FI100214B - Method and arrangement for handover between base station controllers - Google Patents

Description

100214

Method and arrangement for hand-over between base station controllers

The invention relates to a handover between base station controllers in a personal communication system (PCS).

Various cellular radio systems that enable personal wireless communication have been in use for a long time. One such mobile communication system is the European digital mobile communication system GSM (Global System for Mobile Communications). In addition, a new generation of systems is under development, which it is hoped will further expand the capabilities of personal wireless communications. One such system under standardization is the Personal Communication System (PCS) in the United States. Under current assumptions, there will be two types of PCS networks: traditional overlay-type networks and fixed ISDN-type and PSTN-type networks. There will be lu-20 monthly options for the radio interface, one of which is the GSM-based PCS1900 (GSM system operating in the 1900 MOz frequency band).

Modifying an existing mobile system standard (such as GSM or DCS1800) into a PCS overlay network (such as PCS1900) is a relatively straightforward process. 25 More problematic, on the other hand, are PCS networks of the fixed ISDN and PSTN type, which use a normal fixed local area network (LE) instead of a mobile switching center, in which case such an ISDN / PSTN-based network is not directly suitable for, for example, GSM network architecture.

, · 30 In a GSM-based overlay network, the mobile switching center is a central unit of the network, but in an ISDN / PSTN-based network, the local exchange LE has no features supporting the mobile network at all. In the future, the local exchange LE can be expected to include a small number of 35 common features that support the connection of mobile communication networks (non-call signaling, some type of handover connection support) but may not be very useful for the PCS1900 system, for example.

5 One solution to this problem is presented in "Switching and Signaling Generic Requirements for Network Access Services to Personal Communication Services (PCS) Provider, GR-2801-CORE, Issue 1, December 1993, Bellcore, Bell Communications Research, in particular Chapter 10 1 , pages 1-10, section 2, pages 1-26 and section 3, pages 133-137 In this Bellcore-type network, the radio interface is a wireless access communication system WACS (Bellcore TR INS-001313) connected to a local area network of a fixed network. is connected to an intelligent network 15 which provides the local exchange with the service logic, databases and operations required for access network mobility management, i.e. the intelligent network AIN (Advanced Intelligent Network) provides centralized subscriber database services, location management, authentication, access control, 20 call control, etc. in the local exchange from which the call control can start the intelligent network operation according to predetermined triggers via the standard AIN interface. Bellcore's system also supports handover, which Bellcore calls * '25 as Automatic Link Transfer (ALT). The purpose of ALT is to ensure continuity of service to the PCS user when signal strength varies during a answered call. The signal strength may vary, for example, if the PCS user is moving or if the conditions in the radio environment change. ^ 30 The purpose of the ALT is to allow an existing answered call to continue without interruption and without the PCS user having to take action to perform the ALT or know that the ALT has occurred. Chapter 3, pages 133-138 of the above-mentioned publication describes the ALT-35 procedure, in which the "anchor point" of the handover is locally 3,100,214 additional centers. That is, when performing ALT from the old base station system (IPS / RPCU) to the new base station system (IPS / RPCU), the exchange is disconnected from the old base station system at the exchange and a connection to the new base station system is established. In this case, the local exchange of the fixed network is the anchor of the connections and signaling. Such a handover using the local exchange as an anchor is possible in new national ISDN exchanges with the required features. However, such a handover solution 10 cannot be considered a good way to proceed, at least in the early stages of PCS systems, as the majority of existing fixed network exchanges are of the older type and therefore the availability of exchanges with the necessary features cannot be guaranteed. In addition, the fact that the anchor point of handover connections is a network element incompatible with an access network standard such as GSM is a problem.

WO 95/01694 discloses a handover between base station systems under a local exchange in a fixed network, in which the anchor point of the handover remains in the mobile communication system. That is, the first base station controller of the call acts as an anchor point to which the original connection established through the local exchange is maintained throughout the call. In the handover, an extension-25 connection is established from the anchor base station controller to another base station controller.

