WO2001030096A1

WO2001030096A1 - Method and network element for establishing a call

Info

Publication number: WO2001030096A1
Application number: PCT/EP1999/007993
Authority: WO
Inventors: Juha Räsänen; Mikko Ohvo
Original assignee: Nokia Corporation
Priority date: 1999-10-21
Filing date: 1999-10-21
Publication date: 2001-04-26
Also published as: AU1265000A

Abstract

The present invention relates to a method and network element for establishing a call between end terminals of a telecommunication system, wherein a first type of connection is established and monitored by a network function to which the first type of connection is routed in order to detect a signal of a second type of connection in a signal flow of the first type of connection. Based on the detection result of the network function, a call modification procedure to the second type of connection is initiated. Thereby, a call which is established by starting with a first type of connection and swapping to a second type of connection can be provided in a network without establishing a control signal detection functionality in the end terminals of the network.

Description

Method and network element for establishing a call

FIELD OF THE INVENTION

The present invention relates to a method and network element for establishing a call between end terminals of a telecommunication system in which a fixed network may be connected to a mobile network such as a GSM (Global System for Mobile communications) or a UMTS (Universal Mobile Telecommunications System) network.

BACKGROUND OF THE INVENTION

In recent years, multimedia telephone terminals which can be connected to fixed networks have been developed. The terminals provide real-time video, audio, or data or any combination thereof, between two multimedia telephone terminals over a voice band network connection. Communication may be either one-way or two-way. A multipoint communication using a separate Multipoint

Control Unit (MCU) among more than two terminals is also possible. Furthermore, the multimedia telephone terminals can be integrated in PCs or workstations, or can be standalone units.

Interworking between PLMNs (Public Land Mobile Networks) and PSTNs (Public Switched Telephone Networks) is currently being specified in third generation mobile systems. One of the items to be specified is a call type where a video/multimedia call is started with a speech phase, and during the speech phase the call is modified into a multimedia call according to the ITU-T H.324 recommendation .

PSTN video phones supporting the above speech-first-then- video functionality use an in-band signaling specified in the ITU-T V.δbis recommendation to signal the modification from the speech phase to the multimedia call. This V.δbis swap procedure can be initiated by either one of the connected end terminals. The procedure starts with sending and detecting dual and single audio frequencies as specified in the V.8bis recommendation. Thus, V.8bis control signals that initiate the transaction (initiating signals) and V.δbis control signals that are sent in response to the initiating signal during an automatic call establishment (responding signals) are tone based. The signals are made of two segments. Segment 1 consists of a dual tone pair, which is detectable in the presence of interfering voice or other audio. Segment 2 is a signal tone which identifies the signal. Control signals sent by the initiating station use one dual tone pair for segment one. Signals sent by the responding station use a different tone pair for segment one.

Accordingly, interworking with the PSTN requires an initiation of a swap procedure from speech to video (using a 3.1 kHz Audio (modem) for transmission). However, if a PSTN entity activates a swap to a speech, the V.δbis frequencies are lost in the PLMN and the swap procedure fails .

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a method and network element for establishing a call between end terminals of a telecommunication system, by means of which a swap procedure from a first type of connection to a second type of connection can be provided between a PSTN and a PLMN. This object is achieved by a method for establishing a call between end terminals of a telecommunication system, comprising the steps of: establishing a first type of connection between the end terminals; providing a network function of a second type of connection for detecting a signal of the second type of connection in a signal flow of the first type of connection; routing said the type of connection to the network function; and initiating a call modification procedure to the second type of connection in response to the detection result of the network function.

Furthermore, the above object is achieved by a network element for establishing a call between end terminals of a telecommunication system, comprising: control means for performing a call modification procedure from a first type of connection to a second type of connection in response to a detection result supplied to the control means; wherein the detection result indicates the detection of a signal for the second type of connection in a signal flow of the first type of connection; and wherein the network element is used in a part of the second type of connection.

Accordingly, the swap procedure from the first type of connection to the second type of connection can be initiated on the basis of a network function provided for detecting a signal sent from the fixed network in order to initiate the second type of connection, wherein the detection result provided by the network function is used to initiate a network call modification procedure to the second type of connection. Thereby, the call establishment can be provided without a modification of the end terminals. The signal can be any signal, wherein the call modification procedure may be initiated on the basis of any type of signal characteristic, such as frame number or structure or type of signal (e.g. control signal). As an example, the control signal may be an ITU-T V.δbis control signal .

