United States Patent (19)
`Hamalainen et al.
`
`54. DATA TRANSMISSION IN A RADIO
`TELEPHONE NETWORK
`
`75 Inventors: Jari Hamalainen, Tampere; Timo
`Jokiaho, Vantaa, both of Finland
`73) Assignee: Nokia Mobile Phones Ltd., United
`Kingdom
`
`21 Appl. No.:724,375
`22 Filed:
`Oct. 1, 1996
`Related U.S. Application Data
`63 Continuation of Ser. No. 301,340, Sep. 6, 1994, abandoned.
`30
`Foreign Application Priority Data
`Sep. 6, 1993
`FI
`Finland ...................
`......... 933894
`(51) Int. Cl' ........................... He4Q 720
`52 U.S. C. ...........
`... 455,403; 455/452; 455/560
`58 Field of Search ..................................... 455/403,422,
`455/450, 452,455, 509, 516,550,560,
`435; 370/389, 338
`
`56
`
`References Cited
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`8/1988 Rozenbit ............................... 37084
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`O
`-
`5,166,929 11/1992 Lo ...... did hetic to
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`0048854A1 4/1982 European Pat. Off..
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`0.369 535A3 5/1990 European Pat. Off. ....... H04Q 7/04
`
`88 is
`
`94.
`
`USOO58O2465A
`Patent Number:
`11
`45) Date of Patent:
`
`5,802.465
`Sep. 1, 1998
`
`European Pat. Off. ......... H04Q 7/04
`O 399 6 A3 1/1990
`European Pat. Off..
`O399.612A2
`1/1990
`European Pat. Off. .
`O58798OA2 3/1994
`2 270 815 3/1994 United Kingdom.
`WO 94/10767 5/1994 WIPO.
`OTHER PUBLICATIONS
`IEEE Transactions On Vehicular Technology, "Voice and
`Data Integration in the Air-Interface of a Microcellular
`Mobile Communication System", vol. 42, No. 1, Feb. 93.
`DeVile, J.M., "A Reservation Based Multiple Access
`Scheme For A Future Universal Mobile Telecommunica
`tions System”, Seventh IEEEuropean Conf. OnMobile And
`Personal Communications, 15 Dec. 1993, pp. 210-215.
`(List continued on next page.)
`Primary Examiner-Dwayne D. Bost
`Assistant Examiner-William G. Trost
`Attorney, Agent, or Firm-Perman & Green, LLP
`57
`ABSTRACT
`For bidirectional transmission of packet data, a packet data
`service unit (Agent) is disposed in a digital cellular system
`connected to be in association with a Mobile Switching
`Center, and connecting the cellular network to the date
`network. As a mobile station is connected to the packet data
`service unit, signalling related to connection formation
`characteristics of the network is first accomplished. As a
`result thereof, the mobile station and the data service unit are
`provided with a number of stored parameters relating to each
`other. This situation creates or is called a virtual channel.
`When a mobile station wants to transmit or receive data
`packets between the mobile station and the data service unit
`a packet data transfer channel is established making use of
`the parameters of the virtual channel and thereby using
`substantially less signalling than the channel establishment
`signalling characteristic of the network, one part thereof
`being a radio channel and the other part a time slot in a
`digital trunkline. On termination of data packet transfer, at
`least said radio channel is disassembled but the virtual
`channel is maintained until the disconnection of the mobile
`station from the data service.
`
`32 Claims, 7 Drawing Sheets
`
`
`
`LOCA CHANNES
`
`RAFFIC CHAMNES-TCH
`
`CONTRO CHANNES-CCH
`
`
`
`
`
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`
`
`
`
`
`
`
`
`BROADCAST CHANNES
`FREQUENCY CORRECTION CHANNEL-FCCH
`SYNCHRONIZATION CHANNEL-SC
`CEL BROADCAST CHANNE-CBCH
`BROADCAST CONTROL CHANNEL-BCCH
`COMMON CHANNELS
`RANDOM ACCESS CHANNE-RACH
`PAGING CHANNEL-PCH
`ACCESS GRANT CHANNEL-AGCH
`DEDICAEO CONROL CHANNE
`STAND ALONE, DEDICATED CONTROL CHANNEL-SDCCH
`FAST ASSOCATED CONTROL CHANNE-FACCH
`SOW ASSOCATED CONROL CHANNE-SACCH
`
`
`
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`

`5,802,465
`Page 2
`
`
`
`U.S. PATENT DOCUMENTS
`3/1993 Dahlin .................................. 3700.
