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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
Source: uiOne: Developing the core UI, BREW Conference 2005, Qualcomm Inc.
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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
Source: uiOne: Developing the core UI, BREW Conference 2005, Qualcomm Inc.
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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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Mobile Computing Research Areas contd.
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 Computing Research Areas contd.
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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Recent Research Papers
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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Recent Research Papers
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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Recent Research Papers
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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RWC results (2 of 4)
A=32
x1=2 x2=1
awnd2=11
awnd1=21
31% change
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RWC results (3 of 4)
0.1% loss
No RWC
Thruput
variations due to
random losses
A=32 packets
x1=x2=1
awnd1=awnd2=16
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RWC results (4 of 4)
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
vijay.raisinghani@tcs.com
rvijay@it.iitb.ac.in
http://www.it.iitb.ac.in/~rvijayhttp://www.it.iitb.ac.in/~sri
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