WO2008088243A1

WO2008088243A1 - Changing communication paths

Info

Publication number: WO2008088243A1
Application number: PCT/SE2007/000029
Authority: WO
Inventors: Andreas Olsson; Erik Westerberg; Lars Boncz
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2007-01-15
Filing date: 2007-01-15
Publication date: 2008-07-24
Anticipated expiration: 2009-07-15
Also published as: WO2008088245A1; AR064914A1

Abstract

When a communication path between a mobile station (1) and a first telecommunication network (A) is to be replaced with a communication path between the mobile station and a second telecommunication network (B), a toggling procedure or dual scheduling mode is used. In 5 this procedure the mobile station continues, during a transitional period, to communicate using the communication path with the first network and in time intervals between periods in which the communication with the first network is scheduled it performs signaling with the second network to set up a communication path with the second network. After having set up the communication path with the second network the mobile station instead uses this communication path. This method may give a minimum interruption of the communication for the mobile station. A similar method can be used also when the mobile station only requires some signaling with the second network.

Description

CHANGING COMMUNICATION PATHS TECHNICAL FIELD

The present invention is related to a method for changing a communication path between a mobile station and a first network to a different communication path between the mobile station and a second network. BACKGROUND

La 3GPP a standardization work for the next radio access network is ongoing, called LTE (Long Term Evolution). Networks according to the LTE standard will be packet switched only networks, i.e. no circuit switched traffic will be supported in such networks. Another example of radio access networks that go towards packet switched only traffic are networks according to WiMax (Worldwide Interoperability for Microwave Access, a wireless industry coalition). Hence communication of speech will be carried out by VoIP in such networks. In a multi network scenario it is important to have at least one network that can provide coverage, since else the end- user can be without service. It is also important to provide a smooth transition for services between the different network for good end-user perceived service quality. E.g. in the case where an LTE network fails to provide coverage it will be important that e.g. a GSM (Global System for Mobile communication) network can provide a continuation of a speech call started in LTE and that the interruption during a move from an LTE network to the GSM network is minimal.

This complexity is not a problem that is new for moves between an LTE network and a GSM network. It has been observed in WiFi (Wireless Fidelity) discussions as well. The problem is to keep the service outage short so that the end-user does not perceive a quality degradation during the move. A prior art solution to the problem has been to introduce dual radio units ("dual radio"), i.e. radio circuitry specially adapted to communication with a WiFi network is installed in the mobile station in addition to parallel radio circuitry specially adapted for communication with a network of another kind, using e.g. a different wavelength band. The dual radio solution is not a recommendation for LTE-GSM co-existence due to the increased cost of the mobile stations.

To introduce a "normal" packet switched LTE handover to a circuit switched GSM network requires signaling between the respective MSC (Mobile Switching Center) of the GSM network and the MME/UPE (Mobility Management Entity/User Plane Entity) in the LTE system, see Fig.

1. The GSM network further includes a BTS (Base Transceiver Station), i.e. base station, and a

BSC (Base Station Controller), the interface between these devices called Abis and the interface between the MSC and the BSC called A. The LTE network includes a base station called eNode

B and Sl is that standardized name of the interface between the eNode B and the MME/UPE. Here, a mobile station 1 (MS), also called a mobile terminal, simply a terminal, a mobile unit, a mobile device etc. and e.g. being a cellular telephone or mobile telephone, communicates through the node 3, i.e. the base station eNode B, in an LTE network and is going to use instead a 2G network and will then communicate through a base station 5 thereof. The necessary signaling to make this happen is indicated by the dashed circle 7. However, such signaling is not desirable in LTE networks due to the fact that the age of the protocols supported by the MSC of the 2G network would give a large cost for adapting the core network, not shown.

For the terminal 1 to make a hard break from an LTE network and perform a terminal initiated call re-establishment would at least take 1 s, which is well above the requirement of the time period of 300 ms stated in the document 3GPP TS 22.278 vl.0.0. SUMMARY

It is an object of the invention to provide an efficient method of replacing a communication path between a mobile station and a first telecommunication network with a communication path between the mobile station and a second telecommunication network.

It is another object of the invention to provide a mobile station adapted to efficiently replace a communication path between a mobile station and a first telecommunication network with a communication path between the mobile station and a second telecommunication network.

