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Tata Consultancy Services ltd. 17 November 2010 1

Research and Latest Trends

inMobile Computing

Mobile Computing with Recent trends and Future Challenges

TCET-ISTE

22nd July 2006

Vijay T. Raisinghani

slides available on http://www.it.iitb.ac.in/~rvijay


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Mobile Computing

Two word definition in itself: computing while mobile

Could be wireless or even wired Laptop connection over WiFi or Ethernet

Application could be local on the device or connecting to server overnetwork

Mobile computing becoming synonymous with wirelessmobile computing

Key characteristics

Low device resources (interface, display, memory, battery,CPU)

Disconnected operationWrt Wireless Low / varying bandwidth (compared to wire-line)

Handoffs/changing servers

Disconnections


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Latest trends in Mobile Computing

Converged devices (communication, consumer electronics, computing)

Phone, Radio/TV, Camera, PC all in one

Seamless mobility

Mobility across heterogeneous wireless networks (WiFi GSM)

Device operating systems

Moving towards Linux from Symbian and Windows CE

Motorola has already introduced Linux smart phones

BREW (Binary Runtime Environment for Wireless) from Qualcomm

Device form factor

Global Positioning System

Built-in sensorsGait sensors for security

Ad-hoc networks

M-Commerce


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Latest Trends in Mobile Computing -

Examples

Killer Applications

Real-time gaming, video telephony, web-browsing,

multiplayer games, streaming video/audio. An example

below:

Network

WiFi Mesh networks to provide outdoor mobile connectivity

WiMAX (802.16): Being rolled out in many countries

802.16e Mobile WiMAX

Movie PosterWith

Visual Code

Cell phone with

camera/code scanner

Server

with

video clips

Code

Media clip


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Latest Trends in Mobile Computing Examples

BREW

Binary Runtime for Wireless Environment (BREW)provides a framework for creating applications on awide variety of mobile devices

Application examples: Email, IM, navigation (locationbased), address content sync, games, etc

Product of QUALCOMM Internet Services, a divisionQUALCOMM Incorporated

BREW applications run on phones on which BREWApplication Execution Environment (AEE) is present.AEE is loaded by the manufacturers using the BREWPorting Kit


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BREW (contd.)

BREW is thin and fast

Platform sits right on top of chip system software, enabling

fast C/C++ native applications

BREW is open

Supports other languages beyond native C/C++, including

alternative execution environments such as Java, Extensible

Markup Language (XML), and Flash

Source: Qualcomm Inc.


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BREW SDK

Facilitates development of software applications

Provides

general development and debugging tools

sample applications with source codereference material and user guides

phone emulator: lets developers run applications on PC

BREW SDK is available on Qualcomm website free of

cost

Microsoft VC++ is used as the development enviroment

DLL can be used on emulator

ARM compiler used to create mod file for handset


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BREW uiOneTM

Traditional application

Source: uiOne: Developing the core UI, BREW Conference 2005, Qualcomm Inc.


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BREW uiOneTM

uiOne application



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BREW uiOneTM

Flexible application

Layout, etc. defined on the

server

UI look and feel can be

changed by changing code on

server

Enables dynamic user

experience



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Research in Mobile Computing


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Mobile Computing Example

Wireless medium

Wireline

Mobile infrastructure

Data Server

Mobile device

Example Scenario

User


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Selected Mobile Computing

Journals/Conferences

Journals

IEEE: Transactions on Mobile Computing (TMC)

ACM: Mobile Computing and Communications Review (MC2R)

Conferences

ACM Mobile Computing and Networking (MobiCom)

IEEE Infocom

IEEE/ACM Conference on COMmunication System softWAre

and MiddlewaRE (COMSWARE)

Asian International Mobile Computing Conference (AMOC)


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Mobile Computing Research Areas

Overview

Wireless medium

Wireline

Mobile infrastructure

Data ServerMobile device

User


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Mobile Computing Research Overlap

Networking and Distributed Systems

Fault tolerance

Operating Systems

Power management, disconnected operation

Computer Architecture

Wearable computers

Software Engineering

Dynamic reconfiguration

Human Computer Interaction

Context awareness

Security and Privacy

Biometric authentication

Sensing and Actuation

Location sensing, robotics

Source: Carnegie Mellon, http://www.csd.cs.cmu.edu/research/areas/mopercomp/


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Mobile Computing Research Areas

