WO2002034000A2

WO2002034000A2 - Arrangement and method for the identification of msc/sgsn in non-hierarchical organised mobile network

Info

Publication number: WO2002034000A2
Application number: PCT/EP2001/011986
Authority: WO
Inventors: Tore Martin Hagen
Original assignee: Telefonaktiebolaget L M Ericsson (Publ)
Priority date: 2000-10-16
Filing date: 2001-10-16
Publication date: 2002-04-25
Also published as: NO313028B1; WO2002034000A3; NO20005206L; AU2002221690A1; NO20005206D0

Abstract

The present invention relates to an arrangement in a non-hierarchical organised mobile network. In such networks, a Mobile Station is assigned an MSC/SGSN taken from a pool of available MSC/SGSNs. In other words, the relationship between LA/RA and MSC/SGSN, characteristic for a hierarchical organised network, is broken. When a new MSC/SGSN is assigned, information as to which MSC/SGSN that previously served the Mobile Station has to be supplied. For this end, each MSC/SGSN is arranged to issue TMSI/P-TMSIs from the full range of possible TMSI/P-TMSIs, and to assign dedicated sub-ranges for use in the individual LA/RAs.

Description

ARRANGEMENT AND METHOD FOR THE IDENTIFICATION OF MSC/SGSN IN NON-HIERARCHICAL ORGANISED MOBILE NETWORK

Technical Field

This invention is applicable in mobile phone networks.

Background

Today the nodes in a mobile system are ordered in a hierarchic way. The Location and Routing areas are controlled by one RNC and each RNC is controlled by one MSC and one SGSN, see figure 2.

The MSC node is used for speech and circuit switched data traffic, and the SGSN node is used for packet switched data traffic .

The mobile user in such a system is identified by a temporary identity, which is assigned to the user by the MSC and the SGSN. These two temporary identities are handled separately. The MSC handles the TMSI parameter and the SGSN the P-TMSI parameter. The TMSI/P-TMSI is only valid in the domain of an MSC/SGSN.

When the mobile user moves from one Routing area that is controlled by an SGSN to another Routing area that is controlled by another SGSN, the user will do a "Routing area update procedure", see figure 4. In this procedure, the mobile user will inform the new SGSN about his old Routing area and his old P-TMSI. The new SGSN will then recognise that this Routing area is covered by another SGSN. The new SGSN will then contact the old SGSN with a message containing the old RAI and old P-TMSI, to get information about the mobile user.

The key for this system to work is that each Routing area is only covered by one SGSN. For users who are attached to the circuit switched domain, the procedure is exactly the same except that the terms "Lo^¬ cation area," "MSC" and "TMSI" are used instead of "Routing area," "SGSN" and ^* P-TMSI."

s When a user turns off his phone he will be detached from the network. When the user turns on the phone again an Attach procedure will be initiated (figure 5) . This procedure is similar to the "Location/Routing Area update" in the way that the mobile user informs the MSG/SGNS that he wants to attach o and gives his old TMSI/P-TMSI and Location/Routing Area, whereupon the new MSC/SGSN will contact the old MSC/SGSN to get user information.

In the future, there will be mobile networks that are not ordered in a hierarchic way. For these networks, all the MSCs s and SGSNs are placed in pools and all the MSCs/SGSNs will be able to serve all the RNCs. Since the MSCs/SGSNs can serve all the RNCs they can also serve all the Location/Routing areas, see figure 2. A network ordered in this non-hierarchic way is also called a "Pooled MSC/SGSN network."

0 When a mobile user has moved into or attaches to a Location/ Routing area, the RNC will chose one of the MSCs/SGSNs to handle this mobile user. The algorithm the RNC uses for this selection is out of the scope of this invention.

Problem

s When a mobile user moves to a new Location/Routing area he will start the "Location/Routing area update procedure" (figure 4) . If the network is built up in a non-hierarchic way the RNC will pick one of the MSCs/SGSNs. This new MSC/SGSN will then receive information about the user's old TMSI/P- 0 TMSI and the old Location/Routing area. The problem for this new MSC/SGSN is that it cannot determine which MSC/SGSN that was serving this mobile user previously. It is not even possible for the new MSC/SGSN to detect if the mobile user was attached to the same MSC/SGSN previously. The same problem also arises when a user attaches to a network.

Known solutions

Known solution number one is to introduce a new parameter m the system, called Core Network Element Identity, which identifies the MSCs and SGSNs. If the mobile user includes this new identity in the messages sent from the mobile, the MSC/SGSN is able to find out which MSC/SGSN was serving this mobile user previously.

However, this introduces a new parameter into the messages passed between the MSC/SGSN and the mobile user. The user equipment therefore has to be updated. Since many cellular phones will be out on the market before this new parameter is introduced, this solution is not feasible.

