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EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
EMM Procedure 5. Periodic TAU
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EMM Procedure 5. Periodic TAU

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  • Good Composition of SRB.

    You can get also some good reads on Signalling Radio Bearers – SRB in LTE
    http://telecomcoach.com/signalling-radio-bearers-srb-lte/

    System Information Block – SIB in LTE
    http://telecomcoach.com/system-information-block-sib-in-lte/
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  • 1. Netmanias Technical Document: EMM Procedure 5. Periodic TAU 가 www.nmcgroups.com About NMC Consulting Group NMC Consulting Group is an advanced and professional network consulting company, specializing in IP network areas (e.g., FTTH, Metro Ethernet and IP/MPLS), service areas (e.g., IPTV, IMS and CDN), and wireless network areas (e.g., Mobile WiMAX, LTE and Wi-Fi) since 2002. Copyright © 2002-2014 NMC Consulting Group. All rights reserved. EMM Procedure 5. Periodic TAU Table of Contents I. Introduction II. Concept of Periodic TAU III. Procedure of Periodic TAU IV. EPS Entity Information: Before/After Periodic TAU V. Closing This document, as the fifth of the EMM Procedure series, will describe the periodic TAU procedure, as defined as EMM Case 5 in our technical document, “Eleven EMM Cases in an EMM Scenario”. This procedure is used when a UE, while staying inactive in ECM/RRC-Idle state, informs the MME of its current location (TAI, Tracking Area Identity) upon expiration of the periodic TAU timer. Between a UE and MME, no bearer (E-RAB) is set up, and only a signaling connection (ECM connection) is established. We will learn how the ECM connection is released and the UE returns to Idle state once a new TA is reported. We will also look into how information elements in EPS entities are different before and after the periodic TAU procedure. February 19, 2014 (Initial Released: May 24, 2012) www.netmanias.com NMC Consulting Group (tech@netmanias.com)
  • 2. EMM Procedure 5. Periodic TAU 1 Netmanias LTE Technical Documents Visit http://www.netmanias.com to view and download more technical documents. Index Topic Document Title Document presented here 1 Network Architecture LTE Network Architecture: Basic 2 Identification LTE Identification I: UE and ME Identifiers 3 LTE Identification II: NE and Location Identifiers 4 LTE Identification III: EPS Session/Bearer Identifiers 5 Security LTE Security I: LTE Security Concept and LTE Authentication 6 LTE Security II: NAS and AS Security 7 QoS LTE QoS: SDF and EPS Bearer QoS 8 EMM LTE EMM and ECM States 9 Eleven EMM Cases in an EMM Scenario 10 LTE EMM Procedure 1. Initial Attach - Part 1. Cases of Initial Attach 11 LTE EMM Procedure 1. Initial Attach - Part 2. Call Flow of Initial Attach 12 LTE EMM Procedure 2. Detach 13 LTE EMM Procedure 3. S1 Release 14 LTE EMM Procedure 4. Service Request 15 LTE EMM Procedure 5. Periodic TAU O 16 LTE EMM Procedure 6. Handover without TAU - Part 1. Overview of LTE Handover 17 LTE EMM Procedure 6. Handover without TAU - Part 2. X2 Handover 18 LTE EMM Procedure 6. Handover without TAU - Part 3. S1 Handover 19 LTE EMM Procedure 7. Cell Reselection without TAU 20 LTE EMM Procedure 8 & 9. Handover and Cell Reselection with TAU 21 LTE EMM Procedure 10 & 11. Move to Another City and Attach 22 PCC LTE Policy and Charging Control (PCC) 23 Charging LTE Charging I: Offline 24 LTE Charging II: Online (TBD) 25 IP Address Allocation LTE IP Address Allocation Schemes I: Basic 26 LTE IP Address Allocation Schemes II: A Case for Two Cities