Generally, a time mapped scheduling for receiving from/communicating with two different systems or networks is used. Then, the mobile station operates in two radio access technologies in a repeated, alternating manner, for some time period. In this time the mobile station toggles between the two systems in some suitable way and a scheduling map may be used for timing in the toggling procedure. Hence, during this time period the mobile station in communicating with a second telecommunication network while never releasing the communication path with the first telecommunication network. An aspect of the scheduling is that time gaps in a communication path between a mobile station and a first network are created in order to allow the mobile station to communicate with a second network.

The method can generally allow signaling between a mobile station and a second telecommunication network when the mobile station already is communicating with a first telecommunication network over a first communication path between the mobile station and the first telecommunication network. Then the mobile station continues to communicate using the first communication path with the first network and in the time intervals between periods in which the communication with the first network is scheduled or is performed, the mobile station can perform signaling with the second network to e.g. set up a second communication path with the second network.

The method can in particular be used for replacing a first communication path between a mobile station and a first telecommunication network with a second communication path between the mobile station and a second telecommunication network, i.e. moving or changing a communication path over which voice and/or other end user data are transmitted. The second network may be of a kind different from that of the first network, such as using a different radio access technology, e.g. using a different standard. During a transitional period the mobile station can then continue to communicate using the first communication path with the first network and in time intervals between periods in which the communication with the first network is scheduled it can perform the signaling with the second network necessary to set up a communication path with the second network. After having set up the communication path with the second network the mobile station can continue or proceed to use only this communication path for transmitting the voice or other end user data.

The first network may be arranged to send to the mobile station and before the transitional period, information on times, when said signaling with the second network is allowed. Such information can include a scheduling map or other information from which a suitable scheduling map can be derived. The time intervals for scheduling the communication between the two networks and the mobile station, i.e. the scheduling, may be determined in accordance with the timing or frame structures of the two networks and in some cases only the timing or frame structure of the second network has to be considered. The information on the times when the signaling with the second network is to take place can in some cases be sent from the mobile station to the second network and before the transitional period. In the case where the second network is a GSM network, the mobile station can send, before said transitional period, a request for an SDCCH to the GSM network. The mobile station may in some case send information about the timing of the frame structure of the second network to the first network.

A mobile station for executing the method must be capable of communicating through both the first and second networks, in particular by using the same radio circuits, and hence it may include a unit for handling communication with the first system and another unit for handling communication with the second system. The mobile station suitably includes a dual scheduling unit that is e.g. adapted to command, when a communication path between the mobile station and the first telecommunication network is to be replaced with a communication path between the mobile station and the second telecommunication network or generally when some signaling with the second network is desired:

- that first respective circuits/units of the mobile station are to continue, during some period, to communicate using the communication path with the first network, and

- that second respective circuits/units of the mobile station are to perform, in time intervals between periods in which the communication with the first network is scheduled, signaling with the second network to e.g. set up a communication path with the second network.

After the second respective circuits/units have set up the communication path with the second network, the first respective circuits/units can suitably stop communicating through the first network, and the second respective circuits/units are now used for communication over the now set-up communication path with the second network.

A base station for the first telecommunication network may also include a dual scheduling unit. The base station is then suitable adapted to be in communication, when a mobile station for which a communication path is already established through the base station and the first telecommunication network requires some signaling with a second, different telecommunication network, only during periods set according to a scheduling map. Such a scheduling map may incur that the time periods during which the base station is in communication over said communication with the mobile station occur more seldom than before or more seldom than during ordinary operation. This may allow the mobile station to communicate in the intervals between the time periods with the second network. Using the method as described herein e.g. a short interruption may be achieved when moving to a new communication path.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods, processes, instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

While the novel features of the invention are set forth with particularly in the appended claims, a complete understanding of the invention, both as to organization and content, and of the above and other features thereof may be gained from and the invention will be better appreciated from a consideration of the following detailed description of non-limiting embodiments presented hereinbelow with reference to the accompanying drawings, in which:

- Fig, 1 is a schematic illustrating a mobile station that is communicating in an LTE network but will start instead communicating in a 2G network, - Fig, 2 is a schematic of the general layout of a mobile station that is communicating in an LTE network and uses a dual scheduling method for starting communicating in a 2G network,