`5,199,031
`5,239,678 8/1993 Grube et al.
`455,541 X
`5,276,680
`1/1994 Messenger .
`... 379/63 X
`5,359,603 10/1994 McTiffin ...
`... 370/94.1
`5,404,355 4/1995 Raith ..........
`... 37095.1
`5,404,392
`4/1995 Miller et al. ...
`... 379/59 X
`5,420,864 5/1995 Dahlin et al. ..
`........... 370/95.3
`5.430,724
`7/1995 Fall et al...
`... 370/95.3 X
`5.434,847
`7/1995 Kou ....................
`........... 370/17
`5,487,065
`1/1996 Acampora et al. ................... 379/63 X
`OTHER PUBLICATIONS
`Ziegeler, R. et al., "An Experimental implementation of the
`PRMAProtocol for Wireless Communication", IEEE, 1993,
`pp. 909-912.
`Mouly, et al., The GSM System for Mobile Communica
`tions, 1992, France, pp. 215-216, 231-241, 346-349.
`Hodges, M.R.L., The GSM radio interface, British Telecom
`Technology Journal vol. 8 No. 1, Jan. 1990, pp. 31-43.
`"European digital cellular telecommunications system
`(Phase 2); Mobile radio interface layer3 specification(GSM)
`04.08)", ESTI, May 1995, pp. 37-40, 183-186.
`"European digital cellular telecommunications system
`(Phase 2); Physical layer on the radio path General descrip
`tion (GSM 05.01)” ETSI, May 1995, pp. 1-19.
`"European digital cellular telecommunications system
`(Phase 2); Channel coding (GSM 05.03), ESTI, Aug. 1995,
`pp. 1-5 and Mar. 1995, pp. 1-31.
`
`Electronics and Communication Journal, vol. 5, No. 3, 1
`Jun. 1993, pp. 180-186, Dunlop, J., "A Reservation Based
`Access Mechanism For 3rd Generation Cellular Systems".
`IEEE Transactions On Vehicular Technology, vol.39,No. 4,
`1 Nov. 1990, pp. 340-351, Mitrou et al. "A Reservation
`Multiple Access Protocol For Microcellular Mobile-Com
`municatin Systems".
`Finnish Office Action dated 2 Aug. 1994 on Finnish priority
`application No. 933894 and English translation thereof.
`S. Chakraborty, Data interworking with GSM, Proceedings
`of 5th Nordic Seminar on Digital Mobile Radio Communi
`cations, pp. 389–395, DMR V, Helsinki '92.
`R. Tafazoli, B. G. Evans, Interworking and integration of
`the Inmarsat Standard-M with the Pan-European GSM
`system, Proceedings of 3rd
`International Mobile Satellite Conference, Jet Propulsion
`Lab, CA, 1993.
`E.J. Younger, K.H. Bennet, R. Hartley-Davies, AModel for
`a broadband cellular wireless networkfor digital communi
`cations, Compter Networks and ISDN Systems, vol. 26, No.
`4, Netherlands, 1993.
`Data Networks, D. Bertsekas, R. Gallager, Prentice-Hall
`Inc., 1987 New Jersey, Chapters 2.7 and 2.83, pp. 91, 92,
`99, 100, 101.