  • 3. EMM Procedure 5. Periodic TAU 2 Abbreviations AKA Authentication and Key Agreement ASME Access Security Management Entity DL Downlink DRB Data Radio Bearer ECGI E-UTRAN Cell Global Identifier ECM EPS Connection Management EMM EPS Mobility Management eNB Evolved Node B EPS Evolved Packet System E-RAB E-UTRAN Radio Access Bearer E-UTRAN Evolved Universal Terrestrial Radio Access Network GUMMEI Globally Unique MME ID GUTI Globally Unique Temporary Identifier HSS Home Subscriber Server KSI Key Set Identifier LTE Long Term Evolution MAC Message Authentication Code MME Mobility Management Entity NAS Non Access Stratum PCRF Policy and Charging Rule Function P-GW Packet Data Network Gateway RRC Radio Resource Control S1AP S1 Application Protocol S-GW Serving Gateway TA Tracking Area TAI Tracking Area Identity TAU Tracking Area Update TIN Temporary Identifier used in Next update UE User Equipment
  • 4. EMM Procedure 5. Periodic TAU 3 I. Introduction This document describes the periodic TAU (Tracking Area Update) procedure defined as EMM Case 5 in our technical document, “Eleven EMM Cases in an EMM Scenario” [1]. This procedure is performed when a UE which entered ECM/RRC-Idle state in the network due to no traffic periodically updates the network (MME) with its current location. A TAU procedure is initiated when a UE enters a new TA that is not in the list of TAIs allocated by the MME at the time of the UE’s attach, or when the TAU timer expires. The EMM Case 5 presented in this document is related to the periodic TAU procedure performed by a UE upon expiration of the TAU timer. A UE in Idle state reports its current location to the MME by sending a TAU Request message when the TAU timer expires. After transiting to ECM/RRC-Connected state, and performing the periodic TAU procedure, the UE returns to Idle state. This document explains the periodic TAU procedure performed by a UE in Idle state in an LTE network. Chapter II explains the concept of periodic TAU, and Chapter III describes its specific procedures. Finally, Chapter VI summarizes how information elements in EPS entities are different before and after the procedure. II. Concept of Periodic TAU A UE, while in Connected state, has an established end-to-end EPS bearer connecting the UE to the network (P-GW). The network (MME) keeps track of which cell the UE is located in. So, if there is any traffic destined to the UE, the network can deliver it immediately. However, if a UE enters Idle state, the signaling connection and bearers (E-RAB bearer) between the UE and the network (MME) are all released. Then, the network (MME) loses track of the UE’s location. The network should always be aware of the current location of all UEs, whether in Active or Idle state, in order to deliver traffic to UEs that are in Idle state. So, those in Idle states should report their current location, i.e. in which TA (Tracking Area) they are located, to the network (MME) periodically even when there is no data to deliver. A TA is a group of cells, and managed by MME. The location of UEs in Idle state is recognized at a TA level. To this end, MME provides a UE with a TAI list and TAU timer (T3412) as included in a Attach Accept message when the UE initially attaches the network. Using them, the UE performs a TAU procedure upon expiration of the TAU timer. When MME receives TA information from a UE, it updates the UE’s current location information (TA, cell) to keep the latest information. In case there is traffic destined to the UE while it is in Idle state, the MME informs the UE about the new traffic by sending a Paging Message to the cells in the TA that has been reported by the UE as its current location1 . Figure 1 shows an example of a TAU procedure performed by a UE in Idle state. The UE (UE1) has attached Cell 2 in eNB1 upon its initial attach, and has been allocated a TAI list (e.g. TAI={TAI1, TAI2}) and TAU timer (e.g. 1 Paging in a larger area means more cells to page. So it has a higher chance of locating a particular UE fast, but can cause higher paging load. On the other hand, paging in a smaller area means fewer cells to page. So, it has a lower chance of locating the UE fast, but causes less paging load. Efficient ways to page are beyond the scope of this document, and hence will not be discussed here.
