Architecture and Handoff with S-RNC

Fatih Ulupinar, Peerapol Tinnakornsrisuphap, Jun Wang

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Potential Architecture with S-RNC

HomeAgent

eBTS

S-RNC

AccessGateway

eBTS eBTS

IAP

AccessGateway

eBTS

S-RNC

eBTS eBTS

WiFiAP

PDIF

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Pros & Cons of S-RNC

• Potential benefits of separating S-RNC from eBS

– Reliability of Users session• Centrally located S-RNC provides higher reliability to user’s session

compared to eBTS deployed at the edge.

– Provide UATI stability as IAP moves between eBSes.• Note, UATI HA can provide UATI stability using an off-the-shelf

solution.• Separate S-RNC solution does not require a UATI-HA

– Centralize paging area management

• Disadvantages of S-RNC

– Additional protocol complexity as new interfaces has to be defined

– One more (S-RNC) air interface aware node has to be built

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Functions of S-RNC

• Session Anchor (Session Storage Point)

– UATI Points to S-RNC

• Paging and Location Management

• Idle State Management

• EAP Authenticator Functions (see EAP Authenticator Placement contribution)

– AAA Client

• Optionally served as IAP when the AT is in idle State:

– Buffer Incoming User Data when the AT is in idle state

– PMIP Client

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Related Entities• Internet Attachment Point (IAP) – the entity that the AGW points its

tunnel for FL traffic to

• S-RNC is a separate functional entity from AN. However, the AT always maintain a logical route to S-RNC, i.e., S-RNC is also a member of the Active Set

• S-RNC can either be a stand-alone entity, collocated with AGW or collocated with eBS. This allows flexible deployment options based on operators and vendors’ requirements

• As a member of the Active Set, S-RNC may become IAP if appropriate– Alternatively, UMB air-interface allows S-RNC to disable data through S-

RNC route if S-RNC cannot handle user data

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S-RNC Interfaces

• Interface between S-RNC and eBS:

– Same as inter-eBS interface

– Key is distributed to the eBS

• Interface between S-RNC and AGW:

– No specific 3GPP2 signaling interface is needed between S-RNC and AGW

– Same as interface between eBS and AGW

– PMIP tunneling can be established when the AT moves to idle

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Paging Options

• Allows both the following options:

– Option 1: (IAP (Data Anchor) is always separate than S-RNC)• IAP receives the data from AG• IAP contacts S-RNC for paging• S-RNC pages via other APs• AT accesses APx• APx retrieves data from the IAP and forwards to AT• APx starts L3 HO to itself

– Option 2: (S-RNC is the IAP when idle)• S-RNC receives data from AG• S-RNC pages via other APs• AT accesses APx• APx retrieves data from the S-RNC and forwards to AT• APx starts L3 HO to itself

• If an S-RNC vendor can not handle user data, then it can use option 1

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Paging (Option1)

AN2 IAP ANAT AN1 AN3

10. Traffic Channel established

6. AN3 pages the AT in the designated paging cycle

2. AT registers with S-RNC through AN3 (UATI)

3. Paging Request

5. PagingRequest

5. Paging Request

6. AN2 pages the AT in the designated paging cycle

6. AN1 pages the AT in the designated paging cycle

7.AT requests connection with AN1 (UATI)

Data Data

AGW

Registration Trigger

Data

S-RNC

4. S-RNC determines paging area of the AT

based on AT’s registration

5. PagingRequest

8. AN1 retrieves a copy of the session

1. IAP doesn’t change when AT goes to Idle

9. AN1 establishes L3 Tunnel

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Paging (Option2)

AN2AT AN1 AN3

8. Traffic Channel established

5. AN3 pages the AT in the designated paging cycle

2. AT registers with IAP through AN3 (UATI)

4. PagingRequest

4. Paging Request

5. AN2 pages the AT in the designated paging cycle

5. AN1 pages the AT in the designated paging cycle

6. AT requests connection with AN1 (UATI)

Data Data

AGW

Registration Trigger

Data

S-RNC

1. S-RNC becomes IAP when AT goes to Idle

4. PagingRequest

7. AN1 retrieves a copy of the session and establishes L3 Tunnel

3. S-RNC determines paging area of the AT

based on AT’s registration

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Why Data should be buffered in IAP?- If AGW buffers the data when AT is idle

• AGW needs to be aware of the status of the AT (active/idle)

