(22) Date of Filing 08.10.1993
`
`
`(71) Applicant(s)
`
`Nokia Telecommunications OY
`
`
`(52) UK CL(Edition N)
`H4L LDSC L1H10 LiH3
`
`(56) Documents Cited
`GB 2225512 A
`
`WO 93/16560 A1
`
`
`
`
`(58) Field of Search
`UK CL(Edition L) H4K KYX KY4 KY4D KY4D14 KY4D8
`KY4P , H4L LDSD
`INT CL® HO40.7/04
`ONLINE : WPI
`
`(Incorporated in Finland)
`
`Makkylan Puistotie 1, SF-02600 Espoo, Finland
`
`Nokia Mobile Phones Limited
`
`(Incorporatedin Finland)
`
`P.O. Box 86, SF-24101 Salo, Finland
`
`w»UK Patent Application 1 GB on2 282731 aA
`
`(43) Date of A Publication 12.04.1995
`
`(51)
`INTCL§
`(21) Application No 9320815.5
`H040 7/38
`
`
`
`
`
`(72)
`
`Inventor(s)
`John Byrne
`Teuvo Jarvela
`Sanna Maenpaa
`
`
`(74) Agent and/or Address for Service
`Frank B Dehn & Co
`Imperial House, 15-19 Kingsway, LONDON,
`WC2B 6UZ, United Kingdom
`
`(54) Handover procedure in a dual-mode telecommunications network
`
`(57) A dual mode terminal 20 comprises a combined mobile station 21 and a cordless telephone 22 and can
`communicate with both a base station of a mobile radio system and a basestation (fixed part) of the cordless
`telephone system. Transfer of a call from the base station of the mobile radio system to a base station of the
`cordless telephone system takes place by a terminal-initiated set-up message transmitted (e.g. in response to
`a detected signal quality) via the mobile station section and the mobile radio system basestation and via the
`cordless telephone section to the cordless telephone system basestation. The set-up message includes the ID
`of the terminal and a call re-establishmentindicator.
`
`21
`
`22
`
` CONTROL
`
`UNIT
`
`FIG. 2
`
`Theprint reflects an assignment of the application under the provisions of Section 30 of the Patents Act 1977.
`
`Vlelcse?¢aD
`
`1
`
`SAMSUNG 1070
`SAMSUNG1070
`SAMSUNG v. SMART MOBILE
`SAMSUNGv. SMART MOBILE
`IPR2022-01004
`IPR2022-01004
`
`1
`
`
`
`
`(71) Applicant(s)
`
`Nokia Telecommunications OY
`
`
`(52) UK CL(Edition N)
`H4L LDSC L1H10 LiH3
`
`(56) Documents Cited
`GB 2225512 A
`
`WO 93/16560 A1
`
`
`
`
`(58) Field of Search
`UK CL(Edition L) H4K KYX KY4 KY4D KY4D14 KY4D8
`KY4P , H4L LDSD
`INT CL® HO40.7/04
`ONLINE : WPI
`
`(Incorporated in Finland)
`
`Makkylan Puistotie 1, SF-02600 Espoo, Finland
`
`Nokia Mobile Phones Limited
`
`(Incorporatedin Finland)
`
`P.O. Box 86, SF-24101 Salo, Finland
`
`w»UK Patent Application 1 GB on2 282731 aA
`
`(43) Date of A Publication 12.04.1995
`
`(51)
`INTCL§
`(21) Application No 9320815.5
`H040 7/38
`
`
`
`
`
`(72)
`
`Inventor(s)
`John Byrne
`Teuvo Jarvela
`Sanna Maenpaa
`
`
`(74) Agent and/or Address for Service
`Frank B Dehn & Co
`Imperial House, 15-19 Kingsway, LONDON,
`WC2B 6UZ, United Kingdom
`
`(54) Handover procedure in a dual-mode telecommunications network
`
`(57) A dual mode terminal 20 comprises a combined mobile station 21 and a cordless telephone 22 and can
`communicate with both a base station of a mobile radio system and a basestation (fixed part) of the cordless
`telephone system. Transfer of a call from the base station of the mobile radio system to a base station of the
`cordless telephone system takes place by a terminal-initiated set-up message transmitted (e.g. in response to
`a detected signal quality) via the mobile station section and the mobile radio system basestation and via the
`cordless telephone section to the cordless telephone system basestation. The set-up message includes the ID
`of the terminal and a call re-establishmentindicator.
