1 WLAN-GPRS Integration for Next-Generation Mobile Data Network 報告人 : 李偉晟 18 / 6 / 2003 Apostolis K. Salkintzis, Chad Fors, and Rajesh Pazhyannur Motorola IEEE Wireless Communications Magazine October 2002

2 Outline Motivation The general aspects of integrated WLAN-cellular network Interworking architecture  Tight Couple Architecture  Loose Couple Architecture Conclusion

3 Motivation The operator has the large investments made for new spectrum in which to offer 3G services, but 3G data technology is not available And 2.5G(GPRS) cellular data technology is available in large coverage, but can't meet business and multimedia application requirement The recent evolution and successful deployment of WLAN systems worldwide, and its high data rate An integrated network combines the strenghths of each, provides users with ubiquitous data service.

4 The general aspects of integrated WLAN-cellular network Who owns the WLAN?  Cellular operator  Wireless Internet Service Provider(WISP) Session Mobility

5 Interworking Architecture The Tight Couple Architecture The Loose Couple Architecture External Packet data network Gi Loose coupling point HLR SGSN Gb Gr Gn/p Iu-ps UTRAN GRPS RAN Tight coupling point MS Mobiel station Um Uu GGSN Gc HLR:Home location register SGSN:Serving GPRS support node GGSN:Gateway GPRS support node

6 The Tight Couple Architecture

7 Benefits Seamless service continuation across WLAN and GPRS Reuse of GPRS AAA  Authentication, Authorization, and Accouting Reuse of GPRS infrastructure Access to core GPRS services

8 WLAN System Description A WLAN network is deployed with one or more off-the-shelf access ponts(APs) APs are connected by means of a distribution system(DS) In the system, DS is a LAN (IEEE 802.3) APs behave like base stations The service area of a AP  is a basic service set (BSS) Each WLAN composes many BSSs,  all form an ESS The WLAN is considered like any other GPRS routing area (RA:group of cells) in the system

9 GIF:GPRS Interworking function CG:Charging gateway HLR:Home location register AuC:Authentication center SGSN:Serving GPRS support node GGSN:Gateway GPRS support node BSS:Basic service set AP:Access point Firewall Operator's IP network standar service set(ESS) Beacon (SSID) BSS-1BSS-2BSS-3 Feature Servers Internet WLAN network Distribution system Dual mode MS GIF 48-bit 802 MAC address (AuC) HLR CG GPRS core Billing mediator Billing system Radio Access Network (UTRAN/ GPRS RAN) SGSN GGSN AP Gb All mobile terminals and the GIF use MAC address

10 New Component GPRS interworking function ( GIF )  Is connected to a DS and to a serving GPRS support node (SGSN)  Provide a standardized interface to the GPRS core network  Hides the WLAN particularities WLAN adaptation function ( WAF )  Identifies when the MS associates with a valid AP  Informs the LLC layer, which subsequently redirects signaling and data traffic to the WLAN

11 LLC WLAN Adaptation Function (WAF) WLAN radio subsystem GPRS radio subsystem Um Gb WLAN access network GPRS access network GPRS core network GPRS Interworking Function (GIF) Dual-mode MS WLAN access network Defined by New interworking componets

12 Protocol Architecture MAC X PHY User dataGMM/SMSNDCP LLC WAF RLC/MAC GPRS PHY Um Dual-mode MSAccess pointGPRS interworking Function (GIF) MAC 10Base-T or other 10Base-T or other MAC PHY (e.g. G.703/704) FR NS BSSGP WAF Gb SGSN

13 WLAN Adaptation Function Functions ：  Signals the activation of WLAN interface when the mobile enters a WLAN area  Supports the paging procedures (SGSN pages the MS)  Transfers PDUs (Packet Data Unit) between mobiles and GIF  Supports QoS (transmission scheduling in GIF and the MS)  Transfers the TLLI and QoS information in the WAF header

14 WLAN Adaptation Function (cont.) TLLI ( Temporary Logical Link Identifier )  Is used by GIF to update an internal mapping table that correlates TLLI and MS's MAC addresses  The SGSN uses TLLI as MS address informatioin, whereas the WLAN utilizes MAC addresses

15 WLAN Adaptation Function (cont.)

16 GIF/RAI Discovery Procedure 1. MS’s WAF send Discovery Request,SA=MS,DA=Broadcast,IMSI Start 2. Data is directed to the AP with BSSID 3. The AP broadcast this message to the DS 4. The GIF receive this message,associate the IMSI with the MS's MAC address 5. Then the GIF's WAF Responds Discovery Response,GIF's MAC Address, WLAN's RAI 6. The MS receives this response, stores the GIF address and the RAI 7. The MS notifies the GMM layer that the current GPRS RA has changed 8. The GMM layer notifies the SGSN that the MS has change RA End

17 The Loose Couple Architecture

18 System Description The WLAN network is coupled with the GPRS network in the operator’s IP network

19 CAG:Cellular acess gateway CG:Charging gateway HLR:Home location register AuC:Authentication center SGSN:Serving GPRS support node GGSN:Gateway GPRS support node AAA:Authentication, authorization, accounting FA:Foreign agent HA:Home agent Dual mode MS Internet Operator's IP network Billing system FA WLAN network GPRS core (AuC) HLR CG HA AAA FA CAG Billing mediator Feature Servers Radio Access Network (UTRAN/ GPRS RAN) SGSN GGSN Firewall AP

20 Authentication The Extensible Authentication Protocol(EAP) ：  Performs authentication of the MS  Passing the subscriber identity  Passing SIM-based authentication data  Encrypted session key The cellular accesss gateway(CAG) acts as an authenticator for WLAN users

21 MS APCAGHLR 5. Send authentication info 2. EAPOW-request/identity 7. RADIUS access-challenge 10. RADIUS access-request 1. EAPOW-start 12. EAP-sucess 13. EAP-key 8. EAP-request(RAND) 9. EAP-response(SRES) 3. EAPOW -response/identity (IMSI) 4. RADIUS access-request (IMSI) 6. Send authentication info ack RAND XRES 11. RADIUS access-accept if XRES == SRES (AAA server) [Signed Result]

22 Encryption Weakness of the WLAN standard in its encryption technology Wired Equivalent Privacy(WEP)  is a relatively inefficient encryption scheme With the use of EAP, WEP may be enhaced by the use of a unique session key (EAPOW-Key) for each user of the WLAN

23 Billing Integrated billing is achieved via the billing mediator function The billing mediator  convert accounting statistics from both the GPRS and WLAN access networks into a format of the particular billing system used by the operator The AP in the WLAN will report accounting statistics to the CAG The GPRS core will report accounting statistics (via CG) pertaining to GPRS usage

24 Sesson Mobility Mobile IP (MIP) can be used to provide seeion mobility across GPRS and WLAN domain The MIP framework contains ：  A MIP client (MS)  A foreign agent (FA)  A home agent (HA) The FA in the GPRS resides in the GGSN; in the WLAN can reside in an access router The HA is located in the operator's network

25 Sesson Mobility (cont.) When the MS move from one system to another system The MS performs a MIP registeration via the FA The FA provides a care-of address to the HA to completes the registeration The FA acts as the proxy on behalf of the MS for the life of the registeration The FA then associates the care-of address with that of the MS Start End

26 Conclusion The recent evolution and successful deployment of WLAN sustems worldwide has fueled the need for interworking mechanisms between WLANs and cellar data networks such as GPRS Tight coupling is fit for the cellular operator having WLAN Loose coupling is fit for the wireless network composed of a large number of WLAN operators and cellular operators WLAN technology will play an important role in supplementing wide-area cellular network

27 The End !