`
`Ex.1040
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`

`U.S. Patent
`
`Sep. 1, 1998
`
`Sheet 1 of 7
`
`5,802,465
`
`BTS
`
`
`
`FIG.1A
`PRIOR ART
`
`BTS
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`LOCATION
`UPDATING
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`NETWORK
`OS
`OR
`TCP/IP
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`FIG.1B
`
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`U.S. Patent
`
`Sep. 1, 1998
`
`Sheet 2 of 7
`
`5,802,465
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`APPLEINC./ Page 4 of 19
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`Ex.1040
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`

`U.S. Patent
`
`Sep. 1, 1998
`
`Sheet 3 of 7
`
`5,802,465
`
`MS
`
`NETWORK
`
`CHANNEL REQUEST
`MMEDIATE ASSIGNMENT
`
`AUTHENTICATION
`
`START CIPHERING
`
`TMS REALLOCATION
`
`FIG.4
`
`MS
`
`
`
`
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`
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`MS
`
`
`
`PACKET DATA CHANNEL REQUEST
`PACKET DATA ASSIGNMENT
`
`NETWORK
`
`
`
`
`
`NETWORK
`
`FIG.5
`
`DISCONNECT
`
`RELEASE
`RELEASE COMPLETED
`CHANNEL RELEASE
`
`FIG.6
`
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`

`U.S. Patent
`
`Sep. 1, 1998
`
`Sheet 4 of 7
`
`5,802.465
`
`MS
`
`NETWORK
`
`VIRTUAL SESSION INTIALIZATION
`
`FIG.8
`
`PACKET DATA CHANNEL REQUEST
`
`BSS
`
`
`
`
`
`
`
`MS
`
`RACH
`
`TCH
`TCH
`TCH
`TCH
`
`
`
`FG.9
`
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`

`U.S. Patent
`
`Sep. 1, 1998
`
`Sheet 5 of 7
`
`5,802.465
`
`MS
`
`PCH
`
`
`
`RACH
`AGCH
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`BSS
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`PACKET DATA PAGING MESSAGE
`PACKET DATA CHANNEL RECUEST
`PACKET DATA ASSIGNMENT
`
`PACKET DATA TRANSFER
`PACKET DATA ACKNOWLEDGE
`
`PACKET DATA TRANSFER
`PACKET DATA ACKNOWLEDGE
`
`FIG.10
`
`FIG.11
`
`MS
`
`
`
`NETWORK
`
`PACKET DATA CHANNEL REQUEST
`PACKET DATA ASSIGNMENT
`SHORTENED SIGNALING
`DATA PACKET
`DATA PACKET
`TCH CHANNEL DISCONNECTION
`
`FIG.15
`
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`U.S. Patent
`U.S. Patent
`
`Sep. 1, 1998
`Sep. 1, 1998
`
`Sheet 6 of 7
`Sheet 6 of 7
`
`5,802,465
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`

`U.S. Patent
`
`Sep. 1, 1998
`
`Sheet 7 of 7
`
`5,802.465
`
`MS
`
`
`
`BSS
`
`PCH
`RACH
`
`TCH
`TCH
`
`TCH
`TCH
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`RACH
`PCH
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`RACH
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`TCH
`TCH
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`RACH
`PCH
`
`RACH
`
`PCH
`
`PACKET DATA PAGING MESSAGE--DATA
`PACKET DATA CHANNEL REOUEST
`PACKET DATA ASSIGNMENT TO TCH
`
`PACKET DATA TRANSFER
`PACKET DATA ACKNOWLEDGE
`
`PACKET DATA TRANSFER (TO RACH
`PACKET DATA ACKNOWLEDGE
`
`START TIMER
`OR COUNTER
`
`PACKET DATA TRANSFER
`PACKET DATA ACKNOWLEDGE
`
`PACKET DATA TRANSFER TO TCH
`PACKET DATA ACKNOWLEDGE
`
`PACKET DATA TRANSFER (RACH
`PACKET DATA ACKNOWLEDGE
`
`PACKET DATA TRANSFER
`PACKET DATA ACKNOWLEDGE
`
`PACKET DATA TRANSFER (TO TCH
`PACKET DATA ACKNOWLEDGE
`
`FIG.14
`
`NOT EXPRED
`BEFORE SWITCH
`REQUEST
`
`START TIMER
`
`TIME OUT
`FORCED END
`OF CONNECTION
`
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`

`1
`DATA TRANSMISSION IN A RADO
`TELEPHONE NETWORK
`
`5,802.465
`
`O
`
`5
`
`This is a continuation of application Ser. No. 08/301,340
`filed on Sep. 6, 1994, now abandoned.
`FIELD OF INVENTION
`The present invention relates to the transmission of data
`in a radio telephone network.
`BACKGROUND OF THE INVENTION
`An example of a radio telephone network, in this case a
`conventional digital cellular network, is shown in FIG. 1A.