`
`21
`
`22
`
` CONTROL
`
`UNIT
`
`FIG. 2
`
`Theprint reflects an assignment of the application under the provisions of Section 30 of the Patents Act 1977.
`
`Vlelcse?¢aD
`
`1
`
`SAMSUNG 1070
`SAMSUNG1070
`SAMSUNG v. SMART MOBILE
`SAMSUNGv. SMART MOBILE
`IPR2022-01004
`IPR2022-01004
`
`1
`
`
`
`RADIO
`INTERFACE
`
`ee
`PUBLIC
`
`=2laos
`
`3
`
`BSS
`
`DECT
`
`-
`
`OFFICE GSM/
`
`DECT
`
`DUAL MODE
`DECT aa TERMINAL
`FP
`PUBLIC
`
`FIG.
`
`1
`
`2
`
`
`
`2/2
`
`
`
`CONTROL
`UNIT
`
`FIG. 2
`
`CLEAR| COMPLETE
`
`DM ASSIGN COMPLETE
`7)
`
`DM ASSIGN REQ 3)
`
`[CLEAR COMMAND
`
`FIG. 3
`
`3
`
`
`
`2282731
`
`Dual mode subscriber terminal and a handover procedure of
`the
`dual
`mode
`subscriber
`terminal
`in
`a mobile
`
`telecommunications network
`
`The invention relates to a mobile telecommunica-
`
`tions system including a fixed network comprising mobile
`exchanges, base stations for mobile stations, and cordless
`
`telephone base stations connected to and under control of
`said mobile
`exchanges.
`In particular,
`the
`present
`invention relates to a method for performing handover from
`the base stations for mobile stations to the cordless
`
`telephone base stations.
`
`Conventional cordless telephones operate as an ex-
`
`tension to the Public Switched Telephone Network (PSTN). A
`
`cordless telephone system consists of a portable handset
`
`and a base station (a fixed part) connected to PSTN. The
`first cordless telephone systems were analog systems, such
`as CT1. Recently digital cordless telephone systems,
`such
`
`as CT2 and DECT (Digital European Cordless Telephone) have
`
`been introduced. When a cordless telephone is a subscriber
`of PSTN,
`it is accessed by dialing the telephone number
`associated with the fixed subscriber connection to which
`
`the base station is connected. Also the subscriber has
`
`10
`
`15
`
`20
`
`25
`
`In CT2
`access to the PSTN only via the home base station.
`and DECT, also a telepoint service is introduced, whereby
`
`a subscriber to the service can make calls away from home
`
`via a public base station. Also a common air interface for
`
`cordless telephones was
`
`introduced to facilitate roaming
`
`between systems and so to improve service coverage for the
`use.
`
`30
`
`There has also been a proposal to combine a cor-
`
`dless
`telephone
`system with
`a
`cellular mobile
`telecommunications system to further improve the roaming
`capabilities by means of utilization of
`the mobility
`control of
`the cellular network. When combined with the
`
`35
`
`4
`
`
`
`the
`the roaming of
`systems,
`mobile telecommunications
`cordless telephone handsets within the cordless telephone
`systems
`is
`fully supported. However,
`the
`cordless
`telephone handset
`is not
`able
`to utilize the more
`extensive
`radio coverage
`of
`the
`supporting cellular
`network or to perform handover
`to or
`from the cellular
`network. This disadvantage is due to several reasons.
`Firstly,
`the radic interfaces
`of cordless te-
`lephone systems and the mobile radio systems are usually
`incompatible.
`
`Secondly,
`the handover procedures are different. In
`cordless
`telephone systems,
`the handover procedure is
`usually
`initiated by
`the
`portable
`terminal. More
`
`particularly, when a cordless telephone terminal considers
`it necessary to change from one base station to another,
`
`the frequency band and selects the
`scans
`the terminal
`appropriate base station for the handover.
`In most of the
`mobile telephone systems the handover is controlled by the
`network. The mobile station only measures the quality of
`the radio connection and forwards the measuring results to
`the
`fixed network. One of
`ths network elements,
`for
`
`example a mobile exchange, makes a decision for handover
`on the basis of the obtained information.
`
`It is an object of the invention to provide a dual
`mode subscriber terminal capable to roam between a cor-
`dliess telephone system and a mobile radio system suppor-
`ting it.
`
`It is another object of the invention to provide a
`method for performing handover from a mobile radio system
`to a cordless telephone system supported by said mobile
`telecommunications system.
