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23/4/20

Non-optimized Handoff Enhancement

HUAWEI Zhiming Li lizhiming@huawei.com Jie Zhao zhao.jie@huawei.com

13 September. 2010

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China Telecom Chengli Mei meichl@ctbri.com.cn

Ericsson Ahmad Muhanna ahmad.muhanna@ericsson.com Ke-Chi Jang ke-chijang@ericsson.com

slide 2

Motivation

Enabling eHRPD-LTE dual mode UE to early-register on eHRPD

directly over eHRPD access.

slide 3

Working assumptions and Key Features

Assumption 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 4

Early-Registration over eHRPD Access Call Flow(UE camps on LTE first)

UE eAN/ePCF AN-AAA HSGW HSSP-GWPCRF AAAS-GW

1 . Power on

PMIPv6 Tunnel

2 . LTE Initial Attach

4 . eHRPD Session Negotiation, PPP setup and Authentication

9 .

5 . - Req (PDN-ID, Attach Type…)

. VSNCP Config- Ack ( PDN-ID…)

. VSNCP Config- Ack (PDN-ID)

. VSNCP Config- Req ( PDN-ID)

UE initiates eHRPD connection release into dormant state

VSNCP Config

6

8

7

3. UE enters LTE idle state, discovers eHRPD network and tunes to eHRPD network

UE powers on

UE finds a candidate cell of LTE

UE camps on the LTE network

UE switches to eHRPD network and performs early-registration

over eHRPD access

UE switches back to LTE

UE stays in idle and finds a candidate eHRPD cell

UE stays in idle and finds a candidate eHRPD cell

UE stays in idle and finds a candidate eHRPD cell

10. UE Switches

back to LTE

,

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

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 and HSGW can negotiate the capability of early-registration over eHRPD access during LCP

slide 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 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

early-registration

attempt no PPP

context

Non-optimized with

early-registration

Normal non-optimized

handoff

Normal Non-

optimized

handoff

Normal Non-

optimized handoff

Normal Non-

optimized handoff

Normal Non-

optimized handoff

Optimized handoff

Support Registration

over S101

Normal Non-

optimized

handoff

Normal Non-

optimized handoff

Optimized Handoff

using S101

Optimized Handoff

using S101

Optimized handoff and

non-optimized handoff

with early-registration

Non-optimized

with early-

registration

Normal Non-

optimized handoff

Optimized handoff

using S101

Optimized Handoff

using S101

slide 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 8

Handover Call FlowUE eAN/ePCF S-eAN HSGW HSSP-GWPCRF

10. PMIP Binding Update

11. PMIP Binding Ack

AAA

3. UATIAssignment + TCA

1. ConnectionRequest

2. A13 Session Transfer

0. Decision to handover to eHRPD

5. A11'-Registration Request

OPTIONAL PROCEDURE

S-GW

17. 3GPP EPS Resource release

4. UATIAssignmentComplete + TCC

OPTIONAL PROCEDURE16. Other PDN connection Setup

15. Network Initiated Dedicated Bearer Setup

OPTIONAL PROCEDURE

6. A11'-Registration Reply

9. VSNCP Config-Req (PDN-ID(s), Attach Type (Handover))

12. VSNCP Config-Ack (PDN-ID…)

13. VSNCP Config-Req (PDN-ID)

14. VSNCP Config-Ack (PDN-ID)

7. LCP Echo Req/Reply (Active PDN(s))

8. Retrieve context from HSS

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

slide 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 UE initiates the TFT process

No PPP context UE establishes the PPP session UE initiates the TFT process

slide 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 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 None None

SGW None None

eAN/

ePCF

Legacy AN needs to be software upgraded to evolved

AN/ePCF

None

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 None

AAA . Need to support STa and SWx for authentication &

authorization.

. Need to support S6b.

None

PDN GW Need to support S6b None

PCRF None None

UE Needs to support an additional attach type ”

Registration”

Add one new Attach type “Registration” in

VSNCP Config-Req message. (X.S0057)

slide 12

Recommendation

Adopt the early-registration over eHRPD access

solution in X.P0057 -A

slide 13

BackupInformative Only

slide 14

eHRPD Session Maintenance – KeepAlive Procedures

UE eAN/ePCF eNB S-GW P-GW

3. KeepAliveRequest

4 KeepAliveResponse

2. If UE is in LTE idle state, then tunes to eHRPD network; if UE is in active state, the UE either defers the KeepAlive request until turns to idle state, or tunes to eHRPD directly under the case described in next page

5. UE switches back to LTE

1. UE on LTE

slide 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 16

eHRPD Session Maintenance – Subnet Change

UET-eAN/ePCF

4. UATI Assignment procedure

HSGW S-GW P-GW

2b. QuickConfig & SectorParameters

Subnet change, tune on eHRPD and perform UATI Assignment

procedure

S-eAN/ePCF

4. A13 Session Transfer

3. UE is in LTE idle state and tunes

to eHRPD

5. UE switches back to LTE

1. UE on LTE

7. Release A10 connection

6. Establish A10 connection

eNB

2a. SIB8(ZoneId)

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 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 Stop/abort HRPD registration procedures and tune to LTE

KeepAlive For the dual receiver case, UE may receive Paging message LTE

Continue HRPD KeepAlive procedure and tune to LTE Uplink Data ready for Transmission

Buffer data. Complete HRPD KeepAlive procedure and tune to LTE Subnet change

For the dual receiver case, UE may receive Paging message LTE Stop/abort HRPD UATI Assignment procedures and tune to LTE

Uplink Data ready for Transmission Stop/abort HRPD UATI Assignment procedures and tune to LTE

PPP context maintenance 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

Stop/abort HRPD registration procedures and tune to LTE