Modularized Two Step Vertical Handoff Scheme In Integrated WWAN and WLAN

1. Modularized Two Step Vertical Handoff Scheme In Integrated WWAN and WLAN Shimin Li Ying Wang

2. What is Vertical Handoff • Vertical handoff is the handoff between different network • Horizontal handoff is the handoff within the same network

3. Outline • Motivation and Objective • Overview of WWAN and WLAN • Integration Architecture and Mobile IP • Modularized Two Step Handoff Scheme • Conclusion • Reference

4. 1. Motivation • WWAN: low rate, high cost and wide coverage • WLAN: high rate, low cost and small coverage usually deployed at hotspots • Combines the 3G WWAN and the IEEE 802.11 WLAN together will benefit to operator and customer

5. 1. Objective • To make the integration effective, vertical handoff between the two networks is necessary • Major problems in Vertical Handoff in integrate network Delay Loss packet Billing • In this presentation, we focus on real time application. It needs low delay during the vertical handoff

6. 1. Related works • In [1] tight coupling, loose coupling and Mobile IP were introduced • [2] and [3] introduce FFT and MAC layer sensing for handoff decision, but the solution need improve because handoff decision does not consider different situation • [4] introduce the multi tunnel idea, but did not get a easy implement solution

7. 2 Overview of WWAN and WLAN • Architecture of WWAN (CDMA 2000) • Architecture of WLAN

8. Architecture of WWAN (CDMA 2000)

9. LAN LAN Internet Hub/Switch Hub/Switch Router Architecture of WLAN

10. 3 Integration Architecture and Mobile IP • Tight coupling • Loose coupling • Mobile IP

11. Internet CDMA2000 CoreNetwork Tight Coupling Loose Coupling CDMA2000 BSC WLAN Gateway WLAN Gateway BS WLANAccessPoint

12. Tight coupling • Basic idea • disadvantage

13. Loose coupling • Basic idea • Advantage

14. Mobile IP

15. 4 Modularized Two Step Handoff Scheme

16. Pre-Handoff Message Physical Signal Decision Module Action Module Pre-Handoff MAC Signal Handoff Message Handoff Main idea of Modularized Two Step Handoff Scheme 1

17. Main idea of Modularized Two Step Handoff Scheme 2 • Decision module Sensing physical layer and MAC layer Sending message to Action module • Action module Receiving message from Decision module Performing handoff action • Interface between two modules Pre-handoff message Handoff message • There only two message sequences allowed Pre-handoff message followed by pre-handoff message Pre-handoff message followed by handoff message

18. Main idea of Modularized Two Step Handoff Scheme 3 • Handoff process include two step Pre handoff step handoff step • When the HA receives the pre handoff message, it begins to multi-tunnel the packet. It copies the IP packet destined to MN and sends them to the FA in WLAN and WWAN respectively. • When the mobile node meet the handoff condition, it execute handoff.

19. 4.1 Decision Module • Different with horizontal handoff • Handoff from WWAN to WLAN • Handoff from WLAN to WWAN

20. Different with horizontal handoff • No comparable signal strength • When moves from WWAN to WLAN, can not be triggered by signal decay

21. 4.1.1 Handoff decision from WWAN to WLAN • Physical-layer sensing • MAC-Layer Sensing • Handoff decision scheme

22. Physical-layer sensing • WLAN air interface will be periodically turned on to scan the signal of WLAN • Once the user moves into WLAN, a valid WLAN service set identifier (SSID) will be detected • If received signal strength index (RSSI) be larger than a preset threshold R1 then send pre-handoff message to Action module

23. MAC-Layer Sensing • Goal: detect the WLAN network condition, such as available bandwidth and MAC-layer access delay • NAV (Network Allocation Vector) is the main scheme used in WLAN to avoid collision by setting a busy duration on hearing frame transmissions from other mobile hosts • By listening to and collecting the NAV in MAC layer, we can obtain the available bandwidth and access delay in MAC • Observe the NAV for T times and calculate the average NAV in this observation window. If the average NAV is smaller than a threshold N1, roaming into WLAN is granted; otherwise, the user stays in WWAN