`
`in a mobile telecom-
`invention is,
`One aspect of
`munications system including a fixed network comprising
`mobile exchanges,
`first base stations connected to said
`mobile exchanges, and second base stations of a cordless
`
`10
`
`2S
`
`20
`
`25
`
`30
`
`35
`
`5
`
`
`
`being
`stations
`base
`second
`said
`system,
`telephone
`connected to and under control of said mobile exchanges,
`dual mode subscriber terminals having a mobile station
`
`part for radio communication with said first base stations
`and a cordless telephone part for radio communication with
`
`said second base stations;
`
`a method for performing han-
`
`dover from one of said first base stations to one of said
`
`second base stations, comprising the steps of
`
`initiating a call re-establishment procedure from
`said cordless telephone part of said dual mode terminal
`during an on-going call via said mobile station part of
`said dual-mode
`terminal
`and one of
`said first base
`
`stations,
`sending a call setup message from said cordless
`telephone part of said dual mode terminal
`to one of said
`
`second base stations having an appropriate field strength,
`
`said message including a terminal identity and a call re-
`
`establishment message indicator,
`sending a call re-establishment message from said
`one of said second base stations to one of said mobile
`
`exchanges
`
`in response to receipt of
`
`said call
`
`setup
`
`message with said call re-establishment
`
`indicator,
`
`said
`
`call re-establishing message including said terminal iden-
`
`tity,
`
`re-establishing said on-going call to said cordless
`
`telephone part of said dual mode terminal via said one of
`said second base stations.
`
`Another aspect of
`
`the invention is,
`
`in a mobile
`
`telecommunications system including a fixed network comp-
`
`rising mobile exchanges, first base stations connected to
`
`said mobile exchanges,
`
`and second base stations of
`
`a
`
`cordless telephone system, said second base stations being
`
`connected to and under control of said mobile exchanges; a
`
`dual mode subscriber terminal comprising
`
`a mobile station part for radio communication with
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`6
`
`
`
`said first base stations,
`
`a cordless telephone part for radio communication
`with said second base stations,
`
`responsively to detecting a predetermined
`means,
`conditition during an on going call via one of said first
`base stations and said mobile station part of said dual
`mode terminal, for activating said cordless telephone part
`of
`said dual mode
`terminal
`to initiate a call
`re-
`
`establishment procedure, and
`means for sending a call setup message to said one
`
`of said second base stations from said cordless telephone
`
`part of said dual mode terminal, said message including a
`
`terminal
`indicator.
`
`identity and a call
`
`re-establishment message
`
`In the invention, a dual mode terminal is utilized,
`
`in which a mobile station of a mobile radio system and a
`
`cordless telephone are combined. This kind of terminal can
`have a communicate with both base stations of the mobile
`
`radio system and base
`
`stations
`
`(fixed part)
`
`of
`
`the
`
`in the case of this
`cordless telephone system. Handover
`dual mode terminal can imply the transfer of a call from a
`
`base station of the mobile radio system to a base station
`
`the
`the cordless telephone system. As noted before,
`of
`primary problem in this concept is that two systems utili-
`zing different
`handover principles
`are
`combined.
`In
`
`cordless telephone systems,
`
`such as DECT, handover
`
`is a
`
`terminal controlled procedure and the terminal will make a
`decision when the handover is needed.
`In the mobile radio
`
`the network will always decide when
`such as GSM,
`system,
`to perform a handover. The inventive solution is to use a
`
`call re-establishment procedure for handover, because it
`is a terminal initiated procedure and is a feasible proce-
`dure in mobile radio systems, such as GSM. Thus, by using
`a call
`re-establishment procedure handover can be ini-
`tiated by a dual mode terminal having connection with a
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`7
`
`
`
`base station of the mobile radio system. The call re-esta-
`blishment procedure in mobile radio systems is basically
`intended for maintaining and re-establishing a call
`in a
`case where a mobile station loses a connection to a base
`
`station during a call and has to search for a new base
`station.
`The mobile
`radio
`network maintains
`all
`
`connections and resources associated with a call
`
`in the
`
`network,
`
`and if a call
`
`re-establishment message is re-
`
`ceived from a terminal within a predetermined period of
`
`the call is re-established. Thus,
`time,
`a short break in the connection. Now,
`
`there will be only
`this call re-esta-
`
`blishment procedure is utilized in a novel manner for in-
`ter-system handover between a cordless telephone system
`
`and the supporting mobile radio system.
