WO2014076014A1

WO2014076014A1 - Methods and nodes in a gsm network

Info

Publication number: WO2014076014A1
Application number: PCT/EP2013/073422
Authority: WO
Inventors: Paul Schliwa-Bertling; Ravitej BALLAKUR; John Walter Diachina
Original assignee: Telefonaktiebolaget LM Ericsson AB
Current assignee: Telefonaktiebolaget LM Ericsson AB
Priority date: 2012-11-13
Filing date: 2013-11-08
Publication date: 2014-05-22
Anticipated expiration: 2015-05-13

Abstract

The present disclosure relates to a method performed by a mobile station (MS) ₂ supporting network sharing in a GSM mobile telecommunications network 1also supporting network sharing. The method comprises sending a GPRS Transparent Transport Protocol (GTTP)message I to a base station controller (BSC) ₃ in the telecommunications network. The GTTP message comprises an indication of a selected Public Land Mobile Network (PLMN). The present disclosure also relates to a mobile station, as well as a network node e.g. a BSC.

Description

METHODS AND NODES IN A GSM NETWORK

TECHNICAL FIELD

The present disclosure relates to a methods performed by a mobile station (MS) and a network node e.g. a Base Station Controller (BSC) supporting network sharing in a GSM mobile telecommunications network, as well as to such an MS and network node.

BACKGROUND

Network sharing is an optional feature in the Third Generation Partnership Project (3GPP) that allows different core network operators to share the same shared radio access network (see 3GPP Technical Specification (TS) 23.251). When network sharing is in use within a given network cell, the network broadcasts, as part of system information, the PLMN identities of the Public Land Mobile Networks (PLMN:s) sharing the cell. A mobile station (MS) supporting network sharing uses this information for its PLMN (re)selection processes and indicates the selected PLMN to the Base Station Subsystem (BSS) thereby allowing it to be served by the core network corresponding to the selected PLMN. The MS needs to send the PLMN information (i.e. its preferred PLMN) each time it registers using a foreign Temporary Logical Link Identity (TLLI) or a random TLLI. It has been previously proposed to indicate the preferred PLMN of an MS using the PLMN Index as part of the Radio Link Control (RLC) header in the first block transferring the Packet Services (PS) domain Non Access Stratum (NAS) signalling message having a foreign or Random TLLI. The PLMN Index which is a 3 bit field (to cater for up to 5 different operators) is required at the Base Station Controller (BSC) for the network sharing to be completely specified.

SUMMARY

The approach mentioned in the background section caters to the NAS signalling Packet Data Units (PDU:s), sent in the PS Domain (via an uplink Temporary Block Flow, TBF). However, according to legacy operation, it is quite possible for the MS (or user terminal) to transmit the NAS signalling message using GTTP (GPRS Transparent Transport Protocol) over the Fast Associated Control Channel (FACCH) of an existing Circuit Switched (CS) domain radio resource. This is possible if the MS and the network supports Dual Transfer Mode (DTM), wherein a MS can operate using both PS and CS domain radio resources at the same time, and the NAS signalling message size is below the maximum set by the network.

In this legacy DTM scenario, it will not be possible for the MS to transmit the PLMN Index to the BSC when the GTTP based option is used for NAS signalling . Currently the GTTP Information message includes the TLLI of the mobile station and the Logical Link Control (LLC) PDU along with the header information, as shown in Table l (below). As such, if this legacy GTTP based option for sending a NAS signalling message is used after an MS has just completed CS handover to a GSM (Global System for Mobile

Communications or "2G") cell where network sharing is supported, the BSS might not be able to distinguish the MS's preferred PLMN for the PS domain and may therefore potentially associate a less than optimum PLMN for the PS domain after the MS performs NAS signalling and then continues to remain in the same RA (Routing Area). According to an aspect of the present disclosure, there is provided a method performed by a mobile station (MS) supporting network sharing in a Global System for Mobile Communications (GSM) mobile telecommunications network. The method comprises sending a General Packet Radio Service (GPRS) Transparent Transport Protocol (GTTP) message to a base station controller (BSC) in the telecommunications network. The GTTP message comprises an indication of a selected Public Land Mobile Network (PLMN).

According to another aspect of the present disclosure, there is provided a computer program product comprising computer-executable components for causing an MS to perform an embodiment of a method of the present disclosure when the computer-executable components are run on processor circuitry comprised in the MS. According to another aspect of the present disclosure, there is provided an MS supporting network sharing in a GSM mobile telecommunications network. The MS comprises processor circuitry, and a storage unit storing instructions that, when executed by the processor circuitry, cause the MS to send a GTTP message to a BSC in the telecommunications network. The GTTP message comprises an indication of a selected PLMN.