- Fig. 3 is a schematic of combined general system including two networks and a mobile station, in which a dual scheduling method is used for changing a communication path between the mobile station and one of the networks to instead extend between the mobile station and the other of the networks, - Fig. 4 is a schematic of the timing for communication between an MS and a BS in a GSM network at call set-up on the SDCCH (Stand Alone Dedicated Control Channel). ,

- Fig. 5 is a timing diagram when changing a communication path from a mobile station to a first network to a communication path from a mobile station to a second, different network, - Fig. 6 is a flow diagram of steps taken in the mobile station in a method in which a radio node in a first system initiates a dual scheduling mode,

- Fig. 7 is a flow diagram of steps taken in a radio node in a first system using the same method as in Fig. 6,

- Fig. 8 is a flow diagram of steps taken in a radio node in a second system in a method in which a mobile terminal communicates the structure of a dual scheduling map to the second system,

- Fig. 9 is a timing diagram similar to Fig. 5 when changing communication for voice through an LTE network to instead pass a GSM network,

- Fig. 10 is a block diagram of a mobile station showing some components that may be used in a dual scheduling procedure, and - Fig. 11 is a block diagram of a base station showing some components that may be used in a dual scheduling procedure.

DETAILED DESCRIPTION

A method will now be described for transferring communication, such as telephone call, with a mobile station 1, that is currently communicating through a base station BS_A in a first network A to a second network B, in particular to a base station BS_B thereof, see Fig. 3. During the transition period a time mapped scheduling is used for receiving from or communicating in the two networks, also called systems or radio systems and being e.g. mobile telephony networks. During this period the mobile station 1 operates in two radio access technologies at the same time and toggles between them. After the SC_B of network B has set-up a path therethrough, this fact may, if required, be signaled also to system A and thereafter the mobile station only communicates in the second network B. Using this time scheduled dual mode for transferring the communication can minimize the interruption so that the user of the mobile station 1 may experience only a very little disturbance of the communication or may even hardly notice the interruption. The scheduling during the transition period can be made so that packets or frames are received only during predefined intervals in one system time, this leaving the remaining time for the mobile station to interact with the other system. In the schematic of Fig. 2 the dual scheduling mode is illustrated for the specific example of a transition from communication in an LTE network to a 2G network such as a GSM network.

The general scheduling method is illustrated in the diagram of Fig. 5. Initially, in the first period pi the mobile station 1 (MS) is communicating with system A only. Initiated either by the mobile station or system A, the mobile station enters the dual scheduling mode, also called an alternating scheduling mode, i.e. it starts an alternating scheduling period p2. In period p2 the system is in an alternating scheduling mode in which the mobile station 1 alternates in its communication with systems A and B. The inter-radio technology alternating scheduling pattern is assumed to be known by both the first system A, the second system B and the mobile station. In the period p3 the mobile station 1 has left the alternating scheduling period and is communicating with system B only.

The knowledge of the inter-radio technology alternating scheduling pattern that is used in the dual scheduling mode can be obtained in different ways such as: - The pattern may be predefined by standardization for both the first system A, the second system B and the mobile station 1.

- The pattern may be predefined by standardization for only the first system A and the mobile station 1 whereas the second system B then can be unaware that the procedure of alternating between the two systems takes place. This presupposes that the first system A and the mobile .^■ station know the time structure when system^" B is in communication with the mobile station. Then, the first system A and the mobile station utilize gaps existing in this time structure to communicate between them. E.g. the SDCCH frame structure for a GSM network, see fig 4., may ;_, be known to system A and the mobile station 1. :

- A set of alternative scheduling patterns may be predefined by standardization for both the first system A, the second system B and the mobile station 1. Then these three parties have to •■^' negotiate for which one to use.