`Still another aspect of
`the invention is,
`
`in a
`
`mobile telecommunications system including a fixed network
`
`comprising mobile exchanges,
`
`cordless
`
`telephones,
`
`base
`
`said base
`system,
`telephone
`cordless
`a
`stations of
`stations being connected to and under control of said
`mobile exchanges;
`a method for performing handover
`from
`one of said cordless telephone system base stations to
`
`another, comprising the steps of
`
`loess of connection
`a
`detecting low quality or
`between a cordless telephone terminal and one of said base
`stations during an on-going call,
`
`detecting an appropriate field strength of another
`said base stations by said cordless
`telephone
`one of
`terminal,
`
`sending a call setup message to said another one of
`said base stations from said cordless telephone terminal,
`said message including a terminal identity and a call re-
`establishment message indicator,
`
`sending a call re-establishment message from said
`another one of said base stations to one of said mobile
`
`exchanges
`
`in response to receipt of
`
`said call
`
`setup
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`8
`
`
`
`indicator, said
`message with said call re-establishment
`call re-establishing message including said terminal iden-
`
`tity,
`
`re-establishing said on-going call to said cordless
`telephone terminal via said another one of said base sta-
`tions from said one of said mobile exchanges.
`Still another aspect of the invention is a mobile
`telecommunications
`system including
`a
`fixed network
`comprising
`mobile
`exchanges,
`cordless
`telephone
`terminals,
`base stations of a cordless telephone system,
`said base stations being connected to and under control of
`said mobile exchanges; means for performing handover from
`one of said cordless telephone base stations to another,
`said means comprising
`means
`for detecting low quality or
`
`loss
`
`of
`
`connection between a cordless telephone terminal and one
`
`of said base stations during an on-going call,
`
`means for detecting an appropriate field strength
`
`of another one of said base stations by said cordless
`
`telephone terminal,
`setup messace to said
`means
`for sending a call
`another one of
`said base stations from said cordless
`
`telephone terminal,
`
`said message
`
`including a
`
`terminal
`
`identity and a call re-establishment message indicator,
`
`means for sending a call re-establishment message
`from said another one of said base stations to one of said
`
`mobile exchanges in response to receipt of said call setup
`message with said call re-establishment
`indicator, said
`
`call re-establishing message including said terminal iden-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`tity,
`
`means
`
`for re-establishing said on-going call
`
`to
`
`said cordless telephone terminal via said another one of
`said base stations from said one of said mobile exchanges.
`The call re-establishment handover procedure accor-
`ding to the invention may be applied also to handover bet-
`
`35
`
`9
`
`
`
`ween
`
`two base
`
`stations
`
`(fixed parts)
`
`of
`
`a cordless
`
`a
`telephone system connected to a mobile exchange of
`mobile radio system.
`In that case the terminal may also be
`an ordinary cordless telephone terminal
`instead of
`the
`dual mode terminal according to the invention.
`The invention will be described more specifically
`
`with reference to the attached drawings,
`
`in which
`
`Figure 1 shows a general diagram of a mobile radio
`
`system which supports cordless telephone systems,
`Figure 2
`shows a general diagram of a dual mode
`subscriber terminal according the invention, and
`Figure 3
`is a signalling diagram for the handover
`method according to the invention.
`In the following the invention will be described
`using digital cellular radio system known as GSM (Groupes
`
`Speciale Mobile) as an example of the mobile radio system
`and DECT (Digital European Cordless Telephone) as an exam-
`ple of cordless telephone systems. However,
`the invention
`is not
`intended to be restricted to these systems. The
`invention may be applied to any mobile radio system which
`
`has a call re-establishment capability,
`
`and to any cor-
`
`dless telephone system.
`
`Figure
`
`1
`
`shows
`
`the
`
`functional
`
`environment
`
`of
`
`GSM/DECT dual mode terminal. In figure 1, both base stati-
`
`ons BSS of GSM system and fixed parts FP of DECT system
`are connected to the GSM mobile exchange MSC. One of the
`
`DECT fixed parts FP
`
`is shown to be connected to the
`
`private branch exchange PBX which is further connected to
`
`the MSC. The MSC may be connected to other MSC:s,
`PSTN
`(Public Switched Telephone Network) or
`ISDN (Integrated
`
`Services Data Network). The MSC is also connected to the
`
`visitor location register VLR, which is a data base main-
`taining subscriber files on the subscribers visiting in
`the area of the MSC, and to a home location register HLR
`which is a data base maintaining subscriber files on all
`
`10
`
`15
`
`20
`
`25
`
`30
`
`10
`
`10
`
`
`
`to an
`further
`and
`system,
`in the
`subscribers
`the
`identity
`authentication center AC and to an equipment
`register EIR. For more detailed description of the ope-
`ration and structure of GSM system, a reference is made to
`GSM specifications and to a book "The GSM system for mobi-
`le communication", M. Mouly and M. Pautet, Palaiseau,
`
`France,
`
`ISBN:2 9507190-0-7.
