United States Patent 55
`6,115,615
`Sep. 5, 2000
`[45] Date of Patent:
`Ota et al.
`
`[11] Patent Number:
`
`US006115615A
`
`[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
`
`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.” JEICE Trans. Commun.,
`vol. E75—-B, No. 2, Feb. 1992, pp. 67-75.
`
`[30]
`
`Foreign Application Priority Data
`
`Feb. 26, 1996
`Feb. 10, 1997
`
`[IP]
`[IP]
`
`Japan vccsscsssssetescsscsssssseeeseesss 8-037601
`Japan vccsccssssseeescsscsssssseeeseesss 9-026263
`
`Primary Examiner—Salvatore Cangialosi
`Attorney, Agent, or Firm—Oliff & Berridge, PLC
`
`[57]
`
`ABSTRACT
`
`Tent, Cd eeecccceeeeecessnneeeceenteeeeenneees HO04B 7/26
`PSL]
`An overlay cellular communication network, which includes
`[52] U.S. Ch.eee 455/553; 455/552; 455/445
`a first base station for providing a first cellular communi-
`[58] Field of Search oo... eceeeeees 455/554, 555,
`cation network havingafirst cell size, and a second base
`455/426, 445, 432, 552, 463, 462, 437,
`station for providing a second cellular communication net-
`work which coversthefirst cellular communication network
`440, 553; 370/338, 328; 359/118, 145
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`and has a secondcell size, is provided to determine a proper
`transmission route immediately and to cover a broad area
`communication network with certainty.
`
`1/1994 Ota.
`5,282,257
`A mobile station belonging to an overlay communication
`4/1994 Sawyeret al. eee 455/445
`5,301,400
`network, which includes a micro cell havingafirst cell size
`5,396,647
`3/1995 Thompsonetal... 455/440
`and a macro cell having a second cell size, has an mobile
`5,400,338
`3/1995 Flammeretal. ....
`. 455/445
`station identification addressin the application layer defined
`5,479,595
`12/1995 Israelsson.........
`we 359/145
`by the OSI reference model, and also has a plurality of
`5,506,887
`4/1996 Emeryet al.
`.
`. 455/445
`addresses, each of the plurality of addresses belonging to
`5,598,458
`1/1997 Bales et al.
`......
`«. 455/418
`one of the data link layer through the presentation layer
`5,640,676
`6/1997 Garneurz etal.
`. 455/437
`defined by the OSI reference model, which represent routes
`5,732,127
`3/1998 Hayes ou...
`wee 379/115
`5,812,531
`9/1998 Cheung et al. oc 455/445
`to reach the mobile station. A transmitting route is deter-
`mined by combining properly the mobile station identifica-
`FOREIGN PATENT DOCUMENTS
`tion address and the address representing a route.
`
`
`
`2-162846
`2-235447
`
`6/1990
`9/1990
`
`Japan .
`Japan .
`
`20 Claims, 19 Drawing Sheets
`
`ROUTE-1
`
`ROUTING
`DATABASE
`
`*S.”
`
`APPLICATION. LAYER
`LEVEL ADDRESS
`217
`
`ROUTE-2
`
`213
`
`215
`
`APPLICATION LAYER
`LEVEL ADDRESS
`
`1
`
`SAMSUNG 1016
`
`
`
`
`-
`
`-
`
`N
`
`SAMSUNG 1016
`
`1
`
`

`

`U.S. Patent
`
`6,115,615
`
`Sep. 5, 2000
`
`Sheet 1 of 19
`
`FIG.1
`
`2
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 2 of 19
`
`6,115,615
`
`20
`
`21
`
`
`INFORMATION
`PROCESSING
`BODY
`
`
`
`
`
` INTERFACE
`SWITCHING
`
`
`
`
`
`FREE SPACE
`RADIO
`LIGHT
`WAVE
`
`
`INTERFACE
`
`
`
`3
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 3 of 19
`
`6,115,615
`
`aee
`
`
`
`
`PP
`
`
`VIRTUAL CIRCUIT
`
`
`SWITCHING
`
`RADIO WAVE
`
`
`
`
`- | | | | | | | | | | | | | | 4 | | | | | | | | | | a
`
`
`
`
`
`TRANSPORT
`SWITCHER
`
`IP
`(MOBILE—IP)
`
`(CSMA)
`CONTENTION
`
`INFRARED LIGHT
`
`APPLICATION
`LAYER
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`PRESENTATION
`LAYER
`
`
`
`
`
`
`
`
`
`SESSION
`LAYER
`
`TRANSPORT
`LAYER
`
`NETWORK
`LAYER
`
`DATA LINK
`LAYER
`
`PHYSICAL
`LAYER
`
`4
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 4 of 19
`
`6,115,615
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`U.S. Patent
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`Sep. 5
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`Sheet 5 of 19
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`6,115,615
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`U.S. Patent
`
`6,115,615
`
`Sep. 5, 2000
`
`Sheet 6 of 19
`
`FIG.6
`
`7
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 7 of 19
`
`6,115,615
`
`20
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`41
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`
`INFORMATION
`PROCESSING
`BODY
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`INTERFACE
`SWITCHING
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`RADIO
`WAVE
`INTERFACE
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`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 8 of 19
`
`6,115,615
`
`APPLICATION
`LAYER
`
`PRESENTATION
`LAYER
`
`
`
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`
`
`
`
`
`SESSION
`LAYER
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`TRANSPORT
`LA
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`NETWORK
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`LAYER
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`PHYSICAL
`LAYER
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`ADDRESS
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`NETWORK SWITCHER
`(IP ADDRESS)
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`9
