Week #15 LTE-WLAN Aggregation (LWA) 教育部行動寬頻尖端技術人才培育計畫-小細胞基站聯盟中心 示範課程：行動寬頻網路之異質性存取 Week #15 LTE-WLAN Aggregation (LWA) 助理教授：吳俊興 助教：王瑞元 國立高雄大學 資訊工程學系
Outline Introduction to LWA LWA Architecture LWAAP E-UTRAN and Wireless LAN (WLAN) Xw in Layer 1 Signaling Transport Xw Application Protocol (XwAP) Xw Data Transport Xw Interface User Plane Protocol 參考資料:http://www.2cm.com.tw/news_print.asp?sn=1611040016
LTE-WLAN Aggregation (LWA) (TS36.300/22A) E-UTRAN supports LWA operation whereby a UE in RRC_CONNECTED is configured by the eNB to utilize radio resources of LTE and WLAN WLAN AP/AC only interacts with eNB; no interaction with the Core Network LWA is controlled by eNB, based on UE measurement reporting When LWA is activated, eNB configures one or more bearers as LWA bearers Two scenarios are supported depending on the backhaul connection between LTE and WLAN Collocated LWA scenario for an ideal/internal backhaul Non-collocated LWA scenario for a non-ideal backhaul WLAN Termination (WT) terminates the Xw interface for WLAN C-Plane connectivity of eNB and WT for LWA U-Plane connectivity of eNB and WT for LWA
LWA Radio Protocol Architecture In LWA, the radio protocol architecture that a particular bearer uses depends on the LWA backhaul scenario and how the bearer is set up Two bearer types exist for LWA: split LWA bearer and switched LWA bearer LWA Radio Protocol Architecture for the Collocated Scenario LWA allows a single bearer to be configured to utilize LTE and WLAN simultaneously Split and switched bearers are supported R13 LWA supports aggregation in downlink only, while uplink transmission is always on LTE Packets (PDCP PDUs) belonging to LWA bearer can be sent by eNB via LTE or WLAN simultaneously LWA uses EtherType 0x9E65 allocated by IEEE RAC LWA Radio Protocol Architecture for the Non-Collocated Scenario
LWA and LWIP LWA(LTE WLAN Aggregation) 將運行於授權頻譜的 LTE及非授權頻譜的WiFi在PDCP實現聚合，並由LTE eNB做統一調度控制 此技術WiFi AP(WT)和LTE eNB間必須要有一個Xw介面溝通，若以小型small cell實現，則經常是以LTE和WiFi一體化設備方式實現，確保可靠性與低延時 LWIP(LTE WLAN Radio Level Integration with IPsec Tunnel) LWIP技術不須改動舊有的WLAN架構設備，藉由UE透過WLAN建立IPSec通道至LTE eNB上的Security Gateway，即可實現LTE與WLAN的聚合 參考資料:http://www.2cm.com.tw/news_print.asp?sn=1611040016
LWAAP LTE與無線區域網路聚合適配協定(LTE-WLAN AggregationAdaptation Protocol, LWAAP)，在此層協定中，執行資料連線載體(Data Radio Bearer, DRB)的辨識碼附加，同時添加於基地台端與用戶設備端，以支援多重 LWA 載體的能力
LWA : User Plane (Non-collocated) 在U-plan(user plane)層面, LTE與WLAN是被聚合於Packet Data Convergence Protocol(PDCP)層. The Xw-U interface is used to deliver LWAAP PDUs between eNB and WT
LWA : Control Plane (Non-collocated) eNB-WT control plane signaling for LWA is performed by means of Xw-C interface signaling
LWA : Mobility A WLAN mobility set is a set of one or more WLAN Access Points (APs) identified by one or more BSSID/HESSID/SSIDs, within which WLAN mobility mechanisms apply while the UE is configured with LWA bearer(s) i.e., the UE may perform mobility between WLAN APs belonging to the mobility set without informing the eNB 以移動集合(mobility-set)替代一群存取點(agroup of Aps)，每個 mobility-set 的識別(ID)可能是基礎服務組識別碼 (BSSID)、同質延伸服務識別碼(HESSID)、或服務組識別碼(SSID)，相同 mobility-set 的存取點(AP)會有相同 SSID。 eNB 提供一組 mobility-set 給 UE，UE 在任何時間點都只能連結到一個 mobility-set。 mobility-set 內的 APs 都連接到同一個 WT；一個WT 可以連接多個 mobility-sets。 若 UE 在相同 mobility-set 的 APs 間移動，可以不通知 eNB；若發生跨 mobility-sets 的移動，則需要由 eNB 控制。
LWA : Operation WT Addition WT Modification WT Release
eLWA eLWA 五大項目標，分別為透過無線區域網路 (Wireless Local Area Networks, WLAN)的 上行資料傳送 移動管理優化 支援 60GHz 頻段 資訊收集與回饋 自動建立鄰近基 3 台關係(Automatic Neighbour Relation, ANR) 3GPP RAN2 #93, #96
eLWA-更新的上行傳輸的系統架構圖 3GPP RAN2 #96 有關上行資料傳輸，可能造成的封包序號不同步 留給用戶設備(UE)自行處理 目前的PDCP狀態回報與LWA狀態回報的資訊
