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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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)