WO2002098154A1

WO2002098154A1 - Connecting the bsc of a gsm base station subsystem to an rnc of a umts system to achieve support for the iu interface in the gsm base station subsystem

Info

Publication number: WO2002098154A1
Application number: PCT/SE2002/001026
Authority: WO
Inventors: Alan Leddy; William Warrillow
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2001-05-30
Filing date: 2002-05-29
Publication date: 2002-12-05
Also published as: SE0101892D0

Abstract

The present invention relates to a method and apparatus for improving the network architecture of a mobile radio system. In one embodiment of the invention, the base station controller of a GSM base station subsystem is connected to a radio network controller in order to achieve support for the Iu interface in the GSM base station subsystem.

Description

Connecting" the BSC of a GSM base station subsystem to an RNC of a UMTS system to achieve support for the IU interface in the GSM base station subsystem.

Field of the invention

The present invention relates generally to the field of mobile radio communications, and more particularly to a method and apparatus for improving the network architecture of a mobile radio system.

Background

The mobile radio communications technology is continuously evolving. At the same time as new standards are being developed, improvements are made within already existing standards. Many operators of mobile radio networks rely on their mobile radio networks of an already existing standard, while investments are being made in mobile radio networks of a new standard. It is desirable that, where possible, the functionality of the existing standard is evolved to incorporate some of the functionality of the new standard.

The GSM (Global System for Mobile communication) standard and the UMTS (Universal

Mobile Telephony System) standard is a good example of an existing standard (GSM) and a standard under development (UMTS) which will co-exist in the same geographic areas, and networks operating according to the two standards will possibly be operated by the same operator. While the UMTS standard is being developed, efforts are made to extend the GSM standard to include some functionality of the UMTS standard. An example of this is GERAN (GSM/EDGE Radio Access Network), which is a solution, presently being standardised, for connecting the GSM air interface with the UMTS core network (see 3rd Generation Partnership Project Technical Specification (TS) 43.051, which is hereby incorporated by reference). By using the UMTS interface, Iu, for communication between the GSM base station subsystem and the core network, the functionality of GSM can be extended. An example of functionality which could be supported by GSM when the Iu interface is introduced as an interface between the GSM base station subsystem and the core network is real-time processing of data calls. Summary

A problem to which one aspect of the present invention relates is how to improve the network architecture of a mobile radio system.

This problem is addressed by a mobile radio system comprising at least a first mobile radio network which has a core network and a base station subsystem. The base station subsystem comprises a base transceiver station and a base station controller, the base station controller being connected to the core network. The base station subsystem further comprises a further node, which is connected to the core network. The further node is capable of passing traffic to/from the core network over a first interface. The base station controller and the further node are connected to each other via a connection, over which connection traffic can be passed by use of a second interface.

By the inventive mobile radio system is achieved that traffic can be passed to/from the base station subsystem from/to the core network via the first interface.

In one aspect of the invention, the further node is a second base station controller, designed for operation according to a standard of mobile radio telephony different to the standard according to which said first mobile radio network is operated. Hereby is achieved that development costs can be kept low. Furthermore, migration of subscribers from the standard used by the first mobile radio network to the standard according to which the second base station controller is designed to operate is facilitated. The standard according to which the first mobile radio network is operating could e.g. be the GSM standard, and the second base station controller could e.g. be a radio network controller designed for operation according to the UMTS standard. The first interface could then be the Iu interface.

In one embodiment of the invention, at least one protocol of the first interface is terminated, on the base station subsystem side of the first interface, at the further node. Hereby is achieved that support for the at least one protocol will not have to be introduced in the base station controller. E.g., if the first interface is the Iu interface, and the further node is a radio network controller, the ATM protocol could be terminated at the radio network controller. In one embodiment of the invention, the second interface is based on the ethernet protocol. Hereby is achieved that the connection between the base station controller and the further node is a fast connection. The OSE delta signalling process, internal to the OSE Delta operating system, could then be used on top of the ethernet protocol, or another protocol could be used on top of ehternet. In another embodiment, the protocol stack used on the second interface could comprise the El protocol, the PPP protocol and the IP protocol.