`
`Figure 2 shows a general view of a GSM/DECT dual
`mode subscriber terminal 20 according to the invention.
`
`The terminal 20 consists of a GSM mobile station part MS
`
`21 and a DECT portable terminal part PP 22. The GSM part
`
`is used when communicating
`MS of the dual mode terminal
`with GSM base stations. The DECT part PP of the dual mode
`terminal is used when communicating with DECT fixed parts
`FP. Both MS and PP include all the necessary equipment,
`
`and
`signalling
`for
`transceivers,
`radio
`as
`such
`communicating over the respective radio interface. It is
`
`some functions
`least
`normally advantageous to embody at
`and circuits,
`such as display, keyboard, power supply,
`etc., by means of a common circuitry. In Fig. 2, a common
`control unit 23 is connected to MS and PP parts of
`the
`dual mode terminal for controlling the cperation thereof.
`The GSM network provides a full mobility management
`
`support
`
`for the cordless telephone systems connected to
`
`it. Thus,
`
`the GSM network maintains files on the cordless
`
`telephone subscribers and the current location thereof and
`is therefore able to route the calls addressed to the cor-
`
`dless telephone to their current locations. Basically,
`
`the
`
`cordless telephone subscribers are handled in a similar
`manner with the ordinary GSM subscribers.
`Thus,
`the dual mode terminal according to the in-
`vention is capable of communicating with both GSM base
`stations and DECT base stations
`(fixed parts) FP. Con-
`
`sequently,
`
`a dual mode terminal should also be able to
`
`roam anywhere in the system. However, problems are encoun-
`
`10
`
`i5
`
`20
`
`25
`
`30
`
`35
`
`11
`
`11
`
`
`
`tered when the handover from GSM base station BSS to DECT
`
`is required, since in the DECT
`(or vice versa)
`fixed part
`system handover is a terminal controlled procedure and the
`terminal will make a decision when the handover is needed.
`
`In the GSM system network will always decide when to
`
`perform a handover.
`According to the invention, a GSM/DECT dual mode
`terminal can imply a transfer of a call from a GSM base
`station BSS to a DECT fixed part FP by utilizing a call
`re-establishment procedure for handover. The call
`re-
`establishment procedure is a feasible procedure in GSM,
`and is originally intended for situations where mobile
`station loses connection to a current base station during
`
`a call, searches a new base station and sends a call re-
`
`establishment message to the network, e.g.
`
`to the mobile
`
`exchange controlling the call. The network will maintain
`all connections and resources associated with the call for
`
`a predetermined period of time after losing the connecti-
`
`on, and if the call re-establishment message is received
`
`within this period,
`the call will be re-established via
`the new base station. The call re-establishment procedure
`
`is a terminal initiated procedure in SSM, and therefore,
`by using the call re-establishment procedure a handover
`can be initiated by a terminal
`from GSM to DECT.
`
`The inventive handever procedure is described in
`
`the following with reference to figure 3. Call re-esta-
`blishment procedure is a standard procedure in GSM, but in
`DECT specifications only call
`re-establishment within a
`single fixed part FP is completely defined. No proper met-
`hod for using call re-establishment when handing over from
`an old FP to a new FP has been defined in DECT.
`In the
`
`10
`
`15
`
`20
`
`25
`
`30
`
`following is described how the call re-establishment may
`be carried out in the GSM/DECT concept.
`Referring to figure 3,
`let us
`
`the
`
`assume
`
`that
`
`35
`
`mobile station part MS of
`
`the dual mode terminal 20 is
`
`12
`
`12
`
`
`
`communicating with a GSM base station BSS. Subsequently
`the MS part notices that
`the connection to the base
`station BSS has been lost, or
`that
`the quality of
`the
`connection is low, e.g. a field strengh received is under
`
`a predetermined threshold. The MS part furher notices that
`it is unable to establish a new connection to another GSM
`
`base station BSS. Subsequently,
`
`the MS part of the dual
`
`mode terminal 20 requests the portable cordless telephone
`part PP of the dual mode terminal
`to initiate a call re-
`
`establishment procedure.
