(19) TZZ Z_T

(11) EP 2 704 456 A1

(12) EUROPEAN PATENT APPLICATION

(43) Date of publication: (51) Int Cl.: 05.03.2014 Bulletin 2014/10 H04W 4/00 (2009.01) H04W 76/02 (2009.01)

(21) Application number: 13181635.7

(22) Date of filing: 25.08.2013

(84) Designated Contracting States: (71) Applicant: HTC Corporation AL AT BE BG CH CY CZ DE DK EE ES FI FR GB Taoyuan County 330 (TW) GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR (72) Inventor: Liao, Ching-Yu Designated Extension States: 330 Taoyuan City (TW) BA ME (74) Representative: Konkonen, Tomi-Matti Juhani (30) Priority: 29.08.2012 US 201261694276 P Murgitroyd & Company 22.08.2013 US 201313974005 Scotland House 165-169 Scotland Street Glasgow G5 8PL (GB)

(54) Method of Handling Non-Access Stratum Message and Related Communication Device

(57) Amethod ofhandling non- accessstratum (NAS) level to a network in the wireless communication system, mobility management (MM) messages for a user equip- and storing a priority indicator indicating the first priority ment in a wireless communication system when the user level in a nonvolatile memory if the user equipment re- equipment is configured for dual priority includes sending ceives a NAS MM reject message with a mobility man- a first NAS MM request message containing a first priority agement back-off (MMBK) timer from the network. EP 2 704 456 A1

Printed by Jouve, 75001 PARIS (FR) 1 EP 2 704 456 A1 2

Description the clear of the PPF, the core network cannot page the UE during the period of the implicit detach timer. If the Background of the Invention implicit detach timer expires before the UE contacts the network, the network shall implicitly detach the UE. The 1. Field of the Invention 5 implicit detach timer shall be stopped when a NAS sign- aling connection is established for the UE. [0001] The present invention relates to a method used [0005] NAS level congestion control contains functions in a wireless communication system and related commu- of "APN based congestion control" and "General NAS nication device, and more particularly, to a method of level Mobility Management control". The use of the APN handling non-access stratum (NAS) messages in a wire- 10 based congestion control is for avoiding and handling of less communication system and related communication EMM and ESM signalling congestion associated with device. UEs with a particular APN. With General NAS level Mo- bility Management control, the MME may also use the 2. Description of the Prior Art reject of NAS level Mobility Management signaling re- 15 quests under general congestion conditions. [0002] A long-term evolution (LTE) system supporting [0006] When the NAS level mobility management con- the 3GPP Rel-8 standard and/or the 3GPP Rel- 9 stand- gestion control is applied due to network overload or con- ard is developed by the 3rd Generation Partnership gestion, the MME rejects an attach request, a tracking Project (3GPP) as a successor of a universal mobile tel- area update (TAU), a routing area update (RAU) or a ecommunications system (UMTS), for further enhancing 20 service request from the UE, and the MME replies the performance of the UMTS to satisfy users’ increasing UE with a mobility management back-off timer (MMBK) needs. The LTE system includes a new radio interface in a reject message. Then, the MME/ SGSN enforces the and radio network architecture that provides a high data MMBK timer by immediately rejecting any subsequent rate, low latency, packet optimization, and