Policy Enabled Handoff Across Heterogeneous Wireless Networks

8/14/2019 Policy Enabled Handoff Across Heterogeneous Wireless Networks

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Policy Enabled Handoff

Across

Heterogeneous Wireless

Networks

Helen W and Jochen GieseComputer Science, Berkeley.


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Outline

Abstract of the Paper

Policy Enabled Handoff System

- Case and Principles

- Operating Environment

- Policy Specification/Model

- Dealing with the Handoff Synchronization Problem

Implementation of the Policy Enabled handoff System- Programming Model

- Software Architecture

Conclusions and Future Work


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Abstract

Integration of Heterogeneous networks

Hand off issues in such networks (includes policy making)

Software Architecture/Support for Heterogeneous Networks

This paper presents a sample description of a heterogeneous

wireless network architecture and focuses on a novel handoff

mechanisms to achieve optimum performance.

The heterogeneous infrastructure experimented was on four types of networks

- Infrared LAN, WaveLAN, Metricomm, GSM Cellular.


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Some terms/ideas of Interest

Vertical Handoff- Intercellular Handoff- Handoff between cells of different

networks.

Features of Vertical Handoff-

Vertical handoff is simple and embedded in the system.

The mobile host always switches to the smallest coverage area.

**************************************************************

Horizontal handoff- Intracellular Handoff- Handoff between cells of the same

network.

Feature of Horizontal Handoff-

Horizontal handoff decision takes place based on received signal strength.


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What was the

Problemthen

?????

Firstly, The problem was sometimes frequent and unnecessary handoffs.

Secondly, These handoff decisions did not consider system dynamics such as

Thirdly, the handoff synchronization problem.- The problem of overloading a

network by mobile users simultaneously connecting at the same instant of time.

So, Berkeley came up with some policy deciding when a handoff is necessary.


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We here describe the factors that Berkeley thought that affect the handoff

system

Non- Dynamic factors

Bandwidth, latency

Power consumption

Charge Model

Dynamic factors

Network conditions such as load, traffic.

User conditions such as mobility


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Berkeley's Handoff Policy- Case and Principles

Network technologies differ in terms of bandwidth, latency, power

consumption and potentially their charge model.

The issue was how to integrate these seamlessly.

-Seamless ness was proposed to be achieved

-Handoff latency was proposed to be low enough not to

disrupt the running applications.

The automation of switching from one network to another is based on theprinciple of user involvement with minimal user interaction.

User involvement was required for the policy specification.

Handoff decisions and operations are all done at the mobile host. Periodically,

the mobile host collects current dynamic conditions, and consults with a pol-icy module on which is the best reachable network.


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Policy Specification/Model

Berkeley embedded its handoff decision policy to one equation

The cost of using a network n is a function of several parameters such as

the bandwidth it can offer(Bn), the power consumption of using the network

access device (Pn) and the cost (Cn) using the network and is represented as...

Costn = f(Bn, Pn, Cn)

For a given network.

a) Bandwidth parameter is calculated periodically( Note that available BW

is inversely proportional to the number of users)

b) Power Consumption are fixed

c) Cost parameters are fixed


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Policy Specification/Model (Contd)

Costn = f (Bn, Pn, Cn)

Normalization is done.N(x).. (Why..)

Costn = f (N(Bn), N(Pn), N(Cn))

The function is further expressed as

Costn = wb*N(Bn), wp* N(Pn), wc*N(Cn))

Where wb, wp and wc are weight values and sum to 1.

The setting of these values are determined by the user


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These were Berkeleys Specs for the simulated network

The Simple Mobile IP Architecture follows


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Stability Period (To avoid frequent handoffs)

Stability period is a defined as the waiting period before handoffs.

The system calculates the cost function of each reachable network periodically

and hands off to the better network if a network is consistently better for

astability period.

Only if the network is consistently better than the current one in use for the

stability perioddoes the mobile host perform handoff.

If a mobile user only transiently transfers to a better network, the gain fromusing the network may be diminished by the handover overhead and short usage

duration.


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Handoff Synchronization vs. Desynchronization

The left diagram shows instability due to simultaneous handoffs

whereas that instability is eliminated by incorporating stability period.


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Implementation of the Policy Enabled Handoff

System - Programming Model


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Implementation of the Policy Enabled Handoff

System Software Architecture


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Performance of the Berkeley Prototype

Four networks were included in the prototype:

1) IBM Infrared LAN, 2) Lucent WaveLAN, 3)

The Metricom Ricochet network, 4) and the GSMcellular.

Performance was based on handoff latency.

Handoff latency is the amount of time for a

mobile host to handoff to a given network.

Handoff latencies were measured from ten trials

of manually triggered handoffs.


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Future Work

1) Discovering Parameter Interdependency

This is important since varying one parameter can cause

changes to the rest of them. It includes understanding

and modeling the relationship between these system

parameters.

2) Redefining the policy model for various application levels

Users can specify priorities or different classes of QOSrequirements for each application such as real time and

non- real time. This can be easily incorporated into the

policy model.

Documents

Policy Enabled Handoff Across Heterogeneous Wireless Networks