slide 1 of 16 internet service in developing regions through network coding mike p. wittie, kevin c....

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Internet Service in Developing RegionsThrough Network Coding

Mike P. Wittie, Kevin C. Almeroth, Elizabeth M. Belding,

Department of Computer Science

UC Santa Barbara

Ivica Rimac, Volker Hilt

Bell Labs

Alcatel-Lucent

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Networking and the Digital Divide

• The Digital Divide– Low penetration of Internet services– Higher price– Lack of adequate infrastructure

• Success of cellular deployments– No data services– High subscription price

• Rural mesh networks– Local communication patterns

• Goals: – Low cost data communications– Leverage cellular deployments– Cater to local communications

US Europe India Sub-saharan Africa

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50

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Broadband price (USD/month)

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Multihop Cellular Networks (MCNs)

• Cellular network augmented by client-to-client Wi-Fi communications [Lin00] (A)

• Rural (sparse) MCNs– Large cell area– Large per-client spectrum usage

• Local traffic patterns (B):– Cannot use cell tower– Cannot form end-to-end paths

• Need: efficient opportunistic client-to-client forwarding in sparse MCNs

A. B.

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Delay Tolerant Networks (DTNs)

• Epidemic Routing [Vahdat00]– Bundled data forwarded during

every contact for eventual delivery– Flood scoping by hop-count or TTL

• PRoPHET [Lindgren04]– Transitive destination contact

probability as routing metric– Data forwarded up a routing metric

gradient

• But, high cost of flooding creates network congestion

• Cloud Routing (CR) [Wittie09]– Network and traffic state disseminated

over a control channel– Forwards a small set of data copies– Lower forwarding cost and higher network

throughput

• But, replication wastes network resources

S

D

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Intra-flow Network Coding (NC)

• Forwards randomly encoded data on each path

• With high probability, data arriving on multiple paths is innovative

• Codes are embedded in packets themselves [Chou03]

𝑛 bytes of data 𝐷𝑝×𝑛/𝑝 data matrix 𝐸𝑝×𝑝 encoding matrix, initially 𝐼 𝒗1×𝑝,𝒗𝑖 ∈𝒢ℱ(8) Coded piece: ሾ 𝒗𝐸 | 𝒗𝐷 ሿ1×(𝑝+𝑛/𝑝)

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D

൦

𝒗1𝐸1𝒗2𝐸2⋮𝒗3𝐸3||||𝒗1𝐷1𝒗1𝐷1⋮𝒗1𝐷1

൪𝐺𝑎𝑢𝑠𝑠𝑖𝑎𝑛 𝑒𝑙𝑖𝑚.ሱۛ ۛ ۛ ۛ ۛ ۛ ۛ ۛ ۛ ۛ ሮ ൦ 𝐼 |||| 𝐷 ൪

𝑝×(𝑝+𝑛/𝑝)

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NC in DTNs

• Network Coding Probabilistic Routing (NCPR) [Widmer05]– Each node forwards floor(d)

coded pieces and additional coded piece with probability d-floor(d)

– Stops forwarding after ceil(d) coded pieces

– New innovative coded pieces reset forwarding cap

• But, tradeoff between high delivery rates and high load

• Need a more efficient mechanism for reliability

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Semi-Innovative Set Routing (SISR)

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Linearly independent?

Coded pieces required to decode bundle: 𝑏= 𝑝

Redundant coded pieces: 𝑟= 𝑏4

Maximum coded pieces at node (bundle fraction): 𝑓= 𝑟

b rb – f f

SISR (scissor) forwards: small forwarding footprint (CR) fraction of data on each path

through NC (NCPR)

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Given a set of coded pieces 𝐶, ȁ'𝐶ȁ'= 𝑏+ 𝑟,𝑟≥ 1, we can construct a set of SISs over 𝐶, such that any subset of 𝐶 of size 𝑏 has full rank.