improved sys- request from the UE targeting at connecting to the APN tem capacity and coverage. In the LTE system, a radio 25 before the MMBK timer is expired. access network known as an evolved universal terrestrial [0007] When the UE is configured for dual priority, the radio access network (E-UTRAN) includes a plurality of UE is configured for NAS signaling low priority and also evolved Node-Bs (eNBs) for communicating with a plu- configured to override the NAS signaling low priority in- rality of user equipments (UEs) and communicates with dicator. For example, the UE is allowed to initiate a NAS a core network including a mobility management entity 30 mobility management (MM) request message without in- (MME), a serving gateway, etc. for NAS (Non Access dicating low access priority while an MMBK timer for an- Stratum) control. In UMTS system, a Serving GPRS Sup- other NAS MM request message with a low priority indi- port Node (SGSN) is responsible for the delivery of data cator is running. However, if the UE is switched off and packets to the mobile devices back and forth within its then switched on before the expiry of an MMBK timer, geographical service area, including packet routing and 35 the UE cannot determine which priority level the MMBK transfer, mobility management (attach/detach and loca- timer is associated to. In such a situation, the perform- tion management), logicallink management, and authen- ance of the UE may be decreased. tication and charging functions. The MME provides the [0008] Similar problems occur when the UE configured control plane function for mobility between LTE and 2G/ for dual priority has received a session management 3G access networks with the S3 interface terminating at 40 back-off (SMBK) timer for a specific APN. the MME from the SGSN. [0009] Thus, how to handle NAS messages and back- [0003] An access point name (APN) is used in the LTE off timers properly when the UE is configured for dual and LTE-advanced (LTE-A) systems for establishing priority is a topic to be addressed and discussed in the packet data connections, and is managed by the MME. industry. Further, the APN is used for identifying a packet data 45 network (PDN) or a service type (e.g. multimedia mes- Summary of the Invention saging service (MMS)), wherein the PDN or the service type is carried on the packet data connections. [0010] It is an object of present invention to provide [0004] The core network manages the mobile reacha- handling non-access stratum messages. bility by using mobile reachable timer, paging proceed 50 This object can be achieves by the features defined in factor (PPF), and implicit detach timer. The core network the independent claims. Further enhancements are char- supervises the periodic tracking/ routing/location area up- acterised by the dependent claims. At least one embod- dating procedure of the UE via the mobile reachable tim- iment of the present invention therefore provides a meth- er. By default, the mobile reachable timer is set slightly od and related communication device for handling non- larger than the periodic TAU/RAU/LAU timer. Upon ex- 55 access stratum (NAS) messages so that the communi- piry of the mobile reachable timer, the network shall clear cation device configured for dual priority can operate the PPF flag and start the implicit detach timer. The value properly when a back-off timer is running. of the implicit detach timer is network dependent. Due to [0011] At least one embodiment of the present inven-