Abbreviations & Definitions E-UTRAN : Evolved Universal Terrestrial Radio Access Network O&M : Operations & Maintenance Xw : logical interface between eNB and WT WT : WLAN Termination IANA : Internet Assigned Numbers Authority IETF : Internet Engineering Task Force PPP : Point-to-Point Protocol RFC : Request for Comments SCTP : Stream Control Transmission Protocol Elementary Procedure:a unit of interaction between an eNB and WT, consists of an initiating message and possibly a response message Class 1: Elementary Procedures with response (success or failure), Class 2: Elementary Procedures without response E-RAB : E-UTRAN Radio Access Bearer. An E-RAB uniquely identifies the concatenation of an S1 Bearer and the corresponding Data Radio Bearer. When an E-RAB exists, there is a one-to-one mapping between this E-RAB and an EPS bearer of the Non Access Stratum
Definitions and Terms LWA bearer : in LTE-WLAN Aggregation, a bearer whose radio protocols are located in both the eNB and the WLAN to use both eNB and WLAN resources WLAN Termination : the logical node that terminates the Xw interface on the WLAN side. PDCP : Packet Data Convergence Protocol RCLWI : RAN Controlled LTE-WLAN Interworking EP Elementary Procedure IE Information Element SN Sequence Number TAC Tracking Area Code UE User Equipment LWA LTE/WLAN Aggregation RCL WI : RAN Controlled LTE-WLAN Interworking Xw UP : Xw User Plane 3GPP TR 21.905: "Vocabulary for 3GPP Specifications"
Layer 1 (Physical layer) on the Xw Interface Interface to physical medium Frame delineation Line clock extraction capability Transmission quality control The support of any suitable layer 1 technique - like point-to-point or point-to-multipoint techniques - shall not be prevented Interface to management plane Performance monitoring functions Alarm status reporting functions Synchronization source management 3GPP TS 36.411: “Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1 ”
Xw Signaling Bearer Signaling Transport Functions Provision of reliable transfer of Xw-AP message over Xw interface Provision of networking and routeing function Provision of redundancy in the signalling network Support for flow control and congestion control Protocols Figure : Xw signalling bearer protocol stack The Transport Network Layer is based on IP transport, comprising SCTP on top of IP
Protocol Stack Data link layer : IP layer : Transport layer : The support of any suitable Data Link Layer protocol, e.g. PPP, Ethernet IP layer : The eNB shall support Ipv6 and/or Ipv4 The IP layer of Xw only supports point-to-point transmission for delivering Xw-AP message The eNB shall support the Diffserv Code Point marking Transport layer : There shall be only one SCTP association established between one eNB and WT pair The eNB shall establish the SCTP association A single pair of stream identifiers shall be reserved for the sole use of XwAP elementary procedures that utilize non UE-associated signalling At least one pair of stream identifiers shall be reserved for the sole use of XwAP elementary procedures that utilize UE-associated signalling A single UE-associated signalling shall use one SCTP stream and the stream should not be changed during the communication of the UE-associated signalling The SCTP congestion control may, using an implementation specific mechanism, initiate higher layer protocols to reduce the signalling traffic at the source and prioritise certain messages
XwAP Services the services offered between an eNB and WT The Xw interface XwAP(Xw Application Protocol) procedures UE-associated XwAP procedures :handle the configuration and modification to support LWA for a specific UE Non UE-associated procedures :support LWA and RCLWI, and are not related to a specific UE Parallel transactions Unless explicitly indicated in the procedure specification at any instance in time one protocol peer shall have a maximum of one ongoing XwAP procedure related to a certain UE
Non-collocated LWA Overall Architecture
Services Expected from Signalling Transport The signalling connection shall provide in sequence delivery of XwAP messages XwAP shall be notified if the signalling connection breaks Xw signalling transport is described in TS 36.462
Mapping between XwAP Functions and XwAP EPs Elementary Procedure(s) WLAN Status Reporting WT Status Reporting Initiation WT Status Reporting Setting up the Xw Xw Setup WT Configuration Update LTE-WLAN Aggregation WT Addition Preparation WT Association Confirmation eNB Initiated WT Modification WT Initiated WT Modification eNB Initiated WT Release WT Initiated WT Release Reporting of General Error Situations Error Indication Resetting the Xw Reset
