Mobile/Wireless Networking: Overview and Principles

Chunyi Peng

Fall 2015

Family  of  Networks  

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Mobile networks

WiFi (802.11a/b/g/n/ac…) 4G/3G: LTE, HSPA, EVDO, UMTS,…

WiMax, Satellite ….

Wireless networks

Bluetooth, NFC (RFID), WSN, … (not strictly)

whitespace 60GHz

Access (Edge) networks

Ethernet (LAN)

Cable, DSL …

Fiber optic

Internet Core Network (tier-1 ISP)

Data center ATM CDN …

Family  of  Networks:  Factor  Makers  

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Wireless networks

Access networks

Internet

Mobile networks

Interconnection end-to-end layering: TCP/IP packet switched … Edge last hop

Wireless broadcast Interference coverage …

Mobility

Roadmap  of  Mobile  Networking  •  From basic to advanced

– Principles, basic techniques – Key change factor – Challenge and opportunities – New problems/forms – Solution heuristics – New design

•  Hot topics – Problem, motivation, challenge, solution,

limitation -> another new problem C. Peng (OSU) 4

Principles  (ex:  scheduling)  Wireless  (ex:  TCP)  

Wireless  in  Mobile  (ex:  EERA)  Cellular  (ex:  CSFB)  

Hot  Topic  

Hot  Topic  

Hot  Topic  …  

DESIGN GUIDELINES FOR INTERNET & WIRELESS MOBILE NETWORKS

C. Peng (OSU) 5 Ref: most slides from Prof Lu’s CS211

Outline •  The Problem

•  The Design Goals

•  The Solution: design principles – Wired Internet – Wireless and mobility

•  The Future C. Peng (OSU) 6

The Problem: What is new from the wired Internet??? •  Fundamental challenges for wireless and

mobile networking design: – WIRELESS – MOBILITY

–  Is it so obvious and too trivial???

•  Map into each layer of the protocol stack

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Application

Middleware and OS

Transport Layer

Network Layer

Link sublayer MAC sublayer

Wireless Impact on Protocol Stack

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Ø  Partial network connectivity

Ø Diverse data losses

Ø  Changing network quality: delay, throughput

v Opportunistic connectivity v Time-varying link bandwidth

o  Location-dependent error o  Hidden terminals

Ø  Connection, disconnection

Ø Disconnection,

reconnection

ü Mobility-induced data losses

v Topology change v Time-varying capacity

o  Link-layer handoff o  Varying link quality

Application

Middleware and OS

Transport Layer

Network Layer

Link sublayer MAC sublayer

Mobility Impact on Protocol Stack

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The Goals •  Hide nasty impact of wireless

– SAME QUALITY AS WIRED LINK !!

•  Offer seamless services while mobile

•  Overall, “Anytime, anywhere” services

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The Design Guidelines •  How to develop the solution?

•  The foundation for wireless networking is the Internet design guidelines – End-to-end argument – Not for cellular networks (we talk it later)

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Key Design Decision •  How do you divide functionalities among

layers and across different components in the network? – Given the freedom to implement a few

functionalities in multiple “places” of the system (physical devices, or layers of protocols), where to implement them?

•  Goals: – Correctness, completeness, performance tradeoffs

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Options •  Telcom approach: “Smart CORE, Dumb Terminal”

– The core ensures reliability

•  TCP/IP approach: “Smart Terminal, Dumb CORE” – The terminal ensures reliability, while the core retains

simplicity –  Implicit assumption made: terminals have more

capabilities: computing power, storage, memory, etc.

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End-to-End Argument •  Think twice before implementing a

functionality that you believe that is useful to an application at a lower layer

•  If the application can implement a functionality correctly, implement it a lower layer only as a performance enhancement

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OS

Appl.

OS

Appl.

Host A Host B

OK

Example: Reliable File Transfer

•  Solution 1: make each step reliable, and then concatenate them

•  Solution 2: end-to-end check and retry

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Discussion on Solution 1 •  Ensuring reliability at every step is incomplete

– What happens if the sender or/and receiver misbehave?

