Telecommunication system

Abstract: A telecommunications system comprising at least one mobile station and at least two possible paths of different transmission protocols, through which calls to and from the mobile station can be routed, wherein the mobile station is provided with a single address regardless of the path over which a call is to be routed. For an incoming call, a means for assigning a mobile station roaming number (MSRN), based upon the path through which a call is to be routed is used.

Description: Field of the Invention This invention relates to telecommunications systems. In particular, but not exclusively, it relates to improvements relating to the Universal Mobile Telecommunications System (UMTS). Background to the Invention A UMTS mobile station (MS) can be connected via a radio interface both as a traditional phone terminal, and as an Internet protocol (IP) terminal. With an IP connection and an associated quality of service mechanism, a terminal can make and receive a voice call via either the circuit-switch domain or the packet-switch domain over which packet based voice service can be provided. Acoordingly, an MS has two modes; it can act as a traditional mobile voice terminal and as a voice over Internet protocol (VoIP) terminal. However, there are some problems associated with this unique configuration. One problem is that of how to address a mobile station for calls set up using different paths. Existing PSTN/ISDN systems route a call based upon a called party number. For the packet-switch (PS) path, the mobile station can be addressed using its IP address, using an e-mail-like address or by using a call party number assigned specifically for the mobile station. The call party number is sometimes referred to as an E164 number, after ITU document E164 relating to international telecommunication numbering or may be referred to as an MSISDN (mobile station ISDN) number. Since a PSTN terminal can only use digit numbers, the solution is generally to assign an MSISDN number for a mobile station as well. A problem then arises as to how to address the MS so that a call can follow either the circuit-switch (CS) path or the packet-switch (PS) path, using the two modes of the MS correspondingly. Furthermore, the network operator needs the option to control and select the path for an incoming call. An operator can provide two alternative (CS or PS) paths for a call between an MS and other points. The operator may require some control over the path selection on a per-call basis. One straightforward solution is to use two separate E164 numbers for each mobile station, each number corresponding to the particular path so that one number corresponds to the PS path and another number to the CS path. This has drawbacks. It is not user friendly and imposes extra management complexity. The user of a mobile station needs to manage two different telephone numbers and to make them known to those who may contact him. In many cases, users at both ends do not care which path is to be used to make a call. A transparent approach is therefore preferred. On the other hand, the use of different phone numbers makes it very difficult for an operator to control and select the path for incoming calls, as this is predefined by the number called. There are two signalling interfaces between a mobile network and other networks for PS and CS paths respectively. Thus, calls arriving at a mobile switching centre (MSC) will go through the CS path and calls arriving at a gateway/signalling-gateway will use the PS path. The present invention arose in an attempt to improve over the present situation. It is known from published European patent application EP-A-0526764 to provide a telecommunications system comprising at least one mobile station and at least two possible paths of different transmission protocols, through which calls to and from the mobile station can be routed, wherein the mobile station is provided with a single address regardless of the path over which a call is to be routed, wherein one of the paths is a circuit-switch path, the system including means for selecting the path to be used, depending upon one or more selected criteria. Summary of the Invention The present invention is characterised over the disclosure of EP-A-0526764 in that another of the paths is a packet-switch path, the criteria being dependent upon the traffic loads on the circuit-switch and packet-switch paths. Preferably, the communications system is a UMTS (Universal Mobile Telecommunications System) 1. In embodiments of the invention, a means for assigning a mobile station roaming number for the mobile station, based upon the path through which a call is, or is to be, routed, is provided. This can be an extended functionality of a visiting location register (VLR). According to the present invention there is further provided a method of routing calls to or from a mobile station of a telecommunications system, wherein at least two possible paths of different protocols are available, over which calls to and from the mobile station can be routed, the paths comprising a circuit-switch path, the method comprising assigning a single address to the mobile station regardless of the path over which the call is