1. 助理教授：吳俊興 助教：王瑞元、許力中 國立高雄大學 資訊工程學系
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 #16 LTE/WLAN Radio Level Integration Using IPsec Tunnel (LWIP) Encapsulation
助理教授：吳俊興
助教：王瑞元、許力中
國立高雄大學 資訊工程學系

2. LWIP - LTE/WLAN Radio Level Integration with IPsec Tunnel (LWIP)
MME / S - GW 1
WLAN
eNB UE I P
LWIP-SeGW
UE uses WLAN via IPSec tunnel between eNB and UE
Fast time to market, use of legacy WLAN infrastructure
WLAN is hidden from CN
Except for WLAN authentication

3. Motivation
LWIP was introduced in Release-13 to address the operator needs
To leverage the capacity available from the large incumbent WLAN network base where modifications to WLAN
As required by LWA would not be feasible because of hardware, architectural or operational constraints
The use of WLAN resources in downlink and uplink is controlled by the eNB, and bypasses the LTE user plane protocol stack
LWIP allows use of combined LTE and WLAN capacity for a user by allowing either inter-bearer distribution or intra-bearer per IP flow distribution across the LTE and WLAN radio links

4. Overview LWIP is controlled by eNB, based on UE measurement reporting
LWIP feature allows a UE in RRC_CONNECTED to be configured by the eNB to utilize WLAN radio resources via IPsec tunnelling
Connectivity between eNB and WLAN is over IP
(TS Section 22A.3)

5. LWIP Tunnel
IP packets transferred between the UE and LWIP-SeGW are encapsulated using IPSec
Provide security to the packets that traverse WLAN
Uplink and downlink data supported over WLAN
Multiple bearers can be offloaded via IPSec
The IP packets are then transported between the LWIP-SeGW and eNB
The end to end path between the UE and eNB via the WLAN network is referred to as the LWIP tunnel

6. Security and Transparence
For security reasons IPsec tunnel is terminated in LWIP-SeGW in eNB
Single IPSec tunnel per UE for UL and DL data
IPsec tunnel is transparent to WLAN infrastructure
There are no standardized network interfaces in LWIP

7. LWIP Protocol Architecture

8. LWIP Protocol Stack

9. Security Gateway (SeGW)
The use of insecure third party broadband for backhauling mobile voice and multimedia data from small cells exposes the mobile operator’s core network to IP-based attacks, user identity theft and fraud
The SeGW provides market-leading IP Security/Internet Key Exchange Version 2 (IPsec/IKEv2) tunnel performance
The SeGW is a carrier class gateway for secure, scalable fixed mobile convergence solutions
The SeGW provides mobile operators with a complete Security Gateway solution for security and aggregation of 3G (HNB), 4G LTE (HeNB) and 3GPP2 cdma cellular small cells, including femtocells, picocells or metrocells

10. Definitions, Symbols and Abbreviations
The terms and definitions given in TR 21.905
Data Radio Bearer -DRB
Internet Protocol -IP
LTE/WLAN Radio Level Integration Using Ipsec(security) Tunnel -LWIP
LWIP Encapsulation Protocol -LWIPEP
Generic Routing and Encapsulation -GRE
Packet Data Convergence Protocol -PDCP
Protocol Data Unit -PDU
Radio Resource Control -RRC
Service Access Point -SAP
Service Data Unit -SDU

11. Bearer over LWIP Tunnel
The data bearer refers to the EPS bearer mapped to the Data Radio Bearer (DRB) which is maintained on the LTE side
The DRB configuration on the LTE access corresponding to the data bearer using IPsec resources shall not be released
A single IPSec tunnel is used per UE for all the data bearers that are configured to send and/ or receive data over WLAN
Each data bearer may be configured so that traffic for that bearer can be routed over the IPsec tunnel in either only downlink or both uplink and downlink over WLAN
The RRC_Connection_Reconfiguration message provides the necessary parameters for the UE to initiate the establishment of the IPSec tunnel for the DRB