In one embodiment of the inventive mobile radio system, the further node could be part of a second base station subsystem of a second mobile radio network. The further node would then be connected to at least one radio transceiver station. In this embodiment, said connection could be further used for information exchange between the base station subsystem of the first mobile radio network and the second base station subsystem. Hereby is achieved that traffic management could be improved. In one aspect of this embodiment, said information exchange uses said second interface.

In one embodiment of the inventive system, the base station controller of the first network and the further node are physically co-located. Hereby is achieved that said connection is short and fast. Information exchange can hence be made efficient.

The problem to which the present invention relates is further addressed by a base station subsystem operable in a GSM mobile radio network. The base station subsystem comprises at least one radio transceiver station and a base station controller connected to a core network. The base station controller is capable of passing traffic to/from the core network over the A and Gb interfaces. The base station subsystem further comprises a radio network controller, connected to said core network, capable of passing traffic to/from the core network via the Iu interface. The base station controller and the radio network controller are connected via a connection over which traffic, intended for Iu interface communication between a mobile station and the core network, can be passed.

By the inventive base station subsystem is achieved that traffic intended for the Iu interface can be passed between the core network and a GSM mobile station, via the GSM base station subsystem. The problem is further met by a method of providing support for Iu interface communication to/from a MS in a GSM mobile radio network. The GSM mobile radio network comprises at least one base station subsystem and a core network. The base station subsystem comprises at least one radio transceiver station and a base station controller. The base station controller is connected to the core network and is capable of traffic transmission to/from the core network over the A and Gb interfaces. The GSM base station subsystem enables mobile stations to communicate in a certain area. The method comprises the steps of connecting a radio network controller to the base station controller, enabling traffic transmission between the radio network controller and the base station controller over an interface and transmitting traffic to/from a mobile station, communicating with the core network, over the connection between the base station controller and the radio network controller when said traffic to/from a mobile station is intended for Iu communication. The radio network controller is further connected to the core network and is capable of traffic transmission to/from the core network over the Iu interface.

Brief description of the drawings

The present invention will now be discussed in more detail with reference to preferred embodiments of the present invention, given only by way of example, and illustrated in the accompanying drawings, in which:

Fig. 1 is a schematic overview of a mobile radio network.

Fig. 2 is a schematic overview of a mobile radio system comprising an example of the inventive GERAN base station subsystem.

Fig. 3 a is an example of a protocol stack used for traffic transmission over an interface between a base station controller and a radio network controller.

Fig. 3b is an alternative protocol stack which could be used for traffic transmission between a base station controller and a radio network controller. Detailed description

The general architecture of a mobile radio network 100 is schematically illustrated in Fig. 1. Mobile radio network 100 provides radio communication to users of Mobile Stations (MS). In Fig. 1, MS 105 is shown to communicate within the mobile radio network 100 via a Base Transceiver Station (BTS) 110 using a radio link 115. Several BTSs belonging to the mobile radio network may be connected together via a Base Station Controller (BSC) 120. The BTSs 110 and the BSC 120 forms what is referred to as the base station subsystem 125.

The BSC 120 is in turn connected to a core network 130, which controls calls to and from other networks such as Public Switched Telephony Networks (PSTN), Integrated Services Digital Networks (ISDN), other Public Land Mobile Networks (PLMNs), the internet etc. In the GSM standard, the BSC 120 communicates with the core network 130 via the nodes MSC (Mobile services Switching Centre) 135 and SGSN (Switching General packet radio services Support Node) 140. The MSC 135 is responsible for switching circuit switched connections, while the SGSN 140 is used for switching packet switched connections. The communication protocol used within GSM for communication over the connection 145 between the BSC 120 and the MSC 135 is referred to as the A-interface, while the communication protocol used over the connection 150 between the BSC 120 and the SGSN 140 is referred to as the Gb-interface (see e.g. GSM TS 03.02 and GSM TS 03.60 for further information on these interfaces).

