WO2002001903A1

WO2002001903A1 - Call set-up in a mobile telecommunications system

Info

Publication number: WO2002001903A1
Application number: PCT/EP2001/007014
Authority: WO
Inventors: Hannu VAINIOMÄKI; Reijo Pekkala
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2000-06-28
Filing date: 2001-06-20
Publication date: 2002-01-03
Also published as: AU2001279676A1; GB2367207A; GB0015665D0; TW508930B; AR028763A1; GB2367207B

Abstract

A method of re-establishing a call connection to a User Equipment (UE) 3 in a UMTS mobile telecommunications network. The method comprises extending the T3240 timer by sending a new timer value to the UE in an IE of a RELEASE or CALL PROCEEDING message relating to the original call. A connection SETUP message is sent from the network to the UE 3, the SETUP message including an Information Element (IE) containing a Stream Identifier (SI) identifying a bearer previously established between the UE 3 and the network, and using the identified bearer for a new connection between the UE 3 and the network.

Description

CALL SET-UP IN A MOBILE TELECOMMUNICATIONS SYSTEM

Field of the Invention

The present invention relates to call set-up in a mobile telecommunications network and more particularly to call set-up in a third generation mobile telecommunications network.

Background to the Invention

The European Telecommunications Standardisation Institute (ETSI) is currently in the process of standardising a new set of protocols for third generation mobile telecommunications systems. The set of protocols is known collectively as Universal Mobile Telecommunications System (UMTS). Figure 1 illustrates schematically a part of a Universal Mobile Telecommunications System (UMTS) network. The network includes a core network part 1, which may be a network handling voice calls using UMTS Mobile-services Switching Centres (UMSCs) or may be a data network such as a General Packet Radio Service (GPRS) network including Serving GPRS Support Nodes (SGSNs). In Figure 1 the UMSCs and SGSNs are indicated generally with the reference numeral 2. User Equipment (UE) 3 is coupled to the core network 1 via an access network 4 referred to as a Universal Terrestrial Radio Access Network (UTRAN). More particularly, the UMSCs/SGSNs 2 are connected to Radio Network Controllers (RNCs) 5,6 of the UTRAN 4 over an interface referred to as the Iu interface.

Each RNC 5 forms part of a Radio Network Subsystem (RNSs) 7,8 which also comprises a set of Base Transceiver Stations 9 referred to in UMTS terminology as Node B's. The interface between a RNC 5,6 and a Node B 9 is known as the Iub interface. A Node B 9 provides the connection point for a UE 3 to the UTRAN 4, and the interface between the Node B 9 and the UE 3 is known as the Uu interface. The RNS (RNS 7 in Figure 1) which connects a UE 3 to the core network 1 at any given time is referred to as the Serving RNS (SRNS) for that particular UE 3. In particular, the SRNS controls the Radio Resource (RR) connection between itself and the UE. Figure 2 illustrates in very general terms the bearer structure used by UTRAN to carry user data between the UE 3 and the core network 1. When it is required to establish a user plane connection, the responsible UMSC or SGSN 2 instructs the UTRAN 4 to establish a logical connection between the UMSC or SGSN 2 and the UE 3. This logical connection is referred to as a Radio Access Bearer (RAB). The established RAB inherits requirements of the requested UMTS service, e.g. Quality of Service, etc. Based on the inherited requirements of the RAB, the RNC 5,6 establishes user plane connections with the core network 1 (i.e. UMSC or SGSN 2) and with the UE 3. The connection between the RNC 5,6 and the core network 1 is referred to as the Iu bearer whilst the connection between the RNC 5,6 and the UE 3 is referred to as the Radio Bearer (RB). Both of these bearers represent further logical channels, with the RNC performing a mapping between them. The bearers themselves are mapped onto appropriate traffic channels for transmission over the respective interfaces (Iu and Uu).

The UMTS Radio Access Bearer (RAB) service provides a transport connection service through the UTRAN, which uses Asynchronous Transfer Mode (ATM) in the connection between the RNC 5,6 and the core network 1. WCDMA radio traffic channels are allocated by the controllers in the RNC 5,6 and are physically implemented by the Node Bs 9 over the radio interface to the UE 3. The actual radio link resources correspond to individual CDMA spreading codes.

A single UE 3 may be associated with one or more RABs. For example, a UE 3 may simultaneously make use of one RAB established for a voice call, and another RAB established for a data call. The RNC 5,6 uses RAB IDs (allocated by the core network) to distinguish between these different RABs. UEs supporting the MULTICALL feature (i.e. where several RABs and calls may exist simultaneously) identify a certain bearer by using the so-called Stream Identifier (SI), which is used by the serving MSC as the RAB ID. Regarding calls terminating at a UE, the CALL CONFIRMED CC message (sent by the UE) contains a new SI value to identify the RAB to be established. During the subsequent RAB assignment, the network uses the received SI as the RAB ID which is sent back to the SRNC and to the UE. The SRNC associates the received RAB ID with the RB identity and the Iu Bearer Identity. If the network does not support MULTICALL, a UE can use only the SI value "1". Regarding calls originating from a UE, the SETUP CC message (sent from the UE) contains a new SI value to identify the RAB to be established. Figure 3 illustrates the flow of signalling information in a UMTS network, where protocol IEs are presented with solid line boxes and concepts are presented with broken line boxes.