Known solution number two to the problem is making the

TMSI/P-TMSI unique inside a PLMN and that each MSC/SGSN only has a given range of the total TMSl/P-TMSI. If the mobile user initiates a "Location/Routing area update procedure", the new MSC/SGSN will see that the TMSl/P-TMSI belongs to an- other MSC/SGSN and can then contact the old MSC/SGSN to get the information about the mobile user.

The disadvantage with solution number two is that it limits the number of mobile users that can connect to a PLMN since the TMSI/P-TMSI must be unique inside a whole PLMN and is only 32 bit long. The limitation should not be a problem today, but with an increasing number of machine-to-machine communication this could be a problem in the future. In addition, the operator might use one or more bits in the TMSl/P- TMSI to indicate if there has been a restart in the MSC/SGSN. Brief summary of the invention

The problems outlined above are solved in an arrangement according to the present invention.

In this arrangement, each MSC/SGSN is allowed to use the full range of TMSI/P-TMSI, and allocate specific sub-sets of said TMSI/P-TMSI for use in each LA/RA. This allocation is specific for each MSC/SGSN. This means that the MSC/SGSNs will divide the available TMSl/P-TMSIs in an LA/RA between them^¬ selves. In another LA/RA, the TMSI/P-TMSIs will be divided according to another relationship. This way, an MSC/SGSN receiving the TMSI/P-TMSI and LAl/RAI from an MS during, e.g., an attach procedure, can decide the identity of the old MSC/SGSN by comparing the two identifiers. At the same time, the full ranges of TMSl/P-TMSIs are available for use, dis- tributed among the MSC/SGSNs.

For an exact definition of the scope of the invention, reference is made to the appended patent claims.

Brief description of the drawings.

Fig. 1 is a table showing how P-TMSIs are distributed in four different RAs served by three SGSNs. The P-TMSIs are distrib^¬ uted according to the inventive method.

Fig. 2 is a schematic view over a current mobile network in which the LA/PAs are organised in a hierarchic relationship to the MSC/SGSNs.

Fig. 3 is a schematic view of the solutions that are now emerging, in which the MSC/SGSNs are organised in a pool jointly serving all LA/RAs .

Fig. 4 is a diagram showing the individual steps performed during an RA update. Fig. 5 is a diagram showing the steps of an attach procedure.

Detailed description of the invention.

Reference is made to Fig. 2 showing the hierarchical organisation of present mobile phone networks. Each LA/RA is as- signed a particular MSC/SGSN. There is thus no doubt as to which MSC/SGSN a particular LA/RA belongs.

If a mobile user in a mobile network detects that he has moved to another Routing Area (Fig. 4), he will inform the SGSN serving the new RA, by issuing a message, 1. The old RAI and P-TMSI will be included in this message. Information about the new RAI is included by the new RNC.

When the new SGSN receives the message, it detects from the RAI that this mobile user was previously attached to another SGSN. The old SGSN is therefore contacted, 2, to get informa- tion about this user. The old P-TMSI and old RAI are included in the message towards the old SGSN. The procedures for updates towards the other nodes in the network have been omitted in the figure.

In step 4, the mobile user is informed that it has been at- tached to another RA and is given a new P-TMSI, which is valid for this SGSN.

Fig. 5 shows the attach procedure for a mobile user. This procedure is in many ways similar to the RA update procedure described above.

When the mobile user turns on his phone, a message is issued to inform the SGSN that he wants to attach, step 1.

In this particular case, when the SGSN receives the message, it detects from the RAI that this mobile user was previously attached to another SGSN. The old SGSN is therefore contacted to get information about this user, step 2. The old P-TMSI and old RAI are included in the message towards the old SGSN.

In step 4, the mobile user is informed that it has been attached to another RA and is given a new P-TMSI, which is valid for this SGSN.

If these procedures are performed in a hierarchical organised network, it will be very easy for the new SGSN to find the identity of the old SGSN, as this information can be decided directly from the P-TMSI.

Fig. 3 shows a modern mobile network in which the SGSNs are organised in a pool. This means that if a mobile station, e.g., enters a new Routing Area, the RNC will pick a SGSN from the pool and designate this to serve the mobile station. When an SGSN is given a new mobile station, it has to find out which SGSN that previously served the mobile station, to fetch information regarding the mobile station. The problem is that the new SGSN cannot deduct this from the P-TMSI.

According the present invention, the solution to the problem is to let each MSC/SGSN use the full range of the TMSl/P- TMSI, and then only use part of the TMSI/P-TMSI in each Location/Routing area. The way that each MSC/SGSN distributes the TMSI/P-TMSI area between each Location/Routing area must be co-ordinated so that no TMSI/P-TMSIs overlap within a Location/Routing area.

Fig. 1 shows an example of where the P-TMSI is in the range 0-OxFFFFFFFF and the different RAIs are called a, b, c and d.

