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
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
S-GW
MME
MME / S-GW
S1-U
S1-MME
S1
S1
Xw-C
WT
Xw
Xw-U
WT
WT
eNB
eNB
Xw
Xw
eNB
Xw
eNB
WT
C-Plane connectivity of
eNB and WT for LWA
U-Plane connectivity of
eNB and WT for LWA
3
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
LTE
Bearer
Split LWA
Bearer
S1
Switched LWA
Bearer
S1
PDCP
PDCP
RLC
RLC
PDCP
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
LWAAP
MAC
WLAN
eNB
LTE
Bearer
Split LWA
Bearer
S1
PDCP
Switched LWA
Bearer
S1
PDCP
LWA Radio Protocol Architecture
for the Non-Collocated Scenario
PDCP
Xw
RLC
RLC
LWAAP
MAC
WLAN
eNB
WT
4
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
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)
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
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-tomultipoint 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 (EUTRAN); 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 :
• 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
MME / S-GW
S1
S1
WT
Xw
Xw
Xw
eNB
Xw
eNB
WT
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
Function
WLAN Status Reporting
Elementary Procedure(s)
a) WT Status Reporting Initiation
b) WT Status Reporting
Setting up the Xw
WT Configuration Update
LTE-WLAN Aggregation
Xw Setup
WT Configuration Update
a) WT Addition Preparation
b) WT Association Confirmation
c) eNB Initiated WT Modification
d) WT Initiated WT Modification
e) eNB Initiated WT Release
f) WT Initiated WT Release
Reporting of General Error Situations
Resetting the Xw
Error Indication
Reset
XwAP Procedures
Class 1 Elementary Procedures
Elementary Procedure
Initiating Message
Successful Outcome
Unsuccessful Outcome
Response message
Response message
Xw Setup
Xw SETUP REQUEST
Xw SETUP RESPONSE
Xw SETUP FAILURE
WT Configuration Update
WT CONFIGURATION
UPDATE
WT CONFIGURATION
UPDATE FAILURE
WT Status Reporting
Initiation
WT STATUS
REQUEST
WT CONFIGURATION
UPDATE
ACKNOWLEDGE
WT STATUS
RESPONSE
WT Addition Preparation
WT ADDITION
REQUEST
WT ADDITION REQUEST
REJECT
eNB Initiated WT
Modification
WT MODIFICATION
REQUEST
WT Initiated WT
Modification
WT MODIFICATION
REQUIRED
WT ADDITION
REQUEST
ACKNOWLEDGE
WT MODIFICATION
REQUEST
ACKNOWLEDGE
WT MODIFICATION
CONFIRM
WT Initiated WT Release
WT RELEASE
REQUIRED
RESET REQUEST
WT RELEASE
CONFIRM
RESET RESPONSE
Reset
WT STATUS FAILURE
WT MODIFICATION
REQUEST REJECT
WT MODIFICATION
REFUSE
XwAP Procedures
Class 2 Elementary Procedures
Elementary Procedure
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
eNB
• Start
–WT initiate the requested measurement
–Report Characteristics IE
»The type of objects WT shall perform measurements on
WT
WT STATUS REQUEST
WT STATUS RESPONSE
• 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
eNB
WT
WT STATUS REQUEST
WT STATUS FAILURE
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
eNB
WT
WT STATUS REPORT
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 UEassociated 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
eNB
WT
ERROR INDICATION
eNB
WT
ERROR INDICATION
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
eNB
– Abort any other ongoing procedures
WT
RESET
• Except another Reset procedure
– Delete all the context information related to
the initiating node
BB
RESET RESPONSE
• 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
eNB
WT
RESET
RESET RESPONSE
BB
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)
eNB
– E-RAB Level QoS Parameters IE
WT
WT ADDITION REQUEST
• Allocation and Retention Priority IE
WT ADDITION REQUEST ACKNOWLEDGE
–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
requested E-RAB
REQUEST
ACKNOWLEDGE
message(WT->eNB),
– 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
eNB
WT
WT ADDITION REQUEST
WT ADDITION REQUEST REJECT
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 ERAB Level QoS Parameters IE which contains a QCI IE indicating a GBR
bearer , and which does not contain the GBR QoS Information IE
– The WT shall consider the establishment of the corresponding E-RAB as failed
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
eNB
WT
– GBR QoS Information IE
• eNB may therefore need to monitor
the bit rate of offloaded GBR bearers
– Serving PLMN IE
WT MODIFICATION REQUEST
WT MODIFICATION REQUEST ACKNOWLEDGE
• 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
WT
WT MODIFICATION REQUEST
WT MODIFICATION REQUEST REJECT
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 ERAB 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
eNB
WT
WT MODIFICATION REQUIRED
WT MODIFICATION CONFIRM
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
eNB
WT
WT MODIFICATION REQUIRED
WT MODIFICATION REFUSE
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
eNB
WT
WT RELEASE REQUEST
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
eNB
WT
WT RELEASE REQUIRED
WT RELEASE CONFIRM
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
eNB
WT
WT ASSOCIATION CONFIRMATION
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
GTP-U
UDP
IPv6 (RFC 2460)
and/or
IPv4 (RFC 791)
Data link layer
Physical layer
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
LTE
Bearer
Split LWA
Bearer
S1
PDCP
Switched LWA
Bearer
S1
PDCP
PDCP
Xw
RLC
RLC
LWAAP
MAC
WLAN
eNB
WT
LWA Radio Protocol Architecture
for the Collocated Scenario
LTE
Bearer
Split LWA
Bearer
S1
Switched LWA
Bearer
S1
PDCP
PDCP
RLC
RLC
PDCP
LWAAP
MAC
WLAN
eNB
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
eNB
WT
DL USER DATA
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
eNB
WT
DL DATA DELIVERY STATUS
References
• LWA
– 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
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