2 3 EP 2 704 456 A1 4 tion discloses a method of handling non-access stratum skill in the art after reading the following detailed descrip- (NAS) mobility management (MM) messages for a user tion of the preferred embodiment that is illustrated in the equipment in a wireless communication system when the various figures and drawings. user equipment is configured for dual priority. The meth- od includes sending a first NAS MM request message 5 Brief Description of the Drawings containing a first priority level to a network in the wireless communication system; and storing a priority indicator [0016] FIG. 1 is a schematic diagram of a wireless com- indicating the first priority level in a non- volatile memory munications system according to an example of the if the user equipment receives a NAS MM reject message present invention. with a mobility management back- off (MMBK) timer from 10 [0017] FIG. 2 is a schematic diagram of a communica- the network. tion device according to an example of the present in- [0012] At least one embodiment of the present inven- vention. tion further discloses a method of handling non-access [0018] FIG. 3 is a flowchart of a process according to stratum (NAS) session management (SM) messages for an example of the present invention. a user equipment in a wireless communication system 15 [0019] FIG. 4 is a flowchart of a process according to when the user equipment is configured for dual priority. an example of the present invention. The method includes sending a first NAS SM request message containing a first priority level for a specific ac- Detailed Description cess point name (APN) to a network in the wireless com- munication system; and storing a priority indicator indi- 20 [0020] Please refer to FIG. 1, which is a schematic di- cating the first priority level for the specific APN in a non- agram of a wireless communication system 10 according volatile memory if the user equipment receives a NAS toan example of the presentinvention. The wireless com- SM reject message with a session management back- munication system 10, such as a General Packet Radio off (SMBK) timer for the specific APN from the network. Service (GPRS) system, a Global System for Mobile [0013] At least one embodiment of the present inven- 25 communications (GSM) system, a Universal Mobile Tel- tion further discloses a communication device for han- ecommunications System (UMTS), a Long Term Evolu- dling non-access stratum (NAS) mobility management tion (LTE) system, a Long Term Evolution-advanced (MM) messages in a wireless communication system, (LTE-A) system, or other mobile communication sys- wherein the communication device is configured for dual tems, is briefly composed of a network and a plurality of priority. The communication device includes a process- 30 user equipments (UEs). In FIG. 1, the network and the ing means and a storage unit. The storage unit is coupled UEs are simply utilized for illustrating the structure of the to the processing means for storing a program code, wireless communication system 10. which instructs the processing means to send a first NAS [0021] For the LTE system or other mobile communi- MM request message containing a first priority level to a cation systems alike, the network can be referred as to network in the wireless communication system, and store 35 an E-UTRAN (evolved-UTRAN) comprising a plurality of a priority indicator indicating the first priority level in non- evolved Node-Bs (eNBs) and relays. The network may volatile memory if the communication device receives a also comprise a mobility management entity (MME), NAS MM reject message with a mobility management which is responsible for the delivery of data packets to back-off (MMBK) timer from the network. the UEs back and forth within its geographical service [0014] At least one embodiment of the present inven- 40 area, including packet routing and transfer, mobility man- tion further discloses a communication device of handling agement (attach/detach and tracking area manage- non-access stratum (NAS) session management (SM) ment), session management (PDN connection establish- messages in a wireless communication system, wherein ment/disconnect), logical link management, and authen- the communication device is configured for dual priority. tication and charging functions. In addition, the MME may The communication device includes a processing means 45 serve as a local mobility anchor for inter-working with and a storage unit. The storage unit is coupled to the other radio access technologies (RATs) (e.g. GSM and processing means for storing a program code, which in- UMTS). structs the processing means to send a first NAS SM [0022] For the UMTS or other mobile communication request message containing a first priority level for a spe- systems alike, the network can be referred as to a cific access point name (APN) to a network in the wireless 50 UTRAN, which comprises a plurality of Node-Bs (NBs). communication system, and store a priority indicator in- Thenetwork may also comprise a ServingGPRS Support dicating the first priority level for the specific APN in non- Node (SGSN), which is responsible for the delivery of volatile memory if the communication device receives a data packets to the UEs back and forth within its geo- NAS SM reject message with a session management graphical service area, including packet routing and back-off (SMBK) timer for the specific APN from the net- 55 transfer, mobility management (attach/detach and track- work. ing area management), session management (PDP Con- [0015] These and other objectives of the present in- text establishment/disconnect), logical link manage- vention will no doubt become obvious to those of ordinary ment, and authentication and charging functions.