It is an object of the present invention to provide an improved handover between base station controllers that is flexible and independent of the characteristics of a local area network in a fixed network.

This is accomplished by an arrangement for performing handover between base station controllers in a communication system comprising a fixed network local exchange; mobile stations; base station systems that provide 35 mobile stations with a wireless access network to a local exchange, each base station system including a base station controller and base stations; transmission lines on which the local exchange is connected to the base station controllers; characterized in that the control of the handover between the 5 base station controllers is arranged in the base station controllers so that the first base station controller of the call acts as an anchor point to which the original connection established via the local exchange is maintained and in a handover situation is connected to another base station controller; the base station controllers are adapted to decide whether the handover onward connection is a local call connected via the ISDN-15 local exchange or a connection established via said fixed transmission connection, and to notify the other base station controller of the selection.

The invention also relates to a method for performing handover 20 between base station controllers in a communication system comprising a fixed exchange local exchange; base station systems that form a wireless access network for mobile stations to a local exchange, each base station system including a base station controller and base stations; and transmission lines connecting the local exchange to the base station controllers, the method comprising establishing a call connection from the local exchange to the first base station controller serving the mobile station. 30, a handover is performed to transfer the call and the mobile station from the first base station controller to the second base station controller. According to the invention, the method is characterized in that the handover is controlled from the base station controllers independently of the expensive exchange, the call connection is maintained from the local exchange to the first base station controller, it is decided in the first or second base station control via the transmission link, the decision-making base station controller notifies the switching type of the selected handover to the second base station controller, a downlink connection according to the selected switching type is established from the first base station controller to the second base station controller.

In the invention, the first base station controller acts as a "anchor" for the handovers in a manner known per se, via which the original voice connection is connected from the local exchange to the base station and further by radio to the mobile station. When handovering to the second base station controller, the original connection between the local exchange and its first base station controller is maintained and a downlink is established from the first base station controller to the second base station controller either as a local call through the local exchange (s) or through a fixed connection between base station controllers. The handover is controlled from the tu-25 station controllers. Thanks to the solution according to the invention, the "anchor" and the controller of the handover are a network element of the radio system, i.e. the base station controller, and the local exchange only connects according to the instructions of the base station controllers. In a handover using a fixed connection, the local exchange 30 does not participate in the handover in any way. Since the handover according to the invention does not require any additional features from the local exchange, the handover can also be implemented under the current local exchange types.

Fixed connections between base station controllers can be established in the network at least where handovers 6 100214 between these base station controllers often occur. Fixed connections reduce handover-related signaling and are less expensive compared to local calls connected through a local exchange.

5 The free capacity of another existing local call can also be used to establish an extension connection. This is possible when the speech coding / data rate of the radio system is so low (e.g., 13 kbits) that multiple speech / data signals can be placed on a single 64 or 56 kbits transmission channel.

Base station controllers have the flexibility to choose the type of Hando blood onward connection: local call or fixed connection. Two transmission lines are required for each connection, one for each transmission direction. If 15 new local calls are established for the handover extension connection, both base station controllers can independently select the transmission lines to the local exchange, which connects them together. If the handover extension connection is established via a fixed connection or the free space of an existing local call is used, it is important to know which side decides on the connection type and reserves the connection. If both sides were allowed to make reservations independently of each other, the same lines could be booked simultaneously from both ends. To overcome this problem, the decision-making responsibility may be given to one of the two station controllers. The decision is then signaled to the other party. The base station controller can delegate decision making to another base station controller by not specifying the connection type in the signaling. It is also possible for base station controllers to negotiate connection type and connection.