Summary

User and Mobile Device

Interface design, authentication, innovative applications,

security, performance improvement, software defined radio

Mobile Infrastructure

Integration and internetworking of wired and wireless

systems, support for seamless mobility, quality of service

Modeling Analysis and Simulation

Mobile agents

Wireless Test beds for Technology evaluation

Ad-hoc networks

Underwater networks


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Mobile Computing Research Areas Details

User and Mobile Device

Userinterface for small form factors (ergonomics)

Wearable computing

Value engineering (cost reduction)Safety

Authentication (e.g. biometrics)

Adaptive applications

Innovative applications Traffic updates, high-speed toll payment

Electronic wallets, e-Payments


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Mobile Computing Research Areas Details

User and mobile device (contd)

Support forseamless mobility

Cross layer feedback (protocol stack)

Multiple interfaces; software defined radio

Performance improvement

Reduction of resource requirements (e.g. CPU, battery,

etc.)

Cache management

Security (e.g. preventing virus attacks)

Mobile databases

Location tracking


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Mobile Computing Research Areas contd.

Mobile Infrastructure (includes back-end servers)

Architecture, protocols, algorithms to cope with mobility, limitedbandwidth, and intermittent connectivity

Interaction between different layers of mobile/wireless systems

Integration and internetworking of wired and wireless systems

Adaptive systemsSupport for seamless mobility

Call continuation

Authentication

Quality of service (e.g. for multimedia transmission)

Fault-tolerant networksAuthentication, billing and payment

Location dependent applications

Middleware for transcoding


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Modeling Analysis and Simulation

Performance evaluation

RF capacity simulation and analysis

Traffic analysis

Simulation and analysis of wireless protocols and standards

Simulation languages and tools

Modeling and analysis of speech, audio and wireless

transmission

Ad-hoc networks

Infrastructure-less networking

Partitioned operation

Delay tolerant networking


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Mobile agents

Wireless Test beds for Technology evaluation

Design and evaluation of test beds

Techniques for reproducibility of real-world testing

Tools for measurement, collection and analysis

Underwater networks

Range is severely limitedMedium access control


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Recent Research Papers

MobiCom 2005

Pradeep Kyasanur, Nitin Vaidya (University of Illinois at

Urbana-Champaign, US)

In an ad-hoc network scenario they study the impact on

network capacity of the number of channels and number

of interfaces on a mobile device

Bhaskaran Raman, Kameswari Chebrolu (IIT Kanpur, IN)

802.11 in long-distance mesh networks being

designed/used for low-cost rural connectivity. Theydescribe a new MAC protocol suited for such networks in

terms of efficiency


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IEEE TMC 2006

Ying Cai, et al, (Iowa State, US)

Real-time monitoring ofmovement of mobile nodes in a

region. Performance improvement proposed for lowering

communication and processing costs.

Mobile patient monitored using sensor network. Data is

transmitted using 3G network.


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Infocom 2006

Srinath Perur, Sridhar Iyer (IIT Bombay)

Reachability in sparse mobile ad-hoc networks. Proposed

a new way of deciding how connected is a sparse ad-

hoc network, by looking at connected node pairs.

Raghuraman Rangarajan, Sridhar Iyer (IIT Bombay)

WIND: A tool for capacity-constrained design of multi-tier

wireless networks

COMSWARE 2006

Vijay Raisinghani (TCS), Sridhar Iyer (IIT Bombay)

Optimized communication stacks for wireless devices


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MC2R

Sangheon Pack, et al (Seoul National University, Korea)

Selective neighbor caching scheme forfast handoffin

IEEE 802.11 wireless networks: Considering hand-off

patterns a mobile nodes context is propagated to

selected neighboring access points

Paul Grace, et al (Lancaster, UK)

Middleware proposed to enable mobile client to discover

services and interact with them


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Tata Consultancy Services ltd. 17 November 2010 26

Detailed Example:

Cross Layer Feedback in Mobile Devices


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Typical Mobile Wireless Network

MWN characteristicsHigh bit error rate of wireless channel

Mobility induced disconnections


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Typical Protocol Stack Architecture

Layered

Application

Transport

Network

MAC

Physical

User programs, interface

Connection management,flow/error control (e.g. TCP)

Routing, addressing (e.g. IP)

Error free tx; medium access

(e.g. 802.11)

Tx of raw bits (e.g. 802.11)