12. DL/UL of a Data Bearer
For the DL of a data bearer, the packets received from the IPsec tunnel are forwarded directly to upper layers
For the UL, the eNB configures the UE to route the uplink data either via LTE or via WLAN using RRC signaling
If routed via WLAN then all UL traffic of the data bearer is offloaded to the WLAN
UL bearer packets sent over the LWIP tunnel are encapsulated using LWIPEP as specified in TS with the ‘Key’ field in the LWIPEP header populated with the DRB Identity associated with offloaded UL bearer

13. Release of a LWIP Tunnel
The release of the IPSec tunnel is initiated by the eNB
Upon receiving the Handover Command or on transition to RRC_IDLE state, the UE shall autonomously release IPsec tunnel configuration and the use of it by the data bearers
A UE supporting LWIP may be configured for WLAN measurements as per subclause 22A.1.5.

14. LWIP Mobility
The same mobility concept as specified in 22A.1.4 for LWA is also used for LWIP
Since WT node does not exist in LWIP operation, WT related description and procedures does not apply to LWIP
Mobility Set should be considered as the set of WLAN APs across which UE can perform mobility without informing the eNB, when applying the concept for LWIP operation

15. Issue with Multiple WLAN Interworking
E-UTRAN does not configure LWIP with DC, LWA or RCLWI simultaneously for the same UE.
If LWIP and RAN assisted WLAN interworking are simultaneously configured for the same UE, in RRC Connected, the UE only applies LWIP

16. LWIP Operation LWIP Tunnel Setup and Data Bearer Configuration
The UE uses the parameters in the new radio resource configuration to setup the IPsec tunnel with the LWIP-SeGW to complete the establishment of the LWIP tunnel with the eNB over the WLAN access
eNB may add or remove data bearers to utilise the LWIP tunnel at any time after the establishment of the LWIP tunnel by sending the RRCConnectionReconfiguration message to the UE
1.eNB配置UE執行用於LWIP操作的WLAN測量。
2.UE應用新配置並使用RRCConnectionReconfigurationComplete消息進行答复。
3.UE向eNB發送WLAN測量。
4.eNB向UE發送包括WLAN移動性集合的RRCConnectionReconfiguration消息。
5.UE應用新配置和具有RRCConnectionReconfigurationComplete消息的應答。
6.如果還沒有關聯，則UE考慮移動性集合與WLAN相關聯。
7.UE向eNB發送WLAN關聯的確認。
8.eNB向UE發送RRCConnectionReconfiguration消息，包括必要的參數以在WLAN上建立IPSec隧道，並且可以配置數據承載以利用IPsec隧道。
9.UE應用新配置和具有RRCConnectionReconfigurationComplete消息的應答。
UE使用新無線電資源配置中的參數來與LWIP-SeGW建立IPsec隧道，以通過WLAN接入完成與eNB的LWIP隧道的建立。 eNB可以在通過向UE發送RRCConnectionReconfiguration消息來建立LWIP隧道之後的任何時間添加或刪除數據承載以利用LWIP隧道。

17. LWIP Tunnel for Data Bearer Setup Procedure
1. The eNB configures the UE to perform WLAN measurements for LWIP operation 2. The UE applies the new configuration and replies with RRCConnectionReconfigurationComplete message 3. UE sends WLAN measurements to the eNB 4. The eNB sends the RRCConnectionReconfiguration message to the UE including the WLAN mobility set 5. The UE applies the new configuration and replies with RRCConnectionReconfigurationComplete message 6. UE associates with WLAN in consideration of the mobility set, if not already associated 7. UE sends confirmation of the WLAN association to the eNB 8. The eNB sends the RRCConnectionReconfiguration message to the UE including the necessary parameters to establish IPSec tunnel over WLAN and may, configure data bearers to utilise the IPsec tunnel 9. The UE applies the new configuration and replies with RRCConnectionReconfigurationComplete message

18. Reconfiguration to Remove WLAN Resources

19. Remove Reconfiguration Procedure
UE and eNB have the LWIP tunnel setup via WLAN
1. The UE is configured to receive data from a data bearer over the LWIP tunnel
2. The eNB determines that it needs to remove the WLAN resources for the data bearer
3. The eNB sends the RRCConnectionReconfiguration message to the UE including the necessary parameters to remove WLAN resources for the data bearer
4. The UE applies the new configuration and replies with RRCConnectionReconfigurationComplete message
5. UE stops receiving data for the data bearer over the LWIP tunnel