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[0023] For the GSM system or other mobile communi- NAS MM request message (e.g., a attach request mes- cation systems alike, the network can be referred as to sage, a tracking area update request message, or an a GSM Edge Radio Access Network (GERAN), which extended service request message) containing the pri- comprises a plurality of base stations (BSs). The network ority level (e.g., low priority level or normal priority level) may also comprise a Mobile Switching Center (MSC), 5 to the network. Under certain conditions (e.g. network which is responsible for the delivery of voice service in a overload or congestion), the network may reply the UE circuit switch manner to the UEs back and forth within its with the MMBK timer, which implies that the UE cannot geographical service area, including mobility manage- resend the NAS MM request message containing the ment (attach/detach and location area management), same priority level before the MMBK timer is expired. In logical link management, and authentication and charg- 10 addition, the UE needs to store the priority indicator in ing functions. the non-volatile memory if the UE receives the MMBK [0024] The UEs can be devices such as mobile timer. In this manner, the UE may check the MMBK timer phones, laptops, tablet computers, electronic books, and and the priority indicator retaining in the non-volatile to portable computer systems. Besides, the network and determine whether it is allowed to initiate a new NAS MM the UE can be seen as a transmitter or receiver according 15 request message after switched off and then switched on. to transmission direction, e.g., for uplink (UL), the UE is [0032] Indetail, theUE initiatesa new NASMM request the transmitter and the network is the receiver, and for message according to the MMBK timer received prior to downlink (DL), the network is the transmitter and the UE switched-off and the priority indicator retained in the non- is the receiver. volatile memory. If the priority indicator indicates that the [0025] Please refer to FIG. 2, which is a schematic di- 20 priority level is low, the UE is allowed to initiate a new agram of a communication device 20 according to an NAS MM request message not containing a low priority example of the present invention. The communication level.If thepriority indicator indicates that thepriority level device 20 can be the UE shown in FIG. 1, but is not limited is not low (i.e., normal priority level), the UE is not allowed herein. The communication device 20 may include a to initiate a new NAS MM request message not containing processing means 200 such as a microprocessor or Ap- 25 a low priority level (i.e., normal priority level) before the plication Specific Integrated Circuit (ASIC), a storage unit expiry of the MMBK timer. As such, no matter whether 210 and a communication interfacing unit 220. The stor- the priority indicator indicates that the priority level is not age unit 210 may be any data storage device that can low(i.e., normal priority level) or low, theUE isnot allowed store a program code 214, accessed by the processing to initiate a new NAS MM request message containing a means 200. Examples of the storage unit 210 include but 30 low priority level before the expiry of the MMBK timer. In are not limited to a subscriber identity module (SIM), other words, the UE is not allowed to initiate a new NAS read-only memory (ROM), flash memory, random-ac- MM request message containing a low priority level be- cess memory (RAM), CD-ROM/DVD-ROM, magnetic fore the expiry of the MMBK timer. tape, hard disk, and optical data storage device. The [0033] Noticeably, the process 30 is an example of the communication interfacing unit 220 is preferably a radio 35 present invention. Those skilled in the art should readily transceiver and can transmit and receive wireless signals make combinations, modifications and/or alterations on (e.g., messages or packets) according to processing re- the abovementioned description and examples. For ex- sults of the processing means 200. ample, the priority indicator should be stored in the non- [0026] Please refer to FIG. 3, which is a flowchart of a volatile memory before the UE is switched off, but the process 30 according to an example of the present in- 40 timing is not limited. In an embodiment, the UE may store vention. The process 30 is utilized for a UE to handle the priority indicator indicating the priority level in the non- non-access stratum (NAS) mobility management (MM) volatile memory whenever the user equipment receives messages in the wireless communication system 10 a NAS MM reject message with the MMBK timer from shown in FIG. 1, wherein the UE is configured for dual the network. In another embodiment, the UE may store priority. The process 30 is implemented by the commu- 45 the priority indicator indicating the first priority level in the nication device 20 and may be compiled into the program non-volatile memory just before the user equipment is code 214 to instruct the processing means 200 to execute switched off. the following steps: [0034] Moreover, information about the priority indica- [0027] Step 300: Start. tor and the associated MMBK timer should be handled [0028] Step 302: Send a NAS MM request message 50 independently for different domains. For example, the containing a priority level to a network in the wireless UE may store the priority indicator with the corresponding communication system 10. MMBK timer for a circuit switched (CS) domain (i.e. [0029] Step 304: Store a priority indicator indicating T3246) and the priority indicator with the corresponding the priority level in a non-volatile memory if the UE re- MMBK timer for a packet switched (PS) domain (i.e. ceives a NAS MM reject message with a mobility man- 55 T3346) separately in the non-volatile memory. That is, agement back-off (MMBK) timer from the network. the UE stores two priority indicators for both domains [0030] Step 306: End. along with the associated MMBK timers in the non- vola- [0031] According to the process 30, the UE sends the tile memory.