`The network comprises Base Station Controllers (BSC),
`each of which control a number of Base Transceiver Stations
`(BTS). The BTS and mobile stations (MS) are connected via
`a radio communications channel. A Base Station Controller
`and the base stations with which it is connected form a Base
`Station Subsystem. The BSCs are connected to Mobile
`Switching Centres (MSC) via digital trunk lines which
`control the Base Station Subsystems. The MSCs route
`communication traffic to a general Public Service Telephone
`Network (PSTN) or private networks such as a Local Area
`Network (LAN). A Base Station Controller may also be
`physically located with the Mobile Switching Center. The
`service range of a base station forms a cell and a mobile
`station within the service range is typically served by that
`base station. The mobile station is able to move from one
`cell to another and roam from under the control of one Base
`Station Controller to be under the control of another Con
`troller without losing a connection to the radio telephone
`network.
`In known cellular networks data information can be
`transmitted between the home network of a mobile station
`and a terminal or destination network. The terminal network
`can include a home network, another network of the same
`system, a fixed telephone network, or a data network. The
`network services typically include synchronous and asyn
`chronous circuit-switched data transfer from the cellular
`network to the external telephone network PSTN, to a
`circuit-switched date network or an ISDN network. Sugges
`tions have also been made on implementing asynchronous
`packet switching to an external packet switched data net
`work.
`As shown in F.G. 1A, data transmitted by a mobile station
`enters a data Inter Working Functions unit, IWF, associated
`with the Mobile Switching Centre, from there via a modem
`to the Centre wherefromitis further transmitted, e.g., via the
`PSTN, to a target means or target data network, such as a
`private LAN network. The transition network is thus the
`general telephone network.
`A typical method of data transmission between networks
`and also within a network is circuit switching, in which a
`transfer channel is established for the transfer of data.
`Establishing a channel is a time-consuming operation and
`requires a lot of signalling, such as sending a control channel
`request and assignment of a channel, authentication checks,
`installation of an encrypting mode and others, before the
`channel is set up for transferring data information. Circuit
`switching, when applied for data transfer, is uneconomical
`since the transfer needs a wide frequency band. Also a user
`is charged inrespective of whether data is transmitted or not
`This is because in a circuit-switched network the channel
`has to be maintained until all data information has been
`transmitted, which regarding the capacity is uneconomical.
`Since charging of the user is usually based on the length of
`
`2
`the reserved connection time in the circuit-switched
`network, the user is obliged to pay for "nil" because the time
`used for the actual data transfer is a minor part of the total
`connection time. Typically, cellular networks have primarily
`been optimized for speech transfer, and for that purpose,
`circuit-switched data transfer is appropriate.
`In a digital cellular network, such as in the European
`GSM network and in the American network of the EA/TIA
`(Electronic Industries Association/Telecommunication
`Industry Association) standards, suggestions have been
`made on data communication as packets, as so-called packet
`data e.g., in the patent U.S. Pat. No. 4,887,265. This patent
`discloses a system in which several mobile stations send
`packet data to one base station using the same channel.
`When the Base Station Controller receives an assignment
`request for a data channel from the mobile station, it
`transmits a channel assignment to the mobile station,
`whereby the mobile station moves on that data channel. The
`same channel is also available for use for all other mobile
`stations within the range of said cell. A request, a channel
`assignment and transfer on a channel require a considerable
`amount of signalling. Handover of a data connection from
`one base station to another is also possible in this system. In
`the system disclosed by the patent, a permanent channel is
`provided for packet transfer, being constantly available,
`inrespective of a momentary need.
`SUMMARY OF THE INVENTION
`According to a first aspect of the invention there is
`provided a radio telephone system comprising:
`a mobile station; and
`a fixed station, wherein a parameter of the mobile station
`for setting up a data communication channel is capable
`of being stored by the fixed station and a parameter of
`the fixed station for setting up a data communication
`channel is capable of being stored by the mobile
`station, for forming a virtual data communication chan
`nel between the mobile station and the fixed station,
`thereby expediting establishment of a real data com
`munication channel.
`According to a second aspect of the invention there is
`provided a method of transmitting data in a radio telephone
`network comprising:
`storing a parameter of a mobile station for setting up a
`date communication channel at a fixed station; and
`storing a parameter of the fixed station for setting up a
`data communication channel at the mobile station, for
`forming a virtual data communication channel between
`the mobile station and the fixed station, thereby expe
`diting establishment of a real data communication
`channel.
`According to a third aspect of the invention there is
`provided a radio telephone adapted to store a parameter for
`setting up a communication channel of a fixed station for
`forming a virtual data communication channel with the fixed
`station thereby expediting establishment of a real data
`communication channel.
`These aspects of the invention provide the advantage that
`a real data communication channel can be established
`quickly and when a mobile station desires to transmit data.