Depending on which standard is used for communication in mobile radio network 100, the functionality, implementation and name of the nodes shown in Fig. 1 may vary. The terminology used in Fig. 1 is the terminology of a mobile radio network operating according to the GSM standard. However, similar nodes would be found in mobile radio networks of other standard. For example, in a mobile radio network operating according to the UMTS standard, the base transceiver station and the base station controller are referred to as the Node B and the radio network controller, respectively. The network architecture of the GSM standard is further described in GSM TS 03.02 and GSM TS 03.60. The network architecture of the UMTS standard is described in 3^rd Generation Partnership Project TS 23.002. According to the standard defined in 3^rd Generation Partnership Project TS 43.051, there now exists an option to implement a GSM base station subsystem 125 which can communicate with the core network 130 via an interface referred to as the Iu interface. The Iu interface has previously been defined for communication in the UMTS standard, see 3 ^rd Generation Partnership Project TS 25.410. In the UMTS standard, the Iu interface is used for communication between the UMTS base station controller (radio network controller) and the core network 130.

A GSM base station subsystem 125, with the capability of communicating over the Iu interface, is referred to as a GERAN base station subsystem. The Iu interface consists of two parts: the lu-cs for circuit switched communication with the MSC 135 and the lu-ps for packet switched communication with the SGSN 140. In order to provide backwards compatibility, the GERAN base station subsystem should support the traditional GSM interfaces, A and Gb, as well as the Iu interface.

The Iu interface is based on the ATM protocol. The GSM base station subsystem 125, shown in Fig. 1, is not standardised to support ATM communication. However, a solution to the problem of how to extend the functionality of the GSM base station subsystem 125 in order to provide support for Iu interface communication is presented in Fig. 2. An inventive GERAN base station subsystem 200 is shown in Fig. 2, in which the BSC 120 is connected to a UMTS base station controller 205 via a connection 210. The UMTS base station controller 205 will in the following be referred to as the RNC (Radio Network Controller) 205. A new interface, in the following referred to as the X interface, is introduced for traffic transmission between the BSC 120 and the RNC 205 over the connection 210. Traffic transmitted over connection 210 could e.g. be control signalling, and/or user data, relating to end user calls or data sessions.

MS 105 of Fig. 2 can be a mobile station operable in A/Gb-mode, or MS 105 can be a mobile station operable in Iu mode. When the MS 105 is operable in A/Gb-mode, then the traffic to/from the MS 105 is intended for the A or Gb interface, while the traffic to/from the MS 105 is intended for the Iu interface when the MS 105 is operating in the Iu mode. Traffic intended for A/Gb-interface communication can be transmitted to/from the BSC 120 from/to the core network 130 over the connections 145 or 150, while traffic intended for Iu interface communication, can be transmitted to/from the BSC 120 from/to the RNC 205 over the connection 210, using the new X interface. The RNC 205, which supports ATM communication, can in turn transmit/receive the traffic to/from the MSC 135 or the SGSN 140 over connections 215 or 220, using the lu-cs or the lu-ps, respectively. In the BSC 120, logic can be introduced for distinguishing between MS originated traffic intended for the Iu interface, which should be transmitted on connection 210 using the X interface, and MS originated traffic intended for the A/Gb interface, which should be transmitted on connections 145 or 150 using the A interface or the Gb interface, respectively.

The solution, presented in Fig. 2, to the problem of how to introduce ATM support in the GERAN base station subsystem 200, has many advantages. A first advantage is that no support for the ATM protocol has to be introduced in the base station controller 120, since the ATM protocol of the Iu interface can be terminated at the RNC 205. Another major advantage is that equipment already developed can be re-used in a new environment, keeping development costs and development times low. Yet another great advantage is that the migration of subscribers from a GSM network to a UMTS network, owned by the same operator, will be facilitated.

