1. An Agile Vertical Handoff Scheme for Heterogeneous Networks Hsung-Pin Chang Department of Computer Science National Chung Hsing University Taichung, Taiwan, R.O.C.

2. Outline  Motivation  Related work How to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

3. Outline  Motivation  Related work How to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

4. Hierarchical Overlay Network  Many different communications systems coexist around us Ethernet, Wireless LAN, GPRS, 3G …  Each owns different characteristics Bandwidth, delay, cost ……  Hierarchical overlay network The combination of these heterogeneous networks

5. Example: An Overlay Networks Campus-wide (3G, GPRS) Building-wide (WLAN) Room-wide (Ethernet)

6. Horizontal versus Vertical Handoff  Problem: handoffs Horizontal handoff  The same kind of network technology  Ex: BSS to BSS Vertical handoff  Different kinds of network technologies  Ex: Wireless LAN to 3G <= what we are addressed

7. Horizontal Handoff AP BSS Internet

8. Vertical Handoff WCDMA WLAN AP BS Internet

9. Outline  Motivation  Related work: how to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

10. Previous Approaches to Vertical Handoff 1/2  Mobile IP/Infrastructure Based Approaches  Mobile IP with multicast Care-of-address is changed to a multicast address  Integration of WLAN and GPRS  Integration of WLAN and 3G Problem  Require modification of network infrastructure Hindrance to deployment  Need to be keep up to data New technologies are always introduced

11. Previous Approaches to Vertical Handoff 2/2  End-to-end based Application layer  SIP (Session Initiation Protocol) Transport layer: enable TCP connection alive even the underlying IP address is changed  TCP-R  TCP Migrate Between transport layer and network layer  C. Guo, et. al., “ A Seamless and Proactive End-to-End Mobility Solution for Roaming Across Heterogeneous Wireless Networks, ” IEEE JSAC, 22(5), pp.834-848. Jun. 2004

12. Network Applications BSD Sockets TCPUDP User Kernel Socket Interface Transport Layer IP PPPSLIPEthernet Network Devices Network Layer LCT Table Translation A Seamless and Proactive End-to-End Solutions for Roaming Across Heterogeneous Wireless Networks (1/4)

13. Original address Original port Mapped address Mapped port Ap1A WLANWLAN LANLAN LANLAN Nego A B Tell B that A support vertical handoff Nego+Ack B A B Tell A ok. Notify C B A Ack B C A B C Original address Original port Mapped address Mapped port Ap1A Mobile Client Fixed Host … Original address Original port Mapped address Mapped port Ap1Cp2 Original address Original port Mapped address Mapped port Ap1Cp2 A Seamless and Proactive End-to-End Solutions for Roaming Across Heterogeneous Wireless Networks (2/4)

14. Handoff Layer Application Handoff Layer Kernel Application Kernel ABAB CB Table Lookup 圖 3 封包表頭替換過程 A Seamless and Proactive End-to-End Solutions for Roaming Across Heterogeneous Wireless Networks (3/4)

15. A Seamless and Proactive End-to-End Solutions for Roaming Across Heterogeneous Wireless Networks (4/4)  Problems NAT issue  Require an S/N (Subscription/Notification) Server  Modify the infrastructure TCP performance  Do not consider

16. Outline  Motivation  Related work: how to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

17. How to pass NAT gateway ?  Problem Communication must always be initiated by the private network  Solution Use the previous IP address as the source IP address

18. WLAN Fixed Host Ethernet NAT AP Switch Update New IP address Problem

19. WLAN Fixed Host Ethernet NAT AP Switch Update Old IP address Solution

20. Outline  Motivation  Related work: how to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ? => CWND-Restore  Experiments  Conclusion

21. How to adapt TCP behavior ?  Problem TCP consider packet loss as network congestion Slow down …  But … now packet lose is because “ handoff ”  Solution CWND-Restore

