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doc.: IEEE 802.11-00/xxx

Submission

WLAN-Cellular InterworkingRajesh S. Pazhyannur

GTSS, Motorola

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Contributors

• Chad Fors• Nat Natarajan• Johanna Wild• All from GTSS, Motorola

• Contact Address

Rajesh S. Pazhyannur, QA6283@email.mot.com

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Outline

• Introduction• Architectural Approaches• Standardization Efforts• Experiences from Feasibility Study

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Introduction

• WLAN Segments– Public Hotspots

• Airports, Cafes, etc– Enterprises– Residences

• Primary Focus – Public Hotspots and Cellular Data Systems– Integrated “Data” Services

• Important Area not Discussed– Integrating Enterprise WLAN with Cellular Voice

need pictureneed picture

                       

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Cellular Coverage

AreaWLAN Hotspots

Motivation

• Ubiquitous Wireless Data Network– WLAN in Hotspot, GPRS/CDMA-1X in Macro

• Cellular Operator Benefits– Augment Cellular Data Service

– Leverage/Reuse existing investment in Cellular Data System for WLAN service

– Attract WLAN users to Cellular Data Service

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

High-Level Requirements

• Authentication– authentication provided by cellular operator

– “common” authentication

• Billing– Single Bill based on combined data usage

• Session Mobility– Handoff between WLAN and Cellular

• Support WLAN Roaming– Third Party owned WLAN Hotspots

• Access to Applications from WLAN– IMS (Messaging)

November 21, 2002

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doc.: IEEE 802.11-00/xxx

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Architectural Approaches

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

WLAN-Cellular Integration

• Multiple Approaches– Loosely coupled architecture

– Tightly coupled architecture

– No coupling

– Proprietary architectures (vendor-specific solutions)

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Tight and Loose Coupling

• Tight Coupling– Hierarchical relationship between WLAN and Cellular

• WLAN as an alternate access network

• WLAN traffic routed through cellular core network

• Loose Coupling– WLAN as peer IP access network

– Maintain distinct systems for bearer traffic

– Reuse AAA services for WLAN

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Tightly Coupled WLAN-GPRS System

WLAN NetworkWLAN Network

GPRSRAN

GPRS CoreInternet

Operator’s IP Network

GGSNFirewall

BillingBilling System System BillingBilling System System

S-CDRCG

Billing MediatorBilling Mediator

IWUIWU

HLR(AuC)

SIM SIM

SGSN

Gi

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Loosely Coupled WLAN-GPRS System

GPRSRAN

SGSN

Internet

GGSN

Operator’sIP Network

WLAN System (operator owned)

Firewall

HLR(AuC)

AAA server

WLAN System (Third party)

Billing Billing MediatorMediatorBilling Billing

MediatorMediator

Billing System BillingBilling System System

CG

Home Agent

HLR IWU

Proxy AAA

November 21, 2002

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Submission

Gf

Uu

Um

D

Gi

Gn

Iu

Gc

CE

Gp

Gs

Signalling and Data Transfer Interface

Signalling Interface

MSC/VLR

TE MT BSS TEPDN

GrIu

HLR

Other PLMN

SGSN

GGSN

Gd

SM-SCSMS-GMSC

SMS-IWMSC

GGSN

EIRSGSN

GnCGF

GaGa

BillingSystem

Gb

TE MT BSS

R

A

R

Loose Coupling Point

Tight Coupling Point GPRS

Tight Coupling Point UMTS

Reference Architecture

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

No Coupling

• Maintain separate systems• Two separate services

– Separate sign-on for WLAN and Cellular Data

– Separate bills

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Standardization Efforts

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Standardization Groups

• 3GPP– GPRS and UMTS Systems– One year ago– Interworking Scenarios Document

• 3GPP2– CDMA 1X Systems– 4Q, 2002– Stage 1 Document

• IETF– Authentication/Security, Mobility

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

3GPP and WLAN

• Feasibility Study

Highlights• Six Interworking scenarios

– Incremental Functionality

• Interworking based on IP as common layer– Independent of WLAN radio technology

• Reuse standard WLAN mechanisms

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

3GPP

• Six Scenarios for WLAN-Cellular Interworking– Scenario 1: Common Billing and Customer Care