Applicationhas very lowawareness ofphysical layerand vice-versa

Layeredarchitecture:Layer n hasfunctionspecificService AccessPoints forlayers n-1,n+1


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Layered example: TCP

In wireless networks

many packet losses are due to bit errors

TCP on packet loss

assumes network congestionreduces throughput

TCPs congestion assumption fails

unaware of wireless physical layer reduction in send window inappropriate


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Cross layer feedback: Motivation

Protocol stack layering useful: software engineering

perspective

Strictly layered stacks do not perform well over wireless

networksnetwork conditions are highly variable: random

errors; intermittent disconnection

mobile nodes are resource poor

Several assumptions from fixed wired networks do

not hold for wireless: packet losses, disconnections,

mobility


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Observation

Cross layer information can help improve performance

over wireless networks

Upper to lower layers

TCP timer informationapplication QoS requirements

user feedback

Lower to upper layers

link characteristics

network connectivity status


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Some existing approaches

TCP thruput information to tune physical layer power(Chiang. IEEE JSAC, 2005)

ATCP / RWC for TCP (Raisinghani VT, Singh A, Iyer S. IEEE ICPWC,2002)

TCP QoS information to adapt link layerretransmissions (Chiasserini, Meo. IEEE Globecom, 2001)

Layer2 information to MobileIP for IP handoff(Wu, et al.MONET, 2001 )

TCP fast retransmit (Caceres, Iftode. IEEE JSAC 95)


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Cross Layer Feedback:

Optimizing TCP for MWN

Several approaches focus on mitigating

Adverse effect of wireless channel

Mobility induced disconnections

Any approach involves one or more of:Fixed Host (FH) TCP stack modification

Base Station (BS) per-connection support

Mobile Host (MH) TCP stack modification Typically assume TCP sender at the FH


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Our approach: Optimizing TCP for MWN

Modification to TCP stack at MH only

Optimizing TCP to mitigate effect of

mobility induced disconnections

Focus on TCP sender at Fixed Host (FH) Approach: Use ofcross-layer feedback


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Our approach: Optimizing TCP for MWN

Receiver Window Control

Based on user feedback idea

User indicates application priorities

System maps priorities to TCP receiver windowcontrol


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User feedback on mobile devices

User experience bound by resource poor mobile

devices

Limited memory

Limited battery lifeWireless channel problems


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User feedback: Motivation

Cross layer feedback has useful optimizations

Designed for standard problems: handoff, link layerretx, etc.

Optimizations may not fulfill user needs

User aware of exact self needs

User can take better decisions which are contrary tosystem behavior

Required for improving user experience


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User feedback: Motivation

Various proposals exist for using cross layer feedback

No proposals to use dynamic user feedback on wireless

device

Idea could be useful for device mfrs


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User Feedback

User feedback examples:

Impending disconnection information

Dynamic changes in application priorities

For example: In view of impendingdisconnection, an ongoing FTP may becomemore important than an ongoing videoconference; contrary to default system priorities

System can avoid performance degradation by

mapping user input to protocol specific actions

E.g. Map user priorities to TCP receiver windowof each application on device


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Background: TCP receiver window

Reflects receivers available buffer through advertisedwindow (awnd) in ACKs

Optimum awnd = bandwidth*delay (bdp) to fill pipe andmaximize sender throughput

awnd < bdp decreases sender throughput

Each application on MH may require different awnd,according to bdp


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Receiver Window Control (RWC)

Exploits idea: Sender throughput decreases as awnd< bdp

Higher awnd for high priority applications

Restrict awnd for low priority applications

Assume total awnd is a fixed resource

(Re)distribute awnd according to priority

Results in download bandwidth change forapplications on device


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RWC results (1 of 4)

A=32 packets

x1=x2=1

awnd1=awnd2=16


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A=32

x1=2 x2=1

awnd2=11

awnd1=21

31% change


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0.1% loss

No RWC

Thruput

variations due to

random losses

A=32 packets

x1=x2=1

awnd1=awnd2=16


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0.1 % loss

Thruput stillincreases for

higher priority

application


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Our approach to TCP:

Summary

Our approach to optimizing TCP in MWN

Mitigates effect of mobility induced

disconnections

Requires modification to TCP stack at MH

only

Uses upper layer feedback fordynamic

priorities

Novelty: User in the loop


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Cross Layer Feedback: Issues

How to pass layer n information to layer m ?