  • 5. EMM Procedure 5. Periodic TAU 4 T3412=60 mins) through the Attach Accept message sent from the MME. Later, after transiting to Idle state, it travels from ❶  ❷  ❸  ❹. For the purposes of this example, we assume i) the UE travels between only the TAs that are in the TAI list initially allocated through the Attach Accept message, ii) the MME the UE reports its TA information to is the one the UE’s context is stored in, and iii) both the UE and the MME have kept the NAS security context (KNASint, KNASenc, etc.) valid. Figure 1. Concept of Periodic TAU After attaching and transiting to Idle state in Cell 2, UE1 wakes up and establishes an ECM signaling connection with the MME when the TAU timer expires at T1. Next, it sends the MME a TAU Request (TAI=TAI1, Last Visited TAI=TAI1) message that includes the TAI of its current cell, and the last visited TAI (the one reported through the last TAU request) (❶). Then, UE1 returns to Idle state when it receives a TAU Accept message. After receiving the TAU Request message from the Idle UE, the MME checks whether the UE’s last TAI (TAI of MME Cell 1 (TAI 1) Cell 2 (TAI 1) Cell 3 (TAI 1) Cell 4 (TAI 1) Cell 7 (TAI 1) Cell 8 (TAI 1) Cell 6 (TAI 1) Cell 9 (TAI 1) Cell 5 (TAI 1) Cell 10 (TAI 2) Cell 13 (TAI 2) Cell 14 (TAI 2) Cell 12 (TAI 2) Cell 15 (TAI 2) Cell 11 (TAI 2) TAI=1,LastVisitedTAI=1 TAURequest TAUAccept UE1: TAI1 TAURequest TAUAccept UE1: TAI1 TAURequest TAUAccept UE1: TAI2 TAURequest TAUAcceptUE1: TAI2 UE1 MME TA 2 eNB2 eNB3 eNB5 eNB1 eNB4 TAURequest TAURequest TAURequest TAURequest T3412 t t1 t2 t3 t4T3412 T3412T3412 1 2 3 4 EMM-Registered + ECM-Idle + RRC-Idle TAI List: TAI1, TAI2 EMM-Registered + ECM-Connected + RRC-Connected TAI List: TAI1, TAI2 TAI=1,LastVisitedTAI=1 TAI=2,LastVisitedTAI=1 TAI=2,LastVisitedTAI=2 1 2 3 4 TA 1
  • 6. EMM Procedure 5. Periodic TAU 5 Last TAU) has been changed or not, and updates it with the latest information if it has been changed. If there is traffic heading to UE1, and thus the S-GW notifies the MME of the DL traffic, the MME finds out which TA the UE was in last time based on the TAI of Last TAU information, and sends a Paging Message to the cells in the TA (see our LTE technical document, “LTE EMM Procedure 4. Service Request” [2] for detailed information). Later, if UE1 moves to Cell 4, and the TAU timer expires (❷), UE1 sends the MME a TAU Request (TAI=TAI1, Last Visited TAI=TAI1) message as it is still in TA1. If UE1 moves to Cell 11, and the timer expires (❸), it sends the MME a TAU Request (TAI=TAI2, Last Visited TAI=TAI1) message, including TAI2 instead of TAI1, as now it belongs to TA2. Then the MME accordingly updates UE1’s TAI of Last TAU with TAI2. Figure 2 shows the connections established, and the states of UE and MME in the user and control planes before and after the periodic TAU procedure. Figure 2. Connections and States before/after TAU A UE’s states before, during and after a periodic TAU procedure are as follows: (i) Before the procedure, the UE stays in EMM-Registered, ECM-Idle and RRC-Idle state, and any eNB S-GWMME PCRFHSS SPRP-GWUE ECM Connection S5 GTP-C ConnectionS11 GTP-C ConnectionS1 Signaling ConnectionRRC Connection ECM-Connected RRC-Connected EMM-Registered RRC-Connected ECM-Connected EMM-Registered 1) Connections and States before Periodic TAU Control Plane Connection User Plane Connection (Bearer) States S5 GTP-C ConnectionS11 GTP-C Connection S5 BearerS1 Bearer ReleasedDRB Released ECM Connection Released S1 Signaling ReleasedRRC Released Control Plane Connection EMM-Registered EMM-Registered ECM-Idle RRC-Idle RRC-Idle ECM-Idle S1 TEID (UL) States User Plane Connection (Bearer) 2) Connections and States during Periodic TAU 3) Connections and States after Periodic TAU User Plane Connection (Bearer) S5 GTP-C ConnectionS11 GTP-C Connection S5 BearerS1 Bearer ReleasedDRB Released ECM Connection Released S1 Signaling ReleasedRRC Released Control Plane Connection EMM-Registered EMM-Registered ECM-Idle RRC-Idle RRC-Idle ECM-Idle S1 TEID (UL) States S5 BearerS1 Bearer ReleasedDRB Released S1 TEID (UL)