`In between the transmission of data the real data commu
`nication channel can be switched to a virtual data commu
`nication channel ready for quick reestablishment. Thus, a
`communication channel does not have to be continually
`open, even during no actual transmission of data. Thus, the
`costs of transmitting data are reduced.
`
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`5,802.465
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`3
`Alternatively, the virtual data communication channel can
`be formed if a mobile station having data transmission
`capability registers with the fixed station, or if a mobile
`station registered with the fixed station requests a data
`communication channel. An advantage of forming a virtual
`data communication channel only when a mobile station
`requests a data communication channel is that unnecessary
`signalling is avoided.
`Optionally, the data communication channel can be a
`channel usually reserved for speech transmissions, or sig
`nalling or control transmissions. A particular advantage of
`using signalling or control channels is that the transmission
`of data does not reduce the number of speech channels
`available to the users of the system.
`Advantageously, the data communication channel is
`adapted for transmitting packet data, which is a transmission
`form particularly suitable for use with a data communication
`channel which can quickly be opened or closed.
`Another advantage is that data packets can be created at
`the mobile stations and transferred directly to a data network
`without the need for transition networks, such as Packet
`Assembler/Disassemblers (PADs) or using the PSTN.
`Additionally, the mobile station itself can receive packet
`data, i.e. the system is bidirectional.
`An appropriate existing cellular system currently in use is,
`for instance, the European GSM system.
`Embodiments of the invention will now be described by
`way of example only and with reference to the drawings, in
`which:
`
`O
`
`15
`
`35
`
`4
`paging calls, etc. The respective time slots constitute a
`logical channel, of which a great number may be available.
`In digital cellular networks, a mobile station can send and
`receive data on a traffic channel particularly intended for
`speech and data transfer. Both of them cannot be transmitted
`simultaneously but the user or the network makes a selection
`which thereof is to be transferred. Data as well as speech are
`sent as bursts on a radio channel. This means that in a
`transmission time slot a brief data burst is transmitted in the
`middle of the time slot so that a considerable part of the total
`time used for transmission means the time between the
`bursts when no information is transferred.
`A particular type of data service known as packet data
`service has been defined in the GSM network. In this
`service, the number selected by a data transmitting mobile
`station informs the network that a circuit-switched connec
`tion has to be created to a packet assembling or disassem
`bling unit performing the connection with a data network,
`such as X.25, which can be a Packet Assembler/
`Disassembler (PAD) or a Packet Handler (PH). The Packet
`Assembler/Disassembler can be placed in association with
`or also behind the ISDN network. The mobile station sends
`data as continuous data flow, not as packets, to PAD or PH,
`which forms the data packets and transmits them onwards
`via the data network to the target. If PH is a so-called Basic
`Packet Handler, the data connection is always located via a
`given point PH, even in any network. The Basic Data
`Handler also supports the mobile terminated direction in
`data transmission. On the other hand, the mobile terminated
`direction is not supported by the so-called dedicated Packet
`Handler, nor PAD. The traffic between the mobile station
`and the packaging means imitates synchronous or asynchro
`nous data transfer, wherebelow a radio traffic protocol RLP
`is located.
`In the data packet service of the GSM networknopackets
`are produced in the mobile stations, but in PAD. The traffic
`is unidirectional also in the sense that the connection is
`mobile station-originated, i.e., the station should send a
`request to the networkfor creation of a data connection. No
`packets can be sent to the mobile station unless the station
`itself has first requested the opening of a line. It is also to be
`noted that data is conducted via the telephone network, the
`pricing of the data transfer whereof being much higher than
`pricing of transfer within a data network.
`The sending and reception function of data packets can be
`arranged to be positioned in all mobile stations or in some
`of them only. For the mobile stations without such function,
`a packet data transfer is to be completely opaque so that
`mobile stations of different types are enabled to function
`without any problems in the network simultaneously. Thus,
`the packet data feature is an additional service provided by
`the network, though requiring that the mobile station pos
`sesses a property to use such service. The implementation of
`the system must be such that it requires only a few changes
`in digital cellular systems in current use and, as an additional
`feature, it is well appropriate for use in current systems such
`as GSM, DCS 1800 operating in 1.8 GHz range or PCN.
`In new networks a so-called Short Message Service is
`most often determined, wherewith a mobile station is
`enabled to transmit and receive temporally short messages.