According to another aspect of the present disclosure, there is provided a computer program comprising computer program code which is able to, when run on processor circuitry of an MS supporting network sharing in a GSM mobile telecommunications network, cause the MS to send a GTTP message to a BSC in the telecommunications network. The GTTP message comprises an indication of a selected PLMN.

According to another aspect of the present disclosure, there is provided a method performed in a first network node supporting network sharing in a GSM mobile telecommunications network. The method comprises receiving a GTTP message from an MS in the telecommunications network. The GTTP message comprises an indication of a selected PLMN.

According to another aspect of the present disclosure, there is provided a computer program product comprising computer-executable components for causing a first network node to perform an embodiment of a method of the present disclosure when the computer-executable components are run on processor circuitry comprised in said first network node.

According to another aspect of the present disclosure, there is provided a first network node supporting network sharing in a GSM mobile

telecommunications network. The first network node comprises processor circuitry, and a storage unit storing instructions that, when executed by the processor circuitry, cause the first network node to receive a GTTP message from an MS in the telecommunications network. The GTTP message comprises an indication of a selected PLMN. According to another aspect of the present disclosure, there is provided a computer program comprising computer program code which is able to, when run on processor circuitry of a first network node supporting network sharing in a GSM mobile telecommunications network, cause said first network node to receive a GTTP message from an MS in the

telecommunications network. The GTTP message comprises an indication of a selected PLMN.

According to another aspect of the present disclosure, there is provided a computer program product comprising an embodiment of a computer program of the present disclosure and a computer readable means on which the computer program is stored.

It is an advantage to use a GTTP message for allowing an MS to inform a BSS (typically a BSC of the BSS) in a GSM network of a PLMN it has selected, when the BSS supports network sharing and provides a plurality of different PLMNs in a shared network cell. Specifically, by using a GTTP message, a MS is allowed to inform the BSS of a selected PLMN in CS domain, e.g. following a CS handover to a GSM Enhanced Data rates for GSM Evolution (EDGE) Radio Access Network (GERAN) cell wherein the MS determines that there is a need to perform NAS signalling in the new serving cell while its call remains active in the CS domain.

In some embodiments, the MS supports Dual Transfer Mode (DTM).

In some embodiments, the indication of the selected PLMN comprises a four bit PLMN index. In some embodiments, the four bit PLMN Index (40) is encoded as o o o 1 to indicate PLMN identity of the Common PLMN broadcast in SYSTEM INFORMATION TYPE 3/4, as o o 1 o to indicate PLMN identity of the first Additional PLMN in the network sharing information broadcast in SYSTEM INFORMATION TYPE 22, as o o 1 1 to indicate PLMN identity of the second Additional PLMN in the network sharing information broadcast in SYSTEM INFORMATION TYPE 22, as o 1 o o to indicate PLMN identity of the third Additional PLMN in the network sharing information broadcast in SYSTEM INFORMATION TYPE 22, or as o l o l to indicate PLMN identity of the fourth Additional PLMN in the network sharing information broadcast in SYSTEM INFORMATION TYPE 22. In some embodiments, the indication of the selected PLMN is comprised in a Skip Indicator information element in the GTTP message. In some

embodiments, the Skip Indicator IE comprises a non-zero value.

In some embodiments, a GTTP Protocol Discriminator (PD) IE in the GTTP message is used to indicate that the indication of a selected PLMN is comprised in said GTTP message. In some embodiments, a four bit value of 1 1 1 o in the PD IE indicates that said PD IE is extended to include the indication of a selected PLMN. In some embodiments, the extended PD IE is extended to one octet length and comprises a four bit PLMN Index indicating the selected PLMN. In some embodiments, an Information Element Identifier associated with the indication of a selected PLMN is added at the end of a Logical Link Control Packet Data Unit IE in the GTTP message.

Embodiments of the present disclosure are implemented in network nodes and user terminals (MS) in a mobile telecommunication system. The implementation is suitably made by adapting existing hardware and software to carry out the operations described in the various approaches and embodiments set forth herein.

The implementation in the Mobile station and BSC may be simple and the potential for interoperability issues resulting from any wrong mobile station behaviour may be reduced or eliminated.

Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the element, apparatus, component, means, step, etc." are to be interpreted openly as referring to at least one instance of the element, apparatus, component, means, step, etc., unless explicitly stated otherwise. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless explicitly stated. The use of "first", "second" etc. for different features/components of the present disclosure are only intended to distinguish the features/components from other similar features/components and not to impart any order or hierarchy to the features/components.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments will be described, by way of example, with reference to the accompanying drawings, in which:

Fig l is a schematic illustration of an embodiment of a telecommunications network in accordance with the present disclosure.

Fig 2 is a schematic block diagram of an embodiment of a mobile station (MS) of the present disclosure. Fig 3 is a schematic block diagram of an embodiment of a base station controller (BSC) of the present disclosure.

Fig 4 is a schematic illustration of an embodiment of a PLMN index in accordance with the present disclosure.

Fig 5 is a schematic illustration of an embodiment of a skip indicator IE of a GTTP message in accordance with the present disclosure.

Fig 6 is a schematic illustration of an embodiment of an extended protocol discriminator (PD) IE of a GTTP message in accordance with the present disclosure.

Fig 7 is a schematic illustration of an embodiment of an LLC PDU IE of a GTTP message associated with a PLMN index, in accordance with the present disclosure. Fig 8 is a schematic flow chart of an embodiment of a method of the present disclosure.

Fig 9 is a schematic flow chart of another embodiment of a method of the present disclosure. Fig 10 is a schematic signalling diagram illustrating an embodiment of a method and a network in accordance with the present disclosure.

Fig 11 is a schematic illustration of an embodiment of a computer program product of the present disclosure.

DETAILED DESCRIPTION

Embodiments will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments are shown.

However, other embodiments in many different forms are possible within the scope of the present disclosure. Rather, the following embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like numbers refer to like elements throughout the description.

The present disclosure relates to control signalling in a mobile

telecommunications network, and more specifically indication of a selected Public Land Mobile Network (PLMN) using the GPRS Transparent Transport Protocol (GTTP) message structure, shown in table 1 below.

PD is Protocol Discriminator, TLLI is Temporary Logical Link Identity and LLC PDU is Logical Link Control Packet Data Unit. M means mandatory IE. V means a value with a fixed length. LV means the information element has a length and the value. N means the size of the total IE which would be anything greater or equal to 2. For example if the length is i,the value of the LLV PDU contained can be at least 2. These are generic terms used in the 3GPP type-length-value (TLV) format.

Figure 1 schematically shows an embodiment of a telecommunication network 1 in accordance with the present disclosure. The network 1 comprises a core network (CN) 6 connected to a radio access network (RAN) for radio communication with a mobile station (MS) 2. The RAN is in accordance with a GSM communication standard and comprises a plurality of base station subsystems (BSS) 5, of which one is shown in figure 1. The BSS 5 comprises a base transceiver station 4, comprising the means for radio communication part of the BSS 5, and a base station controller (BSC) 3 for controlling and using the BTS 4. In accordance with the GSM standards, the MS 2 may be in circuit switched (CS) domain, e.g. for a voice call, and/or in packet switched (PS) domain, e.g. for data communication (internet protocol (IP) data). In the CS domain, the MS 2 can send a GTTP message T over the FACCH of CS domain radio resources.

Figure 2 schematically illustrates an embodiment of an MS 2 of the present disclosure. The MS 2 comprises processor circuitry 21 e.g. a central processing unit (CPU). The processor circuitry 21 may comprise one or a plurality of processing units in the form of microprocessor(s). However, other suitable devices with computing capabilities could be comprised in the processor 21, e.g. an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or a complex programmable logic device (CPLD). The processor 21 is configured to run one or several computer program(s) or software stored in a storage unit 22 e.g. a memory. The storage unit is regarded as a computer readable means and may e.g. be in the form of a Random Access Memory (RAM), a Flash memory or other solid state memory, or a hard disk, or be a combination thereof. The processor circuitry 21 is also configured to store data in the storage unit 22, as needed. The MS 2 also comprises a transmitter 23, a receiver 24 and an antenna 25, which may be combined to form a transceiver or be present as distinct units within the MS 2. The transmitter 23 is configured to cooperate with the processor circuitry to transform data bits to be transmitted over a radio interface to a suitable radio signal to a BSC 3 in accordance with the radio access