  • 7. EMM Procedure 5. Periodic TAU 6 resources allocated by E-UTRAN, i.e. the E-RAB (except for the uplink S1 bearer) and ECM signaling connection between the UE and the MME, are kept released. (ii) During the procedure, the UE stays in EMM-Registered, ECM-Connected and RRC-Connected state. The periodic TAU procedure is different from procedures for initial attach or service request in that no E-RAB (between UE and MME) is set up, and only the signaling connection (ECN signaling connection) for delivering periodic TAU-related NAS messages is set up during this procedure. (iii)After the procedure, the ECM signaling connection set between the two entities is released, releasing the E-UTRAN resources. Then, the UE returns to EMM-Registered, ECM-Idle and RRC-Idle state again. Figure 3 is another illustration that shows the state transition of a UE before/after a periodic TAU procedure. Upon the expiration of T3412, the UE which has been in Idle state sends the MME a TAU Request message to report its current TA and last TA (then it transits to Connected state). Then the MME returns a TAU Accept message to the UE after updating the UE’s location information (TA). As a result, the signaling connection between the two entities is released, and the UE transits back to Idle state. Figure 3. State Transition of a User Performing Periodic TAU III. Procedure of Periodic TAU Figure 4 and 5 illustrate procedures for a periodic TAU by a UE in Idle state. In Figure 4, the NAS layer at UE reports its new TA to the MME by sending a TAU Request message with its update type indicated as “Periodic Updating”2 . As a “Periodic Updating” type TAU does not require bearer establishment, the UE sends a TAU Request message after establishing an ECM signaling connection only. When it receives a TAU Accept message, it releases the ECM signaling connection. The TAU Request message is sent as integrity-protected with KNASint, the NAS integrity key (i.e. by including NAS-MAC). So, the MME decides whether to perform UE authentication or not by conducting an integrity check on the message. 2 If a UE, in ECM/RRC-Connected state, moves into a cell that is not in the TAI list, a TAU Request message is sent with its update type indicated as “TA Updating”. EMM-Registered ECM-Connected RRC-Connected RRC-Idle ECM-Idle TAU Accept TAU Request EMM-Registered Before Periodic TAU After Periodic TAU T3412 Expiry 1 23 4 5
  • 8. EMM Procedure 5. Periodic TAU 7 Figure 4. Procedure for Periodic TAU (1) ❶ Periodic TAU Triggering 1) [UE] TAU Timer Expiry The UE in Idle state triggers a periodic TAU procedure to report its current location to the MME upon expiration of the TAU timer (T3412). ❷ ECM Connection Establishment) and TA Report The NAS layer at the UE i) configures a TAU Request message, and ii) sends it with RRC parameters (e.g. old GUMMEI3 ) down to the RRC layer at the UE. 2), 3) [UE – eNB] RRC Connection Establishment Upon receiving the TAU Request message, the RRC layer at the UE sends the eNB an RRC Connection Request message, requesting dedicated signaling resources. The eNB establishes an RRC connection by allocating an SRB channel and sending the UE an RRC Connection Setup message (see our Initial Attach document [4] for detailed procedures). 3 It identifies the MME that a UE was last registered at in the LTE network, and is derived from the UE’s GUTI [3]. [Optional] If NAS message is not Integrity Protected or Integrity Check Failed, MME triggers UE authentication eNB S-GWMME PCRFHSS SPRP-GWUE S5 BearerS1 Bearer ReleasedDRB Released ECM Connection Released S5 GTP-CS11 GTP-CS1 Signaling ReleasedRRC Released ECM-Idle RRC-Idle EMM-Registered RRC-Idle ECM-Idle EMM-Registered 4) TAU Request Update Type=Periodic Updating, GUTI, Last Visited TAI, KSIASME, NAS-MAC 2) RRC Connection Request 3) RRC Connection Setup 5) RRC Connection Setup Complete Ciphering and Integrity Protected