`A transfer of a short message requires, however, standard
`connection formation routines, thus requiring part of the
`frequency band and limiting the amount of data to be
`transferred.
`For transferring packet data no allocated radio channel
`and data route via the network are maintained continuously.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1A presents a cellular network in accordance with
`the prior art,
`FIG. 1B presents a cellular network in accordance with
`the present invention
`FIG. 2 is a schematic presentation of the logical channels
`of the GSM system,
`FIG. 3 illustrates the configuration of a channel request,
`FIG. 4 presents the starting signalling of a virtual channel,
`F.G. 5 presents the steps of transferring packet data,
`FIG. 6 presents the terminating signalling of the virtual
`channel,
`FIG. 7 presents a phase after a channel has been
`assembled,
`F.G. 8 is a diagrammatic presentation of a base station,
`FIG. 9 illustrates mobile phone originated data transfer,
`FIG. 10 illustrates data transfer terminating in a mobile
`phone,
`FIG. 11 presents a format of a packet data message,
`FIG. 12 presents aformat of another packet data message,
`FIG. 13 presents an order of a RACH frame for a standard
`burst,
`FIG. 14 presents the phases of a packet data transfer, and
`FIG. 15 presents signalling when a connection is broken
`at interfaces.
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`DETALED DESCRIPTION OF EMBODMENTS
`OF THE INVENTION
`In a particular example of a cellular network, the physical
`channel of a mobile station and a base station, that is, a radio
`frequency channel, consists of consecutive frames which in
`turn consist of time slots, in one of which the transmission
`is performed, the reception in another, in another listening to
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`In accordance with the invention, a virtual channel is
`arranged for data packet transfer in the network between the
`mobile station and the Mobile Switching Center. When a
`phone provided with a packet data function enters the range
`of the Mobile Switching Center, assigned as a user of the
`packet data service, all necessary signalling is executed,
`whereafter the Center, or more specifically, the packet data
`service unit (Agent) in association therewith is provided
`with all the information it needs concerning the phone and
`establishing a true transfer channel. Such data, containing in
`fact information about the location of the phone, is called a
`virtual channel. The virtual channel is thus a virtual con
`nection between the mobile station and the data service unit,
`enabling fast transition into data transfer mode, paying
`regard to the parameters stored in the memories of the
`mobile station and the data service unit. When packet data
`has to be transferred from the phone to the network, or vice
`versa, no complete signalling is needed between the phone
`and the Center, since that was carried out earlier; instead, a
`true transfer route can be set up extremely fast and with very
`low-level signalling between the mobile station and the
`packet data service unit (Agent), whereupon the packets are
`transferred. The transfer route, or at least the radio channel,
`is released as soon as there is no packet data to be trans
`ferred. Instead, the virtual channel is kept in constant
`preparedness as long as the mobile station is listed in the
`data service. In accordance with the present invention, a
`very rapid connection to the packet data transfer mode can
`be made, and the transfer route is kept reserved only when
`there is something to be transferred.
`Ameans to control the transfer of packet data is arranged
`to be in conjunction with the Mobile Switching Center, and
`is known as a data service unit (Agent), which can be a
`computer or a process. It is a data service center provided
`with a number of connection services and which has access
`to other networks and the services thereof. The Agent has
`beenplaced logically in association with aMobile Switching
`Center MSC, though the physical location can be inside the
`Center as part of the processes thereof or outside the Center
`in the form of one or more computers connected via a
`transmission link to the Center. The basis of the Agent is an
`Interface Unit IFU connecting the cellular network to
`another network, such as to TCP/IP or OSInetworks (TCP=
`Transmission Control Protocol, IP=Internet Protocol, OSes
`Open Systems Interconnection). Thus, a mobile station MS
`provided with a packet data function communicates by
`means of the data service unit (Agent) with the other
`networks, and the virtual channel is placed specifically
`between it and the data service unit (Agent). Therefore, each
`mobile station utilizing the packet data service under the
`control of the Mobile Switching Center is supervised by the
`data service unit (Agent) in association with the Mobile
`Switching Center.