Semi-Innovative Sets (SISs)

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D

SIS 𝑠 is a set of linearly independent coded pieces

𝐶

SIS1SIS2SIS3

every possible union of 𝑠𝑖,𝑠𝑗

𝑠1,𝑠2,⋯,𝑠 |𝐶|𝑏/2ඈ s1 s2 s3

b rb – f f

f

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Semi-Innovative Sets (SISs)

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SISs can be constructed to tolerate any number of losses 𝑙 = 𝑟/𝑓ہ ≥𝑓,ۂ 𝑟

𝑙 = 3 → 𝐶= 2𝑏,𝑓= 13 SIS1

every possible union of 𝑠𝑖,𝑠𝑗 SIS2SIS3SIS4SIS5SIS6

b rb rf ff b – f r-2f

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SISR in an MCN

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While the number of SISs grows

exponentially as ቆቒ𝑏+𝑟𝑏/2ቓ2 ቇ, each

node only needs to maintain

ቒ𝑏+𝑟𝑏/2ቓ− 1 SISs

n2 n3

When 𝑑 coded pieces are delivered, the global encoding adjusts accordingly

D

SIS1SIS2SIS3SIS4SIS5SIS6

ሺ𝑥,𝑦ሻ,𝒗𝐸

Embedded codes disseminated over the control channel to announce forwarding progress

b rb rSIS1SIS2SIS3SIS4SIS5SIS6

d

n1

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SISR Cloud Progress Example

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Evaluation Setup

• Want to compare SISR with CR and NCPR– NCPR – flooding and network coding– CR – small set of bundle copies– SISR – network coded bundle + redundancy

• Configuration details:– Area, node density and mobility models a rural community– Single flow between a node pair at different distances– Interested in evaluating:

• Bundle forwarding cost • End-to-end delay• Control channel load

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Forwarding Cost

• Forwarding cost – the amount of data forwarded

in the network before delivery

• NCPR – high cost of flooding• CR – high cost of replication• SISR – lowest cost

– Fraction of data on each path– Improvements for multiple

simultaneous flows

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Overhead of Control Traffic

• Control channel load– Position updates– Bundle progress notifications– Data encoding vectors (SISR

only)

• Cellular channel gain– Bundle size minus control traffic

• Prevalence of position updates• Higher gain for multiple flows• Gain higher for CR, but SISR

easier on client resources

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A. B.

Conclusions and Future Work

• Introduced Semi-Innovative Set Routing (SISR)

• End-to-end management of NC and forwarding mechanisms

– Only innovative data forwarded– Tolerates any number of losses

• 2X reduction in forwarding cost– Lower cost of infrastructure and data

services– Make data services affordable for more

clients

• Future work:– Adaptation to different

network settings– Directional mesh

networks with smart antennas

– Different ratios of data and control traffic propagation speeds

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b rSIS1SIS2SIS3SIS4SIS5SIS6

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Thank You

Mike [email protected]

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Q & A

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Backup Slides

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Evaluation Setup

• Want to compare SISR with CR and NCPR

• Configuration details:– Area, node density and

mobility models a rural community

– Single flow between random node pair

– NCPR – d configured for 100% delivery at 6km

– CR – lower forwarding cost at delay comparable to larger clouds

– SISR – lowest delay at 6km

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Bundle Delay

• Delay– end-to-end forwarding delay of

entire bundle (all coded pieces)

• SISR - last copy delay• NCPR – nodes use up

forwarding allowance before delivery

• CR – first copy delay

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Multihop Cellular Networks (MCNs)

• Cellular network augmented by client-to-client Wi-Fi communications [Lin00]

• MCNs can:– Reduce cellular channel load

(A)– Extend cell coverage (B, C)

• MCNs make cellular infrastructure go further

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MCNs in Developing Regions

• Sparse MCNs– Fewer clients and larger cell area– Larger per-client spectrum usage

• Local data communications– Regional caches (B)– Opportunistic client-to-client

communications (C)

• Our focus: opportunistic client-to-client forwarding in sparse MCNs

slide 1 of 16 internet service in developing regions through network coding mike p. wittie, kevin c....

Documents

chou03 s d slide

reliability s d slide

b r b ff slide

local communications

sparse mcns slide

control channel load

forwarding cost forwarding

low cost data communications