There are several different ways to implement the invention presented in Fig. 2, where a connection between the BSC 120 and an RNC 205 is used to facilitate an Iu based traffic transmission between the GERAN base station subsystem 200 and the core network 130. In one embodiment, the RNC 205 is co-located with the BSC 120. The connection 210 will then be a short and fast connection. The new interface X could e.g. use ethernet as the layer 1 and 2 interface protocol. An example of a protocol stack which could be used on the interface X is shown in Fig. 3a. A signalling protocol internal to the operating system OSE delta is used on top of ethernet to support the relay transfer function. This signalling protocol is referred to as the OSE Delta signalling process. Any application in the BSC 120 or the RNC 205 could avail of the relay transfer function to communicate with a peer application the RNC 205 or the BSC 120, respectively. Other protocols could alternatively be used on top of ethernet in this embodiment. In another embodiment of the invention, the BSC 120 and the RNC 205 are not co-located. If the BSC 120 and the RNC 205 are located far apart, it would be preferable to use another protocol stack than the protocol stack shown in Fig. 3a, since ethernet is not efficient on large distances. The protocol stack used for communication on the X interface could then e.g. be the protocol stack shown in Fig. 3b. The El protocol, defined in ITU-T specifications G.703 and G.704, is used as the physical layer in the exemplary protocol stack shown in Fig. 3b, with a Point to Point Protocol (PPP) supporting the layer 2 transport. Internet Protocol (IP) communication could then be used on top of the PPP protocol, and a User Diagram Protocol (UDP) could be used on top of the IP protocol in order to support the relay transfer function. Some or all of the protocols in the protocol stack in Fig. 3b could be exchanged for other protocols. The frame relay protocol could e.g. be used instead of the PPP protocol. The protocol stack shown in Fig. 3b could be used regardless of the size of the distance between the BSC 120 and the RNC 205.

In Fig. 2, the RNC 205 is shown to support a base transceiver station 225, the base transceiver station 225 being a Node B designed for communication in a UMTS network. A UMTS base station subsystem 240 of the UMTS network comprises the RNC 205 and the base transceiver station 225. A MS 230 is shown to communicate in the UMTS network over a radio link 235, based on the UMTS air interface. Hence, the RNC 205 is logically a part of the GERAN base station subsystem 200, as well as a node in a UMTS base station subsystem 240. In another embodiment of the invention, there are no base transceiver stations 225 connected to the RNC 205.

In the embodiment of the invention presented in Fig. 2, where the RNC 205 is part of a UMTS base station subsystem 240, the connection 210 could further be used for signalling between the GERAN base station subsystem 200 and the UMTS base station subsystem 240. An information exchange application in the BSC 120 and the RNC 205 could then use the relay transfer function of interface X, of which examples are given in Fig. 3. In one embodiment of the invention, the RNSAP (Radio Network Application Part) protocol, defined in 3^rd Generation Partnership Project TS 25.423, could be used to support the information exchange. The introduction of the possibility of information exchange between a GERAN base station subsystem 200 and a UMTS base station subsystem 240, located in the same geographic area, will introduce many opportunities for improving the management of traffic in the area. An example of information which could be transmitted over the connection 210 is information regarding the respective loads in the GERAN base station subsystem 200 and the UMTS base station subsystem 240. This information could then e.g. be used by the RNC 205 and the BSC 120 in making hand-over decisions for MSs 105/230 capable of transmitting over both the GSM radio link 115 and the UMTS radio link 235. In order to make the information exchange between the BSC 120 and the RNC 205 efficient, it would be advantageous to locate the RNC 205 in the vicinity of the BSC 120. Real time information exchange between the BSC 120 and the RNC 205 would then be much cheaper than if the two nodes were situated far apart.

One skilled in the art will appreciate that the present invention is not limited to the embodiments disclosed in the accompanying drawings and the foregoing detailed description, which are presented for purposes of illustration only, but it can be implemented in a number of different ways, and it is defined by the following claims.

Claims

1. A mobile radio system comprising at least a first mobile radio network, the first mobile radio network having a core network and a base station subsystem comprising a base transceiver station and a base station controller, the base station controller being connected to the core network, the mobile radio system characterised by the base station subsystem further comprising a further node, the further node being connected to the core network, the further node being capable of passing traffic to/from the core network over a first interface; and the base station controller and the further node being connected to each other via a connection, over which connection traffic can be passed by use of a second interface.