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 9 of 19
`
`6,115,615
`
`FIG.9
`
`10
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 10 of 19
`
`6,115,615
`
`11
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 11 of 19
`
`6,115,615
`
`20
`
`
` INTERFACE
`SWITCHING
`
`
`FREE SPACE
`LIGHT
`
`
`
`21
`
`FIG. 12
`
`12
`
`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 12 of 19
`
`6,115,615
`
`a M
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`OBILE STATION
`ADDRESS
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`APPLICATION
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`PRESENTATION
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`DATA LINK
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`FIG. 13
`
`13
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`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 13 of 19
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`6,115,615
`
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`14
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`

`

`Sheet 14 of 19
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`6,115,615
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`U.S. Patent
`
`Sep. 5, 2000
`
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`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 15 of 19
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`6,115,615
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`U.S. Patent
`
`Sep. 5, 2000
`
`6,115,615
`
`Sheet 16 of 19
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`FIG.17
`
`17
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`

`

`U.S. Patent
`
`Sep. 5, 2000
`
`Sheet 17 of 19
`
`6,115,615
`
`133
`
`132
`
`131
`
`130 |
`
`FIG.18
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`133
`
`18
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`18
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`U.S. Patent
`
`Sep. 5, 2000
`
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`Sep. 5, 2000
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`Sheet 19 of 19
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`6,115,615
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`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-
`
`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-
`tion relates to a cellular communication network using both
`free space light and a radio waveas 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
`of a packet, which is responsible for information transmis-
`sion.
`
`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-
`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 101@ 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-
`ference between cells. A mobile station 1025 which is near
`
`a boundary between cells, negotiates with the base stations
`1014 and 1015 in orderto select a base station to be linked
`from the base stations 101@ and 1015. This communication
`processis called “hand-over”. This communication network
`is widely used for a mobile telephone or a personal handy
`phone system (PHS).
`As an extension of the above-described cellular commu-
`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,
`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 microcells.
`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
`whereit is unprofitable to build a base station becauseofits
`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-
`lular communication network is spontaneously generated.
`For instance, when a PHS network whosecell size is a few
`hundred meters is built in an area where a mobile telephone
`network whosecell 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.
`
`Asystem in which basestations 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
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`60
`
`65
`
`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
`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-
`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
`machinein 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
`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
`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
`numeral 121 is a room where the remote controller 111 is. A
`reference numeral 122 is a room where the machine 114is.
`Areference 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-
`tion device 130 are classified into a gateway, a router, a
`bridge and a repeater in accordance with OSI (Open Systems
`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
`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-
`connection devices (interconnection device 130), such as a
`gateway, a router, a bridge or a repeater, were connected to
`two networks simultaneously. Meanwhile, a general termi-
`nal (133 in FIG. 18) was not connected to two networks
`simultaneously.
`FIG. 20 schematically shows how a packet is encapsu-
`lated and decomposed. At the transmission side, a packet is
`transmitted from the top layer
`to the bottom layer,
`successively, of the OSI reference model, and in each layer,
`a headerof the layer (a session header, a transport header, a
`network headeror a data link header) is added to the packet.
