layer. The networks which have different
`15 characteristics, must be connected in and above the network
`layer, that is, by a router or a higher level interconnection
`device. Accordingly, the macro cell base station 6 and the
`wiring network 5 must be connected via a router or a
`gateway.
`The base stations 3a through 3d are connected to the
`wiring network 5 via bridges 13a through 13d, respectively.
`If the infrared wireless LANs used for the micro cell 4a
`through 4d have the same transmission rate as the LAN of
`the wiring network 5 has, each of the base stations 3a
`25 through 3d can be connected to the wiring network 5 via a
`repeater.
`The macro cell 10 employs PPP (Point to Point Protocol)
`as a protocol in the network layer. Instead of PPP, SLIP
`(Serial Line Internet Protocol) can be used. The micro cells
`30 4a through 4d and the wiring network 5 employs IP (Internet
`Protocol) as a protocol in the network layer.
`FIG. 2 shows a configuration of the mobile station 1 or 2.
`Each of the mobile stations 1 and 2 is provided with an
`information processing body 20 like a computer, an interface
`35 21 for a radio wave (PHS), an interface 22 for free space
`light (infrared wireless LAN), and an interface switching
`unit 25 for switching the two interfaces. The interface 21 for
`a radio wave (PHS) has an antenna 23, while the interface
`22 for free space light (infrared wireless LAN) has an optical
`40 unit 24 like a lens. The interface switching unit 25 has not
`only a signal switching feature but also a protocol switching
`feature corresponding to the selected interface. As described
`above, in this embodiment, since the micro cell and the
`macro cell are the logically separated networks, an IP
`45 address used when the mobile station is linked to the macro
`cell base station is different from an IP address used when
`the mobile station is connected to the micro cell base station.
`That is, the mobile station has a kind of routing feature.
`The network side (server or base station) sees the mobile
`50 station with two IP addresses. These two addresses can be
`regarded as addresses indicating routes to reach the mobile
`station. As described later, one of the characteristics of this
`invention is that the address of the mobile station itself is
`provided besides the addresses of indicating routes. Notice
`55 that the address of a path changes when the mobile station
`moves.
`FIG. 3 shows configuration of features among the inter(cid:173)
`face 21 for a radio wave (PHS), the interface 22 for free
`space light (infrared wireless LAN) and the interface switch(cid:173)
`ing unit 25 in accordance with the OSI reference model in
`a communication system of the present invention. The
`interface 21 for a radio wave (PHS) supplies functions 26 in
`the physical layer, the data link layer and the network layer
`for PHS. The interface 22 for free space light (infrared
`wireless LAN) supplies functions 27 in