XwAP Procedures Class 1 Elementary Procedures Initiating Message Successful Outcome Unsuccessful Outcome Response message Xw Setup Xw SETUP REQUEST Xw SETUP RESPONSE Xw SETUP FAILURE WT Configuration Update WT CONFIGURATION UPDATE WT CONFIGURATION UPDATE ACKNOWLEDGE WT CONFIGURATION UPDATE FAILURE WT Status Reporting Initiation WT STATUS REQUEST WT STATUS RESPONSE WT STATUS FAILURE WT Addition Preparation WT ADDITION REQUEST WT ADDITION REQUEST ACKNOWLEDGE WT ADDITION REQUEST REJECT eNB Initiated WT Modification WT MODIFICATION REQUEST WT MODIFICATION REQUEST ACKNOWLEDGE WT MODIFICATION REQUEST REJECT WT Initiated WT Modification WT MODIFICATION REQUIRED WT MODIFICATION CONFIRM WT MODIFICATION REFUSE WT Initiated WT Release WT RELEASE REQUIRED WT RELEASE CONFIRM Reset RESET REQUEST RESET RESPONSE
XwAP Procedures Class 2 Elementary Procedures Initiating Message WT Status Reporting WT STATUS REPORT Error Indication ERROR INDICATION WT Association Confirmation WT ASSOCIATION CONFIRMATION eNB Initiated WT Release WT RELEASE REQUEST
Xw Setup Exchange application level configuration data needed for the eNB and the WT to interoperate correctly over the Xw interface Erases any existing application level configuration data in the two nodes Replaces it by the one received This procedure also resets the Xw interface The procedure uses non-UE-associated signalling
Xw Setup - Successful Operation Xw SETUP REQUEST message(eNB->WT) Xw SETUP RESPONSE message(WT->eNB) A list of relevant WLAN identifiers
Xw Setup - Unsuccessful Operation Xw SETUP FAILURE message (WT->eNB) candidate WT cannot accept the setup An appropriate cause value
Xw Setup - Abnormal Conditions The first message received for a specific TNL association Not an Xw SETUP REQUEST, Xw SETUP RESPONSE, or Xw SETUP FAILURE message Shall be treated as a logical error
WT Configuration Update Update application level configuration data needed for an eNB and a WT to interoperate correctly over the Xw interface The procedure uses non-UE-associated signalling
WT Configuration Update - Successful Operation WT CONFIGURATION UPDATE message (WT->eNB) Include an appropriate set of up-to-date configuration data Added, modified and deleted WLAN identifiers that the WT has just taken into operational use
WT Configuration Update - Unsuccessful Operation CONFIGURATION UPDATE FAILURE message (eNB->WT) an appropriate cause value
WT Status Reporting Initiation This procedure is used by an eNB Request the reporting of load measurements to a WT The procedure uses non-UE-associated signalling
WT Status Reporting Initiation procedure – Successful Operation WT STATUS REQUEST message (eNB->WT) Registration Request IE Start WT initiate the requested measurement Report Characteristics IE The type of objects WT shall perform measurements on Stop WT shall stop all measurements and terminate the reporting Ignore Report Characteristics ,BSS To Report List, Reporting Periodicity, Partial Success Indicator Partial Success Indicator IE : WT provide not all of the information WT STATUS REPORT message(WT->eNB) BSS report list BSS Load IE : first bit WAN Metrics IE : second bit Available Channel Utilization IE : third bit Reporting Periodicity IE : Time interval between two messages WT STATUS RESPONSE message(WT->eNB) Measurement Initiation Result IE : WT initiate the measurement for the admitted measurement objects
WT Status Reporting Initiation Procedure - Unsuccessful Operation WT STATUS FAILURE message None of the requested measurements can be initiated Cause IE Set to an appropriate value for each requested measurement object Complete Failure Cause Information IE