for NAS message between UE and MME GUMMEI 6) Initial UE Message ECGI, TAI Last Visited TAI shall be used to help the MME produce a good list of TAIs for any subsequent TAU Accept message 1) UE in ECM-Idle state detects the TAU timer (T3412) expires T3412 Expiry ECM Connection Establishment & TA Report2 7) UE Authentication 8) NAS Security Setup Authentication Information Request/Authentication Information Answer Authentication Request/Authentication Response Security Mode Command/Security Mode Complete UE Authentication & NAS Security Setup (optional)3 S5 BearerS1 Bearer ReleasedDRB Released ECM Connection S5 GTP-C ConnectionS11 GTP-C ConnectionS1 Signaling ConnectionRRC Connection ECM-Connected RRC-Connected EMM-Registered RRC-Connected ECM-Connected EMM-Registered Periodic TAU Triggering1
  • 9. EMM Procedure 5. Periodic TAU 8 4), 5), 6) [UE  MME] ECM Connection Establishment Request and TA Report The TAU Request message is delivered as included in an RRC Connection Setup Complete message, an RRC message, from the UE to the eNB, and then in an Initial UE Message, an S1AP message, from the eNB to the MME. As the NAS security context has been kept valid between the UE and the MME, the TAU Request message is sent integrity-protected with the NAS integrity key (KNASint) and encrypted with the encryption key (KNASenc). The TAU Request message for the periodic TAU procedure includes the following information: TAU Request (Update Type=Periodic Updating, Active Flag=0, GUTI, Last Visited TAI, KSIASME, NAS- MAC)  Update Type: indicates the TAU type. Set as Periodic Updating when the TAU timer (T3412) is expired  Active Flag: indicates whether there is uplink user traffic data or signaling to send. If there is, this parameter is set as 1, establishing a bearer and maintaining the ECM connection after TAU.  GUTI: UE ID, previously allocated by MME, that MME uses to identify UEs  Last Visited TAI: the TAI reported last time through TAU Request (TAI that UE was last registered at)  KSIASME: index for KASME, the NAS security base key  NAS-MAC: MAC used when the TAU Request message is integrity-protected using the NAS integrity key (KNASint) For faster delivery of the TAU Request message received from the NAS layer, the RRC layer at the UE sends the eNB the message, as piggybacked on an RRC Connection Setup Complete message, the last step of the RRC connection procedures. At this time, the RRC Connection Setup Complete message includes a GUMMEI. This ID is derived from the GUTI that was received from the NAS layer, and indicates at which MME the UE is registered. In general, an eNB can be connected with more than one operator network and MME. So, upon receiving the RRC Connection Setup Complete message, the eNB checks whether the indicated MME is connected with itself or not.4 Then, the eNB sends the TAU Request message as included in an Initial UE Message message to the MME. At this time, the eNB allocates an eNB S1AP UE ID to the Initial UE Message message, and the MME, upon receipt of the Initial UE Message message, allocates an MME S1AP UE ID, setting up an S1 signaling connection between the two entities. This completes an ECM signaling connection between the UE and the MME, allowing the UE to transit to Connected state. ❸ UE Authentication and NAS Security Setup (Optional) 7) [UE – MME – HSS] UE Authentication The MME, upon receiving the TAU Request message from the UE, conducts an integrity check on the NAS-MAC. If the check passes, the MME can skip UE authentication, and continue to use the NAS security context it has kept in delivering NAS messages. If the check fails, it has to perform UE authentication through EPS-AKA.5 4 In EMM Case 5, TAU Request messages sent by UE in Idle state are delivered to the MME that the UE was registered at during initial attach. Cases of sending TAU Request messages to other MME will not be discussed here. 5 MME obtains AVs for the UE from HSS, and performs UE authentication on behalf of the HSS [5].