`At
`the reception side, a packet
`is transmitted from the
`bottom layerto the top layer of the OSI reference model, and
`in each layer, a header correspondingto the layer is removed
`from the packet. A typical gateway relays a packet after
`21
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`6,115,615
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`4
`to any of the free space light interface and the radio
`wave interface;
`at least one fixed first base station, each for communicat-
`ing with the mobile station by wayof 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 secondarea.
`This configuration makesit 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
`FIG. 20 does not showa trailer correspondingto a header,
`possible to use enough high speed communication by posi-
`which is sometimes attached to the end of the packet. That
`tioning the first base station at the important position, and to
`is, a trailer (session trailer, transport trailer, network trailer
`cover a usual area by the communication via the second base
`or data link trailer), which correspondsto a header (session
`station.
`header,
`transport header, network header and data link
`Further, the mobile station can switch not only links to the
`header), can be attached to the packet. A data entity is
`first base station and the second base station, but also links
`sandwiched between a header andtrailer to be capsulated.
`to a plurality of base stations. Accordingly, since the mobile
`Since the header is indispensable, but the trailer is some-
`station can have more communication opportunities,
`the
`times unnecessary, FIG. 20 does not includetrailers.
`communication capacity will increase and the reliability of
`Since light is an electromagnetic wave having extremely
`the network improves.
`high frequency,
`light can carry a broadband modulated
`To achieve the above-described objects, this invention
`signal. But light has a disadvantage that it is easily blocked
`also provides an overlay cellular communication network
`25
`by objects. Therefore, a cellular network using free space
`comprising: a first base station for providingafirst cellular
`light has a disadvantage that a cell is small. In other words,
`communication network of a first cell size;
`more cells are required to cover a particular area.
`a second base station for providing a second cellular
`In the remote control system, the above-described Japa-
`communication network of a second cell size, which
`nese Patent Laid-Open Hei. 2-162846 proposes a system
`covers the first cellular communication network, and
`which uses both a radio waveand light, and compensates by
`a mobile station which has a mobilestation identification
`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.
`
`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
`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
`which layer of OSI reference model corresponds to a pro-
`cess.
`
`10
`
`15
`
`20
`
`30
`
`35
`
`In a general cellular network, the above-described com-
`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
`
`have an ability of information processing such as address
`management.
`SUMMARYOF THE INVENTION
`
`The present invention has been madein 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-
`nication by providing a communication method which in a
`general overlay cellular communication network including a
`spontaneously generated overlay cellular communication
`network described above, make it possible to interconnect a
`macrocell and micro cell. To interconnect the macro cell and
`
`in the overlay cellular communication
`the micro cell
`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 macrocell, 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 lightinterface, a
`radio waveinterface and a switching unit for switching
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`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-
`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.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a schematic diagram illustrating a first embodi-
`ment of the present invention;
`FIG. 2 is a schematic diagram illustrating a configuration
`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
`functions to each compositional element shownin FIG. 7;
`FIG. 9 is a schematic diagram illustrating a third embodi-
`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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`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
`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
`reference model.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`In the following, embodiments of the present invention
`are explained.
`[Embodiment 1]
`FIG. 1 showsa configuration according to a first embodi-
`ment of the present invention. This cellular network com-
`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 CSMAgroupprotocol (i.e. CSMA/CA, CSMA/
`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. PHSis a well-knownvirtual circuit switching
`communication system. Base stations 3a through 3d covers
`the micro cells 4a through 44d,respectively. The base stations
`3a through 3d are connected each other by a wiring network
`5. 10BASE-T is used for the wiring network 5, which
`interconnects the micro cells 4a through 4d. Instead of
`10BASE-T,any Ethernet group networks can be usedfor 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-
`PBX are simply built. A hardware construction of both the
`infrared wireless LAN and the PHS-PBXis 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-
`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
`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 wavesis logically separated from
`a network consisting of micro cells 4a through 4d using free
`space light. This separation is caused by the large difference
`of a transmission rate or a medium control protocol between
`the PHSused 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
`protocolof 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 CSMAprotocol in the
`data link layer. The networks which have different
`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
`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
`4a through 4d and the wiring network 5 employsIP (Internet
`Protocol) as a protocol in the network layer.