22. WLAN Fixed Host Ethernet NAT AP Switch CWND-Restore CWND 20 CWND 2CWND 50

23. Outline  Motivation  Related work: how to achieve seamless vertical handoff ?  Challenge and Contribution How to pass NAT gateway ? How to adapt TCP behavior ?  Experiments  Conclusion

24. System Implementation- Linux Kernel 2.6.11 Ethernet Driver Ethernet Driver WLAN Driver WLAN Driver 3G Applications Connection Manager TCP User Mode Kernel Mode UDP IP Handoff Detection CWND-restore

25. Experimental Platform Fixed HostMobile Host CPU AMD XP 2600+Intel Pentium M 1.4GHz RAM 512 MB256 MB NIC #1 100Mbps Ethernet 100Mbps Fast Ethernet Ethernet NIC #2 Philips 802.11g WLAN miniPCI Adapter NIC #3 Novatel UMTS/WCDMA USB Adapter

26. Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

27. Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

28. TCP Handoff Verification 1/7 Internet Ethernet WCDMA Fixed Host Mobile Host WLAN NAT BS BA C AP Switch Experiment environment

29. TCP Handoff Verification 2/7  LAN to WLAN Handoff

30. TCP Handoff Verification 3/7  WLAN to LAN Handoff

31. TCP Handoff Verification 4/7  LAN to WCDMA Handoff

32. TCP Handoff Verification 5/7  WCDMA to LAN Handoff

33. TCP Handoff Verification 6/7  WLAN to WCDMA Handoff

34. TCP Handoff Verification 7/7  WCDMA to WLAN Handoff

35. Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

36. Handoff Latency 1/2 WCDMA Internet WLAN Fixed Host Mobile Host Ethernet NAT AP Switch BS B A C Experiment environment

37. Handoff Latency 2/2 Handoff Latency (ms) LAN to WLAN3 LAN to WCDMA438 WLAN to LAN1 WLAN to WCDMA503 WCDMA to LAN1 WCDMA to WLAN3

38. Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

39. TCP Handoff Performance 1/8 WCDMA Internet WLAN Fixed Host Mobile Host Ethernet NAT AP Switch BS B A C Experiment environment

40. TCP Handoff Performance 2/8 Original (KB/s)CWND Freeze (KB/s) WLAN to LAN6154.87690.84 LAN to WLAN177.58244.87 WCDMA to LAN2886.365059.62 WCDMA to WLAN138.34237.77 LAN to WCDMA3.643.98 WLAN to WCDMA3.474.12

41. TCP handoff performance 3/8  LAN to WLAN Handoff

42. TCP handoff performance 4/8  WLAN to LAN Handoff

43. TCP handoff performance 5/8  LAN to WCDMA Handoff

44. TCP handoff performance 6/8  WCDMA to LAN Handoff

45. TCP handoff performance 7/8  WCDMA to WLAN Handoff

46. TCP handoff performance 8/8  WLAN to WCDMA Handoff

47. Experiment 2/2  Experiments TCP handoff verification Handoff latency TCP handoff performance UDP handoff verification

48. UDP Handoff Verification 1/3  Experiment environment Switch AP Internet 1. WLAN 2. LAN FH MH

49. UDP Handoff Verification 1/3 Internet WLAN Fixed Host Mobile Host Ethernet AP Switch WLAN A B

50. UDP Handoff Verification 2/3  LAN to WLAN Handoff

51. UDP Handoff Verification 3/3  WLAN to LAN Handoff

52. Outline  Introduction Hierarchy Overlay Network Horizontal v.s. Vertical Handoff  Challenge How to achieve seamless vertical handoff ? How to pass NAT gateway ? How to adapt TCP behavior ? How to adapt application behavior ?  Experiments  Conclusion

53. Conclusion  A Vertical Handoff framework Support NAT while follows the end-to-end discipline  Without an modification to infrastructure Improve TCP performance  CWND Freeze  At most 2.3 times the original TCP