Download Efficient Mobility Management for Vertical Handoff between WWAN

Efficient Mobility Management
for Vertical Handoff between
WWAN and WLAN
IEEE Communications Magazine
November 2003
Authors
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Qian Zhang
Chuanxiong Guo
Zihua Guo
Wenwu Zhu
All come from Wireless and Networking
Group, Microsoft Research Asia
Teammates
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資工所 廖翊均 692410001
資工所 林世敏 692410035
資工所 陳崇凱 692410078
Outline
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Introduction
Connection manager
Virtual connectivity manager
Performance evaluation
conclusions
Introduction
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WLAN vs. WWAN
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Horizontal handoff vs. Vertical handoff
Mobile IP
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IEEE 802.11 vs. GPRS
HA, FA, CoA
Routing, scalability
Migrate
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Reference [8], Proc. Mobicom 2000
End-to-end
Two limitations
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Cannot make mobility transparent to application
Cannot maintain connection under NAT & simultaneous
movement
Introduction
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Proposed approach
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IP-centric
Connection Manager (CM)
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Virtual Connectivity Manager (VC)
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Detect conditions and availability of networks
Maintain connection’s continuity
Local Connection Translation (LCT)
subscription/notification service (S/N)
Roaming decision maker
Context database
Connection Manager
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Handoff from WWAN to WLAN
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Physical Layer Sensing
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Detect the available of the stable WLAN signal
MAC Layer Sensing
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NAV (Network Allocation Vector)
Traffic load vs. NAV occupation
Network-condition-aware handoff
Adaptation of upper layers
Best QoS selected
Connection Manager
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Handoff from WLAN to WWAN
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FFT-Based Decay Detection
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FFT：Fast Fourier Transform
To detect signal decay
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X(1)/N：threshold
N：RSSI sampled number
Connection Manager
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Adaptive Threshold Configuration
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To set an appropriate RSSI threshold
RSSI：Received Signal Strength Indication
S1 = S2 + Δ
Virtual Connectivity Manager
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Problems caused by mobility
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Transparency to application
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Especially important for UDP applications
Transparency to NAT
Simultaneous movements
The VC protocol
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Peer negotiation
Connection maintenance
S/N protocol
Virtual Connectivity Manager
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Local Connection Translation (LCT)
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Mapping relationship between the original and the
current connection information
Solve “transparency to application” problem
Subscription/Notification service (S/N)
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To bridge the two communication parties so that
they can exchange address information
S/N server is publicly addressed and never moves
Solve “transparency to NAT” & “simultaneous
movement” problems
Performance Evaluation
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OS：Windows 2000
CM：manipulates and monitors all wireless
network interfaces via the NDIS device
interface, and provides related information to
the roaming decision maker, which runs in the
system as a background service.
VC：implemented in the system together
with the TCP/IP stack, and is located naturally
between the network and transport layers.
Conclusions
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In this article a novel mobility
management system is proposed for
vertical handoff between WWAN and
WLAN.
The system integrates a CM and a VC.
Collaboration between the CM and VC
accomplishes seamless handoff
between WWAN and WLAN.
Conclusions
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CM：detect the wireless network changes
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MAC sensing
FFT detection
adaptive threshold configuration
VC：maintain connectivity using the
end-to-end principle
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LCT：support application transparency
S/N： support working under NAT and
handling of simultaneous movement