The invention will now be described by way of preferred embodiments with reference to the accompanying drawings, in which Figure 1 is a block diagram illustrating an ISDN-based PCS network according to the invention, 11 7 100214 Figure 2 is a block diagram illustrating the division of mobile switching center functions into functional units for different network elements, Figures 3A, 3B, 3C and 3D show three different ways of performing a handover between base station controllers, Figure 4 is a block diagram showing handover branches in connection with two consecutive handovers, Figures 5A, 5B and 5C show a signaling diagram for generating a new handover AB 'and dismantling the old 10 handover branch AB in Fig. 4, Fig. 6 shows a signaling diagram for a fixed connection handover,

The basic principles of the invention can be applied to the connection of any wireless access network to a local exchange of a fixed network and to an intelligent network. In preferred embodiments of the invention, the access network is a radio system based on the GSM system, such as PCS1900. That is, the access network is modified from the GSM mobile communication system or its 1800 MHz version 20 DCS1800. For details of the GSM system, reference is made to the ETSI GSM Recommendations and to the book "The GSM System for Mobile Communications", M. Mouly & M. Pautet, Palaiseau, France, 1992, ISBN: 2-9507190-0-0-7.

The block diagram of Figure 1 illustrates the network elements of a PCS1900 network based on a fixed network.

The access network PCS1900 comprises base station systems BSS, each of which includes one base station controller BSC and several base stations BTS. The base stations BTS communicate over the radio interface with the personal stations PS (mobile stations). The radio interface between the mobile station PS and the base station BTS and the interface between the base station BTS and the base station controller BSC is similar to that in a conventional overlay-type PCS1900 system and will not be discussed in more detail here. However, unlike a conventional GSM-35 based network, the base station controllers BSC are not connected to a mobile switching center MSC but to a fixed network such as ISDN or a PSTN local exchange LE. In preferred embodiments of the invention, the local exchange is an ISDN exchange. The local exchange LE, in turn, connects to the AIN (Advanced Intelligent Network) service control point SCP via the standard intelligent network interface. In some cases, the smart grid is unnecessary. In this case, the local center itself may contain more intelligent functions. Furthermore, the local exchange LE is connected to the other local exchanges LE or remote exchanges TX of the ISDN network in the same way as the nor-10 destination.

Thus, such a PCS network based on a fixed network is not directly suitable for the GSM architecture, as it does not have a mobile switching center MSC at all. In a conventional overlay type mobile communication network, the mobile switching center MSC is a central unit of the network, but the local exchange of the fixed network does not support the full functionality of the MSC. Therefore, in the present invention, the functions of the mobile switching center are divided into functional units which are placed in the base station controller BSC, except for call control. In addition, the function corresponding to the home location register HLR of the GSM system and at least a part of the function corresponding to the visitor location register are implemented by means of the intelligent network AIN.

. The possible allocation of functional units to 25 different network elements is illustrated in Figure 2.

Functionally, the names of the units all end in the letter F (function) to distinguish between the functional units and the physical network elements (BSC, SCP, LE ...) in which they may be located. The following is a brief description of each functional unit.

The BSCF (Base Station Controller Function) corresponds to the normal BSC functionality in the GSM network.

BSCF + (Base Station Controller Function Additions) - divides the A-interface from the BSCF so that 35 call control goes to the LEF and other signaling to the RSCF it 9 100214 - performs handover (HO) related switching operations as an anchor for connections - converts GSM- based call control ISDN call control 5 - includes various possible interworking functions LEF (local exchange function) contains standard ISDN local exchange LE functions (by default National ISDN3). The LEF may also support non-call 10 (NCA) signaling from the base station system BSS to the service control node SCP. In a preferred embodiment of the invention, no changes to the standard LEF function are proposed, as the ISDN-based PCS1900 system should operate under the LEDN of any standard fixed network ISDN local exchange.

The RSCF (radio system control function) takes care of many tasks of the MSC. It controls radio resources (e.g. generates assignment and handover request instructions and controls handover between base station controller BSCs or local exchange LEs. The RSCF is also a boundary unit between A-interface protocols and MAP protocols.