WT Status Reporting Initiation Procedure – Abnormal Conditions The eNB does not receive either WT STATUS RESPONSE message or WT STATUS FAILURE message The eNB may reinitiate the WT Status Reporting Initiation procedure towards the WT New identical WT STATUS REQUEST Failed WT STATUS RESPONSE : Measurement Initiation Result ID without admitted measurements Registration Request IE is set to "start" and the Report Characteristics IE bitmap is set to "0" Registration Request IE is set to "start" and the Reporting Periodicity IE value is not specified Registration Request IE set to "start" and the eNB Measurement ID IE corresponding to an existing on-going load measurement reporting Registration Request IE is set to "stop" and the WT STATUS REQUEST message does not contain WT Measurement ID IE
WT Status Reporting This procedure is initiated by the WT to report the result of measurements admitted by the WT following a successful WT Status Reporting Initiation procedure WT STATUS REPORT message (WT->eNB) The admitted measurements are the measurements that were successfully initiated during the preceding WT Status Reporting Initiation procedure
Error Indication The Error Indication procedure is initiated by a node to report detected errors in one incoming message cannot be reported by an appropriate failure message. If the error situation arises due to reception of a message which used UE-associated signalling Then the Error Indication procedure uses UE-associated signalling Otherwise the procedure uses non UE-associated signalling
Error Indication Procedure, eNB/WT Originated - Successful Operation ERROR INDICATION message Cause IE Criticality Diagonstics IE eNB UE XwAP ID IE / WT UE XwAP ID IE
Reset Align the resources in the eNB and in the WT in the event of an abnormal failure The procedure resets the Xw interface Not affect the application level configuration data exchanged during The Xw Setup procedure The procedure uses non UE-associated signalling
Reset, eNB/WT-initiated Successful Operation RESET message Receiving node shall Abort any other ongoing procedures Except another Reset procedure Delete all the context information related to the initiating node Except the application level configuration data exchanged during Xw Setup or WT Configuration Update procedures Release the corresponding resources Respond with a RESET RESPONSE message Abnormal condition If Reset procedure is ongoing and the receiving node receives the RESET message from the peer entity on the same Xw interface the receiving node shall respond with the RESET RESPONSE message
WT Addition Preparation Request the WT to allocate resources for LWA operation for a specific UE The procedure uses UE-associated signalling Three cases Successful Operation Unsuccessful Operation Abnormal Operation
WT Addition Preparation - Successful Operation WT ADDITION REQUEST message(eNB->WT) E-RAB Level QoS Parameters IE Allocation and Retention Priority IE Allocation of sources GBR QoS Information IE eNB may therefore need to monitor the bit rate of offloaded GBR bearers Serving PLMN IE The WT may take it into account for the allocation of resources for LWA Reception of the WT ADDITION REQUEST message, WT shall Use the information included in the Mobility Set IE The WLAN Mobility Set configured for LWA Store the WLAN Security Information IE, if included Establish the required security relation towards the UE WT ADDITION REQUEST ACKNOWLEDGE message(WT->eNB), requested E-RAB E-RABs Admitted To Be Added List IE : successfully established E-RABs Not Admitted List IE : failed to be established
WT Addition Preparation - Unsuccessful Operation If the WT is not able to accept at least one of the bearers or a failure occurs during the WT Addition Preparation, the WT sends the WT ADDITION REQUEST REJECT message with an appropriate cause value to the eNB
WT Addition Preparation - Abnormal Conditions If the WT receives a WT ADDITION REQUEST message containing multiple E-RAB ID IEs (in the E-RABs To Be Added List IE) set to the same value The WT shall consider the establishment of the corresponding E-RAB as failed If the WT receives a WT ADDITION REQUEST message containing an E-RAB Level QoS Parameters IE which contains a QCI IE indicating a GBR bearer , and which does not contain the GBR QoS Information IE