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[0035] In addition, the UE may manage a correspond- sponding APNs. ence among the priority indicator, the MMBK timer, and [0043] In detail, the UE initiates a new NAS SM request related information stored in the non-volatile memory. message for a specific APN according to the SMBK timer For example, if the MMBK timer is stopped for any rea- received prior to switched-off and the priority indicator son, the corresponding information is invalid. If the re- 5 retained in the non- volatile memory for the specific APN. maining time of the MMBK timer is zero when the UE is If the priority indicator indicates that the priority level for switched on again, the UE clears the information of pri- the specific APN is low, the UE is allowed to initiate a ority indicator so as to initiate a new NAS MM message new NAS SM request message not containing a low pri- afterward. ority level for the specific APN. If the priority indicator [0036] Please refer to FIG. 4, which is a flowchart of a 10 indicates that the priority level for the specific APN is not process 40 according to an example of the present in- low (i.e., normal priority level), the UE is not allowed to vention. The process 40 is utilized for a UE to handle initiate a new NAS SM request message not containing non-access stratum (NAS) session management (SM) a low priority level (i.e., normal priority level) for the spe- messages in the wireless communication system 10 cific APN before the expiry of the corresponding SMBK shown in FIG. 1, wherein the UE is configured for dual 15 timer. If the priority indicator indicates that the priority priority. The process 40 is implemented by the commu- level is not low (i.e., normal priority level) or low for the nication device 20 and may be compiled into the program specific APN, the UE is not allowed to initiate a new NAS code 214 to instruct the processing means 200 to execute SM request message containing a low priority level for the following steps: the specific APN before the expiry of the corresponding [0037] Step 400: Start. 20 SMBK timer. In other words, the UE is not allowed to [0038] Step 402: Send a first NAS SM request mes- initiate a new NAS SM request message containing a sage containing a first priority level for a specific access low priority level for the specific APN before the expiry point name (APN) to a network in the wireless commu- of the SMBK timer for the specific APN. nication system 10. [0044] Noticeably, the process 40 is an example of the [0039] Step 404: Store a priority indicator indicating 25 present invention. Those skilled in the art should readily the first priority level for the specific APN in a non- volatile make combinations, modifications and/or alterations on memory if the user equipment receives a NAS SM reject the abovementioned description and examples. For ex- message with a session management back-off (SMBK) ample, the priority indicator for the specific APN should timer for the specific APN from the network. be stored in the non-volatile memory before the UE is [0040] Step 406: End. 30 switched off, but the timing is not limited. In an embodi- [0041] According to the process 40, the UE sends the ment, the UE may store the priority indicator indicating NAS SM request message (e.g., a packet data network the priority level for the specific APN in the non-volatile (PDN) connectivity request message, a bearer resource memory whenever the user equipment receives a NAS modification request message, or a bearer resource al- SM reject message with the SMBK timer for the specific location request message) containing the priority level 35 APN from the network. In another embodiment, the UE (e.g., low priority level or normal priority level) for a spe- may store the priority indicator indicating the first priority cific APN to the network. Under certain conditions (e.g. level for the specific APN in the non- volatile memory just network overload or congestion), the network may reply before the user equipment is switched off. the UE with the SMBK timer (e.g., T3396) for the specific [0045] The UE may also manage a correspondence APN, which implies that the UE cannot resend the NAS 40 among the priority indicator, the SMBK timer, the corre- SM request message containing the same priority level sponding APN, and related information stored in the non- for the specific APN before the SMBK timer is expired. volatile memory. For example, if the SMBK timer is In addition, the UE needs to store the priority indicator stopped for any reason, the corresponding information for the specific APN in the non- volatile memory if the UE is invalid. If the remaining time of the SMBK timer for the receives the SMBK timer. In this manner, the UE may 45 specific APN is zero when the UE is switched on again, check the SMBK timer and the priority indicator for the the UE clears the information of corresponding priority specific APN retaining in the non-volatile to determine indicator so as to initiate a new NAS SM message for the whether it is allowed to initiate a new NAS SM request same specific APN afterward. message for the specific APN after switched off and then [0046] The abovementioned steps of the processes 30 switched on. 50 and 40 including suggested steps may be realized by [0042] In other words, the UE may receive SMBK tim- means of hardware, software, firmware, or an electronic ers for different APNs, such that the UE needs to store system. Examples of hardware may include analog, dig- all of the priority indicators with the corresponding SMBK ital and mixed circuits known as microcircuit, microchip, timers for different APNs separately in the non-volatile or silicon chip. Examples of the electronic system may memory. For example, if the UE has received two SMBK 55 includea systemon chip (SOC), system in package (SiP), timers associated to two different congested APNs, the a computer on module (COM), and the communication UE stores two priority indicators indicating respective pri- device 20. ority levels associated to two SMBK timers for the corre- [0047] The type of non-volatile memory used for stor-