2. The mobile radio system according to claim 1, further characterised in that on the base station subsystem side of the first interface, at least one protocol of the first interface used for communication between the further node and the core network is terminated at the further node.

3. The mobile radio system according to any of the above claims, wherein the further node is a second base station controller, designed for operation according to a standard of mobile radio telephony different to the standard according to which said first mobile radio network is operating.

4. The mobile radio system according any of the above claims, wherein the first mobile radio network is operating according to the GSM standard; and the base station controller is a GSM base station controller.

5. The mobile radio system according to any of the above claims, wherein the further node is a radio network controller designed for operation in a UMTS mobile radio network; and the first interface is the Iu interface.

6. The mobile radio system according to claim 4 and 5, wherein the ATM protocol of the Iu interface is terminated at the radio network controller on the base station subsystem side of the Iu interface.

7. The mobile radio system of any of the above claims, wherein said second interface is based on the ethernet protocol.

8. The mobile radio system of claim 7, wherein the OSE delta signalling process is used on top of the ethernet protocol.

9. The mobile radio system of any of claims 1-6, wherein said second interface is based on the El protocol, on top of which the PPP protocol and the IP protocol is used.

10. The mobile radio system of any of the above claims, wherein said further node is part of a second base station subsystem of a second mobile radio network, the further node being connected to at least one radio transceiver station.

11. The mobile radio system of claim 10, wherein said connection is further used for information exchange between the base station subsystem of the first mobile radio network and the second base station subsystem.

12. The mobile radio system of claim 11, wherein said information exchange uses said second interface.

13. The mobile radio system according to any of the above claims, wherein the base station controller of the first network and the further node are physically co- located.

14. A base station subsystem operable in a GSM mobile radio network, the base station subsystem comprising at least one radio transceiver station; a base station controller connected to a core network, the base station controller being capable of passing traffic to/from the core network over the A and Gb interfaces; a radio network controller, connected to said core network, the radio network controller being capable of passing traffic to/from the core network via the Iu interface; a connection between the base station controller and the radio network controller over which traffic, intended for Iu interface communication between a mobile station and the core network, can be passed.

15. The base station subsystem according to claim 14, wherein the radio network controller comprises means for providing termination of the ATM protocol of the Iu interface at the base station subsystem.

16. The base station subsystem according to claim 14 or 15, wherein the radio network controller and the base station controller are physically co- located; and an interface based on ethernet connection is used for traffic transmission on said connection between the base station controller and the radio network controller.

17. The base station subsystem according to any of claims 14-16, wherein the radio network controller further is part of a UMTS base station subsystem; and information can be passed over the connection between the GSM base station subsystem and the UMTS base station subsystem.

18. A method of providing support for Iu interface communication to/from a MS in a GSM mobile radio network, the GSM mobile radio network comprising at least one base station subsystem and a core network, the base station subsystem comprising at least one radio transceiver station and a base station controller, the base station controller being connected to the core network and being capable of traffic transmission to/from the core network over the A and Gb interfaces, the GSM base station subsystem enabling mobile stations to communicate in a certain area, the method characterised by the following steps: connecting a radio network controller, connected to said core network, to the base station controller, the radio network controller being capable of traffic transmission to/from the core network over the Iu interface; enabling traffic transmission between the radio network controller and the base station controller over an interface; and transmitting traffic to/from a mobile station, communicating with the core network via one of said at least one base transceiver stations, over the connection between the base station controller and the radio network controller when said traffic to/from a mobile station is intended for Iu communication.

19. The method of claim 18, wherein the ATM protocol of the Iu interface is terminated at the radio network controller of the base station side of the connection.

20. The method according to claim 18 or 19, wherein the base station controller and the radio network controller are physically co- located; and said interface is based on ethernet transmission.

21. The method according to claim 18-20, wherein the radio network controller is further part of a UMTS base station subsystem, the radio network controller being comiected to at least one UMTS base transceiver station; and transmission of information is enabled between the UMTS base station subsystem and the GSM base station subsystem via the connection between the GSM base station controller and the radio network controller.