– Scenario 2: 3GPP system based Access Control and Charging

– Scenario 3: Access to 3GPP system PS based services

– Scenario 4: Service Continuity

– Scenario 5: Seamless services

– Scenario 6: Access to 3GPP CS Services

• Currently Focused on Scenarios 2 and 3• Advocating a Loose Coupling Architecture

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Non Roaming Reference Model

WLAN Access Network (with or without an intermediate network)

UE

Intranet / Internet

Wr/ Wb

3GPP Home Network

3GPP AAA

HSS

Wx

OCS

CGw/CCF

Wf

Wo

D'/ Gr'

HLR

Packet Data GW

Wn Wi

Wm Scenario 3

The shaded area refers to scenario 3 functionality.

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Roaming Reference Model

The shaded area refers to scenario 3 functionality.

3GPP Home NW

3GPP Visited NW Intranet / Internet

Wm

Intranet / Internet

HSS

OCS CGw CCF

3GPP AAA

Server

CGw CCF

3GPP AAA Proxy

Wr/ Wb

Wx

Wo Wf

WLAN Access Nw (with or without an intermediate Nw)

WLAN

UE

Wr/ Wb

Packet Data GW

Wf

HLR

D’/Gr’

Border GW (Opt) Wn

Packet Data

GW

Wi

Wi

Wn Scenario 3

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Network Selection

• Access Point may have relationship with multiple 3GPP Network Providers

• User wishes to choose the service operator

Operator 1

Operator 2

Operator 3

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Potential Solutions

• WLAN based Solutions1. Multiple SSIDs in the beacon

2. Round Robin SSIDs

3. Multiple BSSIDs:

– One Beacon per SSID

• EAP Based Solution– Prior to Authentication, probe the AP for Systems

supported

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Motorola Feasibility Study

• Advanced Technology Effort– CDMA-1X and GPRS

– Loosely Coupled Architecture

– Investigate implementation issues

– Evaluate commercial offering

• Focus on Functionality– EAP-SIM

– Roaming and Session Mobility

– Accounting and Single Bill

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

EAP-SIM

• Subscriber Identity Module (SIM) has a long history– Smart card that is removable from the phone equipment

– Used to authenticate GSM/GPRS users

• EAP-SIM enables WLAN authentication based on SIM

• Why EAP-SIM? – Cellular Operators like it !!

• Single Point of Provisioning

• Leverage existing resources and assets

– GSM users are conversant with SIM

– Provides a degree of security within the 802.1X framework

– Being standardized within IETF

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

EAP-SIM Operation

Client DeviceClient Device

IP NetworkIP Network

RADIUS RADIUS ServerServer

HLRHLR

IWUIWU

SS7 link

EAP-SIMEAP-SIMServerServer

EAP-SIMEAP-SIMClientClient

Authentication RequestAuthentication Request

GetGet

TripletsTripletsTripletsTriplets

SIM ChallengeSIM ChallengeSuccessSuccess

Challenge ResponseChallenge Response

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

EAP-SIM Issues

• How are SIM Cards administered?– Single SIM versus Multiple SIM

• How does the WLAN user connect to SIM card?– WLAN card is integrated with SIM

– WLAN device (PDA, etc) connected to SIM dongle through USB

– WLAN device has a sleeve to insert SIM (just like phones)

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

WLAN-Cellular Handover

• Handover is accomplished through MIP

• Requires Following Components– MIP Client

– MIP Home Agent

• How does it work?– Mobile is assigned a Home Address.

– When Mobile is away from home, it acquires a Care-of-address

– Mobile IP Client registers Care-of-address with Home Agent

– All IP packets destined to Home Address are intercepted by Home Agent.

