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 1. Motivation and Objective 2. Overview of WWAN and WLAN 3. Integration Architecture and Mobile IP 4. Modularized Two Step Handoff Scheme 5. Conclusion 6. 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 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 Architecture of WLAN Router Internet Hub/Switch LAN Hub/Switch LAN

10 3 Integration Architecture and Mobile IP  Tight coupling  Loose coupling  Mobile IP

11 BS CDMA2000 BSC Internet CDMA2000 Core Network WLAN Access Point WLAN Gateway Tight Coupling Loose Coupling

12 Tight coupling  Basic idea  disadvantage

13 Loose coupling  Basic idea  Advantage

14 Mobile IP

15 4 Modularized Two Step Handoff Scheme

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

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.

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

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

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

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  [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  [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 June 2004  [4]M.Ye, “The mobile IP handoff between hybrid networks”, IEEE, 2002

Thank you!!!