1. Non-optimized Handoff Enhancement
2017/4/24
Non-optimized Handoff Enhancement
China Telecom
Chengli Mei
Ericsson
Ahmad Muhanna
Ke-Chi Jang
HUAWEI
Zhiming Li
Jie Zhao
13 September. 2010
Notice
The contributors grants a free, irrevocable license to 3GPP2 and its Organizational Partners to incorporate text or other copyrightable material contained in the contribution and any modifications thereof in the creation of 3GPP2 publications; to copyright and sell in Organizational Partner’s name any Organizational Partner’s standards publication even though it may include all or portions of this contribution; and at the Organizational Partner’s sole discretion to permit others to reproduce in whole or in part such contribution or the resulting Organizational Partner’s standards publication. The contributors are also willing to grant licenses under such contributor copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing an Organizational Partner’s standard which incorporates this contribution.
This document has been prepared by the contributors to assist the development of specifications by 3GPP2. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on the contributors. The contributors specifically reserves the right to amend or modify the material contained herein and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of the contributors other than provided in the copyright statement above.

2. Motivation
Enabling eHRPD-LTE dual mode UE to early-register on eHRPD directly over eHRPD access.
slide 2

3. Working assumptions and Key Features
Based on Single Transmitter / Dual Receiver (1T/2R) UE or Single Transmitter / Single Receiver (1T/1R) UE
Minimizes changes to the current standards and network elements
Key Features – (1T/1R) UE
Step 1: UE selects and camps on LTE first without any interaction with eHRPD system
Step 2: UE performs eHRPD early-registration directly over eHRPD access during LTE idle state.
Step 3: UE could maintain eHRPD session during LTE idle state
Step 4: Handover Phase – UE HO from LTE to eHRPD
Key Features – (1T/2R) UE
Step 1: UE can camp on either LTE or eHRPD first.
Step 2: UE performs eHRPD early-registration directly over eHRPD access:
During idle state if camped on LTE first.
If UE camp on eHRPD first, UE may perform early-registration on eHRPD first and then move to LTE.
Step 3: UE should be able to maintain eHRPD session during LTE idle state
Step 4: Handover Phase – UE HO from LTE to eHRPD in case the UE camps on LTE first.
slide 3

4. Early-Registration over eHRPD Access Call Flow (UE camps on LTE first)
UE powers on
UE finds a candidate cell of LTE
UE camps on the LTE network
If eNB broadcasts the eHRPD Neighbor cell list, the UE will tune to eHRPD mode to perform session establishment when the UE is in LTE idle state.
UE stays in idle and finds a candidate eHRPD cell
UE and HSGW can negotiate the capability of early-registration over eHRPD access during LCP
UE switches to eHRPD network and performs early-registration over eHRPD access
If Attach Type = “Registration”, HSGW does not setup bearer path with P-GW. Only default PDN connection must to be setup. The UE can optionally establish non-default PDN connection
UE switches back to LTE
10. UE Switches
back to LTE ,
slide 4

5. Details of early-Registration
Upon receiving the eHRPD neighbor cell list broadcasted by eNB, UE initiates early-registration directly over eHRPD access.
UE and HSGW negotiate the capability of early-registration over eHRPD access during LCP. If the HSGW doesn’t support it, UE may terminates the PPP session setup.
UE establishes the default PDN connection with HSGW. The new attach type “Registration” indicates that no PMIP tunnel needs to be setup.
UE can optionally establish the non-default PDN connections with HSGW.
slide 5

6. Roaming Cases Analysis
Network Capability UE
Capability
non-optimized handoff with early-registration.
Normal non-optimized handoff
Optimized handoff (S101)
Optimized handoff (S101) and non-optimized handoff with early-registration
non-optimized handoff with early-registration
Non-optimized with early-registration
early-registration attempt no PPP context
Normal Non-optimized handoff
Optimized handoff Support Registration over S101
Optimized Handoff using S101
Optimized handoff and non-optimized handoff with early-registration
Optimized handoff using S101
slide 6