•  The receiver has to do the check anyway! •  Thus, full functionality can be entirely

implemented at application layer; no need for reliability from lower layers

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More Discussions •  Is there any need to implement reliability at

lower layers?

•  Yes, but only to improve performance •  Example:

– Assume a high error rate on a wireless channel – Then, a reliable communication service at link

layer might help

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Tradeoffs •  Application has more information about the

data and the semantic of the service it requires (e.g., can check only at the end of each data unit)

•  A lower layer has more information about constraints in data transmission (e.g., packet size, error rate)

•  Note: these trade-offs are a direct result of layering! 18 C. Peng (OSU)

Rule of Thumb •  Implementing a functionality at a lower level

should have minimum performance impact on the application that do not use the functionality

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Two Forms of E2E Guideline •  Horizontal: Push complexity outside the

network core, into the end systems – Simple IP router, complex TCP end hosts

•  Vertical: Push design to higher layers of the protocol stack – End-to-end reliability at the transport layer in

TCP/IP – Hop-by-hop reliability at the link layer in telcom

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Summary: End-to-End Argument •  If the application can do it, don NOT do it at a

lower layer -- anyway the application knows the best what it needs – add functionality in lower layers iff it is (1) used

and improves performances of a large number of applications, and (2) does not hurt other applications

•  Success story: Internet

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Reuse, implementation effort (apply layering concepts)

End-to-end argument Performance

Remarks •  Challenge of building a network system: find

the right balance between:

No universal answer: the answer depends on the goals and assumptions!

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Two most popular design rules used in the research community

1.  Adaptation high-dimension dynamics

2.  Coordination

coherent system

What about Wireless & Mobile Networks?

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Adaptation As the Guideline •  Many concrete forms/instantiations of adaptations

–  Adaptation to handle different dimensions of dynamics –  Adapt to channel variations –  Adapt to mobility

•  Adaptation at different layers of protocol stacks –  From PHY, LINK, to TRANSPORT and APP layers

•  Numerous solutions/papers published –  38400 entries for google search “wireless adaptation” –  95800 entries for google search “mobility adaptation” –  40200 entries for google search “802.11 adaptation”

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Research Issues in Adaptation •  What to adapt?

–  how many cases to perform adaptation? •  When to adapt?

– when to invoke specific adaptation? •  stability versus responsiveness

•  How to adapt? –  specific mechanisms/algorithms in adaptation

•  How well to adapt? –  evaluate how different adaptation solutions perform

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Forms of Adaptation •  Opportunistic design approach

– Opportunistically adapt

•  Model-referenced design –  Adapt to trace a reference model

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Opportunistic Design •  Make each perform under peak conditions •  Exploit the system population •  Leverage system diversity

– Multiple receivers, multiple devices, multiple applications/flows, …

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Example: Opportunistic Scheduling

•  How to maximize system throughput by exploiting time-varying channels for each user in a fair way? – Each active user gets a share of the channel

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Dynamics for Each User

•  Each user’s channel varies independently over time due to fading etc.

•  In a large network, it is very likely to be a user with a very good channel at any time.

•  Long-term total throughput can be maximized by opportunistically serving user with the strongest channel

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Resulting Algorithm: Proportional Fair Scheduler •  (Used by Qualcomm EVDO system)

•  Schedule the user with the highest ratio

– Rk = current requested rate of user k – Tk = average throughput of user k in the past tc

time slots

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Opportunistic Performance Gain Increases with # of Users

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Model-Referenced Adaptation •  Ideal model to capture expected behaviors

under idealized situation – e.g., error-free, static settings

•  Track the reference model under realistic conditions/scenarios – Mobility, wireless channel dynamics, …

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Reference Model for Error-Free Channels

backbone

MH #1

MH #2

Base Station Sender

2 1

2 1 4 3 1 Channel status

Time à

2

Example: Scheduling over Channel Errors

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Goal: Each user gets 50% of channel