`
`In response to the request,
`
`the
`
`PP part of
`
`the dual mode
`
`terminal
`
`searches
`
`for
`
`an
`
`appropriate DECT fixed part FP in step 1. If the PP part
`
`detects an appropriate field strength of one of the DECT
`
`re-
`a call
`attempts
`PP part
`the
`FP,
`fixed parts
`fixed part FP by sending a setup
`to that
`establishment
`message CC-SETUP. The call setup message CC-SETUP may be
`modified from a standard CC-SETUP message of DECT common
`interface specification (DECT CI) so that the basic servi-
`ce information element
`in the message can indicate a call
`re-establishment. Alternatively,
`it may be possible to
`
`make an agreement
`
`that a standard CC-SETUP message with
`
`the Basic service element "External Handover Call Set Up"
`which is presently dedicated to other use will interpreted
`as @ call re-establishment message when used in a GSM/DECT
`
`in step 1 in
`environment. Thus, a call setup message sent
`figure 3
`includes
`the following information elements:
`Portable identity and basic service information element
`
`indicating call re-establishment.
`In an alternative embodiment of the invention the
`
`cordless telephone part may independently initiate the
`
`call re-establish procedure without
`
`the request
`
`from the
`
`if it detects an appropriate field strength of
`MS part,
`one of the DECT fixed parts FP.
`In this embodiment of the
`invention,
`the priority of use of the DECT fixed parts for
`calls is higher than the priority of use of the GSM base
`
`10
`
`i5
`
`20
`
`25
`
`30
`
`35
`
`13
`
`13
`
`
`
`11
`
`In other words the fixed parts
`stations BSS for calls.
`are favoured when the dual mode terminal would be able to
`
`establish a connection with both base station types. The
`priority of use may be based on lower costs in a cordless
`system, for example. The PP part informs the MS part that
`a call re-established procedure is iniatiated. Remaining
`
`parts of the procedure are similar to as in the preferred
`embodiment of the invention.
`
`In step 2, having received the CC-SETUP message
`from the PP part of the dual mode terminal,
`the fixed part
`FP can derive from basic service information element that
`
`it is a call re-establishment request. Therefore the fixed
`
`part FP sends a DM CALL RE-ESTABLISHMENT message according
`
`to DSS.1+ protocol
`
`to the MSC. DSS.1+ protocol
`
`is the
`
`DSS.1 protocol enhanced with mobility management. The mes-
`sage includes the following information elements: Portable
`identity and mobile station class mark indicating a DECT-
`terminal.
`
`In step 3 of figure 3, having received the DM CALL
`
`RE-ESTABLISHMENT message the MSC finds out based on the
`
`portable identity all the required informatisn about
`
`the
`
`call. This includes, for example finding out
`the identity
`of the old GSM base station. Subsequently,
`the MSC sends a
`DM ASSIGNMENT REQ message according to DSS.i- protocol to
`the new fixed part. This message
`is used in GSM for
`requesting the
`new base
`station to assign
`radio
`resources.
`This message may
`not
`be
`necessary
`for
`performing call
`re-establishment
`for DECT
`terminals.
`
`However,
`
`it
`
`is preferable to keep this message in the
`
`procedure for consistency from GSM network point of view.
`The message includes the following information elements:
`portable identity.
`
`In step 4, having received the DM ASSIGNMENT REQ
`message the new fixed part FP initiates the connection by
`sending CC CONNECT message according to DECT CI
`to the PP
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`14
`
`14
`
`
`
`12
`
`part of
`
`the dual mode terminal.
`
`In parallel,
`
`the fixed
`
`part FP sends DM ASSIGNMENT COMplete message according to
`DSS.1+ as an acknowledgement
`to the MSC.
`In step 5, having received a CC-CONNECT message
`from the fixed part FP,
`the PP part of
`the dual mode
`terminal sets up the connection.
`In step 6, having received the acknowledgement
`from the new DECT fixed part FP the MSC re-
`message
`establishes the call
`to the PP part of
`the dual mode
`
`terminal via the new fixed part FP. The MSC also initiates
`release of the connection to the old GSM base station BSS
`
`CLEAR
`a
`sending
`by
`specification GSM 08.08.