HOF (handover decision function). This unit has been separated from the RSCF to allow control of 25 handover processes from an even higher level. However, only high-level decisions, such as congestion control, are made in the HOF. The actual handover HO is performed by the BSCF + and is controlled by the RSCF.

The VLRF (visitor location register function) is a traditional VLR divided into two parts: VRL1F and VRL2F. The upper part VLR2F of the VLR is located in the service control point SCP of the intelligent network and the lower part VLR1F is located in the access network, more precisely in the base station controller. According to the currently most advantageous division, the lower VLR1F takes care of authentication, location management, temporary identification, etc., and the upper VLR2F takes care of service control and other matters related to the user profile.

SCF (service control function) is a standard fixed network service control function SCF that provides standard intelligent network services (AIN). It also has the ability to make location queries to the HLRF (corresponding to the gateway MSC situation), local location queries to the VRLF, cooperate with the VRLF to answer AIN queries, 10, and so on.

HLRF (home location register function) is a GSM home register. In addition, the intelligent network includes EIRF (equipment identification register function) and possibly SMS-GIWF (short message service gateway - interwor-15 king function), which, however, need not be described in more detail here.

In a preferred embodiment of the invention, the functional units described above are divided into network elements according to Figure 2: the local exchange LE includes a LEF unit; SCP includes SCF and VLR2F units; the base station controller BSC includes BSCF and BSCF + units and an access manager AM, which includes RSCF, HOF and VLR1F units. Alternatively, the entire VLRF may be located in the BSC or SCP.

25 It should be noted that only the functional units BSCF, BSCF + and LEF deal with the actual voice / da-connections. These functional units, which are at the bottom of the functional model, are bound to route connections (link chain: BSCF, BSCF +, LEF). Other functional units only handle signaling and therefore their allocation may differ from the above if desired.

In a preferred embodiment of the invention, there is further a new alternative signaling path 10 which bypasses the base station controller BSC of the local exchange LE 35 and the service controller.

II

11 100214 between the breakpoint SCP. This makes signaling between the BSC and the HLR simpler. The signaling interfaces LE-BSC and SCP-BSC are called C-interfaces. C-interface signaling may use signaling unrelated to the call of the ISDN network, or alternatively, the Signaling System No. 7 (SS7) network may be used for signaling between the base station controller BSC and the intelligent network AIN related to PCS functions.

The following describes the handover-10 procedures of the invention. In handover, an ongoing call is transferred from one traffic channel to another traffic channel at the same or a neighboring base station. In this way, the continuity of the call is ensured through the signal strength when the quality varies as a result of user movement or as the radio environment 15 changes. The handover between base stations under the same base station controller BSC (base station controller internal handover) is performed in substantially the same manner as in a conventional PCS1900 system and is not significant to the invention. Instead, the present invention provides improvements to the handover between two base station controllers BSCs.

Figures 3A, 3B, 3C and 3D show three different ways to perform a handover between base station controllers BSC. Fig. 3A shows a pre-handover situation in which the connection is connected via the local exchange LE to the base station controller BSC1 and further by radio to the mobile station BS. The aim is to perform a handover so that the call is switched to pass through the base station controller BSC2 to the mobile station BS. Figure 3B shows a prior art handover using 30 local exchanges LE as an anchor, which requires new functions from the local exchange LE. This method of handover may be possible in new ISDN exchanges, but it is not a good implementation in the early stages of BSC systems, as the availability of exchanges with the required features cannot be guaranteed. An additional problem arises from the fact that the anchor of the handover is a network element which does not comply with the standard of the access network (e.g. GSM).

Figure 3C illustrates a local call-based hand-5 over in which the original connection LE-BSC1 is maintained and an additional connection is established between the base station controllers BSC1 and BSC2 via the exchange LE by the local call BSC1-LE-BSC2. Thanks to this solution, the handover anchor is BSC1, and the local exchange LE only connects the connection. Since no additional features are required for the 10 exchanges LE, the handover can be implemented under all existing ISDN exchanges.

