A Smart Decision Model for Vertical Handoff

1
A Smart Decision Model for Vertical Handoff

• Ling-Jyh Chen, Tony Sun, Benny Chen,
• Venkatesh Rajendran, Mario Gerla
• Department of Computer Science, University of
  California at Los Angeles, Los Angeles, CA 90095,
  USA
• Department of Computer Engineering, University
  of California at Santa Cruz, Santa Cruz, CA
  95064, USA
• cclljj, tonysun, cudokido, gerla_at_cs.ucla.edu,
  venkat_at_soe.ucsc.edu

2
Presentation Outline

• Introduction
• Related Work
• Smart Decision Model
• Smart Decision Example
• Conclusion

3
Introduction
4
Problems and Solutions

• Problem
• Mobile devices with multiple network interfaces
  today cannot perform handoff among devices
  without losing existing internet connectiondue
  to change of IP addresses.
• Solution
• Universal Seamless Handoff Architecture (USHA)
  and Handoff Servers (HS).
• Problem
• Determining when to handoff to another interface
  is a complex decision.
• Solution
• Smart Decision Model.

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Definition of Handoff

• Horizontal Handoff
• Occurs when the user switches between different
  network access points of the same kind.
• e.g. Handoff among 802.11 APs.
• Vertical Handoff
• Involves two different network interfaces which
  usually represent different technologies.
• e.g. Handoff from 802.11 to 1xRTT (CDMA 2000).

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Handoff Illustration
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Seamless Handoff

• Defined as a handoff scheme that maintains the
  connectivity of all applications on the mobile
  device when the handoff occurs.
• Aims to provide continuous end-to-end data
  service in the face of any link outages or
  handoff events.
• Design Goal
• low latency
• Minimal packet loss

8
Related Work
9
Related Work Handoff Decision-making

• In Policy-Enabled Handoffs across Heterogeneous
  Wireless Networks, Proc. of ACM WMCSA, 1999, by
  H.J. Wang, R. H. Katz, and J. Giese
• Designed a cost function to decide the best
  moment and interface for vertical handoff.
• Cost functions presented in this paper is very
  preliminary and not able to handle more
  sophisticated configurations.
• Logarithmic functions used in the cost function
  will also have difficulty in representing the
  cost value while the value of the constraint
  factor is zero (e.g. the connection is free of
  charge).

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Related Work Handoff Decision-making

• In Cost Metrics For Decision Problem In Wireless
  Ad Hoc Networking, IEEE CAS Workshop on Wireless
  Communications and Networking, 2002, by M.
  Angermann and J. Kammann
• Modeled handoffs with HTTP traffic.
• May have problems with other types of traffic,
  such as video and audio streaming, where the
  bandwidth demand is much higher than HTTP
  traffic.

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Smart Decision Model
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Testbed Universal Seamless Handoff Architecture
(USHA)
NAT server
All packets are encapsulated and transmitted
using UDP
Applications are bound to the tunnel and
transparent to the handoff.
1xRTT
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Smart Decision Model

• With USHA, mobile hosts are able to select any
  network interface for its connection at any
  time.
• However, still need a model that knows which
  interface to use based on various factors such as
  
• Link Capacity (speed)
• Cost
• Power Consumption
• Solution Smart Decision Model

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Smart Decision Model

• HCCHandoff Control Center
• Provides connection between network interfaces
  and the upper layer applications.
• Composed of
• DM (Device Monitor)
• SM (System Monitor)
• SD (Smart Decision)
• HE (Handoff Executor)

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Smart Decision Model

• DM (Device Monitor)
• Monitors and reports the status of each network
  interface
• Signal strength
• Link capacity
• Power consumption
• SM (System Monitor)
• Monitors and reports system information (e.g.
  current remaining battery)

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Smart Decision Model

• SD (Smart Decision)
• Integrates user preferences and all other
  available information provided by DM, SM to
  achieve a Smart Decision
• HE (Handoff Executor)
• Performs a device handoff if current network
  interface differs from the one determined by SD.

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Smart Decision Process

• Priority Phase
• Add all available interfaces into candidate list.
• Remove user specified devices from the candidate
  list.
• If candidate list is empty, add back removed
  devices from step 1.
• Continue with Normal Phase.
• Normal Phase
• Collect information on every wireless interface
  in the candidate list from the DM component.
• Collect current system status from SM component.
• Use the score function to obtain the score of
  every wireless interface in the candidate list.
• Handoff all current transmissions to the
  interface with the highest score if different
  from current device.

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Priority / Normal Phases

• Necessary in SD to accommodate user-specific
  preferences regarding the usage of network
  interfaces.
• For instance, a user may decide not to use a
  device when it causes undesirable interferences
  to other devices (e.g. 802.11b and 2.4GHz
  cordless phones).
• With priority and normal phases in place, the SD
  module provides flexibility in controlling the
  desired network interface to the user.

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Score Function

• SD deploys a Score Function to calculate a score
  for every wireless interface
• Handoff target device is the network interface
  with the highest score.
• Score Function
• wj weight of factor k
• fj,i normalized score of interface i of factor
  j
• The equation is thus equivalent to
• where e Expense, c Link Capacity, p
  Power Consumption.

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Score Function Breakdown

• Expense
• Link Capacity
• Power Consumption
• Note
• The coefficients a , ß , ? are determined by user
  preference.
• Inverse functions are used to bound results from
  0 to 1.
• M Maximum bandwidth requirement demanded by the
  user.
• Link capacity is calculated using
  CapProbebecause advertised link speed is seldom
  achieved due to link congestion or bad link
  quality.

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Smart Decision Example
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Smart Decision ExampleScenario

• A mobile user currently using 1xRTT on his laptop
  enters a café.
• HCC immediately discovers a usable 802.11b access
  point inside the café and conducts the following
  comparisons
• Expense/Cost
• 1xRTT 1?/min
• 802.11b 10?/min
• Link Capacity
• 1xRTT 100 Kbps
• 802.11b 5 Mbps
• Power Consumption (battery time)
• 1xRTT 4 hours
• 802.11b 2 hours

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Smart Decision ExampleResult

• The mobile user prefers to spend more time in the
  café and feels that cost and connection speed are
  equally important to her, thus
• wp0.4, we 0.3, wc 0.3
• Coefficient obtained from her preference
  previously were
• ai xi / 20 , xi ?/min
• ßi Min(yi, M)/M , M 2Mbps
• ?i 2 / zi , zi hours
• Scores calculated using the score function are
• S1xRTT 0.83
• S802.11b 0.44.
• Since S1xRTT gt S802.11b , HCC decides to continue
  using the 1xRTT interface.

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Conclusion
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Conclusion

• Smart Decision Model provides a solution for
  determining the right time to perform handoffs.
• Our proposed model is able to make smart
  decisions based on
• Available network interfaces and properties (e.g.
  link capacity, power consumption, and link cost).
• System information (e.g. remaining battery).
• User preferences.