7. PPP Session Maintenance
Full PPP context
The UE and the HSGW have full PPP context after the early registration
The HSGW supports PPP inactivity timer, and the UE knows the MAX PPP Inactivity Timer value
For dual receiver case, UE may receive the LCP Echo-Request from HSGW, and sends Echo-Reply in idle state
For single receiver case, if the UE fails to reply the Echo-Request, the HSGW and the UE enter to partial UE context
Partial UE context
The HSGW supports UE Context Maintenance timer
If UE requests one or more PDN connections, HSGW stops the UE Context Maintenance timer, and re-start the PPP inactivity timer
How the UE and the HSGW maintain the partial context, as currently documented in X.S0057
If PPP inactivity timer expires and the UE is NOT able to send any activity, the UE should assume that the context is gone. However, the UE always can check on the context when goes to eHRPD by sending echo-request with PDN-ID to check if the HSGW still maintains that context
slide 7

8. Handover Call Flow slide 8
If Attach Type = “Handover”, HSGW initiates PMIP procedure based on all PDN context received during early registration
slide 8

9. The details of Handover (1/2)
Full PPP context
If UE setups multiple PDN connections during early registration, UE will send one VSNCP message with “Handoff” attach type and PDN-ID(s) to trigger the HSGW perform PMIP procedure.
UE initiates the TFT process
Partial UE context
UE establishes all PDN connections
No PPP context
UE establishes the PPP session
slide 9

10. The details of Handover (2/2)
PMIP trigger
HSGW doesn’t trigger the PMIP Binding when the HSGW receives A11-Registration Request message with Active-Start Airlink Record. It is little different from current spec.
Upon receiving the VSNCP with attach type = handover and one or more PDN-ID from UE, HSGW shall trigger the PMIP Binding
PDN Synchronization
The UE doesn’t need to keep the PDN connections information which is in eHRPD is synchronized with one’s in LTE all the time, UE only update the PDN connections information in eHRPD when it is in idle state in LTE
UE shall perform the PDN connections information synchronization with HSGW via LCP echo during handover
Accounting
For the early-registration and session maintenance, the HSGW doesn’t start accounting process
slide 10

11. Deployment Consideration & Standards Impacts
Node
Deployment impacts
Standard impacts
eNB
eNB needs to broadcast SIB8, including eHRPD related cell parameters and subnet info
None
MME
SGW
eAN/ePCF
Legacy AN needs to be software upgraded to evolved AN/ePCF
HSGW
Needs to support an additional attach type ” Registration”
Add one new Attach type “Registration” in VSNCP Config-Req message. (X.S0057)
HSS
Should be deployed to support the SWx interface
AAA
. Need to support STa and SWx for authentication & authorization.
. Need to support S6b.
PDN GW
Need to support S6b
PCRF UE
slide 11

12. Recommendation
Adopt the early-registration over eHRPD access solution in X.P0057 -A
slide 12

13. Backup Informative Only
slide 13

14. eHRPD Session Maintenance – KeepAlive Procedures
slide 14

15. The details of KeepAlive Process
Concept:
If UE is in Active state, it will set a flag and wait until getting to idle state, at which time UE will switch to eHRPD to maintain the session.
Details:
UE keeps a counter NKeepAliveReq. The counter increase by one when UE detects a period of eHRPD’s inactivity for TSMPClose/NSMPKeepAlive minutes.
Case 1: If 0< NKeepAliveReq < NSMPKeepAlive, UE will set a flag. When UE enters LTE idle mode and the flag is set, UE will tune to eHRPD and send KeepAliveRequest message. Reset NKeepAliveReq to 0 and reset the flag.
Case 2: If NKeepAliveReq = NSMPKeepAlive, UE has two options:
1) UE immediately tune to eHRPD and send KeepAliveRequest message. Reset NKeepAliveReq to 0 and reset the flag. In this scenario, the service in LTE is interrupted.
2) UE gives up the eHRPD session maintenance, just keep the service in LTE
NSMPKeepAlive is set to max 3 per C.S0024.
slide 15

16. eHRPD Session Maintenance – Subnet Change
Note1: For the single receiver case, UE may receive the subnet info from the eNB
Note2: For the dual receiver case, if QuickConfig or SectorParameters message received while UE in LTE active mode,
the UE will defer UATI Assignment to when it goes into LTE idle state
slide 16

17. LTE Paging and UL Data Process
early-registration phase
For the dual receiver case, UE may receive Paging message LTE
Stop/abort HRPD registration procedures and tune to LTE
Uplink Data ready for Transmission
KeepAlive
Continue HRPD KeepAlive procedure and tune to LTE
Buffer data. Complete HRPD KeepAlive procedure and tune to LTE
Subnet change
Stop/abort HRPD UATI Assignment procedures and tune to LTE
PPP context maintenance
slide 17