– Extra signaling messages need to be defined• This will be 3GPP2 UMB specific functionality• Even PDSN right now is not aware of the status of the AT – PCF was created to ‘shield’

such information from PDSN• AGW has two different behaviors depending on the status of the AT – introducing more

race conditions, error scenarios to be addressed (e.g., AT is active while AGW still believes AT is idle) and additional delay

• Air-interface does not only have active and idle state but also has semi-connected state and these may change in the future – change in the air-interface spec should not affect AGW

– Excessive additional signaling load will be introduced• eBS needs to inform AGW every time an AT changes status from active to idle – this is a

very frequent event, for example– To save power, AT may transition to idle state after a short inactivity timer expires – this can be

during a short reading time between each web page or Instant Messaging KeepAlive

– Every time AT wakes up to register, the AGW will receive idle->active indication and then immediately active->idle indication

– Bandwidth between AGW to eBS is likely to be limited and expensive• We do not believe this is a scalable solution when the number of AT served by AGW is

large

• The concept is unproven – no other system has chosen this particular design

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Why Data should be buffered in IAP?- If IAP buffers the data when AT is idle

• If buffering data at the eBS is a concern, then S-RNC can become IAP when AT becomes idle

– Typical amount of data that needs to be buffered when AT is idle is small anyway, e.g., Mobile-Terminated SIP INVITE

• Allow flexibility for deployment options depending on the physical location of S-RNC while the standard can remain option-free

• No need for defining extra interfaces

– Between AGW and BS for AT status update

– Between S-RNC and AGW for paging trigger

• Compatible with the current PDSN functionalities

• Avoid extraneous signaling messages as IAP location is more stable than active/idle states

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Active Set Add (AN2 belongs to same AGW, Interface ID=AGW1 )

ATAN1

(IAP/FLSA/RLSA)

AN2

Phy Signal

AN-AN MsgData MIP Signal

L2 Signal IMS SignalTunneled Data

AT is in connected-state with AN1/S-RNC in the Active Set

RLP Tunnel

[AN2]RouteOpenRequest

(RouteID) UMB:RouteOpenRequestCT-Session

Information Request(SessionSignature)

CT-Session Information Notification

(SessionSignature, Session, IAP ANID)

Active Set Add completes; AN1/AN2/AN3/S-RNC are all in the Active Set

AT wants to add AN2 into Active Set

RouteOpenAccept(Interface ID)

Manycast [AN1-3]:RouteIDMapping UMB:RouteIDMapping

UMB:RouteIDMapping

Ack

Ack

UMB:RouteOpenAccept (Interface ID)

S-RNC

L3TunnelSetup

L3TunnelSetup

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Active Set Add (AN2 belongs to different AGW, Interface ID=AGW1 )

ATAN1

(IAP/FLSA/RLSA)

AN2

Phy Signal

AN-AN MsgData L3 Signal

L2 Signal IMS SignalTunneled Data

Same as singe AG Active Set Add call flow except for Interface ID=AGW2

RLP Tunnel

PMIP BU

PMIP BA (AT’s Prefix /64 or AT’s IP add)

Route Advertisement (AT’s Prefix /64)

S-RNC AGW2

Simple IPv6

MIPv4 FA CoAFA Advertisement (FA CoA)FA Advertisement (FA CoA)

Simple IPv4DHCPDISCOVERw/Rapid Commit

DHCPACK w/Rapid Commit (AT’s IP Add)

New IP Interface Created

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L3 HO w FL Data (Intra-AG HO, no CoA change)

AT SS ANSource IAP AN

AG

AT decides to do L3 handoff

Target IAP AN

NotifyAck

Notify(IAP)

Phy Signal

Backhaul SigData MIP Signal

L2 Signal

L2TP Tunnel

IMS SignalTunneled Data

PMIP-BA

PMIP-BU

IAPMoveReq(SeqNo)

S-RNC

Notify(IAP)

NotifyAck

Data

Data

Data

Notify(IAP)

NotifyAck

IAPAssignment(Accept, NoAck)

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L3 HO w RL Data (Intra-AG HO, no CoA change) *Assuming reverse tunneling through IAP

AT SS ANSource IAP AN

AG

AT decides to do L3 handoff

Target IAP AN

NotifyAck

Notify(IAP)

Phy Signal

Backhaul SigData MIP Signal

L2 Signal

L2TP Tunnel

IMS SignalTunneled Data

PMIP-BA

PMIP-BU

IAPMoveReq(SeqNo)

