Cellular Access Control and Charging for Mobile Operator Wireless Local Area Networks

H. Haverinen, J. Mikkonen and T. Takamaki, Nokia

Wei-Jen, LinAdvanced Network Technology Lab.

Institute of Communications Engineering

National Chung Cheng Universityfoolfish@ant.comm.ccu.edu.tw

Outline

• Introduction• Other Solutions• Architecture• Authentication Protocol• User Identity Format• Authentication in GSM• Authentication and Roaming• Subscriber Identity Privacy• Accounting and Billing• System Implementation• Conclusions

Introduction

• Reusing GSM and GPRS mechanisms for user authentication, access control, subscriber management, operator roaming, and billing.

• Compatible with RADIUS、 EAP, IEEE 802.1x and IEEE 802.11i.

• WLAN service provider is a cellular operator.• SIM-based/RADIUS-based Authentication.• The first public WLAN solutions only provide for

internet or intranet connectivity.

Other Solutions

Reusing GPRS mobility management message. The user’s active GPRS sessions could be transferred to WLAN.

Architecture

RADIUS Proxy

Authentication Server(AAA Server)

Charging Gateway

SS7 NetworkIP Network

802.1x with EAP/SIM

802.11i Ki / IMSI

Authentication Protocol

AAA Network

MAP : Mobile Application PartMTP : Message Transfer Part SCCP : Signaling Connection Control PartTCAP : Transaction Capabilities Application Part

User Identity Format

Network Access Identifier (NAI) : foolfish.lin@comm.ccuSIM-based : [Mobile Country Code][Mobile Network Code][Mobile Subscriber Identification Number]

Authentication in GSM

AAA Network

Ki

IMSI to E.214

Authentication and Roaming

A3/A8

RAND

Kc’/SRES’

(nonce,Kc,RAND) MAC

(nonce,Kc’,RAND) MAC’

Subscriber Identity Privacy

• GSM networks protect the privacy of the subscriber identity with temporary identities (TMSI).

• WLAN system introduces a new type of temporary identities called pseudonyms.

• In the very first connection with an AS, the client always transmits the clear text IMSI and uses pseudonym as the username portion of the NAI in subsequent connections.

Subscriber Identity Privacy

(Encrypted pseudonyms)

Pseudonyms IMSI

Accounting and Billing

GTP’

CDR : Charging Data RecordsCGF : Charging Gateway FunctionalityCG : Charging GatewayBS : Billing SystemGTP’ : GPRS Tunneling Protocol

proprietary

proprietary / FTP

Access Network

Auth. Server

System Implementation

• Nokia Operator Wireless LAN solution release 2.0• Nokia A036 AP

– Linux OS, ARM940, Kernel 2.4.17, PoE

• AS is based on PC-Server (Compaq)– Windows NT 4.0, RADIUS, SIM auth. Software

• 10-20 terminal auth. exchanges/sec. – An average connection time of 30 min, 18,000-36,000 simultane

ous connections.

• For redundancy and load-balancing reasons it’s recommended to have always at least two ASs in a WLAN system.

Conclusions

• The solution is generic enough to be used on any access networks that support EAP.

• Loose coupling architecture.

• Subscriber Identity Privacy issue.