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WLAN-Cellular Interworking Rajesh S. Pazhyannur GTSS, Motorola

WLAN-Cellular Interworking Rajesh S. Pazhyannur GTSS, Motorola. Contributors. Chad Fors Nat Natarajan Johanna Wild All from GTSS, Motorola Contact Address Rajesh S. Pazhyannur, QA6283@email.mot.com. Outline. Introduction Architectural Approaches Standardization Efforts

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WLAN-Cellular Interworking Rajesh S. Pazhyannur GTSS, Motorola

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  1. WLAN-Cellular InterworkingRajesh S. PazhyannurGTSS, Motorola

  2. Contributors • Chad Fors • Nat Natarajan • Johanna Wild • All from GTSS, Motorola • Contact Address Rajesh S. Pazhyannur, QA6283@email.mot.com November 21, 2002

  3. Outline • Introduction • Architectural Approaches • Standardization Efforts • Experiences from Feasibility Study November 21, 2002

  4. 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 picture need picture November 21, 2002

  5. 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 Cellular Coverage Area WLAN Hotspots November 21, 2002

  6. 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

  7. Architectural Approaches November 21, 2002

  8. WLAN-Cellular Integration • Multiple Approaches • Loosely coupled architecture • Tightly coupled architecture • No coupling • Proprietary architectures (vendor-specific solutions) November 21, 2002

  9. 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

  10. Operator’s IP Network GPRS RAN Firewall SGSN HLR (AuC) SIM Billing Mediator Tightly Coupled WLAN-GPRS System GPRS Core Internet Gi GGSN CG S-CDR Billing System WLAN Network IWU November 21, 2002

  11. GPRS RAN Internet SGSN HLR (AuC) Loosely Coupled WLAN-GPRS System HLR IWU AAA server Home Agent Operator’s IP Network Firewall GGSN CG Billing Billing Billing Billing Proxy AAA Mediator Mediator Mediator Mediator Billing Billing System System Billing System WLAN System (operator owned) WLAN System (Third party) November 21, 2002

  12. Reference Architecture Loose Coupling Point Tight Coupling Point GPRS Tight Coupling Point UMTS November 21, 2002

  13. No Coupling • Maintain separate systems • Two separate services • Separate sign-on for WLAN and Cellular Data • Separate bills November 21, 2002

  14. Standardization Efforts November 21, 2002

  15. 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

  16. 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

  17. 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

  18. Non Roaming Reference Model The shaded area refers to scenario 3 functionality. November 21, 2002

  19. Roaming Reference Model The shaded area refers to scenario 3 functionality. November 21, 2002

  20. Operator 1 Operator 2 Operator 3 Network Selection • Access Point may have relationship with multiple 3GPP Network Providers • User wishes to choose the service operator November 21, 2002

  21. Potential Solutions • WLAN based Solutions • Multiple SSIDs in the beacon • Round Robin SSIDs • Multiple BSSIDs: • One Beacon per SSID • EAP Based Solution • Prior to Authentication, probe the AP for Systems supported November 21, 2002

  22. 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

  23. 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

  24. Get Triplets Authentication Request Challenge Response Triplets IP Network SIM Challenge Success EAP-SIM Operation IWU HLR SS7 link RADIUS Server Client Device EAP-SIM Server EAP-SIM Client November 21, 2002

  25. 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

  26. 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

  27. Registration Tunnel Setup Tunnel 192.10.10.10 to 68.10.10.10 WLAN-Cellular Handover (Mobile IP) Web Server Internet MIP Home Agent Home Address: 192.10.10.10 Care-of-Address (Cellular) 68.10.10.10 WLAN System Cellular Network November 21, 2002

  28. Registration Tunnel Setup Tunnel 192.10.10.10 to 104.10.10.10 WLAN-Cellular Handover (Mobile IP) Web Server Internet MIP Home Agent Home Address: 192.10.10.10 Care-of-Address (WLAN) 104.10.10.10 WLAN System Cellular Network November 21, 2002

  29. 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

  30. 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 • Workarounds • Integrated MIP and VPN • Make VPN more “tolerant” of changes November 21, 2002

  31. 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

  32. 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

  33. 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

  34. Billing System Single Bill Billing Mediator Home AAA Proxy AAA Proxy AAA PDSN WLAN APs CDMA Network WLAN Hot-Spot 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. November 21, 2002

  35. 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

  36. 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

  37. Backup November 21, 2002

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