technology (RAT) used by the Radio Access Network (RAN) via which the data bits are to be transmitted. The receiver 24 is configured to cooperate with the processor circuitry 21 to transform a received radio signal to data bits. The antenna 25 may comprise a single antenna or a plurality of antennas, e.g. for different frequencies and/or for MIMO (Multiple Input Multiple Output) communication. The antenna 25 is used by the transmitter 23 and the receiver 24 for transmitting and receiving, respectively, radio signals. The MS 2 is configured to perform an embodiment of a method of the present disclosure and comprises means for performing said method. Figure 3 schematically illustrates an embodiment of a BSC 3 of the present disclosure. The BSC 3 comprises processor circuitry 31 e.g. a central processing unit (CPU). The processor circuitry 31 may comprise one or a plurality of processing units in the form of microprocessor(s). However, other suitable devices with computing capabilities could be comprised in the processor 31, e.g. an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or a complex programmable logic device (CPLD). The processor 31 is configured to run one or several computer program(s) or software stored in a storage unit 32 e.g. a memory. The storage unit is regarded as a computer readable means and may e.g. be in the form of a Random Access Memory (RAM), a Flash memory or other solid state memory, or a hard disk, or be a combination thereof. The processor circuitry 31 is also configured to store data in the storage unit 32, as needed. The BSC 3 also comprises a transmitter 33, a receiver 34 and a communication interface 35, which may be combined to form a transceiver or be present as distinct units within the BSC 3. The transmitter 33 is configured to cooperate with the processor circuitry to transform data bits to be transmitted via a BTS 4 over a radio interface to a suitable radio signal to an MS 2 in accordance with the radio access technology (RAT) used by the Radio Access Network (RAN) via which the data bits are to be transmitted. The receiver 34 is configured to cooperate with the processor circuitry 31 to transform a received radio signal to data bits. The communication interface 35 is, for radio communication, connected via a BTS 4. Additionally, the

communication interface 35 comprises means for wired or wireless (e.g. radio link) communication with the CN 6. The communication interface 35 is used by the transmitter 33 and the receiver 34 for transmitting and receiving, respectively, communication signals. The BSC 3 is configured to perform an embodiment of a method of the present disclosure and comprises means for performing said method.

Figure 4 illustrates an embodiment of a PLMN index 40 (indicating a selected PLMN) according to the present disclosure. The PLMN index is a number of consecutive bits 41-44 in a communication signal. In the example of figure 4, the PLMN index 40 is four bits long (41-44), but any other length is also contemplated, depending on how much information is desired to include in the PLMN index, typically based on the number of PLMNs supported in each cell in the network 1. A length of four bits have been found to be sufficient for most cases, and an example of coding of a four bit PLMN index is given below in Table 2.

Table 2 In accordance with the present disclosure, the PLMN index, or other indication of the selected PLMN, may be included in or otherwise associated with the GTTP message (I) in different parts or information elements (IE) of the GTTP message.

Figure 5 illustrates a situation where a four bit PLMN index 40 is included in the skip indicator IE 50 of the GTTP message. In the legacy case, the four bit skip indicator may always be coded as "o o o o". In accordance with the present disclosure, a non-zero value of the skip index IE may indicate that the skip index IE 50 contains a PLMN index 40. See also Example 1 below.

Figure 6 illustrates a situation where a four bit PLMN index 40 is included in an extended GTTP Protocol Discriminator (PD) IE 61 of the GTTP message. In accordance with 3GPP TS 24.007 (see also Example 2 below), a PD IE 60 can be extended from four bits to a full octet to form an extended PD IE 61. Then, such an extension may indicate that a PLMN index 40 is included in the extended PD IE 61, typically directly following the regular four bit PD IE 60.

Figure 7 illustrates a situation where a four bit PLMN index 40 is included in a new IE in the GTTP message, following the LLC PDU IE 70. A new PLMN information element identifier (IEI) 71 is added to the end of the GTTP message, after the LLC PDU IE 70, extending the GTTP message to include the PLMN index 40 following said PLMN IEI 71. See also Example 3 below.

Figure 8 is a schematic flow chart of an embodiment of a method performed by/in an MS 2. The MS 2 supports network sharing in a GSM

telecommunication network 1. The MS sends 83 a GTTP message (I) to a BSC 3 in the telecommunications network 1. The GTTP message (I) comprises an indication of a selected PLMN. The indication may e.g. be a PLMN index 40 as discussed herein, included in a given part of the GTTP message. Before sending the GTTP message, the MS may include 82 the indication of a selected PLMN, e.g. a PLMN index, in the GTTP message wherein the value of the PLMN index is determined based on information provided to the MS 2 in the received 81 HO command.

A situation where the MS 2 may conveniently send the indication of a selected PLMN is when performing a handover (HO), typically a CS HO. In that case, the MS may receive 81 a HO command from its serving/old BSS 5 (typically from the BSC via the BTS of the serving/old BSS 5). Then, the MS may include 82 a PLMN index 40 in the GTTP message and send 83 the GTTP message to the BSC 3.