Statement of the Invention

The Call Control (CC) entity of a UE may initiate call clearing by following the layer 3 signalling sequence: DISCONNECT, RELEASE, RELEASE COMPLETE, and then entering the CC NULL state. If this results in releasing the last Mobility Management (MM) connection, the UE will enter the MM state WAIT FOR NETWORK COMMAND and will expect the release of the RAB and RR connection. The UE will start the timer T3240 (10 seconds). In the event that the timer expires, the UE will abort the RR connection and clear the RAB, and enter the MM IDLE state.

In the event that the network does not wish to initiate procedures to clear the network connection and the call to the remote end, but rather wishes to maintain the RR connection and the existing RAB for a predefined time so as to retain the option to reestablish the call to the UE, two problems exist. Firstly, if the network subsequently wishes to re-establish the released call connection, it is not possible to re-use the existing RAB for this connection. This is because, according to the current state of the UMTS standard, there is no mechanism for enabling a core network to inform a UE to use an existing RAB for a new connection (although there is a mechanism which enables a UE to inform a core network of a new SI in a CALL CONFIRMED message). A second problem is that the timer T3240 only runs for 10 seconds, which may be too short.

In Japan, there exists a regulatory requirement on operators to allow emergency services to place a call on hold following an attempt to disconnect the call by a calling party. The term "on hold" is used to indicate the maintenance of the network connection, the RR connection, and the existing RAB to the UE. This is to allow the emergency services to subsequently call back to the calling party in a fast and efficient way. Moreover, the same regulatory requirement specifies that the predefined time period of the timer T3240 is extended to 40 seconds. As the network cannot select the SI, it is necessary to establish a new RAB for the call-back, a process which may take time and which may be unsuccessful, e.g. if network resources are occupied. Moreover, should the timer T3240 expire, the UE would become idle, allowing the UE to make a call to some other destination and therefore could be in a busy state when a call-back is attempted. In the event that an emergency call is made from a UE which does not have a Subscriber Identity Module (SIM) inserted into it, the problem is even more serious as the identity of the caller is unknown and a new connection cannot in any case be established by paging the UE.

It is an object of the present invention to overcome or at least mitigate the above noted disadvantages of the current UMTS standards. In particular it is an object of the present invention to allow a network to establish a call connection using a pre-existing RAB. It is also an object of the present invention to allow the extension of the timer T3240. These and other objects are achieved at least in part by defining a new Information Element (IE) for transmission from the network to the UE and which identifies an existing RAB (SI) using which a connection is to be established.

According to a first aspect of the present invention there is provided a method of establishing a call connection or of re-establishing a connection to a User Equipment (UE) in a UMTS mobile telecommunications network, the method comprising the steps of: sending a connection SETUP message from the network to the UE, the SETUP message including an Information Element (IE) containing a Stream Identifier (SI) identifying an existing bearer between the UE and the network; and using the identified bearer for a subsequent connection between the UE and the network.

Embodiments of the present invention allow pre-existing bearers to be used for new (or re-established) connections which are initiated on the network side. As such, these embodiments satisfy certain regulatory requirements such as those in Japan. Preferably, the timer T3240 is extended by sending an LE to the UE from the network, the IE containing a new timer value. This IE may be contained, for example, in a CALL PROCEEDING message sent to the UE during the setup of the original call, or may be contained in a RELEASE message relating to the original call.

The method of the present invention may be employed to reconnect the UE to the network after a previous connection has been placed on hold by the network.

Preferably, the SETUP message is sent to the UE from a node in a core network of the UMTS network, via the UTRAN. For example, this node may be an MSC of a circuit switched core network.

According to a second aspect of the present invention there is provided a mobile telecommunications network comprising: means located in the network for receiving a connection or reconnection request; and means for sending a connection SETUP message to a UE in response to receipt of said request, the SETUP message including an Information Element (IE) containing a

Stream Identifier (SI) identifying a bearer previously established between the UE and the network.

According to a third aspect of the present invention there is provided a method of extending the release timer T3240 for a UE in a UMTS network, the method comprising sending a new timer value from the network to the UE in an Information Element (IE).

The IE may be contained in a CALL PROCEEDING message or in a RELEASE message.

Preferably, the method comprises identifying a call from the UE as a call for which the T3240 timer should be extended, and subsequently carrying out said step of sending a new timer value from the network to the UE in an Information Element (IE). For example, such a call may be a call to an emergency service. Brief Description of the Drawings

Figure 1 illustrates schematically a UMTS network;

Figure 2 illustrates schematically the bearer structure used in the UTRAN part of the UMTS network of Figure 1;

Figure 3 illustrates a signalling flow in a UMTS network; and

Figure 4 is a flow diagram illustrating a method of establishing a call connection in the network of Figure 1.