Idea: Lead/Lag to track difference with ref. model & Swap scheduling order for 1 and 2

Reference Model for Error-Free Channels Time à

backbone MH #1

MH #2

Base Station Sender

2 1

2 1 4 3 1 Channel status

2 4

3

Time à

Example: Scheduling over Channel Errors

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Forms of Coordination •  Cross-Layer design

– Enable close interactions cross non-adjacent layers in the layered protocol stack

•  Coordination via “indirection” – Adaptation-aware proxy provides indirection

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Cross-layer Design

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•  Information sharing, informed decision at other layers •  NOT integrated design by merging layers

Example of Cross-layer Feedback •  PHY info to higher layers

– Link/MAC layer •  Control transmit power, modulations to reduce error

rate or rexmit

– Network layer •  Bit-error rate information in order to switch another

network interface with lower bit-error-rate

– Application layer •  Channel condition information •  Various standard coding techniques for multi-media

applications

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Any Bad Effect? •  Cautionary perspective: •  Undesirable consequences on overall system

performance •  The importance of architecture

– Stability – Robustness – Spaghetti design – hard to upkeep – … – See the posted additional reading for details

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Indirection via “Proxy”

•  Proxy bridges the server and the client •  Move complexity away from both server and

client – Generalized end-to-end argument: “edge” rather than

“end” systems •  Little changes at server & client

client proxy server

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What is NEXT for Wireless and mobile technology?

•  It is not the end of the world, it is the end of the beginning

•  Many new fronts for technology innovation!!!

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Transport Layer Network Layer Link Layer

New Applications, Services, Requirements

New Wireless Communications Technology

Top

Down Bottom

Up

Drivers for Wireless (Mobile) Networking Research

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Bottom Up Driver: Wireless Communications •  Many of them:

– Sector Antenna, antenna arrays, Smart antennas – Adaptive modulation, OFDM, MIMO – Spectrum sharing, cognitive radio, channel

management – Multi-interface radios, device heterogeneity – …

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Challenge: How to exploit these new PHY communication capabilities in the protocols?

Root Cause of Problems •  two largely disconnected communities •  speak different terminologies

– wireless communications: •  Symbols, signals •  probabilistic terms:

–  information theoretic bounds –  confidence factor on symbol reception, …

– wireless networking •  Packets, bits •  deterministic terms

– Correct/wrong binary reception

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Root Cause of Problems (2) •  Two largely disconnected communities •  different methodologies

– wireless communications •  solid theoretic foundation on information theory •  a set of well known assumptions: noises, interferences, etc. •  Theory Design-->Analysis-->prototype in chips-->experiments

– wireless networking •  mostly on heuristics •  network setting “ad hoc”: no agreed benchmarks/base settings •  Heuristic Design-->Simulations--Network Prototype--

>Experiments

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Perspective From Wireless Networking •  We are not on the driver’s seat so far

–  communication has driven the technology so far – we are followers

•  No need to be sad –  still plenty of space

•  the direct communication almost NEVER works in reality at the 1st place!

–  other brothers also facing similar situations sometime •  Internet: PC/hardware industry •  Cellular: mobile phones

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Challenge: How to support such new demands?

Top Down Driver: User Demand •  Many of them: •  New applications

– MMS, P2P image/video sharing, IP TV streaming, … •  New requirements

–  Security, privacy, robustness/dependability, distributed management

•  New services –  Location-based service, Personalized service, …

•  New trends –  Interoperability of different wireless technologies

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New Design Goals 1. High Performance:

–  #1: Does the system work? –  #2: How well does the system work?

•  Technical side: Deliver performance via exploiting PHY capability

2. Resilience –  #3: How long does the system work under failures? –  #4: Will the system continue to work under attacks?

•  Technical side: Renovate the protocols to ensure robustness and security

3. Tradeoff between performance & resilience 47 C. Peng (OSU)

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Concluding  Remarks:                Many  opportuniIes  ahead!