In the flow diagram of Fig. 6 the main steps taken by the mobile station 1 are illustrated for the case where the radio node BSA in system A initiates the dual scheduling mode, hi an alternative embodiment, not illustrated, the dual scheduling mode is initiated by some other part such as the mobile station itself. In a first step 61 the MS 1 receives a request for dual scheduling from the first network A. hi the next step 62 the MS decides whether it is capable of participating in the dual or alternating scheduling mode, i.e. whether it has been enabled for this operational mode such as by modifying its software. This can be performed by the control unit 101 of a dual scheduling 103 in the mobile station, see Fig. 10. If it is capable, an acknowledgement is sent to system A whereby a dual scheduling map is requested from system A in a step 63. This step can be performed by a corresponding unit or module 105 in the dual scheduling unit. Then it is determined in step 64 whether a dual scheduling map has been received, i.e. the map is awaited for some predetermined time, and after or if it has been received a step 65 is executed, such as by a commanding unit 107. hi this step the dual scheduling mode is started by first sending a confirming message to system A and then the toggling sending/receiving procedure is executed. The dual scheduling mode is ended after the communication path to and through system B has been established. The term "communication path" as used herein means a communication path or communication channel having one end at the mobile station 1 and passing through a radio access network into a core network. That a communication path has been established is thus herein taken 5 to mean that a path, suitable for transmitting primarily speech but also data such as streaming data, has been established between the end user's mobile station, through a radio access network into the core network. After the path has been established the procedure is terminated in a step 66. If it was decided in step 62 that the MS 1 is not enabled for dual scheduling or if a dual scheduling map has not been received during a predetermined time, as determined in step 64, a

10 dual scheduling abort message is sent to system A in a step 67. Then the procedure is terminated in the step 66. Thereafter some other procedure, not illustrated or described in detail herein, is used for moving the communication path from system A to system B.

In Fig. 6 the steps required in the case where the mobile station 1 informs system B about the dual scheduling are not illustrated. Such steps can be executed, in accordance with the description •

15 herein, by e.g. a unit 109 for receiving a request for a scheduling map from system B, a unit 111 for sending the scheduling map to system B and a unit 113 for sending an abort message to system B. It is also possible, as is also described herein, that the scheduled times for communicating with the two systems can be determined by e.g. the mobile station 1 itself. This could then be executed by a unit 115 that can contain units 117 and 119 for comparing the timing,

20 i.e. when packets or frames are ordinarily sent, in the two systems and for evaluating said timing, respectively. Such units can use information on the two systems e.g. stored at memory places

121, 123 in a memory 125 of the dual scheduling unit 103. Such a memory then also has a memory area 127 in which the determined or predefined or received scheduling map is stored.

In Fig. 7 the main steps performed in the radio node BSA in system A in the same case where

25 the radio node initiates the dual scheduling mode. In a first step 71 a request for dual scheduling is sent to the MS 1. This step can e.g. be executed by sending unit 131 included in a dual scheduling unit 131 in the node that also includes a control unit 135 and a memory 137, see Fig. 11. Then it is determined, or awaited for predetermined time period, in the next step 72 whether the node has received an acknowledgment message from the MS requesting a dual scheduling

30 map, i.e. information from which the time periods for communication with system A can be derived. After such a message has been received a message including information in regard of the dual scheduling map is sent to the MS 1 in a step 73, as from a unit 139. Then in step 74 the dual scheduling mode is started and performed by a unit 141 and after the MS has established a communication path to system B the procedure is ended in a step 75. If it was determined in step

35 72 that no acknowledgement has been received during the predetermined time, a step 76 is executed in which it is determined whether an abort message in regard of the dual scheduling map has been received. If an abort message has been received, the dual scheduling attempt is aborted in a step 77 and the procedure is terminated in the step 75. If it was determined in step 76 that no abort message has been received it is asked in a step 78 whether the request for dual scheduling has already been sent to the MS 1 a predetermined number times, e.g. 3 times. If it has not, the start step 71 is performed again and otherwise the abort step 77 is performed.

The scheduled times for communicating with the two systems can be determined by e.g. the base station BSA- The control unit 105 or a special unit 143 could be used for e.g. retrieving a predetermined or predefined scheduling map from a memory place 145. The special unit 143 could also determine a suitable scheduling map from knowledge about the timing in systems A and B, this knowledge stored in places 147 and 149, respectively. The unit 143 can then contain units 117 and 119 for comparing the timing and for evaluating said timing, respectively.