Detailed Description of a Preferred Embodiment

The general architecture of a UMTS system has been described above with reference to Figure 1. When the UE 3 is turned on and, for example, a location update requested, it registers with a Radio Network Controller (RNC) 6 of the UMTS Terrestrial Radio Access Network (UTRAN) 4 of the UMTS network, via a Base Station (BS) 9. This RNC 6 is referred to as the "serving RNC" for the UE 3.

As outlined above, it is the UTRAN 4 which is responsible for setting up and tearing down RABs in accordance with RAB requests received from the core network 1 of the UMTS network (winch in turn may be a response to a connection or reconnection request received by the core network 1 from the UE 3 or from some other calling party). More particularly, these functions are provided by a radio resource handling entity of the RNC 6. Only one core network 1 is illustrated in Figure 1, namely a circuit switched (voice) core network 1. For the purpose of the following discussion, it is assumed that a RAB has been allocated to the UE 3 by the UTRAN 4 for the purpose of a voice call between the UE 3 (the calling party) and an emergency service centre (not shown in Figure 1). This RAB has a RAB ID which is unique for the UE in the UTRAN and the associated CN domain, and which is communicated from the serving MSC 2 to both the RNC 6 and the UE 3. The RAB ID corresponds to the Stream Identifier (SI) which is sent from the UE 3 to the MSC 2 in a SETUP message.

In the event that the UE 3 attempts to disconnect the connection to the emergency service centre, the CC entity of the serving MSC 2 in the core network 1 recognises that the connection exists to an emergency service and, instead of disconnecting the connection, extends the T3240 timer to a predefined time (e.g. 40 seconds) by sending the new timer value in a new IE of the RELEASE message. The call is then placed on hold. If no request for re-establishment of the connection is received from the emergency service within the predefined time, the serving MSC 2 terminates the connection by releasing both the network and access side of the held connection. On the other hand, if a re-establishment request is received from the emergency service centre within that time period, the CC entity of the serving MSC 2 generates a call SETUP message for transmission to the UE 3. The SETUP message comprises an Information Element (IE) which contains the SI (RAB ID) which was previously established for the original call. The IEs required for the timer value and the SI may be existing, unused fields of the SETUP and RELEASE (or CALL PROCEEDING) messages or may be an extensions thereto.

The SETUP message is sent to the UE 3, via the UTRAN 4, using a newly established signalling connection. Upon receipt of the SETUP message, the user of the UE 3 may accept or reject the incoming call setup request. In the event that the new call is accepted, the UE is able to adopt the existing RAB for the connection.

The method of re-establishing a call connection is further illustrated in the flow diagram of Figure 4.

It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiment without departing from the scope of the present invention. For example, whilst the embodiment described above concerns a call connection between a UE and an emergency service, the present invention may be employed to re-establish a connection to any third party terminal. The invention may also be employed to establish a connection to a UE, even when no previous corresponding connection has existed but a RAB has been allocated (e.g. for a data call or for a call to some other party).

Claims

1. A method of establishing a call connection or of re-establishing a connection to a User Equipment (UE) in a UMTS mobile telecommunications network, the method comprising the steps of: sending a connection SETUP message from the network to the UE, the SETUP message including an Information Element (IE) containing a Stream Identifier (SI) identifying an existing bearer between the UE and the network; and using the identified bearer for a subsequent connection between the UE and the network.

2. A method according to claim 1, wherein said step of sending a connection SETUP message from the network to the UE follows the placing on hold by the network of a previous connection.

3. A method according to any one of the preceding claims, wherein the SETUP message is sent to the UE from a node in a core network of the UMTS network, via the UTRAN.

4. A method according to claim 3, wherein the timer T3240 is extended by sending an IE to the UE from the network, the IE containing a new timer value.

5. A method according to claim 4, wherein the time IE is contained in a CALL PROCEEDING message sent to the UE during the setup of the original call, or is contained in a RELEASE message relating to the original call.

6. A mobile telecommunications network comprising: means located in the network for receiving a connection or reconnection request; and means for sending a connection SETUP message to a UE in response to receipt of said request, the SETUP message including an Information Element (IE) containing a Stream Identifier (SI) identifying a bearer previously established between the UE and the network.

7. A method of extending the release timer T3240 for a UE in a UMTS network, the method comprising sending a new timer value from the network to the UE in an information Element (IE).

8. A method according to claim 7, wherein the IE is be contained in a CALL PROCEEDING message or in a RELEASE message.

9. A method according to claim 7 or 8 and comprising identifying a call from the UE as a call for which the T3240 timer should be extended, and subsequently carrying out said step of sending a new timer value from the network to the UE in an information Element (IE).