Figure 9, similarly, is a schematic flow chart of an embodiment of a method performed by/in a network node in a GSM telecommunication network 1. The network node supports network sharing in said GSM telecommunication network 1. The network node may e.g. be a BSC 3, but other types of nodes in the network 1 are also contemplated. Herein, the network node is called the first network node, in order to distinguish it from any second or further node(s). The first network node receives 93 a GTTP message (I) from an MS 2 in the telecommunications network 1. The GTTP message (I) comprises an indication of a selected PLMN.

As mentioned above in relation to figure 8, a situation where the MS 2 may conveniently send the indication of a selected PLMN is when it determines that NAS signalling is needed shortly after arriving in a new cell as a result of performing a handover (HO), typically a CS HO. In that case, the first network node may receive 91, from a second network node (e.g. a Mobile Switching Center, MSC, with which the first network node is associated) of the telecommunications network (1), a handover request message regarding said MS 2. Then, the first network node may send 92, to said second node, an acknowledgement of the received 91 handover request message wherein it may include the PLMN index 40 associated with the selected PLMN. The first network node may thus be a node (e.g. BSC 3) of a target/new BSS 5 of a HO. The target/new BSS 5 receives 91 the HO request and acknowledges 92 it. Then, after the second network node has sent a Handover Command to the old BSS and HO of the MS 2 has been completed from the old BSS to the target/new BSS, the target/new BSS 5 receives the indication of a selected PLMN from the MS 2 as part of a GTTP message.

Figure 10 is a schematic signalling diagram illustrating some signalling during an embodiment of a CS HO of an MS 2 from a serving/old BSS 5a to a target/new BSS 5b. Only signalling relevant for the understanding of the present disclosure is included in figure 10. The MS 2 sends a measurement report A to its serving BSS 5a. The serving BSS realises that a HO is desired and sends an indication B that a HO is required to its associated MSC 6. The MSC 6 sends 91 a HO request C to a target BSS 5b, which target BSS 5b responds with an acknowledgement D of the HO request and may include the PLMN index 40 associated with the selected PLMN therein. The MSC can then send a HO command to the serving BSS 5a. The HO command may then include the PLMN index 40 for the target BSS 5b in the Handover Request acknowledgement D, thereby allowing the serving BSS to include the PLMN index in the HO command F which it sends to, and is received 81 by, the MS 2. The MS 2 completes the HO by sending a message G to the new BSS 5b, which responds by sending a HO complete message H to the MSC 6. Then, the MS 2 can send the GTTP message I to the new BSS 5b, wherein the GTTP message comprises the indication of the selected PLMN, typically the PLMN index 40 included within e.g. the skip indicator IE 50. Figure 11 illustrates a computer program product 110. The computer program product 110 comprises a computer readable medium 111 comprising a computer program 112 in the form of computer-executable components 112. The computer program/computer-executable components 112 may be configured to cause an MS 2 or BSC 3, e.g. as discussed herein, for facilitating sending information about selected PLMN in a telecommunication network 1, to perform an embodiment of a method of the present disclosure. The computer program/computer-executable components may be run on the processor circuitry 21 or 31 of the MS/BSC for causing it to perform the method. The computer program product 110 may e.g. be comprised in a storage unit or memory 22 or 32 comprised in the MS/BSC 1 and associated with the processor circuitry 21 or 31. Alternatively, the computer program product 110 may be, or be part of, a separate, e.g. mobile, storage means, such as a computer readable disc, e.g. CD or DVD or hard disc/drive, or a solid state storage medium, e.g. a RAM or Flash memory. Example 1

In this example, it is proposed to use a non-zero value for the four bit Skip indicator information element 50 (part of the GTTP message structure shown in table 1) to indicate the PLMN Index 40 corresponding to the PLMN preferred by a mobile/user terminal (MS) 2 which supports network sharing for the case where the network 1 indicates support of Network sharing via System Information type 3. In all other use cases, a Skip Indicator value of Zero is used. As such, the use of Skip indicator as proposed herein ensures that the currently available NAS signalling message transmission options (i.e. associated with the other information elements supported by a GTTP message I) remain available for the case where the mobile station 2 and network 1 both support network sharing. In this example, the four bit Skip indicator 50 is used to indicate the PLMN Index 40 (as described above). This would not involve any change in the existing message structure of the GTTP message I. Using the Skip indicator for PLMN Index, the network 1 might not ignore the GTTP message but might just ignore the skip indicator, in case a mobile station wrongly sends the non-zero PLMN Index when network has not indicated the presence of Network sharing. However, this should never happen since a mobile station 2 is provided with PLMN index information as part of the handover procedure which would indicate the target cell supports network sharing (and is therefore capable of receiving GTTP messages having a non-zero value for Skip indicator information element).