Preferably, the network function is an interworking function of the mobile network. Thus, the signal flow of the first type of connection merely has to be routed to the interworking function such that the control signal can be detected. This can be achieved by transparently passing the first type of connection through the interworking function, or, as an alternative, by branching an incoming channel of the first type of connection to the interworking function.

In particular, the interworking function may be an interworking modem function. Thereby, the modem function can be used to modulate the video/multimedia call in the mobile network.

Alternatively, the network function may be an exchange terminal function or a echo canceler function. Thus, the control signal is detected by a separate function or network element. In this case the interworking function for initiating the call modification procedure is made available to the call in response to the detection result.

The call modification procedure may be an In-Call Modification procedure, which initiates the change of the radio channel configuration in order to achieve a connection suitable for the second type of connection.

Preferably, the first type of connection is a speech connection and the second type of connection is a video or multimedia connection. However, any other combination or order is possible.

Furthermore, the interworking unit may comprise an interworking modem function, wherein the control means may be arranged to perform control so as to connect said second type of connection through the interworking modem function. Thereby, the video signal can be adapted to the mobile channel.

Furthermore, the interworking unit may comprise a detecting means for detecting the control signal. In this case, the control means may be arranged to control the interworking modem function so as to pass the signal flow of the first type of connection transparently through. Accordingly, during the first type of connection, the interworking unit is merely used for detection purposes, whereas, after the establishment of the second type of connection, the interworking unit is used to provide the required interworking modem function.

Alternatively, the interworking unit may be controlled by the mobile network so as to receive an incoming channel branched from the first type of connection. In this case, the speech connection does not have to be passed through the interworking modem function, such that network sources can be saved.

However, the detection means does not have to be arranged in the interworking unit. It may be arranged in another network element, wherein the control means is arranged to receive the detection result from the other network element. In particular, the other network element may be an exchange terminal or an echo canceler. In this case, the interworking unit is made available to the call by the mobile network after the control signal has been detected. BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present invention will be described in greater detail on the basis of a preferred embodiment with reference to the accompanying drawings, in which:

Fig. 1 shows a block diagram of a telecommunication system in which a mobile network is connected to a fixed network;

Fig. 2 shows a basic flow diagram of a method for establishing a call according to the preferred embodiment of the present invention;

Fig. 3 shows a basic diagram of an example of a connection between a switching unit and an interworking unit according to the preferred embodiment;

Fig. 4 shows a basic block diagram of another example of a connection between a switching unit and an interworking unit according to the preferred embodiment;

Fig. 5 shows a basic block diagram of a network element according to an example of the preferred embodiment of the present invention; and

Fig. 6 shows a basic block diagram of two network elements with a separate detection and call modification function according to another example of the preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The preferred embodiment of the present invention will be described on the basis of a multimedia connection between a fixed network 4 and a mobile network, as shown in Fig. 1. According to Fig. 1, a multimedia terminal equipment (TE) 5 is connected via the fixed network 4 such as a PSTN or the like to a mobile terminal or mobile station (MS) 1 of the mobile network.

The MS 1 is radio-connected to a Base Station Subsystem (BSS 2) which is connected to a Mobile Switching Center (MSC) 30. The BSS 2 is a system of Base Station equipment (transceiver, controllers etc.) which is viewed from the MSC 30 through a single interface as being the entity responsible for communicating with the MS 1 in a certain area. The radio equipment of the BSS 2 may support one or more cells. The BSS 2 consists of one Base Station controller and one or more Base Transceiver Stations. The MSC 30 is an exchange which performes all switching and signaling functions for mobile stations located in a geographical area designated as the MSC area. The MSC 30 has to take into account the impact of the allocation of radio resources and the mobile nature of the subscribers and has to perform at least procedures required for allocation registration and handover of the MS 1.

At the MSC 30, an interworking unit or function (IWF) 31 is provided for adapting protocol features used in the mobile network to protocol features used in the fixed network 4.

The MSC 30 and the IWF 31 may be arranged in a single network element, as shown in Fig. 1. Furthermore, the IWF

31 is connected to the fixed network 4 via an exchange terminal (ET) 32 connected to a trunk line towards the fixed network. The ET 32 is used to provide a connection or adaptation to the trunk line.