`The Agent performs at least some of the following func
`tions: It
`registers all telephones provided with a packet data func
`tion under the control of the Mobile Switching Center,
`informs the phone of a message to anrive,
`removes the phone from the register after terminating of
`connection,
`transfers the messages of the phone to the rest of the
`network,
`transfers the messages from the rest of the network to the
`phone,
`buffers messages with a view to efficient transmission via
`the network,
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`when necessary, performs encrypting/decrypting,
`when necessary, performs compression/decompression
`between the phone and the Agent,
`updates the data base thereof (location updating),
`receives messages addressed to the paging channel.
`Normally, the virtual channel is initialized when the user
`starts using the packet data service, and the channel is
`terminated after the user leaves the service. During the time
`between the start and the termination, i.e., while being
`connected with the service, the mobile station is able to
`move and transfer from one cell to another. The handover
`function prerequires disassembling the virtual channel and
`assembling a new one. The handover is practically unob
`servable by the user.
`When entering the cell area, a mobile station listens to the
`System Info channel, characteristic of all cellular networks
`and constant transmission from the base station, being
`therethrough informed if the packet data service is in use in
`the network or in the cell. A System Info message may
`include an identification referring e.g., to the packet data
`service. When a mobile station wants to be connected to a
`packet data service, it transmits via a base station to the
`network a request for setting up a virtual channel. The
`request commences in the network a standard control sig
`nalling sequence utilized thereby and characteristic of said
`network, in which the authentication of the requester is
`checked, encrypting is started and the requester is provided
`with an interim identification number. The Agent in asso
`ciation with the Mobile Switching Center controlling the
`packet service, is also informed, whereby it includes the
`supervision of the mobile phone under the control thereof.
`The Mobile Switching Center maintains an ongoing register
`on the location of the mobile station, whereby handover
`from one cell to another is possible and a fast preparedness
`to transfer to data transmission or reception exists because
`there is no need for the phone to request separately for a
`traffic channel.
`Instead of a System Info message, it is also possible to
`operate so that the mobile station requests the network via a
`short message service whether the packet data function is
`engaged. The network responds by an equal message of the
`short message service. The short message services (SMS)
`are a service mostly included in the digital networks.
`The control signalling associated with the management of
`the data connection between the data service unit (Agent) in
`association with the Mobile Station and the Mobile Switch
`ing Center MSC is executed along with the data messages in
`the signalling plane.The functions in the signalling plane are
`provided with functions for setting up, maintaining and
`terminating a connection between the cellular network and
`the other networks. It also includes functions for updating
`the register, authentication, and a function for providing an
`interim subscriber number TMSL.
`Aplurality of protocols are available for use in the transfer
`of data packets between the mobile station and the data
`service unit (Agent). The radio interface sets, however,
`certain limits, such as a requirement for minimizing the
`amount of data transmitted across the interface. The amount
`can be minimized by compressing the data section of the
`packets. The data are compressed prior to transmission, e.g.,
`by means of V.42bis compression algorithm, and the
`receiver decompresses the data using the same algorithm.
`Also the bit amount in the header of the data packets may be
`reduced. Such functions are attended to by a Virtual Channel
`Protocol, which also attends to the control messages
`between the agent and the mobile station, as well as adapts
`the packets of the upper protocols into the Radio Link
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`Protocol (RLP) frames. A paging message transmitted to all
`mobile stations (broadcast) of the cell or to certain mobile
`stations (multicast) is transmitted on the data section of the
`broadcast or the multicast protocols, respectively.
`After the virtual channel has been assembled between the
`mobile station and the base station, the mobile station can
`neither start nor receive ordinary calls. Instead, the trans
`mission and reception of short messages SMS is possible.
`When wishing to transmit data packets, a mobile stations
`ends a request to the networkfor channel assignment. Since
`the majority of the signalling needed in establishing a
`channel has been already executed at the beginning of
`creating the virtual connection, the setting up of a data
`packet transfer channel extending from the mobile station to
`the Agent, required at this moment, is fast. This means a
`short time from the channel assignment request to transmis
`sion of packets.
`The transmission may be accomplished according to a
`first or second embodiment of the invention. When a user of
`the mobile station switches off the packet data function on
`termination of data transmission or when the network ter
`minates the connection, the data route is disassembled and
`the radio channel is released; optionally, the virtual channel
`may be maintained.
`A packet data session refers to the time commencing
`when a user starts a packet data function (informs of his
`desire to be connected to the service), and ending when the
`user terminates the service. In the course of the session the
`user may transmit packets both to a terminal network and
`receive them from the source network Roaming and han
`dover are possible. In the course of a session one or sever