  • 10. EMM Procedure 5. Periodic TAU 9 8) [UE – MME] NAS Security Setup Once the UE is authenticated in Step 7), NAS security keys (KNASenc, KNASint) to be used in communicating NAS messages are generated based on a new KASME and through a NAS security setup procedure. Figure 5. Procedures for Periodic TAU (2) ❹ TA Update 9) [MME  S-GW] TA Update When the MME receives the TAU Request message from the UE, it resets the TAU timer (T3412), and sends the S-GW a Modify Bearer Request message, forwarding the UE’s location information (ECGI, TAI). 10) EPS Session Modification (Optional) The S-GW that receives the UE location information checks whether the UE’s cell (ECGI) or TA (TAI) is changed or not. If changed, it sends a Modify Bearer Request to the P-GW to inform such change. Then, the P-GW reports the same to the PCRF through an EPS session modification procedure.6 6 During UE’s initial attach, PCRF can provide MME, S-GW and P-GW with its reporting policies on UE location changes through Change Reporting Action parameters included in a CCA message [4]. [Optional] If ECGI or TAI is changed IMSI, UE IP, ECGI, TAI eNB S-GWMME PCRFHSS SPRP-GWUE 16) UE Context Release Command 17) RRC Connection Release 18) UE Context Release Complete Cause=User Inactivity S5 BearerS1 Bearer ReleasedDRB Released ECM Connection Released S5 GTP-CS11 GTP-CS1 Signaling ReleasedRRC Released ECM-Idle RRC-Idle EMM-Registered RRC-Idle ECM-Idle EMM-Registered 12) MME may give new GUTI and TAI List 13) TAU Accept GUTI, TAI List 9) Modify Bearer Reqeust EPS Bearer ID, ECGI, TAI EPS Bearer ID 11) Modify Bearer Response 14) UE sets TIN=GUTI and updates TAI List if these are changed 15) TAU Complete UL Information Transfer Uplink NAS Transport Downlink NAS Transport DL Information Transfer TA Update4 10) EPS Session Modification (optional) ECM Connection Release5 Acknowledge of IP-CAN Session Modification (CCA) Indication of IP-CAN Session Modification (CCR) Modify Bearer Request Modify Bearer Response EPS Bearer ID EPS Bearer ID, ECGI, TAI [Optional] UE sends TAU Complete if GUTI was changed
  • 11. EMM Procedure 5. Periodic TAU 10 11) [MME  S-GW] Responding to TA Update Request The S-GW sends the MME a Modify Bearer Response message as a response to the Modify Bearer Request message received in Step 9). 12) [MME] Preparing TAU Accept Message The MME may configure a new TAI list to reflect the current location of the UE, or allocate a new GUTI, depending on implementation. 13) [UE  MME] Sending TAU Accept Message The MME sends the UE a TAU Accept message, as integrity-protected and encrypted. This message is delivered through a Downlink NAS Transport message, an S1AP message, from the eNB to the MME, and then through a DL Information Transfer message, an RRC message, from the UE to the eNB. 14) [UE] Updating TIN and TAI List When the UE receives the TAU Accept message from the MME, it checks the GUTI and TAI list values. If these values are changed, it updates the TIN (Temporary Identifier used in Next update) and the TAI list with these new values. Here, the TIN is a user ID to be used next time the UE sends a TAU Request message, and is updated with the GUTI included in a TAU Accept message every time the message is received. 