S-RNC

Notify(IAP)

NotifyAck

Data Data Data

Data Data Data

Data Data Data

Notify(IAP)

NotifyAck

IAPAssignment(Accept, NoAck)

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L3 HO w RL Data (Intra-AG HO, no CoA change)*Assuming RL data can be directly tunneled from RLSA to AG

AT SS ANSource IAP AN

AG

AT decides to do L3 handoff

Target IAP AN

NotifyAck

Notify(IAP)

Phy Signal

Backhaul SigData MIP Signal

L2 Signal

L2TP Tunnel

IMS SignalTunneled Data

DataAnchorMoveReq(SeqNo)

S-RNC

Notify(IAP)

NotifyAck

Data Data

Data Data

Data Data

Notify(IAP)

NotifyAck

DataAnchorAssignment(Accept/Reject, NoAck)

PMIP-BACK

PMIP-BU

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L3 HO w FL data (Inter-AG HO, CoA change)AT SS AN

Source IAP AN

Source AG

AT decides to do L3 handoff

Target IAP AN

NotifyAck

Notify(IAP)

Phy Signal

Backhaul SigData MIP Signal

L2 Signal

L2TP Tunnel

IMS SignalTunneled Data

PMIP-BACK

PMIP-BU

IAPMoveRequest(SeqNo)

S-RNC

Notify(IAP)

NotifyAck

Data

Data

Leftover data in Source AG

HATargetAG

Notify(IAP)

NotifyAck

IAPAssignmentProcessed( Transaction_ID)

IAPAssignment(T1,Accept, ProcessCompletinAckRequired)

BU

BAck

AT can not drop Target A-AN from AS Data

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L3 HO with RL data (CoA change, Inter-AG HO)*Assuming RL data can be directly tunneled from RLSA to AG

AT SS ANSource IAP AN

Source AG

AT decides to do L3 handoff

Target IAP AN

NotifyAck

Notify(IAP)

Phy Signal

Backhaul SigData MIP Signal

L2 Signal

L2TP Tunnel

IMS SignalTunneled Data

PMIP-BACK

PMIP-BU

DataAnchorMoveRequest(SeqNo)

S-RNC

Notify(IAP)

NotifyAck

Data

Data

HATargetAG

Notify(IAP)

NotifyAck

DataAnchorAssignmentProcessed(TransID)

DataAnchorAssignment(TransId,Accept, ProcessCompletinAckRequired)

BU

BAckData

AT can not drop Target IAP-AN from AS

To AS members

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L3 HO with RL data (CoA change, Inter-AG HO)*Assuming reverse tunneling through IAP

AT SS ANSource IAP AN

Source AG

AT decides to do L3 handoff

Target IAP AN

NotifyAck

Notify(IAP)

Phy Signal

Backhaul SigData MIP Signal

L2 Signal

L2TP Tunnel

IMS SignalTunneled Data

PMIP-BACK

PMIP-BU

DataAnchorMoveRequest(SeqNo)

S-RNC

Notify(IAP)

NotifyAck

Data

Data

HATargetAG

Notify(IAP)

NotifyAck

DataAnchorAssignmentProcessed(TransID)

DataAnchorAssignment(TransId,Accept, ProcessCompletinAckRequired)

BU

BAck

Leftover data from Source A-AN

Data

AT can not drop Target IAP-AN from AS

To AS members

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S-RNC HO

AT SS APPrev

S-RNC

UATIAssign(UATI_n)

TargetS-RNC

UATIComplete(UATI_n,TargetRouteID)

Phy Signal

Backhaul MsgData MIP Signal

L2 Signal

L2TP Tunnel

IMS SignalTunneled Data

To AS members

Start timer to Release Previous

UATI

From AS Members

RouteClose() If Prev S-RNC is not in Radio Active Set

MoveSession

MoveSessionAck(Session, Current IAP,

SessionSig) Allocate UATI_n

MoveSessionCompleted

AGW/LAAA

HAAA

Optional EAP Re-authentication

EAP/RLP or EAP-ER/RLP EAP/AAAEAP/AAA

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Recommendations

• No Specific 3GPP2 signaling interface between S-RNC and AGW

– Same interface as eBS-AGW interface shall be used

• Buffer the incoming data in either S-RNC or IAP when the MS is in idle

• AGW shall be an access agnostic entity