– Home Agent forwards IP packets to Care-of-Address

– As Mobile Moves between WLAN and Cellular

• Care-of-Address Changes but Home Address remains same

• TCP/UDP Sessions based on Home Address are unaffected between handoffs

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

WLAN-Cellular Handover (Mobile IP)

Cellular

Network

Cellular

Network

WLAN

System

WLAN

System

InternetInternet

Web Server

MIP Home Agent

Registration

Tunnel SetupTunnel 192.10.10.10 to 68.10.10.10

Home Address: 192.10.10.10

Care-of-Address (Cellular)

68.10.10.10

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

WLAN-Cellular Handover (Mobile IP)

Cellular

Network

Cellular

Network

WLAN

System

WLAN

System

InternetInternet

Web Server

MIP Home Agent

Registration Tunnel SetupTunnel 192.10.10.10 to 104.10.10.10

Home Address: 192.10.10.10

Care-of-Address (WLAN)

104.10.10.10

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Session Mobility Issues

• Support for Mobile IP in Cellular Systems• NATs and Firewalls• Interaction between VPN and MIP Clients• MIP Handover Performance

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Interaction between VPN and MIP

• VPN Clients intolerant of changes in Route Table– Any Change in route table usually resets the VPN

– Force VPN Re-authentication

• Assume VPN over MIP– MIP running on top of WLAN

– Move out of WLAN coverage into Cellular

– Acquire IP address from Cellular.

– MIP handover from WLAN to Cellular

• Workarounds1. Integrated MIP and VPN

2. Make VPN more “tolerant” of changes

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Support for Mobile IP in Cellular Systems

• 3GPP2 has incorporated MIP– PDSN behaves as FA, Handsets have MIP clients

• 3GPP does not require MIP– Some GGSN providers have MIP capability

• Is FA Care-of-Address Registration important?

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

NATs and Firewalls

• Private IP addresses are a problem for MIP– MIP Clients can register with Home Agent– Home Agent tunnels packets to Private IP address (not the NATted

public IP address)

• Potential Workarounds:– IETF is working on numerous NAT Traversal drafts.

• Tunnel MIP packets within UDP packets

• Firewalls may block tunneled packets– Mobile IP uses IP-in-IP tunnels between HA and Client

• Potential Workaround– Use GRE for tunneling– Change firewall policy to allow MIP packets

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Handoff Delays

• Handoff Delays are still “large” (~4 secs)• Sources of delay

– IP address assignment (DHCP) and authentication

– Detection of Loss of WLAN coverage

– Cellular Data call-setup

• Impact of Delay (> 4 sec) on Applications– Some FTP clients will “hang”

– Streaming Clients sometimes “freeze”

• Adjusting buffer size has “mixed” effect

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Post-Paid Billing

• After successful authentication WLAN AP sends RADIUS Start message to Proxy AAA.

• After logoff (or suitable termination) WLAN AP sends RADIUS STOP message to Proxy AAA.

• AP may send Interim Update messages.

• RADIUS record contains duration, bytes sent/received, unique record identifier

• Home AAA collects RADIUS records from PDSN and WLAN systems

• Billing Mediator mediates WLAN and CDMA 1X records and presents to Billing System

• Billing System creates single bill based on Billing policy.

CDMA Network WLAN Hot-Spot

Billing System

Billing Mediator

Home AAA

WLAN APs

Proxy AAA

PDSN

Proxy AAA

Single Bill

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Billing Issues

• Accounting Records in WLAN Systems– No standards unlike 3GPP and 3GPP2

– Perhaps WECA (??)

– 3GPP2 uses RADIUS accounting records

• Quite different from what APs provide

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Key Conclusions

• WLAN-Cellular Interworking is relatively easy to implement– Most components for Scenarios 1-4 exist

– Does not affect 3GPP and 3GPP2 systems in any significant manner

– High Reuse between 3GPP and 3GPP2 Systems

• Combination Devices may be potential trigger!– Combination PC cards

– Dual-Mode WLAN-Cellular Phones

November 21, 2002

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doc.: IEEE 802.11-00/xxx

Submission

Backup