15) [UE] Acknowledging New GUTI If a new GUTI is allocated by the MME, the UE sends a TAU Complete message to the MME, acknowledging receipt of the new GUTI. ❺ ECM Connection Release 16) [eNB  MME] Requiring E-UTRAN to Release UE Context After updating the UE’s location information, the MME sends a UE Context Release Command message to the eNB in order to release the ECM connection used for delivering messages relating to periodic TAU, and also release the UE context stored in E-UTRAN. 17) [UE  eNB] Releasing RRC Connection Upon receiving the UE Context Release Command message from the MME, the eNB deletes the UE context, and release all the E-UTRAN resources that were allocated to the UE. Then, to the UE, it sends an RRC Connection Release message to release the RRC connection, thereby releasing the SRB (Signaling Radio Bearer) allocated to the UE as well. 18) [eNB  MME] Announcing Release of UE Context from E-UTRAN Also, the eNB sends a UE Context Release Complete message to the MME, indicating the S1 signaling connection has been released. Now, the ECM connection that was established for TAU Request message delivery is released, and the UE transits back to Idle state (ECM/RRC-Idle).
  • 12. EMM Procedure 5. Periodic TAU 11 IV. EPS Entity Information: Before/After Periodic TAU This chapter will describe how information elements in the EPS entities are different before and after the periodic TAU procedure. All the information elements are categorized into UE ID, UE Location, Security, and EPS Session/Bearer information. 4.1 Before Periodic TAU As explained in the EMM scenario document [1], before a periodic TAU procedure is triggered, a UE stays in EMM-Registered, ECM-Idle and RRC-Idle. Therefore, all the information elements stored before the service request in the EMM Case 4 is made remain the same in the EPS entities until a periodic TAU procedure is performed [2]. That is, information elements related to the radio resources allocated by E-UTRAN (eNB) and those related to the EPS bearer and signaling connection established in E-UTRAN (i.e. downlink S1 bearer and S1 signaling information) are now deleted from the EPS entities. In Figure 6, information elements stored in each EPS entity before a periodic TAU procedure is triggered are marked in black. Figure 6. Information in EPS entities before and after Periodic TAU SPRPCRFP-GWS-GWUE eNB IMSI GUTI UE IP address C-RNTI - - LTE K NAS Security Info AS Security Info ECGI TAI TAI List - APN in Use EPS Bearer ID DRB ID - - - QCI - - APN-AMBR (UL) TFT (UL) - IMSI GUTI UE IP address - eNB S1AP UE ID MME S1AP UE ID - NAS Security Info - APN in Use EPS Bearer ID - E-RAB ID S1 TEID (UL/DL) S5 TEID (UL/DL) QCI ARP UE-AMBR (UL/DL) APN-AMBR (UL/DL) - Subscribed Profile (Subscribed QCI, ARP, UE-AMBR, APN-AMBR) ECGI TAI TAI List - IMSI - - - - - LTE K - - - - - MME ID PCRF HSS SPR - - - C-RNTI eNB S1AP UE ID MME S1AP UE ID - - AS Security Info ECGI TAI - - - EPS Bearer ID DRB ID E-RAB ID S1 TEID (UL/DL) - QCI ARP UE-AMBR (UL/DL) - - - Default APN - - - - - - - - - - Subscribed Profile (Subscribed QCI, ARP, UE-AMBR, APN-AMBR) IMSI - - - - - - - - - - - - - - - - - - - Access Profile (Subscribed QCI, ARP, APN-AMBR) - - - - IMSI - UE IP address - - - - - - APN in Use - - - - - QCI* ARP* - APN-AMBR (UL/DL)* SDF Filter* - * PCC Rule ECGI TAI - - IMSI - UE IP address - - - - - - APN in Use EPS Bearer ID - - - S5 TEID (UL/DL) QCI* ARP* - APN-AMBR (UL/DL)* TFT (UL/DL)* - * PCC Rule ECGI TAI - - IMSI - - - - - - - - - EPS Bearer ID - - S1 TEID (UL/DL) S5 TEID (UL/DL) QCI ARP - - - - ECGI TAI - - S5 BearerData Radio Bearer S1 Bearer RRC Connection S1 Signaling Connection ECM ConnectionControl Plane S11 GTP-C S5 GTP-C eNB S-GW P-GWUE MME HSS MME User Plane S1 TEID (UL)