to be routed, wherein the path to be used is selected depending upon one or more selected criteria, characterised by the paths comprising a packet-switch path, and the criteria are dependent upon the traffic loads on the circuit-switch and packet-switch paths. Brief Description of the Drawings Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a UMTS mobile station connected via a radio interface to make and receive voice calls either a circuit-switch or packet-switch domain; Figure 2a shows a circuit-switch path; Figure 2b shows a packet-switch path; and Figure 3 shows an implementation of path selection in an embodiment of the present invention. Detailed Description of Preferred Embodiments of the Invention A UMTS mobile station (MS) can be connected via a radio interface both as an IP terminal and as a traditional mobile voice terminal. With an IP connection and the associated QoS (Quality of Service) mechanism, a terminal can make and receive a voice call via either the circuit-switch domain or the packet-switch domain. This is illustrated in Figure 1. A mobile station 1 is linked by a radio link to the UMTS Terrestrial Radio Access Network, UTRAN 2. A call may then be routed over a circuit-switch path, shown generally as 3, or a packet-switch path shown generally as 4. If the call is to be via the circuit-switch path, then it is passed through a switching circuit 5 which includes a visiting location register VLR 6. It is then routed through the PSTN/ISDN network 8 to a receiving telephone terminal 9. If a call is to be made over the packet-switch path 4, then it is routed via a Serving GPRS Support Node (SGSN) 10 and a gateway GPRS support node 11 to a multi-service packet network 12 and thence onwards to a receiver such as a computer 13. The same paths are of course used when the mobile station is receiving a call. Note that in the Figure the term 3G refers to "third generation". To enable a voice call across packet network and circuit networks, a voice over Internet Protocol Interworking Function VoIP IWF 14 is required. This has two major components, a gatekeeper/signalling gateway 15 and a media gateway 16. The gatekeeper 15 provides call control functionality and supplemental features such as call forwarding, call waiting and multiple-way call. The gatekeeper also provides functions such as address translation, admission control such that permission to complete call and set bandwidth limitations, manages gateways and controls call signalling, call management, reporting and logging. The signalling gateway part provides signalling into working at an interface to the SS7 (Signalling System No. 7) network. The media gateway 16 provides many services such as protocol and media translations. It performs bi-directional synchronous/asynchronous conversion (Time Division Multiplex (TDM) to packet) and signalling inter-working functions including control interface and connection management. HLR 17 is a Home Location Register. Figure 2a shows a typical CS path. Typically, the path comprises a PSTN terminal 9, a PSTN/ISDN network 8, a Gateway Mobile Switching Centre GMSC 5, a mobile switching centre MSC 18, UTRAN 2 and mobile station 1. It is also possible that part of the connection over the PSTN/ISDN backbone is replaced by a packet network together with VoIP IWF. This is not shown, for clarity. The PS path, on the other hand, is shown in Figure 2b and comprises PSTN terminal 9, PSTN/ISDN network 8, VoIP IWF 14, packet network 12, GGSN 11, SGSN 12, UTRAN 2 and the mobile station 1. In embodiments of the invention, a single number (MSISDN number) is used as the address for each mobile station. A mobile station is called using this number regardless of the path to be used within the UMTS PLMN (Public Land Mobile Network). Furthermore, a mobile station initiates a call using this number as the calling party number, again regardless of the path to be used. For incoming calls, in embodiments of the invention, the visiting location register (VLR) may be enhanced or modified so that it can assign a mobile station roaming number (MSRN) for the called mobile station based upon the decision on the path (CS or PS) to be used. Other means for assigning an MSRN may be used. The path selection for incoming calls is made possible by enhancing the VLR. In embodiments of the invention, there can be two parts to this enhancement. Firstly, the enhanced VLR can store the mobile stations capability as a VoIP terminal and the user's preference of accepting a call via VoIP or CS call. Further, when an incoming call arrives from the PSTN/ISDN, the gateway MSC sends an inquiry, via the HLR, to the VLR for the MSRN in order to route the call request to the serving MSC. This inquiry from the HLR contains the IMSI (International Mobile Subscriber Identity) which is derived from the mobile station ISDN number by the HLR of the called mobile station. Upon receiving this inquiry, the VLR assigns a mobile station roaming number, MSRN, based on the decision on how to terminate the call, i.e. via CS or PS paths. The MSRN assigned will then be different (in prefix for example) so that the ISUP (ISDN User Part) message can be sent to the serving MSC or the serving gatekeeper/signalling gateway correspondingly. The