In this example, each SGSN assigns the same number of P-TMSIs to each routing area, but this is not necessary. The important thing is that no P-TMSIs overlap within a routing area or within a SGSN. One problem with this solution arises when the RAI-SGSN ma^¬ trix has to change, for instance after a new SGSN is intro^¬ duced. If a mobile user is given a P-TMSI before a change of the RAI-SGSN matrix change, and then try's to attach again using the old P-TMSI it must be possible for the network to detect that this was an old P-TMSI. A way of doing this is to assign one or more of the bits as revision bits. These revi^¬ sion bits must be updated each time the RAI-SGSN matrix changes. A way of doing this could be to let the last two bits in the TMSl/P-TMSI be the revision bits. The first time the operator makes the RAI-SGSN matrix he will set the two revision bits to ^x00' . After a change in the RAI-SGSN matrix the two revision bits are set to XI ' . If a mobile user tries to attach after the change of the RAI-SGSN matrix, the SGSN will detect that it shall use the old matrix to decide which SGSN was handling this user previously.

This problem is of course also valid for the MSC and Location area domain.

Advantages

Advantages with the new solution compared to the known solution number one is that it is possible to keep the temporary mobile identities and Location/Routing area identities we have today if we change the network to a non-hierarchic network. It also has the benefit that it is not necessary to change the cellular phones .

The advantages with this solution compared to known solution number two is that the number of subscribers that can attach to a PLMN is not limited in the range of the TMSI/P-TMSI parameter . Concepts and abbreviations

Abbreviations

GPRS General Packed Radio Service

LA Location Area

LAI Location Area Identifier

MSC Mobile Services Switching Centre

P-TMSI Packet Temporary Mobile Subscriber Identity

RA Routing Area

RAI Routing Area Identifier

RNC Radio Network Controller

SGSN Serving GPRS Support Node

TMSI Temporary Mobile Subscriber Identity

Concepts

LA A geographical area that is covered by one RNC. Location Area is used for circuit switched services.

LAI Each Location area is identified by a Location Area Identification. This identity consists of 6 decimal digits and a 16 bit binary value. An LAI is unique worldwide.

MSC Node in the mobile network that handles the mobility management and call handling for circuit switched services (speech and circuit switched data)

PLMN This is the mobile network handled by one operator. P-TMSI Same as TMSI, except that it is assigned by the SGSN and that it is unique within the Routing Areas covered by the SGSN.

RA A Routing Area is the same as a Location Area, except that it is used for packet-switched data services. An RA and an LA may cover the same geographical area.

RAI A Routing Area Identification is the same as an LAI, except that it has an 8 bit binary value in addition to the values in the LAI. An RAI is unique worldwide.

RNC Node in the mobile network that handles the radio- traffic and radio-resources towards the mobile user.

SGSN Node in the mobile network that handles the mobility- and session-management for packet switched data services.

TMSI This is a temporary 32 bits identity used to identify the mobile user. The TMSI is assigned to the mobile user by the MSC. Each TMSI is unique within the Location Areas covered by the MSC.

Claims

P A T E N T C L A I M S

1. Arrangement in a mobile phone network, said network including a pool of Mobile Switching Centres/Serving GPRS Support Nodes serving a Mobile Station, said MS being s located in a Location Area/Routing Area, which LA/RA is identified by a Location Area Identifier/Routing Area Identifier and which MS is identified by a Packet Tempo^¬ rary Mobile Subscriber Identity/Temporary Mobile Sub^¬ scriber Identity, said MSC/SGSNs being controlled by a o number of Radio Network Controllers that are adapted to assign an MSC/SGSN to serve the MS by selecting an available MSC/SGSN from said pool of MSC/SGSNs, c h a r a c t e r i z e d i n that for a certain RAI, each MSC/SGSN is given a unique sub-range of the s TMSI/P-TMSI from which MSs within that LAI/RAI may be assigned TMSI/P-TMSIs .

2. Arrangement as claimed in claim 1, c h a r a c t e r i z e d i n that each MSC/SGSN is allowed to use the full range of TMSI/P-TMSIs .

0 3. Method in a mobile network, in which a mobile station is assigned an MSC/SGSN from a pool of available MSC/SGSNs, c h a r a c t e r i z e d i n that each MSC/SGSN is arranged to issue TMSI/P-TMSI from the full range of available TMSl/P-TMSIs, and assign dedicated sub-ranges 5 for use in the individual LA/RAs .

4. Method as claimed in claim 3, in which the mobile station performs an LA/RA update or attachment procedure and issues a message containing the old LAI/RAI and old TMSI/P-TMSI, o c h a r a c t e r i z e d i n that the new MSC/SGSN determines the identity of the old MSC/SGSN from a comparison of said LAI/RAI and TMSI/P-TMSI.