`In step 7,
`having received the CLEAR COMMAND
`message the old base station BSS releases the resources
`
`COMMAND message
`
`according
`
`to
`
`10
`
`15
`
`BSS
`the
`Subsequently,
`call.
`the
`associated with
`acknowledges the release by sending CLEAR COMplete message
`according to the specification GSM 08.08.
`
`In step 8, having received CLEAR COMplete message
`the MSC
`knows
`that
`the old GSM connection has been
`
`20
`
`25
`
`30
`
`released and the handover is completed.
`
`The handover procedure according to the invention
`can be applied also to handover between two DECT fixed
`parts FP connected to mobile exchange MSC.
`In that case
`
`the terminal may also be an crdinary DECT terminal instead
`of the dual mode terminal according to the invention. The
`procedure is similar to that described with reference to
`figure 3 except
`that no GSM base station or
`the mobile
`
`station part MS of the dual mode terminal is involved.
`
`A typical situation where the handover
`occurs is when a dual mode terminal which is in connection
`with a GSM base station outside an office building enters
`the office building covered by a DECT system. Normally,
`
`15
`
`15
`
`
`
`13
`
`this results in the loss of
`
`GSM connection and the
`
`inventive handover procedure is initiated.
`
`The
`figures and the description associated with
`them are intended only to illustrate the present inventi-
`on.
`In its details the present
`invention may vary in the
`
`scope and spirit of the attached claims.
`
`16
`
`16
`
`
`
`14
`
`Claims
`
`1.
`
`In a mobile telecommunications system including
`
`a fixed network comprising mobile exchanges, first base
`stations connected to said mobile exchanges and second
`base stations of a cordless telephone system, said second
`base stations being connected to and under control of said
`mobile exchanges, dual mode subscriber terminals having a
`
`radio communication with said
`for
`mobile station part
`first base stations and a cordless telephone part
`for
`
`radio communication with said second base stations;
`
`a
`
`method for performing handover from one of said first base
`Stations to one of said second base stations, comprising
`
`the steps of
`iniatiating a call re-establishment procedure from
`said cordless telephone part of said dual mode terminal
`during an on-going call via said mobile station part of
`said dual-mode
`terminal
`and one of
`said first base
`
`10
`
`15
`
`20
`
`telephone part of said dual mode terminal
`
`tc one ct said
`
`second base stations having an apprepriate field strength,
`said message including a terminal identity and a call ves-
`establishment message indicator,
`
`sending a call re-establishment message from said
`one of said second base stations to one of said mobile
`
`in response
`exchanges
`message with said call
`
`to receipt of
`re-establishment
`
`said call
`indicator,
`
`setup
`said
`
`call re-establishing message including said terminal iden-
`
`30
`
`tity,
`
`re-establishing saic cn-going call to said cordless
`
`telephone part of said dual mode terminal via said one of
`said second base stations.
`
`35
`
`2. A method according to claim 1, wherein said step
`of initiating said call re-establishment procedure further
`
`17
`
`17
`
`
`
`15
`
`comprises the steps of
`detecting loss or low quality of connection between
`said one of said first base stations and said mobile
`
`station part of said dual mode terminal during an on-going
`
`call,
`
`requesting said cordless telephone part of said
`dual mode
`terminal
`to initiate a call
`re-establishment
`
`procedure.
`
`3. A method according to claim 1, wherein said step
`
`re-establishment procedure is
`initiating said call
`of
`performed in response to a) detecting an appropriate field
`strength of one of said second base stations by said
`cordless telephone part of said dual mode terminal, and b)
`observing that
`the priority of use of said one of said
`second base stations is higher than the priority of use of
`said one of said first base stations.
`
`2 or 3, wherein
`4. A method according to claim 1,
`said step of re-establishing said on-going call comprises
`the steps of
`
`analyzing said call
`
`re-establishment message at
`
`said one of said mobile exchanges,
`
`sending a resource assignment message to said one
`
`of said second base stations,
`
`sending an acknowledgement
`to said one of
`said
`mobile exchanges in response to said resource assignment
`message,
`
`commanding said one of said first base stations to
`the
`resources
`associated with
`the
`former
`
`release
`
`10
`
`5
`
`20
`
`25
`
`30
`
`connection with said mobile station part of said dual mode
`terminal.
`
`In a mobile telecommunications system including
`5.