Moreover, the change proposed here is completely adhering to the Layer 3 standard message structure as currently defined in 24.007

Extract of 3GPP TS 24.007: "11.2.3.1.2 Skip indicator

Bits 5 to 8 of octet 1 of a standard L3 message may be used differently, depending on the protocol and the SAP. The use of this half-octet is consistent for a given PD and SAP. One possibility is that this half-octet contains the skip indicator. Unless otherwise specified in the protocol, the skip indicator IE is a spare field."

The only change required would be in section 10.3.1 of 3GPP TS 44.018 Vii.2.0 GSM/EDGE Radio Access Network Radio Resource Control (RRC) Protocol. Extract of proposed change to 3GPP TS 44.018: "10.3.1 Skip indicator Bits 5 to 8 of the first octet of every Radio Resource management message and GPRS Transparent Transport protocol message contain the skip indicator. A message received with skip indicator different from 0000 shall be ignored for all Radio Resource management message and for GPRS Transparent Transport protocol message if the network does not support network sharing. A message received with skip indicator encoded as 0000 shall not be ignored (unless it is ignored for other reasons). When both the mobile station and network support Network sharing, the mobile station can encode the skip indicator as per the table below. In all other cases the protocol entity sending a Radio Resource management message or GPRS Transparent Transport protocol message shall encode the skip indicator as 0000."

Reference is made to table 2 above.

The Skip indicator based solution above reflects one possibility associated with the general challenge of identifying which of the information elements shown in the GTTP message structure is most appropriate for introducing support for including the PLMN Index 40 for the case where the LLC PDU information element 70 has a PS domain NAS message (For example Routing Area Update or GPRS Attach). It is thus preferred to use an embodiment of Example 1 where the PLMN index is indicated by re-using the existing Skip indicator field in the GTTP message.

The full set of options proposed for including PLMN Index information within the context of a GTTP message comprise the following information elements - GTTP Protocol Discriminator (see example 2 below), as well as the Skip Indicator 50. In addition there is also proposed the addition of an altogether new information element for conveying PLMN Index information (see example 3 below). Example 2

Introduction of a new Protocol discriminator, PD, 61 for GTTP messages I having PLMN Index 40.

From 3GPP TS 24.007, Table 11.2:

Table 3: Protocol discriminator values

*For future evolution an extension mechanism is foreseen which allows the use of protocol discriminators with one octet length, where bits 4 to 1 are coded as 1 1 1 o. Messages of such protocols may not be standard Layer 3 messages. In particular, the rest of the header may not respect the GTTP message structure described in table 1.

In this example, the PD value of 1110 is used (thereby indicating a 1 octet PD information element 61 is present) whereby a code point in the next 4 bits l8

(i.e. the last 4 bits of the 1 octet PD) indicates a GTTP message is present in which case a new field for PLMN Index immediately follows this code point (i.e. it immediately follows the 1 octet PD information element 60)

However, this would mean changes both to the standard specification as well as the implementation both in the network 1 and the mobile station 2. There is also a risk of validation errors.

In addition, for scenarios where a network sharing capable Mobile station 2 wrongly sends the PD 60 of 1110 to a network not indicating Network sharing, then the complete GTTP message I would be ignored. This is as per the Section 8 of 3 GPP TS 44.018.

Example 3

In an alternative, a new Information Element Identifier (IEI) 71 is added at the end of the LLC PDU 70 carried within the GTTP message I, see table 1. This will however increase the message size and there would still exist the potential problem of a BSC 3 ignoring the complete message if the mobile station 2 sends the IE for a network not having network sharing in the particular cell. However, this should never happen since a mobile station is provided with PLMN index information as part of the handover procedure which would indicate the target cell supports network sharing. Below follow some other aspects of the present disclosure.

According to an aspect of the present disclosure, there is provided a mobile station (MS) 2 supporting network sharing in a Global System for Mobile Communications (GSM) mobile telecommunications network 1. The MS comprises means 21, 23, 25 for sending 83 a General Packet Radio Service (GPRS) Transparent Transport Protocol (GTTP) message I to a base station controller (BSC) 3 in the telecommunications network 1. The GTTP message I comprises an indication of a selected Public Land Mobile Network (PLMN).