  • 13. EMM Procedure 5. Periodic TAU 12 4.2 After Periodic TAU After a periodic TAU procedure, the ECM connection is released, and the UE transits back to Idle state (EMM- Registered, ECM-Idle and RRC-Idle) it used to be in before the periodic TAU procedure. The information elements stored in each EPS entity after the periodic TAU procedure are the same as those kept before the procedure, as to be seen in Figure 6. V. Closing We have learned the periodic TAU procedure (“EMM Case 5” in [1]) required when a UE, staying in Idle state (ECM/RRC-Idle) after attaching an LTE network, updates its location upon expiration of the TAU timer. Unlike a service request procedure, this procedure does not require establishment of an E-RAB bearer, but requires establishment of an ECM connection, for TAU. After TAU is performed, the ECM connection is released, allowing the UE to transit back to Idle state. If a UE has uplink data to send (this case is not discussed in this document, though), an E-RAB bearer is set up first, and then the data is sent after TAU, just like in a service request procedure. The subsequent document will cover a case when a UE, in Connected (ECM/RRC- Connected) state, moves between TAs in the TAI list, causing a handover, but no TAU procedure is required. References [1] Netmanias Technical Document, “Eleven EMM Cases in an EMM Scenario”, October 2013, http://www.netmanias.com/en/?m=view&id=techdocs&no=6002 [2] Netmanias Technical Document, “LTE EMM Procedure 4. Service Request”, February 2014, http://www.netmanias.com/en/?m=view&id=techdocs&no=6134 [3] Netmanias Technical Document, “LTE Identification II: NE and Location Identifiers”, August 2013, http://www.netmanias.com/en/?m=view&id=techdocs&no=5906 [4] Netmanias Technical Document, “LTE EMM Procedure 1. Initial Attach – Part 2. Call Flow of Initial Attach”, January 2014, http://www.netmanias.com/en/?m=view&id=techdocs&no=6102 [5] Netmanias Technical Document, “LTE Security I: LTE Security Concept and LTE Authentication”, July 2013, http://www.netmanias.com/en/?m=view&id=techdocs&no=5902 [6] NMC Consulting Group Confidential Internal Report, “E2E LTE Network Design”, August 2010
  • 14. EMM Procedure 5. Periodic TAU About NMC Consulting Group NMC Consulting Group is an advanced and professional network consulting company, specializing in IP network areas (e.g., FTTH, Metro Ethernet and IP/MPLS), service areas (e.g., IPTV, IMS and CDN), and wireless network areas (e.g., Mobile WiMAX, LTE and Wi-Fi) since 2002. Copyright © 2002-2014 NMC Consulting Group. All rights reserved. Carrier WiFi Data Center Migration Wireline Network LTE Mobile Network Mobile WiMAX Carrier Ethernet FTTH Data Center Policy Control/PCRF IPTV/TPS Metro Ethernet MPLS IP Routing 99 00 01 02 03 04 05 06 07 08 09 10 11 12 13 eMBMS/Mobile IPTV Services CDN/Mobile CDN Transparent Caching BSS/OSS Cable TPS Voice/Video Quality IMS LTE Backaul Netmanias Research and Consulting Scope Visit http://www.netmanias.com to view and download more technical documents.

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