operator can decide upon the particular policy to be used to determine the path selection process. For example, this may be based on criteria such as the users terminal capability, i.e. if the terminal is capable of a VoIP call, the user's preference and traffic loads on the CS and PS paths. Figure 3 illustrates how the path selection for an incoming call is supported. It shows an example of an incoming call from the PSTN/ISDN domain 8 to a roaming mobile station 1. The message flow is as follows: Step S1. A caller request is made from the ISDN 8 in an ISUP (ISDN User Part) message, which contains the MSISDN of the called party. Step S2. The gateway mobile switching centre (GMSC) 20 receives the request and issues an inquiry to the HLR 17. Step S3. The HLR, knowing that the called mobile station 1 is currently roaming, issues an inquiry to the VLR 6 in the visiting network 21. Step S4. The VLR replies with a mobile station roaming number (MSRN), which is associated with the gatekeeper/signalling gateway (GK/SG) interface 22 or the MSC interface 23, depending on the path selected. This is shown as "MAP" (MSRN CS,PS ). Step S5. The HLR relays the MSRN back to the GMSC 20. Step S6. The GMSC then continues to route the call either to the MSC 5 or to the GK/SG 22 in the visiting network 21. Step S6a. If the CS path has been selected (as reflected by the MSRN returned) then the call is routed to the MSC. The message flow after that is not shown in the Figure. Step S6b. If the PS path is selected then the call is routed to the GK/SG via PSTN/ISDN. The GK/SG contacts the VLR 6 to provide the mobile identity (IMSI) from the MSRN. The GK then sets up a call to the MS over the PS domain via a PSTN/IP gateway. The message between the GK and mobile station is not shown. Embodiments of the invention allow operators control over how to terminate incoming calls via the PS or CS domains, in a transparent way. This in turn can be used to optimise the use of network resources. The invention can be used for other types of packet radio systems, such as GPRS.

Claims: A telecommunications system comprising at least one mobile station (1) and at least two possible paths (3,4) of different transmission protocols, through which calls to and from the mobile station (1) can be routed, wherein the mobile station (1) is provided with a single address (MSISDN) regardless of the path (3,4) over which a call is to be routed, wherein one (3) of the paths is a circuit-switch path, the system including means (6) for selecting the path to be used, depending upon one or more selected criteria, characterised in that another (4) of the paths is a packet-switch path, the criteria being dependent upon the traffic loads on the circuit-switch and packet-switch paths (3,4). A telecommunications system as claimed in Claim 1 which is a UMTS system. A telecommunications system as claimed in Claim 1 or Claim 2, wherein the single address is a MSISDN number. A telecommunications system as claimed in any of Claims 1 to 3 wherein the criteria includes the terminal capacity, or traffic loading on the signalling paths (3,4). A telecommunications system as claimed in any preceding claim, including means (6) for assigning a mobile station roaming number (MSRN) for the mobile station (1), based upon the path (3,4) through which a call is to be routed. A telecommunications system as claimed in Claim 5, wherein the means for assigning an MSRN is an enhanced Visiting Location Register (VLR,6). A telecommunications system as claimed in Claim 5 or Claim 6, wherein the assigned MSRN determines the path. A method of routing calls to or from a mobile station (1) of a telecommunications system, wherein at least two possible paths (3,4) of different protocols are available, over which calls to and from the mobile station (1) can be routed, the paths (3,4) comprising a circuit-switch path (3), the method comprising assigning a single address (MSISDN) to the mobile station (1) regardless of the path over which the call is to be routed, wherein the path to be used is selected depending upon one or more selected criteria, characterised by the paths (3,4) comprising a packet-switch path (4), and the criteria are dependent upon the traffic loads on the circuit-switch and packet-switch paths (3,4). A method as claimed in Claim 8, wherein the system is a UMTS system. A method as claimed in Claim 8 or Claim 9, wherein the single address is a MSISDN number. A method as claimed in any of Claims 8 to 10, wherein the criteria includes the terminal capacity, or traffic loading on the signalling paths. A method as claimed in any of Claims 8 to 11, including providing means for assigning a mobile station roaming number (MSRN) for the mobile station (1) based upon the path (3,4) through which a call is to be routed. A method as claimed in Claim 12, wherein the MSRN assigning means is an enhanced Visiting Location Register (VLR,6). A method as claimed in Claim 13, wherein the assigned MSRN determined the path.

Inventors: PALAT SUDEEP KUMAR, YAMINI HATEF, YANG JIN, PALAT, SUDEEP KUMAR, YAMINI, HATEF, YANG, JIN
Applicants: LUCENT TECHNOLOGIES INC, LUCENT TECHNOLOGIES INC.
Application year: 1999
Main classification: H04Q7
IPC codes: H04W8, H04W76