5 9 EP 2 704 456 A1 10 ing the priority indicator and/or related information is not 4. The method of claim 2, wherein the user equipment limited, as long as the information can be retained when is not allowed to initiate the second NAS MM request the UE is shut down. For example, the UE may store the message containing a low priority level before the information of the priority indicator along with the asso- expiry of the MMBK timer. ciated the MMBK/SMBK timer in a subscriber identity 5 module (SIM), a universal subscriber identity module 5. The method of claim 2, wherein the user equipment (USIM), or any other non-volatile memory such as flash is not allowed to initiate the second NAS MM request memory, magnetic tape, hard disk, and optical data stor- message not containing a low priority level before age device, holographic memory. the expiry of the MMBK timer if the priority indicator [0048] In conclusion, the present invention provides a 10 indicates the first priority level is not low. method for handling NAS MM messages and NAS SM messages by storing the priority indicator in the non- vol- 6. The method of any one of the preceding claims, atile memory and following the same constraint of the wherein the user equipment stores the priority indi- NAS MM/SM signalling messages received prior to cator indicating the first priority level in the non-vol- switched-off (i.e., MMBK/SMBK timers and priority level) 15 atile memory whenever the user equipment receives after the UE is switched on again. Therefore, the UE can a NAS MM reject message with the MMBK timer from properly determine which kind (i.e., priority level, domain, the network or before the user equipment is switched APN) of NAS MM/SM request message is allowed or not off. allowed to send to the network, so as to prevent the de- crease of the UE or the network performance. 20 7. The method of any one of the preceding claims, [0049] Those skilled in the art will r eadily observe that wherein the first and the second NAS MM request numerous modifications and alterations of the device and messages are attach request messages, tracking ar- method may be made while retaining the teachings of ea update request messages, or extended service the invention. Accordingly, the above disclosure should request messages. be construed as limited only by the metes and bounds 25 of the appended claims. 8. The method of any one of the preceding claims, wherein the priority indicator with the corresponding MMBK timer for a circuit switched (CS) domain and Claims the priority indicator with the corresponding MMBK 30 timer for a packet switched (PS) domain are stored 1. A method of handling non- access stratum (NAS) mo- separately in the non-volatile memory. bility management (MM) messages for a user equip- ment in a wireless communication system when the 9. A method of handling non-access stratum (NAS) user equipment is configured for dual priority, the session management (SM) messages for a user method comprising: 35 equipment in a wireless communication system when the user equipment is configured for dual pri- sending a first NAS MM request message con- ority, the method comprising: taining a first priority level to a network in the wireless communication system; and sending a first NAS SM request message con- storing a priority indicator indicating the first pri- 40 taining a first priority level for a specific access ority level in a non-volatile memory if the user point name (APN) to a network in the wireless equipment receives a NAS MM reject message communication system; and with a mobility management back-off (MMBK) storing a priority indicator indicating the first pri- timer from the network. ority level for the specific APN in a non-volatile 45 memory if the user equipment receives a NAS 2. The method of claim 1, further comprising: SM reject message with a session management back-off (SMBK) timer for the specific APN from determining whether the user equipment is al- the network. lowed to initiate a second NAS MM request mes- sage according to the MMBK timer and the pri- 50 10. The method of claim 9, further comprising: ority indicator retaining in the non- volatile mem- ory after the user equipment is switched off and determining whether the user equipment is al- then switched on. lowed to initiate a second NAS SM request mes- sage forthe specific APNaccording tothe SMBK 3. The method of claim 2, wherein the user equipment 55 timer and the priority indicator for the specific is allowed to initiate the second NAS MM request APN retaining in the non-volatile memory after message not containing a low priority level if the pri- the user equipment is switched off and then ority indicator indicates the first priority level is low. switched on.

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11. The method of claim 10, wherein the user equipment is allowed to initiate the second NAS SM request message not containing a low priority level for the specific APN if the priority indicator indicates the first priority level for the specific APN is low. 5

12. The method of claim 10, wherein the user equipment is not allowed to initiate the second NAS SM request message containing a low priority level for the spe- cific APN before the expiry of the SMBK timer for the 10 specific APN.

13. The method of claim 10, wherein the user equipment is not allowed to initiate the second NAS SM request message not containing a low priority level for the 15 specific APN before the expiry of the SMBK timer for the specific APN if the priority indicator indicates the first priority level for the specific APN is not low.

14. The method of any one of the claims 9-13, wherein 20 the user equipment stores the priority indicator indi- cating the first priority level for the specific APN in the non-volatile memory whenever the user equip- ment receives a NAS SM reject message with the SMBK timer for the specific APN from the network 25 or before the user equipment is switched off.

15. The method of any one of the claims 9-14, wherein the first and the second NAS SM request messages are packet data network (PDN) connectivity request 30 messages, bearer resource modification request messages, or bearer resource allocation request messages.

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