According to another aspect of the present disclosure, there is provided a first network node 3 supporting network sharing in a GSM mobile telecommunications network 1. The first network node 3 comprises means 31, 34, 35 for receiving 93 a GTTP message I from an MS 2 in the

telecommunications network 1. The GTTP message I comprises an indication of a selected PLMN. According to another aspect of the present disclosure, there is provided, in a mobile telecommunications network, a method of signalling an indication of a selected PLMN using the GTTP message structure.

According to another aspect of the present disclosure, there is provided a user terminal 2 configured to signal an indication of a selected PLMN using the GTTP.

According to another aspect of the present disclosure, there is provided a network node 3 configured to receive an indication of a selected PLMN using the GTTP.

In some embodiments, the PLMN index is indicated by re-using the existing Skip indicator field in a GTTP message. In some embodiments, a non-zero value for the 4 bit Skip indicator information element is used to indicate the PLMN Index (corresponding to the PLMN) preferred by a mobile/user terminal which supports network sharing for the case where the network indicates support of Network sharing via System Information type 3. In some embodiments, a Skip Indicator value of Zero is used in all other use cases.

In some embodiments, a PD value of 1110 is used whereby a code point in the next 4 bits indicates a GTTP message is present in which case a new field for PLMN Index immediately follows this code point.

In some embodiments, a new Information IEI containing the PLMN index information is added at the end of the LLC PDU.

Below follows an itemised list of other aspects and embodiments of the present disclosure. Item l. In a mobile telecommunications network, a method of signalling an indication of a selected Public Land Mobile Network, PLMN, using the GPRS Transparent Transport Protocol, GTTP, message structure.

Item 2. A method as in item l, where the PLMN index is indicated by re- using the existing Skip indicator field in a GTTP message.

Item 3. A method as in item 2, where a non-zero value for the 4 bit Skip indicator information element is used to indicate the PLMN Index

(corresponding to the PLMN) preferred by a mobile/user terminal which supports network sharing for the case where the network indicates support of Network sharing via System Information type 3.

Item 4. A method as in item 3, where in all other use cases, a Skip

Indicator value of Zero is used.

Item 5. A method as in item 1, where a PD value of 1110 is used whereby a code point in the next 4 bits indicates a GTTP message is present in which case a new field for PLMN Index immediately follows this code point.

Item 6. A method as in item 1, where a new Information Element

Identifier, IEI, containing the PLMN index information is added at the end of the Logical Link Control Packet Data Unit, LLC PDU.

Item 7. A user terminal configured to signal an indication of a selected Public Land Mobile Network, PLMN, using the GPRS Transparent Transport Protocol, GTTP as set forth in any one of items 1 to 6.

Item 8. A network node configured to receive an indication of a selected Public Land Mobile Network, PLMN, using the GPRS Transparent Transport Protocol, GTTP as set forth in any one of items 1 to 6. The present disclosure has mainly been described above with reference to a few embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the present disclosure, as defined by the appended claims.

Claims

CLAIMS l. A method performed by a mobile station, MS, (2) supporting network sharing in a Global System for Mobile Communications, GSM, mobile telecommunications network (1), the method comprising: sending (83) a General Packet Radio Service, GPRS, Transparent Transport Protocol, GTTP, message (I) to a base station controller, BSC, (3) in the telecommunications network (1); wherein the GTTP message (I) comprises an indication of a selected Public Land Mobile Network, PLMN.

2. The method of claim 1, wherein the MS (2) supports Dual Transfer Mode, DTM.

3. The method of any preceding claim, wherein the indication of the selected PLMN comprises a four bit PLMN index (40).

4. The method of claim 3, wherein the four bit PLMN Index (40) is encoded as o o o 1 to indicate PLMN identity of the Common PLMN broadcast in SYSTEM INFORMATION TYPE 3/4, as o o 1 o to indicate PLMN identity of the first Additional PLMN in the network sharing information broadcast in SYSTEM INFORMATION TYPE 22, as o o 1 1 to indicate PLMN identity of the second Additional PLMN in the network sharing information broadcast in SYSTEM INFORMATION TYPE 22, as o 1 o o to indicate PLMN identity of the third Additional PLMN in the network sharing information broadcast in SYSTEM INFORMATION TYPE 22, or as o 1 o 1 to indicate PLMN identity of the fourth Additional PLMN in the network sharing information broadcast in SYSTEM INFORMATION TYPE 22.

5. The method of any preceding claim, wherein the indication of the selected PLMN is comprised in a Skip Indicator information element, IE, (50) in the GTTP message (I).