In the flow diagram of Fig. 8 the main steps executed by a radio node BS_B in the second system B in a procedure in which the mobile station 1 communicates the structure of the dual scheduling map to system B. In a first step 81 the radio node receives a request for dual scheduling from the MS. Then it is in next step 82 determined whether the node itself if capable of executing dual scheduling. If it is capable, an acknowledgement is sent to the MS 1 in a step 83, the acknowledgement requesting a dual scheduling map. hi step 84 it is determined, or it is waited a predetermined time, whether a dual scheduling map has been received from the MS. After the map has been received, the dual scheduling mode is started in a step 85 and the procedure is ended in a step 86 after a communication path to the second system has been established. If it was determined in step 82 that the radio node is not capable of dual scheduling or if is determined in step 84 that no dual scheduling map has been received after a predetermined time, a message is sent in a step 87 to the MS that the dual scheduling is aborted. Then the procedure is terminated in the step 86.

The general method as described above can, in the case where a communication path is moved from an LTE network to a GSM network, see Fig. 2, be performed as follows.

1. The mobile station 1 communicates only in the LTE network.

2. A change of the communication to GSM instead is decided by the LTE network. 3. The LTE network requests that the mobile station shall start the dual map procedure and contact the GSM network.

4a. The mobile station 1 accesses the GSM system and indicates to the GSM that it should use an

SDCCH for signaling.

4b. The mobile station 1 accesses the GSM system with no indication of the dual scheduling mode or of any need for an SDCCH. This works well if the GSM system does not use "Assignment directly to a TCH (Traffic Channel)" since it will automatically be an SDCCH and the toggle map usage is secured.

4c. The mobile station 1 accesses the GSM system and indicates to the GSM that it should use a toggle map defined for dual mode scheduling. The GSM system then adapts the scheduling of signaling over the air according to the toggle map.

4d. The mobile station 1 accesses the GSM system without a new indication. Then it is up to the mobile station to utilize the existing time gaps in the GSM system and try to synchronize this with the LTE system scheduling.

5a-5d. For the alternatives 4a - 4d the mobile station 1 and the LTE system continue to communicate in the initially existing communication path but only within time periods in which no GSM communication can be assumed to take place.

5c. For the alternative 4c, the GSM system uses the predefined time slots, i.e. in time slots in said allowed time intervals, and performs the signaling procedure required to create a new communication path with the GSM system. 5a, 5b, 5d. For the alternative 4d, the GSM system performs the signaling procedure required to create a new communication path with the mobile station 1 and is unknown about the fact that the mobile station is in communication with the LTE system.

6. The communication path is routed to GSM, e.g. done by IMS (IP Multimedia Subsystem), i.e. all communication with the mobile station 1 is now through the GSM network. 9. The LTE network releases the radio connection with the mobile station when there are no more packets to send.

This specific method is also illustrated in Fig. 9, the time divided in time segments si - s7. si. The MS 1 is engaged in an ongoing voice call over the packet data LTE system. The mobile station receives and sends voice frames via the LTE system. s2. In response to a handover decision the LTE system initiates the period of alternating scheduling and provides the MS 1 with information about the alternating scheduling pattern. s3. The MS 1 uses the first scheduling opportunity in the GSM system to inform the GSM system about the structure of the alternating scheduling pattern that is to be used. s4. In the alternating scheduling mode the MS 1 and the LTE system use the scheduling periods in LTE to exchange voice frames, thus maintaining the voice call in the LTE system. s5. During the GSM scheduling periods the MS 1 and the GSM system establish a GSM circuit switched traffic channel and path up to and through the core network. Such a circuit switched traffic channel is the communication path over the air interface. s6. Once the circuit switched traffic channel has been established in the GSM system the MS 1 sends a message "handover complete" to the GSM system that is forwarded to the LTE system over the core network, compare the arrows at the top of Fig. 2. This message informs the LTE system and the GSM system that the MS 1 is now terminating the alternating scheduling mode and connecting to the GSM circuit switched channel. s7. The mobile station 1 is now using the circuit switched GSM channel to send and transmit voice frames according to the GSM protocols, i.e. a legacy GSM voice call is established.

Using the method as described one or more of the following advantages may be achieved, at least in special cases:

- Only a single radio unit is used, , i.e. single radio technology is used. "Single radio" means that a mobile station can at each instant be in active communication with only one system. - Minimum interruption in the user plane during handover between different networks, in particular between networks of different kinds.