`a fixed network comprising mobile exchanges, first base
`stations connected to said mobile exchanges and second
`base stations of a cordless telephone system, said second
`base stations being connected to and under control of said
`
`35
`
`18
`
`18
`
`
`
`16
`
`mobile
`
`exchanges;
`
`a
`
`dual mode
`
`subscriber
`
`terminal
`
`comprising
`a mobile station part for radio communication with
`
`said first base stations,
`
`a cordless telephone part for radio communication
`with said second base stations,
`means,
`responsively to detecting a predetermined
`conditition during an on going call via one of said first
`base stations and said mobile station part of said dual
`
`mode terminal, for activating said cordiess telephone part
`of
`said dual mode
`terminal
`to initiate a call
`re-
`
`establishment procedure, and
`means for sending a call setup message to said one
`of said second base stations from said cordless telephone
`part of said dual mode terminal, said message including a
`terminal
`identity and a call
`re-establishment message
`indicator.
`
`6. A dual mode
`
`terminal according to claim 5,
`
`wherein said predetermined condition includes at least one
`of
`the following conditions:
`a)
`low quality or loss of
`connection between one of said first base stations and
`
`said mobile station part of said dual mode terminal during
`
`an on-going call, and b) an appropriate field strength ct
`
`one of
`
`said second base
`
`stations,
`
`and wherein said
`
`in said mobile station
`further comprises means
`terminal
`part for requesting said cordless telephone part of said
`dual mode
`terminal
`to initiate a call
`re-establishment
`
`procedure.
`
`7. A dual mode
`
`terminal according to claim 5,
`
`comprising wherein said predetermined condition includes
`
`an appropriate field strenath of one of said second base
`
`stations having the priority of use higher
`than the
`priority of use of said one of said first base stations.
`8.
`In a mobile telecommunications system including
`a fixed network comprising mobile exchanges, cordless te-
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`19
`
`19
`
`
`
`17
`
`lephone terminals, base stations of a cordless telephone
`system, said base stations being connected to and under
`
`control of said mobile exchanges; a method for performing
`handover from one of said cordless telephone base stations
`to another, comprising the steps of
`
`detecting low quality or loss of connection between
`a cordless
`telephone
`terminal
`and one of
`said base
`stations during an on-going call,
`
`detecting an appropriate field strength of another
`
`one of
`
`said base stations by said cordless
`
`telephone
`
`terminal,
`
`sending a call setup message to said another one of
`
`said base stations from said cordless telephone terminal,
`said message including a terminal identity and a call re-
`establishment message indicator,
`
`sending a call re-establishment message from said
`another one of said base stations to one of said mobile
`
`exchanges
`
`in response to receipt of
`
`said call
`
`setup
`
`messace with said call
`
`re-establishment
`
`indicator,
`
`said
`
`call re-establishing message including said terminal iden-
`
`tity,
`
`re-establishing said on-going call to said cordless
`
`telephone terminal via said another one of said base sta-
`
`tions from said one of said mobile exchanges.
`9. A method according to claim 8, wherein said step
`of re-establishing said on-going call comprises the steps
`of
`
`analyzing said call
`
`re-establishment message at
`
`said one of said mobile exchanges,
`sending a resource assignment message to said one
`of said base stations,
`
`sending an acknowledgement
`
`to said one of said
`
`mobile exchanges in response to said resource assignment
`message,
`
`commanding
`
`said one of
`
`said base
`
`stations
`
`to
`
`10
`
`i5
`
`20
`
`25
`
`30
`
`35
`
`20
`
`20
`
`
`
`- 18 =
`
`release the resources associated with the former
`
`connection with said cordless telephone terminal.
`10. A mobile telecommunications system including a
`
`fixed network comprising mobile exchanges, cordless
`
`telephone terminals, base stations of a cordless
`telephone system, said base stations being connected to
`and under control of said mobile exchanges; means for
`performing handover from one of said cordless telephone
`base stations to another, said means comprising
`means for detecting low quality or loss of
`connection between a cordless telephone terminal and one
`of said base stations during an on-going call,
`means for detecting an appropriate field strength of
`another one of said base stations by said cordless
`
`telephone terminal,
`means for sending a call setup message to said
`another one of said base stations from said cordless
`
`telephone terminal, said message including a terminal
`identity and a call re-establishment message indicator,
`
`means for sending a call re-establishment message
`from said another one of said base stations to one of
`
`said mobile exchanges in response to receipt of said call
`setup message with said call re-establishment indicator,
`
`said
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