eNB Initiated WT Modification This procedure is used to enable an eNB to request a WT to modify the UE context at the WT The procedure uses UE-associated signalling
eNB initiated WT Modification – Successful Operation WT MODIFICATION REQUEST message(eNB->WT) UE Context Information IE: E-RABs to be added within the E-RABs To Be Added Item IE E-RABs to be modified within the E-RABs To Be Modified Item IE E-RABs to be released within the E-RABs To Be Released Item IE WLAN security information in the WLAN Security Information IE E-RAB Level QoS Parameters IE Allocation and Retention Priority IE GBR QoS Information IE eNB may therefore need to monitor the bit rate of offloaded GBR bearers Serving PLMN IE The WT may take it into account for the allocation of resources for LWA eNB GTP Tunnel Endpoint IE in the E-RABs To Be Modified Item IE E-RAB level QoS parameter IE WT GTP Tunnel Endpoint IE Mobility Set IE WT MODIFICATION REQUEST ACKNOWLEDGE message (WT->eNB) E-RABs Admitted To Be Added List IE E-RABs Admitted To Be Modified List IE E-RABs Admitted To Be Released List IE E-RABs Not Admitted List IE
eNB initiated WT Modification – Unsuccessful Operation If the WT does not admit any modification requested by the eNB, or a failure occurs during the eNB initiated WT Modification The WT shall send the WT MODIFICATION REQUEST REJECT message to the eNB The message shall contain the Cause IE with an appropriate value
eNB initiated WT Modification, Abnormal Conditions If the WT receives a WT MODIFICATION REQUEST message containing multiple E-RAB ID IEs (in the E-RABs To Be Added List IE and/or the E-RABs To Be Modified List IE) set to the same value The WT shall not admit the action requested for the corresponding E-RABs If the WT receives a WT MODIFICATION REQUEST message containing multiple E-RAB ID IEs (in the E-RAB To Be Released List IE) set to the same value The WT shall initiate the release of one corresponding E-RAB and ignore the duplication of the instances of the selected corresponding E-RABs If the WT receives a WT MODIFICATION REQUEST message containing a E-RAB Level QoS Parameters IE which contains a QCI IE indicating a GBR bearer (as defined in TS 23.203 [13]), and which does not contain the GBR QoS Information IE The WT shall not admit the corresponding E-RAB Interaction with the WT initiated WT Modification procedure: If the eNB, after having initiated the eNB initiated WT Modification procedure, receives the WT MODIFICATION REQUIRED message The eNB shall refuse the WT initiated WT Modification procedure with an appropriate cause value in the Cause IE
WT Initiated WT Modification This procedure is used by the WT to modify the UE context in the WT. In particular, in this Release of the specification, this procedure is used to request to the eNB the release of LWA bearers, or change their WT GTP Tunnel Endpoints The procedure uses UE-associated signalling
WT initiated WT Modification – Successful Operation WT MODIFICATION REQUIRED message(WT->eNB) E-RABs to be released within the E-RABs To Be Released Item IE E-RABs to be modified within the E-RABs To Be Modified Item IE E-RABs To Be Modified Item IE WT GTP Tunnel Endpoint IE The eNB shall use this information to change the Xw transport bearer associated to the concerned E-RAB MODIFICATION CONFIRM message (eNB->WT) E-RABs Confirmed To Be Released List IE DL Forwarding GTP Tunnel Endpoint IE : data forwarding of downlink packets for that bearer E-RABs Confirmed To Be Modified List IE
WT initiated WT Modification – Unsuccessful Operation In case none of the requested modifications can be performed successfully the eNB shall respond with the WT MODIFICATION REFUSE message to the WT with an appropriate cause value in the Cause IE