Figure 3D shows a fixed connection handover. Also in this case, the original connection is maintained between the LE-BSC1 and a "local call" is established between the base station controllers BSC1 and BSC2 while the BSC2 is acting as an anchor. However, in this case, the local call is not established as connected by the exchange LE, but fixed connections between the base station controllers BSC1 and BSC2 are used. It should be noted that these leased lines may physically pass through the exchange LE. The leased lines between the base station controllers BSCs shown in Figure 3D are preferably used where handovers between these base station controllers occur frequently.

25 Subsequent handover based on a local call

Figure 4 shows a call situation in which the original call is established from the exchange LE to the base station controller BSC / A. This is co-identified by the number DNorig. A handover to the base station controller BSC / B is then performed.

: 30 This results in a local call-based handover branch that reserves one line on the BSC / A side of the DNAold anchor and one line on the BSC / B side of the DNBold base station controller. The following describes a new subsequent handover from the base station controller BSC / A to the base station controller BSC / B '. In this handover, a new local call handover branch will be formed, which will reserve the line DNAnew on the BSC / A side of the anchor and the DNBnew line on the BSC / B 'side of the base station controller. After a successful handover, the old handover branch is dismantled. This is the most complex handover mode-5 they will be described with reference to the signaling diagram shown in Figures 5A, 5B and 5C, where the numbering used corresponds to the numbering in the following text.

New messages that are not standard GSM, ISDN, or AIN messages are in lower case. 10 Capital letters are used in messages where there are only changes in the parameters. LEF / A, LEF / B and LEF / B 'are LEF units of base station controllers BSC / A, BSC / B and BSC / B' in the local exchange LE, respectively.

1: The HANDOVER_REQUIRED message starts handover 15 as in GSM. BSCF + only forwards this message to the RSCF.

2: map_select_target is a new message introduced to allow handover decisions to be made higher online. This can be useful if, for example, the RSCF is allocated to the base station controller BSC and the BSC does not consider that there is enough global information about the network load or the like. The message is sent to HOF. The sole purpose of this message is to select the most appropriate target cell (TCI) for the handover and return the Target Number (Tnr) indicating the RCSF associated with the target cell.

25 3: MAP_PREPARE_SUBSEQUENT_HANDOVER is a GSM compliant message. However, the destination number parameter (Tnr) indicates the new visited RCSF and not the mobile switching center MSC.

4: The decision as to which type of coupling should be used for the new handover branch on the B 'side is made in 30 RCSFs. In this example, it is assumed that the RSCF on the anchor side makes this decision. Alternatively, the decision can also be made by B '. Possible connection type options are to establish a local call BSC / A-BSC / B 'via the exchange LE, to use a fixed connection between BSC / A-BSC / B', 35 if any, or to use a previously reserved free 14 100214 but unconnected local connection BSC / A-BSC / B 'or part of a previously reserved local call connection. The RSCF also controls the use of access lines, i.e. from catalog number DN. The RCSF allocates a new access line DNAnew to a new 5 local call containing a new branch A-B '.

MAP_PREPARE_HANDOVER is the same as in GSM, but a new parameter HOCT (handover connection type) has been added, which allows the use of different handover types. The message may also contain other 10 parameters related to the HOCT parameter. The values of the HOCT parameters and any additional parameters are defined in more detail in Table I. For example, in the case of using part of an existing local call, the message could have two additional parameters: DNBnew indicating that the interface line corresponds to 15 existing local calls on the B 'side, and CIC (circuit identity code ) indicating which part of the 64 kbit / s line is used.

5, the B-side RSCF allocates a connection line as a local DNBnew new. It should be noted that in the traditional GSM system, the VLR allocates a han-Dover number to the new branch. Instead, the catalog number DNBnew allocated by the RSCF is closely related to the connection line used. Therefore, it cannot be returned after a handover has been performed like a handover number in a traditional GSM GSM only after the handover branch has been disconnected, as a result of a call disconnection or a new handover. It should also be noted that two connection lines and corresponding catalog numbers are required for the new handover branch.