24. Relationship between NAV and Available bandwidth

25. Relationship between NAV and Mean access delay

26. Handoff decision scheme from WWAN to WLAN • Detecting the RSSI signal, If RSSI>R1, then begin collect NAV and send pre-handoff message to Action module. • If the average NAV <N1, then send handoff message to Action module • Else keep the connection with the WWAN

27. 4.1.2 Handoff decision from WLAN to WWAN • The key problem is how to detect the unavailability and the decay of the WLAN signal • we present an approach that integrate FFT-Based Decay Detection, NAV Occupation and simple physical signal strength for accurately detecting the unavailability of WLAN

28. FFT-Based Decay Detection • Regard sin (-(2πn/N)) as a linear filter applied to the sequence x(N) • x (1) is the most smooth metric because sin(-2πn/N)) is the filter with the least high-frequency component • This will reduce the variation of x (1) even x (n) may vary severely • we can set a threshold F1 for x (1)/N. If x(1)/N is smaller than F1, the signal is considered to be decaying

29. MAC layer sensing • From NAV we can obtain the available bandwidth and access delay in MAC • Set the threshold of average NAV is N2 • If the average NAV>N2, it mean that the delay of WLAN is large, so the user send pre-handoff message to Action module • After short time T, send handoff message to Action module

30. Physical Signal Sensing • Some time the signal of WLAN change very quickly. If the level of the RSSI is small then R3, the user will lose the connection • FFT is not very sensitive in this situation • we select R4=R3+⊿ where ⊿ is the small amount as a threshold. When the signal is less R4 send pre-handoff message to Action module, When the signal is less then R3 then send handoff message

31. Handoff decision scheme from WLAN to WWAN • a)   If RSSI<R4, then send pre-handoff message to Action module; If RSSI<R3, send handoff message In this situation, the user need handoff immediately because the RSSI is too weak. • b)    If RSSI<R2, then begin FFT and send pre-handoff message to Action module If the X (1)/N< F1 then send handoff message • c)    If the NAV occupation > N2 then send pre-handoff message to Action module, after time T send handoff message

32. To avoid Ping-Pong effect • R1>R2>R4>R3; • N1<N2

33. 4.2 Action module • Will be introduced by shimin

34. 5 Conclusion and future work • For real time application a Modularized Two Step Handoff Scheme is proposed for handoff between WWAN and WLAN • In this scheme we design two module and a set of protocols, compare other scheme, it is clear and easy to implement • In this scheme not only physical layer signal but also MAC layer signal be considered • Handoff delay is very little and packet loss can be reduced • Avoids ping-pong effect

35. 6 References • [1]Buddhikot, M.M.; Chandranmenon, G.; Seungjae Han; Yui-Wah Lee; Miller, S.; Salgarelli, L.; “Design and implementation of a WLAN/cdma2000 interworking architecture”IEEE Commun. Mag.,  Volume: 41 ,Issue: 11 ,pp. 90–100 Nov. 2003 • [2] Q. Zhang, C. Guo, Z. Guo, and W. Zhu, “Efficient mobility management for vertical handoff between WWAN and WLAN,” IEEE Commun. Mag., vol. 41, pp. 102–108, Nov. 2003. • [3]Guo, C.; Guo, Z.; Zhang, Q.; Zhu, W.;“A Seamless and Proactive End-to-End Mobility Solution for Roaming Across Heterogeneous Wireless Networks”Selected Areas in Communications, IEEE Journal on ,Volume: 22 ,Issue: 5 , pp.834 - 848June 2004 • [4]M.Ye, “The mobile IP handoff between hybrid networks”, IEEE, 2002

36. Thank you!!!