WT initiated WT Modification - Abnormal Conditions If the value received in the E-RAB ID IE of any of the E-RABs To Be Released Item IE or of the E-RABs To Be Modified Item IE is not known at the eNB the eNB shall regard the procedure as failed and may take appropriate actions like triggering the eNB initiated WT Release procedure Interaction with the eNB initiated WT Modification Preparation procedure: If the WT, after having initiated the WT initiated WT Modification procedure, receives the WT MODIFICATION REQUEST message , the WT shall regard the WT initiated WT Modification Procedure as failed be prepared to receive the WT MODIFICATION REFUSE message from the eNB continue with the eNB initiated WT Modification procedure as specified in eNB Initiated WT Modification
eNB Initiated WT Release The eNB initiated WT Release procedure is triggered by the eNB to initiate the release of the resources for a specific UE The procedure uses UE-associated signalling
eNB initiated WT Release - Successful Operation WT RELEASE REQUEST message (eNB->WT) WT receipt : WT shall stop providing user data to the UE Cause IE : eNB provide appropriate information E-RABs To Be Released Item IE DL Forwarding GTP Tunnel Endpoint IE : the WT may perform data forwarding of downlink packets for that bearer
WT Initiated WT Release This procedure is triggered by the WT to initiate the release of the resources for a specific UE The procedure uses UE-associated signalling
WT-initiated WT Release - Successful Operation WT RELEASE REQUIRED message (WT->eNB) eNB receipt : replies with the WT RELEASE CONFIRM message WT RELEASE CONFIRM message (eNB->WT) E-RABs To Be Released Item IE DL Forwarding GTP Tunnel Endpoint IE : the WT may perform data forwarding of downlink packets for that bearer WT receipt : start data forwarding and stop providing user data to the UE
WT Association Confirmation This procedure is initiated by the WT to give confirmation to the eNB a certain UE successfully associated with the WLAN following a successful WT Addition Preparation procedure The procedure uses UE-associated signalling
WT Association Confirm Procedure – Successful Operation WT ASSOCIATION CONFIRMATION message (WT->eNB) eNB receipt : eNB consider that the UE is associated with the WLAN that user plane data for that UE may be sent to the WT
Xw Data Transport Data Link Layer: any data link protocol that fulfils the requirements toward the upper layer may be used Transport Network Layer for Data Streams over Xw GTP-U : General Packet Radio Service Tunneling Protocol – User Plane(用於為每個PDP context提供一個或多個隧道，用以傳輸用戶數據) GTP :是一組基於IP的通信協議，用於在GSM、UMTS和LTE網絡中承載GPRS There is one UL data stream (if flow control is supported) and one DL data stream per E-RAB at the Xw interface DL(eNB->WT) UL(WT->eNB) Each data stream is carried on a dedicated transport bearer
Xw over UDP/IP Path protocol The UDP port number for GTP-U shall be as defined in TS 29.281 The eNB and the WT over the Xw interface shall support fragmentation and assembly of GTP packets at the IP layer There may be one or several IP addresses in both the eNB and the WT The packet processing function in the source eNB shall send downstream packets corresponding toa given E-RAB to the target WT IP address (received in XwAP) associated to the DL transport bearer of that particular E-RAB The packet processing function in the source WT shall send upstream packets corresponding to a given E-RAB to the target eNB IP address (received in XwAP) associated to the UL transport bearer of that particular E-RAB The Transport Layer Address signalled in XwAP messages is a bit string of 32 bits in case of Ipv4 address according to IETF RFC 791 128 bits in case of Ipv6 address according to IETF RFC 2460
Diffserv Code Point Marking IP Differentiated Services code point marking shall be supported The mapping between traffic categories and Diffserv code points Be configurable by O&M for based on QoS Class Identifier (QCI)/ Label Characteristics and others E-UTRAN traffic parameters Traffic categories are implementation-specific May be determined from the application parameters