· The '30 HANDOVER_REQUEST message is the same as in GSM, but an allocated handover number is sent between RSCF / B' and BSCF + / B 'and not the CIC. This message also includes the HOCT and any Additional Parameters.

6: HANDOVER_REQUEST is as in GSM. HANDOVER_RE-35 QUEST_ack is the same as in GSM. BSCF + / B 'only forwards the message

II

15 100214 A side RCSFrlle. The Layer 3 information parameter (L3info) contains HANDOVER_COMMAND (see section 21).

8: MAP_PREPARE_HANDOVER_ack is as in GSM. The HOCT parameter is also included (see section 11) as defined in Table 5 I. The HOCT parameter (and any Additional Parameters) is sent back to the anchor side to allow connection type negotiation and / or communication resources to be controlled from the B 'side. In this example, the HOCT does not carry any new information to the anchor side 10 A.

9: new_leg_command is a new message linking the RCSF handover control to the BSCF + call control. The RSCF instructs the BSCF + to establish a new handover branch for the current call. The new branch is to use the number DNAnew 15 and the corresponding interconnection lines for the A side BSCF + and DNBnew digits (and the corresponding connection line), the B-side, the BSCF + Act. HOCT says the type of this handover is "new local call".

10: The SETUP message is like in an ISDN network. The local exchange must establish a local call for the handover branch 20.

11, 12, 13: INITIAL_ADDRESS_MESSAGE, CALL_PROCEED-ING and SETUP are as in ISDN.

14: setup_detect is a new message telling RCSF / B 'that the new handover branch is complete. The BSCF + / B '25 is able to link this new branch based on the previously allocated radio resources to the used interface line corresponding to the number DNBnew.

15, 16, 17: ALERTING, ADDRESS_COMPLETE_MESSAGE and ALERTING are as in ISDN.

30 18: new_leg_complete indicates that a new handover branch has been successfully formed.

19: MAP_PRE PARE_S UB S EQUENT_HAN DOVE R_a c k is as in GSM.

20, 21: HAN DOVE R_COMMAN D is as in GSM. The BSCF + / B '35 only forwards the message, but it should also be noted that the CON-16 100214 NECT message can now be sent (see paragraph 25).

25, 26, 27, 28, 29: CONNECT, CONNECT_ACK, ANSWER_MESSAGE, CONNECT and CONNECT_ACK are as in ISDN.

30. connect_detect is a new message telling 5 that the connection line is connected.

31: MAP_SEND_END_SIGNAL is the same as in GSM.

32: switch_leg_command is a new message telling BSCF + / A that the new branch can be used from now on. As a result, the old handover branch can be dropped off. In this example case, the HOCT parameter indicates that the local call associated with the old branch can be dropped (cf. Table I). It should be noted, however, that it is not necessary to disconnect the local call after all the handover branches in it have been disconnected. 15 It is also possible, for example, to maintain the connection waiting for new handover between the branches of the A side and the B-side. In this case, the value of the HOCT parameter is "nothing" (cf. Table I).

33, 34, 35, 36: MAP_S EN D_EN D_SIGNAL_ACK-s message, 20 CLEAR_COMMAND messages and CLEAR_COMPLETE messages are as in GSM. BSCF + / B only passes the CLEAR_COMMAND message and turns off the handover branch.

37, 38, 39: DISCONNECT, RELEASE and RELEASE_COMPLETE are as in ISDN.

25 40: disconnect_detect is a new message indicating that the interface line and catalog number have been released.

41, 42, 43, 44, 45: RELEASE, RELEASE_ACK, DISCONNECT, RELEASE and RELEASE_COMPLETE are as in ISDN.

46: disconnect_detect is a new message stating 30 that the interface line and catalog number have been released.