According to the preferred embodiment of the present invention an interworking towards the fixed network 4 with multimedia calls starting with speech and later being modified into video is performed by a V.8bis support from a modem function provided in the IWF 31 of mobile network. In particular, the IWF 31 initiates an In-Call Modification procedure to change the radio bearer from speech to data. This initiation is performed during the speech phase of the multimedia call on the basis of a detection of the V.δbis initiating control signals, i.e. tone frequencies.

Fig. 2 shows a basic flow diagram of the procedure for establishing the multimedia call in the IWF 31.

When the mobile network, e.g. the MSC 30, detects a call request for a multimedia call, a speech connection is established, wherein the signal flow of the speech connection is monitored by the IWF 31 or another network element through which the speech connection is routed, in order to detect a V.δbis control signal (step S101) .

If a V.δbis initiating control signal is detected in step S102, an In-Call Modification procedure as defined in the specification GSM 04.08/3GPP TS 24.008 is initiated by the IWF 31 (step S103) . If no V.δbis control signal is detected in step S102, the flow returns to step S101 so as to continue the monitoring operation during the speech connection phase.

Fig. 3 shows a basic diagram for a connection between the IWF 31 and the MSC 30, wherein the modem function of the IWF is through-connected during the speech phase of the multimedia connection. Thus, during the establishment of the multimedia call, the MSC 30 performs switching so as to achieve a signal flow as indicated in Fig. 3, wherein the speech phase of the call is routed through the modem function of the IWF 31 in a transparent manner in both directions. Hence, the IWF 31 merely performs a detection function for detecting the V.δbis control signal. Fig. 4 shows another example of a connection between the MSC 30 and the IWF 31 to provide the required monitoring function. In the case shown in Fig. 4, only the incoming channel of the speech connection is branched to the IWF 31 without passing the speech connection through the IWF modem. The connection can, for example, be branched via a conference unit (conference bridge) or in the switching matrix. Thus, the speech connection is only routed through the MSC 30 to the MS 1 via the BSS 2. Nevertheless, the IWF 31 may detect the V.δbis control signal based on the branched incoming channel, to thereby initiate the swap procedure.

Fig. 5 shows a basic block diagram of the IWF 31. According to Fig. 5, the IWF 31 comprises a V.δbis detection unit 311 connected to the fixed network 4 or the ET 32, and arranged to detect the tone frequencies indicating the V.δbis control signals. Furthermore, an IWF modem function 312 is provided which is controlled by an IWF control unit 313 so as to pass the speech transparently through during the speech phase of the multimedia connection. During the speech phase, the V.δbis detection unit 311 monitors the speech signaling. The control of the IWF control unit 313 may be based on a corresponding information received from the MSC 30 in order to indicate a request for an establishment of a multimedia connection.

When the V.δbis detection unit 311 detects an initiating control signal, the IWF control unit 313 initiates an In- Call Modification procedure to change the radio bearer from speech to data.

It is to be noted that the above description of the function of the IWF 31 shown in Fig. 5 is based on a through connection during the speech phase as shown in Fig. 3. However, if the MSC 30 performs switching so as to only branch the incoming channel to the IWF 31, the IWF control unit 313 controls the IWF modem function 312 so as to block or inhibit the signal, wherein the branched incoming channel is merely supplied to the V.δbis detection unit 311 in order to provide the monitoring function without passing the signal through the IWF 31.

Fig. 6 shows an alternative example of the preferred embodiment, wherein the detection function according to step S101 in Fig. 2 is performed in a separate network element such as the ET 32 or an echo canceler connected to the trunk line towards the fixed network 4. According to Fig. 6, the ET 32 or the respective other network element comprises a signal processing unit 322 arranged for performing the signal processing such as echo cancelation required for the connection or respective other network function. Furthermore, a V.δbis detection unit 321 is provided in order to detect the V.δbis control signals received from the fixed network 4.

If a request for an establishment of a multimedia call has been received by the MSC 30, the MSC 30 performs switching so as to route the multimedia call through the IWF 31, wherein the detection result of the V.δbis detection unit

321 is supplied to the IWF control unit 313. In response to the receipt of the detection result, the IWF control unit 313 initiates the In-Call Modification procedure in order to swap to the multimedia connection. During the speech phase, the IWF modem function 312 may be by-passed or transparent based on a corresponding control by the IWF control unit 313.

Alternatively, the detection result of the V.δbis detection unit 321 of the ET 32 may be supplied to the MSC 30 which then performes switching so as to route the connection through the IWF 31. In this case, the MSC 30 supplies a corresponding information to the IWF control unit 313 which then initiates the In-Call Modification procedure.