LTE-WLAN Aggregation For the LWA bearer option the GTP-U protocol over UDP over IP shall be supported as the transport for the downlink user data stream of LWA PDUs and the uplink flow control feedback stream on the Xw interface The GTP-U PDU(Protocol Data Unit) includes a RAN Container with flow control information as specified in TS 36.465 which is carried in the GTP-U extension header The transport bearer is identified by the GTP-U TEID and the IP address of the eNB and WT respectively The DL data stream is used for DL user data transmission from the eNB to the WT The UL data stream is used for UL flow control feedback transmission from the WT to the eNB the packet processing function in the eNB shall send downstream packets corresponding to a given E-RAB to the WT IP address (received in XwAP) associated to the DL transport bearer of that particular E-RAB. The packet processing function in the WT shall send upstream packets corresponding to a given E-RAB to the eNB IP address (received in XwAP) associated to the UL transport bearer of that particular E-RAB in addition, user data forwarding (from WT to eNB ) may be performed by eNB providing another GTP-U TEID to receive the DL data forwarded by the WT
LWA Radio Protocol Architecture for the Non-Collocated Scenario
LWA Radio Protocol Architecture for the Collocated Scenario
Xw User Plane Protocol Using services of the transport network layer in order to allow flow control of user data packets transferred over the Xw interface Provision of Xw UP specific sequence number information for user data transferred from the eNB to the WT for a specific E-RAB configured with the LWA bearer option Information of successful transmission towards or in sequence delivery to the UE of LWAAP PDUs from WT for user data associated with a specific E-RAB configured with the LWA bearer option Information of LWA PDUs that were not transferred towards or not delivered to the UE Information of the currently desired buffer size at the WT for transmitting to the UE user data associated with a specific E-RAB configured with the LWA bearer option Information of the currently minimum desired buffer size at the WT for transmitting to the UE user data associated with all E-RABs configured with the LWA bearer option
Transfer of Downlink User Data Services Expected from the Xw Transport Network Layer Provide Xw-U specific sequence number information at the transfer of user data carrying a DL LWA PDU from the eNB to the WT via the Xw-U interface An Xw user plane instance making use of the Transfer of Downlink User Data procedure is associated to a single E-RAB only. The Transfer of Downlink User Data procedure is invoked whenever user data for that particular E-RAB needs to be sent across the Xw-U interface. The eNB shall assign consecutive Xw-U sequence numbers to each transferred Xw-U packet. The WT shall detect whether an Xw-U packet was lost and memorise the respective sequence number after it has declared the respective Xw-U packet as being “lost”. The WT shall transfer the remaining LWA PDUs towards the UE and memorise the highest Xw-U sequence number of the PDCP PDU that was successfully transferred towards or delivered to the UE.
Downlink Data Delivery Status Provide feedback from the WT to the eNB to allow the eNB to control the downlink user data flow via the WT for the respective E-RAB When the WT decides to trigger the Feedback for Downlink Data Delivery procedure it shall report: a) the highest Xw-U sequence number successfully transferred towards or delivered to the UE among those PDUs received from the eNB; b) the desired buffer size in bytes for the concerned E-RAB; c) the minimum desired buffer size in bytes for the UE; d) the Xw-U packets that were declared as being “lost” by the WT and have not yet been reported to the eNB within the DL DATA DELIVERY STATUS frame.
References LWA eLWA feLWA Stage-2 high level description – TS 36.300, section 22A.1 Stage-3 data plane (PDCP) –TS 36.323 Stage-3 data plane (LWAAP) – TS 36.360 Stage-3 control plane (RRC) – various sections in TS 36.331 Stage-3 control plane network interface (Xw) – TS 36.463, TS 36.462, TS 36.461 Stage-3 data plane network interface (Xw) – TS 36.465. TS 36.464 Stage-3 security aspects – TS 33.401, section X (section number to be allocated) eLWA Rel-14 eLWA Work Item Description (WID) - RP-160600 feLWA Rel-15 FeLWA Motivation – RP-162198