Leased line handover This handover event is simpler than the most complex handover case presented above. A fixed connection between the base station controllers BSCF / A and BSCF / B is now used. This leased line is identified by a new CIC parameter. Also in this example, shown at 100214 π in the signaling diagram of Figure 6, the RSCF on the anchor side A controls the allocation of resources, i.e. the CIC. In the following description, only the differences from the messages described in the signaling diagram of Figures 5A-5C are shown.

5 The value of the HOCT parameter is "permanent connection" in all messages (cf. Table I).

1: CIC has been added to the MAP_PREPARE_HANDOVER message.

This is because the A-side RCSF the need to tell the B-side RCSF for what the circuit of the base station controllers BSC / A and the BSC / 10 B of the fixed connection between employed. In the example of Figures 5A-5C, where the handover was based on a new local call, both the A and B sides could choose the independently used access line and directory number DN.

2: CIC has been added to the HANDOVER_REQUEST message and DNBnew has been removed compared to the case of Figures 5A-5C. The CIC identifies the fixed connection, while DNBnew identifies the access line and is therefore unnecessary in this example. This CIC may be the same as or derived from the CIC in Section 1.

20 3: This CIC is different from the CIC in section 2.

4: DNBnew has been removed, the A-side has decided to use a fixed connection for the handover branch and has already sent the associated CIC. Therefore, a new connection line and the corresponding catalog number DN 25 are not required.

The message new_leg_command is sent instead of the CIC list numbers DNBnew and DNAnew. Only the CIC is needed to connect the handover branch.

The accompanying figures and the related description are intended to illustrate the present invention only.

Although the invention has been described with reference to certain embodiments, it is to be understood that the description is given by way of example only and that changes and modifications may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims (7)

18 100214 An arrangement for performing handover between base station controllers in a communication system comprising a fixed network local exchange (LE), mobile stations (PS), base station systems providing a wireless access network to mobile stations to a local exchange, each base station system including a base station controller (BSC) and a base station controller (BSC) , in which the local exchange is connected to the base station controllers, characterized in that the handover control between the 15 base station controllers (BSCs) is arranged in the base station controllers so that the first base station controller of the call acts as an anchor point to which the original connection to the base station controller, there is a fixed transmission link between at least two base station controllers, one of the base station controllers participating in the handover is adapted to decide whether the handover is a continuation connection 25 a local call connected via a local exchange or a connection established via said fixed transmission link, and to notify the second base station controller of the selection. An arrangement according to claim 1, characterized in that said local call is a new local call established for handover. An arrangement according to claim 1, characterized in that said local call is a previously established local call between base station controllers with free transmission capacity. 19 100214 4. A method for performing handover between base station controllers in a communication system comprising a fixed exchange local exchange; mobile stations; base station systems forming a wireless access network for mobile stations 5 to a local exchange, each base station system including a base station controller and base stations; and transmission lines connecting the local exchange to the base station controllers, the method comprising establishing a call connection from the local exchange to the first base station controller serving the mobile station, handovering the call and transferring the mobile station from the first base station controller to the second base station controller, the handover from the local exchange to the first base station controller, 20 the first or second base station controller decides whether to forward for handover from the first base station controller to the second base station controller as a local call through the local exchange or via a fixed transmission link between base station controllers onward communication from the first base station controller to the second base station ground controller. .30 A method according to claim 4, characterized in that the first base station controller selects a handover network type, the first base station controller sends a prepare handover message to the second base station controller containing a handover connection type parameter indicating the selected connection type, and any additional parameters, which provide more detailed information about the selected connection A method according to claim 4, characterized in that the first base station controller sends a prepare handover message to the second base station controller, which contains a handover switching type parameter whose value indicates that the handover connection type is selectable by the second base station controller, the second base station controller selects the handover switching station a request message containing 15 handover connection type parameters indicating the selected connection type, as well as any additional parameters that provide more detailed information about the selected connection A method according to claim 4, 5 or 6, characterized in that a local call is established using the free capacity of the local call connection used by the second call. Il 21 100214