Cellular Networks and Mobile ComputingCOMS 6998-11, Fall 2012

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Syllabus• Mobile App Development (lecture 2,3)

– Mobile operating systems: iOS and Android – Development environments: Xcode, Eclipse with Android SDK– Programming: Objective-C and android programming

• System Support for Mobile App Optimization (lecture 4,7)– Mobile device power models, energy profiling and ebug debugging– Core OS topics: virtualization, storage and OS support for power and context management

• Interaction with Cellular Networks (lecture 1,5, 8) – Basics of 3G/LTE cellular networks– Mobile application cellular radio resource usage profiling– Measurement-based cellular network and traffic characterization

• Interaction with the Cloud (lecture 6,9)– Mobile cloud computing platform services: push notification, iCloud and Google Cloud Messaging– Mobile cloud computing architecture and programming models

• Mobile Platform Security and Privacy (lecture 10,11,12)– Mobile platform security: malware detection and characterization, attacks and defenses– Mobile data and location privacy: attacks, monitoring tools and defenses

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Mobile App Development: iOS

• iOS Overview• Objective C• Xcode• Model-View-Controller• Blocks and Multithreading• Core Data and Location• iCloud

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Mobile App Development: Android

• Android OS Overview• Eclipse and Android SDK• Application Framework– Activity, content provider, broadcast receiver,

intent

• Networking• Google Cloud Messaging (GCM)

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System Support for Mobile App Optimization

• Mobile device power models, energy profiler and ebug debugging

• Core OS topics: – Virtualization– Storage

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System Calls As Power Triggers

Advantages:– Encapsulates utilization based triggers

• Parameters of system calls

– Captures power behavior of ones that do notnecessarily imply utilization

– Can be traced back to process, thread, function• Eases energy accounting

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Key observation: System call is the interface through which an application communicates with the underlying system

(hardware) and outside world (Internet, GPS, etc.)

Key Idea: Use System Calls as triggers in power modeling

Finite-State-Machine (FSM) as Power Model Representation

Use Finite-State-Machine (FSM)•Nodes: Power states – Base State: No activity on phone– Productive state: Actual utilization– Tail state: No-useful work

•Edges: Transition rules– System calls (start/completion)–Workload (Ex: 50 pkts/sec)– Timeout

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State 1 State

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State 3

Transitions

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Virtualization: Device Namespacesafely,

correctly multiplex access to devices

device namespaces

VP 3VP 2VP 1

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How Apps Use Storage?• Exactly what makes web browsing slow on Android?

– Key lies in understanding how apps use SQLite and FS interface/data/data/com.necla.webview

lib (empty)

cachewebviewCache

6aaa3f00, 03051d8d, …many files (5.5MB)databases

webview.db (14KB)webviewCache.db (129KB)

These files written to SQLite in sync

These files written to FS in write-behind

WebBench Storage Schema

Apps typically store some data in FS (e.g., cache files) and some in a SQLite database (e.g., cache map)– All data through SQLite is written synchronously slow!– Apps often use SQLite oblivious to performance effects

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Interaction with Cellular Networks

• Basics of 3G/LTE cellular networks• Impact of radio access network on mobile

apps– Radio resource usage profiling (ARO)

• Impact of cellular network core on mobile applications– In-depth study of middleboxes in cellular networks– Cellular network architecture characterization and

Implication to CDN

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Cellular Core Network

eNodeB 3 S-GW 2P-GW

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S-GW 1

eNodeB 1

eNodeB 2

Internet andOther IP Networks

GTP Tunnels

UE 2

UE 1

LTE Infrastructure

MME/PCRF/HSS

• UE: user equipment• eNodeB: base station• S-GW: serving

gateway• P-GW: packet data

network gateway• MME: mobility

management entity• HSS: home

subscriber server• PCRF: policy charging

and rule function

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LTE Architecture (Cont’d)

• eNodeB, S-GW and P-GW are involved in session setup, handoff, routing

User Equipment (UE) Gateway

(S-GW)

Mobility Management

Entity (MME)

Network Gateway (P-GW)

Home Subscriber

Server (HSS)

Policy Control and Charging

Rules Function (PCRF)

Station

(eNodeB)

BaseBase ServingServing Packet Data Packet Data

Control Plane

Data Plane

Power Management: LTE• UE runs radio resource

control (RRC) state machine

• Two states: IDLE, CONNECTED

• Discontinuous reception (DRX): monitor one subframe per DRX cylce; receiver sleeps in other subframes

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Power Management: UMTS

• State promotions have promotion delay• State demotions incur tail times

Tail Time

Tail Time

Delay: 1.5sDelay: 2s

Channel Radio Power

IDLE Not allocated

Almost zero

CELL_FACH Shared, Low Speed

Low

CELL_DCH Dedicated, High Speed

High

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Example: RRC State Machinefor a Large Commercial 3G Network

Promo Delay: 2 SecDCH Tail: 5 sec

FACH Tail: 12 sec

DCH: High Power State (high throughput and power consumption)FACH: Low Power State (low throughput and power consumption)

IDLE: No radio resource allocated

Tail TimeWaiting inactivity timers to expire

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ARO: Mobile Application Resource Optimizer

• Motivations:

– Are developers aware of the RRC state machine and its implications on radio resource / energy? NO.

– Do they need a tool for automatically profiling their prototype applications? YES.

– If we provide that visibility, would developers optimize their applications and reduce the network impact? Hopefully YES.

• ARO: Mobile Application Resource Optimizer

– Provide visibility of radio resource and energy utilization.

– Benchmark efficiencies of cellular radio resource and battery life for a specific application

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RRC State Machine Inference • State promotion inference– Determine one of the two promotion procedures– P1: IDLEFACHDCH;P2:IDLEDCH

• State demotion and inactivity time inference– See paper for details

A packet of min bytes never triggers FACHDCH promotion (we use 28B)A packet of max bytes always triggers FACHDCH promotion (we use 1KB)

P1: IDLEFACH, P2:IDLEDCHP1: FACHDCH, P2:Keep on DCH

Normal RTT < 300msRTT w/ Promo > 1500ms

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ARO System Architecture18