internet service in developing regions through network coding
DESCRIPTION
Internet Service in Developing Regions Through 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. Networking and the Digital Divide. The Digital Divide - PowerPoint PPT PresentationTRANSCRIPT
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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 HiltBell Labs
Alcatel-Lucent
Slide 2 of 16
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
0
50
100
150
200
250
300
350
400
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)
S
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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D
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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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D
SISs can be constructed to tolerate any number of losses 𝑙 = ≥𝑓,ۂ�������𝑟/𝑓ہ������� 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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D
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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D
b rSIS1SIS2SIS3SIS4SIS5SIS6
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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