Thus, the above described preferred embodiment enables a swap procedure between the speech phase and the multimedia phase of a multimedia call according to the V.δbis recommendations, wherein a frequency detection functionality is not required in the MS 1 of the mobile network.

It is to be noted, that the present invention may as well be applied in a UMTS network, wherein the BSS 2 corresponds to a radio access network of the UMTS and wherein the MSC 30 corresponds to a radio network controller or a corresponding switching element of the mobile network. Moreover, the present invention may be applied in any telecommunication network, where a swap procedure between a first type of connection and a second type of connection has to be initiated during the first type of connection.

Thereby, a modification of the respective end terminals is not required.

Any type and combination of connections may be swapped. The first type of connection not necessarily has to be a speech connection. An initial video or multimedia connection may as well be switched to a speech connection. Moreover, as already mentioned, the detection may be based on any signal characteristic, such as frame number or structure, type of signal, or other types of characteristics. The discrete hardware blocks shown in Figs. 5 and 6 may be provided by corresponding program routines controlling a processing unit (e.g. CPU) arranged in the respective network element. The preferred embodiment of the invention may thus vary within the scope of the attached claims. In summary, the present invention relates to a method and network element for establishing a call between end terminals of a telecommunication system, wherein a first type of connection is established and monitored by a network function to which the first type of connection is routed in order to detect a signal of a second type of connection in a signal flow of the first type of connection. Based on the detection result of the network function, a call modification procedure to the second type of connection is initiated. Thereby, a call which is established by starting with a first type of connection and swapping to a second type of connection can be provided in a network without establishing a control signal detection functionality in the end terminals of the network.

Claims

1. A method for establishing a call between end terminals of a telecommunication system, comprising the steps of: a) establishing a first type of connection between said end terminals; b) providing a network function of a second type of connection for detecting a signal of said second type of connection in a signal flow of said first type of connection; c) routing said first type of connection to said network function; and d) initiating a call modification procedure to said second type of connection in response to the detection result of said network function

2. A method according to claim 1, wherein said network function is an interworking function of a mobile network.

3. A method according to claim 2, wherein said first type of connection is transparently passed through said interworking function.

4. A method according to claim 2, wherein an incoming channel of said first type of connection is branched to said interworking function.

5. A method according to anyone of claims 2 to 4, wherein said interworking function is an interworking modem function.

6. A method according to claim 1, wherein said network function is an exchange terminal function or an echo canceler function.

. A method according to claim 6, wherein an interworking function for initiating the call modification procedure is made available to said call in response to said detection result.

8. A method according to any one of the preceding claims, wherein said call modification procedure is an In-Call Modification procedure.

9. A method according to any one of the preceding claims, wherein said first type of connection is a speech connection and said second type of connection is a video or multimedia connection.

10. A method according to any one of the prededing claims, wherein said signal is an ITU-T V.δbis control signal.

11. A network element for establishing a call between end terminals (1, 5) of a telecommunication system, comprising: a) control means (313) for performing a call modification procedure from a first type of connection to a second type of connection in response to a detection result supplied to said control means (313) ; b) wherein said detection result indicates the detection of a signal for said second type of connection in a signal flow of said first type of connection; and c) wherein said network element (31) is used in a part of said second type of connection.

12. A network element according to claim 11, wherein said network element is an interworking unit (31) of a mobile network, said interworking unit (31) comprising an interworking modem function (312) , and wherein said control means (313) is arranged to perform control so as to connect said second type of connection through said interworking modem function (312) .

13. A network element according to claim 12, wherein said first type of connection is routed to said interworking unit (31) , said interworking unit (31) comprising a detecting means (311) for detecting said signal.

14. A network element according to claim 13, wherein said control means (313) is arranged to control said interworking modem function (312) so as to pass the signal flow of said first type of connection transparently through.

15. A network element according to claim 13, wherein said interworking unit (31) is controlled by said mobile network so as to receive an incoming channel branched from said first type of connection.

16. A network element according to claim 12, wherein said control means (313) is arranged to receive said detection result from a detection means (321) of another network element (32) through which said first connection is routed.

17. A network element according to claim 16, wherein said other network element is an exchange terminal (32) or an echo canceler.

18. A network element according to any one of claims 11 to

17, wherein said first type of connection is a speech connection, and said second type of connection is a video or multimedia connection.

19. A network element according to any one of claims 11 to

18, wherein said signal is a ITU-T V.δbis control signal.