6. The method of claim 5, wherein the Skip Indicator IE (50) comprises a non-zero value.

7. The method of any preceding claim, wherein a GTTP Protocol

Discriminator, PD, IE (60) in the GTTP message (I) is used to indicate that the indication of a selected PLMN is comprised in said GTTP message.

8. The method of claim 7, wherein a four bit value of 1 1 1 o in the PD IE (60) indicates that said PD IE is extended to include the indication of a selected PLMN.

9. The method of claim 8, wherein the extended PD IE (61) is extended to one octet length and comprises a four bit PLMN Index (40) indicating the selected PLMN.

10. The method of any preceding claim, wherein an Information Element Identifier, IEI, (71) associated with the indication of a selected PLMN is added at the end of a Logical Link Control, LLC, Packet Data Unit, PDU, IE (70) in the GTTP message (I).

11. The method of any preceding claim, further comprising: receiving (81), from the telecommunications network (1), a handover command message comprising a PLMN Index (40) corresponding to the selected PLMN; and including (82) the received (81) PLMN Index (40) in the GTTP message (I) as the indication of a selected PLMN, prior to the sending (83) of the GTTP message.

12. A computer program product (110) comprising computer-executable components (111) for causing a mobile station, MS, (2) to perform the method of any one of claims 1-11 when the computer-executable components are run on processor circuitry (21) comprised in the MS.

13. A mobile station, MS, (2) supporting network sharing in a Global System for Mobile Communications, GSM, mobile telecommunications network (1), the MS comprising: processor circuitry (21); and a storage unit (22) storing instructions that, when executed by the processor circuitry (11), cause the MS (2) to: send a General Packet Radio Service, GPRS, Transparent Transport Protocol, GTTP, message (I) to a base station controller, BSC, (3) in the

telecommunications network (1); wherein the GTTP message (I) comprises an indication of a selected Public Land Mobile Network, PLMN.

14. The MS of claim 13, wherein the storage unit (22) is further storing instructions that, when executed by the processor circuitry (21), cause the MS (2) to: receive (81), from the telecommunications network (1), a handover command message comprising a PLMN Index (40) corresponding to the selected PLMN; and include (82) the received PLMN Index (40) in the GTTP message (I) as the indication of a selected PLMN, prior to the sending of the GTTP message.

15. A computer program (111) comprising computer program code which is able to, when run on processor circuitry (21) of a mobile station, MS, (2) supporting network sharing in a GSM mobile telecommunications network (1), cause the MS to: send (83) a General Packet Radio Service, GPRS, Transparent Transport Protocol, GTTP, message (I) to a base station controller, BSC, (3) in the telecommunications network (1); wherein the GTTP message (I) comprises an indication of a selected Public Land Mobile Network, PLMN.

16. A computer program product (110) comprising a computer program (111) according to claim 15 and a computer readable means (112) on which the computer program is stored.

17. A method performed in a first network node (3) supporting network sharing in a Global System for Mobile Communications, GSM, mobile telecommunications network (1), the method comprising: receiving (93) a General Packet Radio Service, GPRS, Transparent Transport Protocol, GTTP, message (I) from a mobile station, MS, (2) in the

18. The method of claim 17, further comprising, prior to the receiving (93) of the GTTP message (I) : receiving (91), from a second network node (6) of the telecommunications network (1), a handover request message (C) regarding said MS (2); and sending (92), to the second node (6), an acknowledgement (D) of the received (91) handover request message.

19. A computer program product (110) comprising computer-executable components (111) for causing a first network node (3) to perform the method of any one of claims 17-18 when the computer-executable components are run on processor circuitry (31) comprised in said first network node.

20. A first network node (3) supporting network sharing in a Global System for Mobile Communications, GSM, mobile telecommunications network (1), the node comprising: processor circuitry (31); and a storage unit (32) storing instructions that, when executed by the processor circuitry (31), cause the node (3) to: receive a General Packet Radio Service, GPRS, Transparent Transport Protocol, GTTP, message (I) from a mobile station, MS, (2) in the

21. The network node of claim 20, wherein the network node is a base station controller, BSC, (3) for a GSM cell of the selected PLMN.

22. A computer program (111) comprising computer program code which is able to, when run on processor circuitry (31) of a first network node (3) supporting network sharing in a GSM mobile telecommunications network (1), cause said first network node to: receive (93) a GTTP message (I) from a mobile station, MS, (2) in the telecommunications network (1); wherein the GTTP message (I) comprises an indication of a selected PLMN.

23. A computer program product (110) comprising a computer program (111) according to claim 22 and a computer readable means (112) on which the computer program is stored.