When incorporating feedback from other layers in layern

How to protect layer ns correctness, reliability ?

How to resolve conflict due to feedback frommultiple layers to layer n?

How to pass event information to other layers(interrupt v/s polling)?

How to ensure

maintainability of CLF ?

minimum overhead due to CLF ?


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Cross Layer Feedback: Punch hole

approach

Ad-hoc approach

Introduce additional code

in layer for CLFApp

TCP

IP

MAC

Phy

get_handover_info()

Code

block

for

CLF


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CLF:

Punch hole Each additional CLF code

block can slow down datapath (thruput) of layer

Porting CLF will requirerewriting for specific OS

Difficult to control to layerscorrectness since updates

by different CLF codeblocks

Difficult to disable/ removecode intertwined withregular layer code

Difficult to do fastprototyping/additions sincead-hoc

Multiple event monitorswithin a layer could slow

down data path (thruput) of

App

TCP

IP

MAC

Phy


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CLF Architecture

CLF basically stack modification

Multiple ad-hoc cross layer modifications canaffect stack's reliability, efficiency, maintainability

Design goals for architectureEfficiency: minimal overheads (e.g. cpu, memory, datapath delay); enhanced performance

Minimum intrusion: protect stack correctness; easy toextend / reverse CLF

Portability: easy porting to different systems

Rapid prototyping: new CLF idea easy to develop/deploy


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ECLAIR: CLF architecture

Optimizing SubSystem: Crosslayer feedback algorithms

(protocol optimizer PO);

receive layer events; decide

other layers behavior Tuning Layer: Monitor layer

events; API to protocol

optimizer; access layer's

control data structure values

Minimal CLF code instack, if required

e a s


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e a s


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ECLAIR: (e.g.)TL APIs


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Linux internals: TCP (for RWC)

sock.h header file.

Containssocketand tcp data structure


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ECLAIR implementation (Linux): RWC

ECLAIR i l t ti (Li ) RWC


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ECLAIR implementation (Linux): RWC

(contd)


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ECLAIR validation

Simulation: no RWC wget: no RWC

Similar setup; no CLF; equal thruput


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ECLAIR validation

Similar setup; RWC

Simulation: with RWC wget: ECLAIR RWC

per ormance


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per ormance

m applications

n reads

O(m x n)

non-ECLAIRRWC invoked oneach read() read()

involves user-

kernel crossing


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ECLAIR performance(contd)

Performance metrics

Time-space complexity, design complexity, user-kernel

crossing, data path delay

Observations

Performance metric Non-ECLAIR

(get+

setsockopt) x O()

ECLAIR

(ioctl) x O()

User-kernel crossing

(sec)

(20+21) x O(n x m) 83 x O(n)

parameter passing only

Data path delay (sec) (20+21) x O(n x m) -


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ECLAIR: Salient features

Event Notification: TLs provide facility for POs to register forinteresting events at a layer. E.g. TCP can register forhandover events at Mobile-IP layer

Switch on/off: Cross layer system is separate. Can be

easily/dynamically switched on or off. Individual POs may beswitched on/off

Seamless mobility: through POs that monitor/ controlmultiple protocol stacks. E.g., seamless mobility POmonitors CDMA (or GPRS) / WLAN interfaces signal

strength. Algorithm maps signal strength to throughputachievable on interface. PO takes decision to changeinterface

User Tuning Layer(UTL): UTL allows device user or externalentity e.g.: a distributed algorithm or base station, to tune the

device behavior


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Related Work

Sudame, Badrinath, MONET 2001CLF: link conditions; internal ICMP messages /handler

Each application defines application/transport layer

adaptation

Inouye, Binkley, Walpole, Mobicom 1997

CLF: interface add/remove, cost, bandwidth

Adaptation module(per layer) managesadaptation/sequential propagation of (a) events (b)policies

Any to any layer CLF / genericarchitecture/optimizations not discussed


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Future Work

Multiple cross layer interactions could affect protocolcorrectness

Resolve cross layer feedback conflict

Extend ECLAIR for seamless mobility

Add components for interaction with network nodes

ECLAIR is good for asynchronous CLF

Improve ECLAIR for synchronous CLF


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Thank you

[email protected]

[email protected]

http://www.it.iitb.ac.in/~rvijayhttp://www.it.iitb.ac.in/~sri

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