20. LWIP Tunnel Release

21. Release Procedure
1. The eNB determines that it needs to release the LWIP tunnel and initiates the release of the IPsec tunnel between the UE and LWIP-SeGW
2. The eNB sends the RRCConnectionReconfiguration message to the UE including the indication to release the LWIP tunnel
3. The UE applies the new configuration and replies with the RRCConnectionReconfigurationComplete message
4. The UE releases the IPsec tunnel and associated data bearer configuration, and terminates the LWIP tunnel

22. LWIPEP Sublayer

23. LWIPEP Entity RRC is in control of the LWIPEP configuration
Functions of the LWIPEP sublayer are performed by LWIPEP entities
For an LWIPEP entity configured at the eNB
There is a peer LWIPEP entity configured at the UE and vice versa
The LWIPEP entity responsible for
Encapsulating LWIPEP SDUs is referred to as the transmitter
Decapsulating LWIPEP PDUs is referred to as the receiver

24. LWIPEP Operation
An LWIPEP entity receives/delivers LWIPEP SDUs from/to upper layers (i.e. IP) and sends/receives LWIPEP PDUs to/from its peer LWIPEP entity via an LWIP Tunnel
In the uplink direction:
At the UE, when an LWIPEP entity receives an LWIPEP SDU from upper layers, it constructs the corresponding LWIPEP PDU and delivers it to lower layers
At the eNB, when an LWIPEP entity receives an LWIPEP PDU from lower layers, it reassembles the corresponding LWIPEP SDU and delivers it to upper layers

25. LWIP Services Services provided to upper layers
The following services are provided by LWIPEP to upper layers (i.e. IP):transfer of user plane data
Services expected from lower layers
The following services are expected by LWIPEP from lower layers (i.e. LWIP Tunnel):transfer of user plane data
Functions
The following functions are supported by the LWIPEP sublayer:
Transfer of user plane data
Identification of the DRB identity to which the LWIPEP SDU belongs

26. LWIP Procedures Data transfer procedures UL data transfer procedures
When receiving an LWIPEP SDU from upper layers, the LWIPEP entity shall form the LWIPEP PDU
Handling of unknown, unforeseen and erroneous protocol data
When an LWIPEP entity receives an LWIPEP PDU that contains reserved or invalid values, the LWIPEP entity shall:
discard the received PDU

27. LWIPEP Data PDU
An LWIPEP data PDU consists of the LWIPEP header and the LWIPEP SDU

28. LWIPEP Data Bit Strings
LWIPEP data PDU
An LWIPEP PDU is a bit string that is byte aligned (i.e. multiple of 8 bits) in length
Bit strings are represented by tables in which
The most significant bit is the leftmost bit of the first line of the table,
The least significant bit is the rightmost bit on the last line of the table, and
More generally the bit string is to be read from left to right and then in the reading order of the lines
The bit order of each parameter field within an LWIPEP PDU is represented with
the first and most significant bit in the leftmost bit and
the last and least significant bit in the rightmost bit

29. Formats and Parameters
The LWIPEP Header is a GRE header as specified in RFC 2890 and has a fixed size of eight bytes including the Key field
The UE shall set the 5 LSB's of the Key field in the GRE header to the DRB Identity associated with the LWIPEP SDU and set the remaining MSB's to '0‘
All other optional fields are unused, and the values of other fields shall be set as specified in RFC 2784 [4] and RFC 2890

30. References
3GPP TS 36.300: “E-UTRA and E-UTRAN Overall Description; Stage 2”, Section 22A.3
3GPP TS : “LTE/WLAN Radio Level Integration Using IPsec Tunnel (LWIP) Encapsulation; Protocol Specification”
3GPP TR 21.905: “Vocabulary for 3GPP Specifications”
3GPP TS 36.331: “E-UTRA RRC Protocol Specification”
IETF RFC 2784: “Generic Routing Encapsulation (GRE)”
IETF RFC 2890: “Key and Sequence Number Extensions to GRE”