`FIG. 2 showsa 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
`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
`unit 24 like a lens. The interface switching unit 25 has not
`only a signal switching feature but also a protocol switching
`feature correspondingto the selected interface. As described
`above,
`in this embodiment, since the micro cell and the
`macro cell are the logically separated networks, an IP
`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.
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`That is, the mobile station has a kind of routing feature.
`The network side (server or base station) sees the mobile
`station with two IP addresses. These two addresses can be
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`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
`that the address of a path changes when the mobile station
`moves.
`
`FIG. 3 shows configuration of features among the inter-
`face 21 for a radio wave (PHS), the interface 22 for free
`spacelight (infrared wireless LAN) and theinterface switch-
`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 the physical layer,
`the data link layer and the network layer for the infrared
`wireless LAN. The interface switching unit 25 supplies
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`functions 28 which include a whole function from the
`transport layer to the application layer. The functions 28
`receive an information entity to be transmitted, from the
`information processing body 20, add an application header
`including an address in the application layer level to the
`information entity to create a packet, and send the packet to
`the transport layer. The transport layer carries out software
`processing for switching two networks. That is, when the
`packet is sent to the interface 21 for the PHS (radio wave),
`a header including an IP address corresponding to the PPP
`to the packet. Whenthe packet is sentto the interface 22 for
`the free space light (infrared wireless LAN), a different IP
`address is added to the packet. The interface 22 for the free
`space light (infrared wireless LAN) can use a mobile-IP
`instead of IP in the network layer. Since the mobile-IP is a
`protocol suitable for mobile clients, the better control can be
`conducted by using it.
`FIG. 4 schematically shows an encapsulation and decom-
`position of a packet capsule conducted by the interface
`switching unit 25 to switch to one of the radio wave and the
`infrared optical wireless LAN. The difference between this
`embodiment and FIG. 20 is that an application header is
`attached in the application layer. An application layer level
`address indicating a mobile station, is written in the appli-
`cation header.
`Conventionally, the function to switch routes of a packet
`was supplied by a particular server like a router, which
`connects two networks. However, there is no conventional
`technique in that an client (mobile station) supplies the
`function to switch routes of a packet, as this embodiment.
`Thatis, in this invention, a mobilestation is provided with
`a packet switching feature, what is called a routing function,
`and determinesto link to one of the micro cell and the macro
`cell.
`The functions in the network layer and the transport layer
`can be supplied by the information processing body 20. This
`method makes the hardware simple, but increases a burden
`of the software required for the information processing body
`20.
`this embodiment gives a unique
`As described above,
`application layer level address to a mobile station, and
`regards a network layer level address (IP address in this
`embodiment) as an address indicating a route. Therefore, as
`shown in FIG. 5, a server 211 accesses to a mobile station
`213 in accordance with the application layer level address.
`In FIG. 5, there are two routes in the network 212 from the
`server 211 to the mobile station 213, that is, route-1 of
`reference numeral 214 and route-2 of reference numeral 215.
`The server 211 is usually a fixed station. The server 211 has
`a routing database 216, which includes, for example, infor-
`mation of a record file 217. The record file 217 associates an
`application layer level address with two routes (IP addresses,
`for example).
`The information in the routing database is properly
`updated in accordance with a movement of the mobile
`station. A protocol of the known mobile-IP or the virtual-IP
`can be used for the procedure of the update.
`In these
`procedures, each mobile station is given a domicile address,
`and the mobile station informs the domicile address of a
`
`current position, when the mobile station can communicate.
`Here, the domicile address means a server whichis respon-
`sible for address management. When a server which will
`access to a mobile station does not know a current position
`of the mobile station, the server gets the current position,
`more precisely, a routing information to get to the mobile
`station by inquiring of the domicile address (the server
`responsible for address management).
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`FIG. 5 shows routing management conducted by the
`server 211. All servers do not required to have such a
`function, however.It is possible to determine a server which
`executes the routing management of mobile stations, and
`other general servers can depute routing managementto the
`server which executes the routing management. A proxy
`server, which executes a particular service for the other
`servers, is well-known to people skilled in theart.
`The application layer level address can be anything
`unique to a mobilestation. It is possible to use something in
`a form easily understood by people, such as an e-mail
`address or a URLin http, as well as a simple serial number,
`such as telephone number.
`It is also possible to use IP
`address system or Ethernet address system as the application
`layer level addresses. IP address or Ethernet address defines
`a unique address