- the LTE MME/UPE does not have to use an interface towards the MSC.

While specific embodiments of the invention have been illustrated and described herein, it is realized that numerous additional advantages, modifications and changes will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, representative devices and illustrated examples shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within a true spirit and scope of the invention.

Claims

1. A method of replacing a communication path between a mobile station and a first telecommunication network with a communication path between the mobile station and a second telecommunication network, the second network in particular being of a kind different from that of the first network, such as using a different radio access technology, the communication paths in particular adapted to communicate speech or end user data, characterized in - that during a transitional period the mobile station continues to communicate using the communication path with the first network and in time intervals between periods in which the communication with the first network is scheduled perform signaling with the second network to set up a communication path with the second network, and

- that after having set up the communication path with the second network continue or proceed to use this communication path.

2. A method according to claim 1, characterized by the additional step of sending, from the first network to the mobile station and before said transitional period, information on times when said signaling with the second network is allowed.

3. A method according to claim 1, characterized by the additional step of adapting the time intervals for scheduling communication between the two networks and the mobile station in accordance with the frame structures of the two networks.

4. A method according to claim 1, characterized by the additional step of adapting the time intervals for scheduling communication between the first network and the mobile station in accordance with the frame structure of the second network.

5. A method according to claim 1, characterized by the additional step of sending, from the mobile station to the second network and before said transitional period, information on times when said signaling with the second network is to take place.

6. A method according to claim 1 in the case where the second network is a GSM network, characterized by the additional step of sending, from the mobile station to the GSM network and before said transitional period, a request for an SDCCH.

7. A method according to claim 1, characterized by the additional step of sending, from the mobile station to the first network, information about the timing of the frame structure of the second network.

8. A mobile station capable of communicating through first and second networks, characterized in that the mobile station includes a dual scheduling unit adapted to command, when a communication path between the mobile station and a first telecommunication network is to be replaced with a communication path between the mobile station and a second telecommunication network: - first respective circuits/units of the mobile station to continue, during a transitional period, to communicate using the communication path with the first network, and

- second respective circuits/units of the mobile station to perform, in time intervals between periods in which the communication with the first network is scheduled, signaling with the second network to set up a communication path with the second network, and

- after the second respective circuits/units have set up the communication path with the second network, the first respective circuits/units to stop communicating with the first network, and the second respective circuits/units to use the now set-up communication path with the second network.

9. A mobile station according to claim 8, characterized by a memory place for storing information on times when said signaling with the second network can be performed, said second respective circuits/units adapted to use this information when commanded by dual scheduling unit to perform signaling for setting up a communication path.

10. A mobile station according to claim 8, characterized in that the dual scheduling unit includes a sending unit for sending to the second network and before said transitional period, information on times when said signaling with the second network is to take place.

11. A mobile station according to the combination of claims 9 and 10, characterized in that the a sending unit is adapted to retrieve, in sending said information, the information from said memory place.

12. A mobile station according to claim 8, characterized in that the mobile station includes single radio circuitry for communicating both with said first network and said second network.

13. A mobile station according to claim 8, characterized in that the mobile station includes a unit for comparison of the timing of the frame structures in the two networks.

14. A mobile station according to claim 13, characterized in that the mobile station is adapted to report the result of the comparison to at least one of the two networks.

15. A base station for a first telecommunication network, characterized in mat the base station includes a dual scheduling unit adapted to be in communication, when a mobile station for which a communication path is already established through the base station and the first telecommunication network requires signaling with a second, different telecommunication network, such as when the already established communication path is to be replaced with a communication path between the mobile station and the second telecommunication network, only during periods set according to a scheduling map, in particular so that the time periods during which the base station is in communication over said communication with the mobile station occur more seldom than before, this allowing the mobile station to communicate in the intervals between said time periods with the second network.

16. A method of performing signaling between a mobile station and a second telecommunication network when the mobile station is already communicating with a first telecommunication network using a communication path between the mobile station and the first telecommunication network, characterized in - that the mobile station continues to communicate using the communication path with the first network, and

- that in time intervals between periods in which the communication with the first network is scheduled or is performed, the mobile station performs signaling with the second network to e.g. set up a communication path with the second network.