Cooperative Caching in Wireless Multimedia Sensor Nets

Cooperative Caching in Wireless Multimedia Sensor Nets Nikos Dimokas 1 Dimitrios Katsaros 1,2 presentation Yannis Manolopoulos 1 3 rd MobiMedia Conference, Nafpaktos, Greece, 27-29/Augu

Cooperative Caching in Wireless Multimedia Sensor Nets

Nikos Dimokas 1

Dimitrios Katsaros 1,2

(presentation)

Yannis Manolopoulos 1

3 rd MobiMedia Conference, Nafpaktos, Greece, 27-29/August/2007

1 Informatics Dept., Aristotle University, Thessaloniki, Greece

2 Computer & Communication Engin Dept., University of Thessaly, Volos, Greece

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Wireless Sensor Networks (WSNs)

Wireless Sensor Networks features

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What’s so special about WMSNs ?

• [ Ian Akyildiz: Dec’06 ] We have to rethink the computation-communication paradigm of

traditional WSNs

• which focused only on reducing energy consumption

• WMSNs applications have a second goal , as

important as the energy consumption

• delivery of application-level quality of service (QoS)

• mapping of this requirement to network layer metrics, like latency

• This goal has (almost) been ignored in

mainstream research efforts on traditional WSNs

• multi-hop nature of WMSNs implies that wireless link capacity depends on the interference level among nodes

• sensor nodes store rich media (image, video), and must retrieve such media from remote

sensor nodes with short latency

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Our proposal …

• multiple sensor nodes share and coordinate cache data to cut communication cost and exploit the

aggregate cache space of cooperating sensors

• Each sensor node has a

moderate local storage

capacity associated with

it, i.e., a flash memory

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Relevant work (1/2)

• Caching in operating systems, in databases, on the Web

• No extreme resource constraints like WMSNs

• Caching for wireless broadcast cellular networks

• More powerful nodes, and one-hop communication with resource-rich base stations

• Most relevant research works:

• cooperative caching protocols for MANETs

• GroCoca: organize nodes into groups based on their data

request pattern and their mobility pattern

• ECOR, Zone Co-operative, Cluster Cooperative: form

clusters of nodes based either in geographical proximity or utilizing widely known node clustering algorithms for MANETs

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Relevant work (2/2)

Protocols that deviated from such approaches:

• CacheData : intermediate nodes cache the

data to serve future requests instead of

fetching data from their source

• CachePath : mobile nodes cache the data

path and use it to redirect future requests to the nearby node which has the data instead of the faraway origin node

• Amalgamation of them: the champion

HybridCache cooperative caching for MANETs

• One caching work on WSNs

• concerns the placement of caches

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Our contributions …

imply short latency in retrieval

• Description of a cooperative caching

residual energy

component subprotocols

cooperative caching for MANETs, with J-Sim

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A measure of sensor importance

• Let σ uw =σ wu denote the number of shortest paths

from u  V to w  V (by definition, σ uu =0)

• Let σ uw (v) denote the number of shortest paths

from u to w that some vertex v  V lies on

• We define the node importance index NI(v) of a vertex v as:

• Large values for the NI index of a node v indicate

that this node can reach others on relatively short

paths, or that v lies on considerable fractions of

shortest paths connecting others

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The NI index in sample graphs

In parenthesis, the NI index

of the respective node; i.e., 7(156): node with ID 7 has

NI equal to 156.

Nodes with large NI:

Articulation nodes (in

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The cache discovery protocol (1/2)

A sensor node issues a request for a

multimedia item

• Searches its local cache and if it is found (local cache hit) then the K most recent access

timestamps are updated

• Otherwise (local cache miss), the request is broadcasted and received by the mediators

• These check the 2-hop neighbors of the requesting node whether they cache the datum (proximity hit)

• If none of them responds (proximity cache miss), then the request is directed to the Data Center

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The cache discovery protocol (2/2)

When a mediator receives a request, searches its cache

• If it deduces that the request can be satisfied by a neighboring node (remote cache hit), forwards the request to the neighboring node with the

largest residual energy

• If the request can not be satisfied by this

mediator node, then it does not forward it recursively to its own mediators, since this will be done by the routing protocol, e.g., AODV

• If none of the nodes can help, then requested

datum is served by the Data Center (global hit )

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The cache replacement protocol

• Each sensor node first purges the data that it has cached

on behalf of some other node

• Calculate the following function for each cached datum i

• The candidate cache victim is the item which incurs the largest cost

• Inform the mediators about the candidate victim

• If it is cached by a mediator, the metadata are updated

• If not, it is forwarded and cached to the node with the largest residual energy

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Evaluation setting (1/2)

• We compared NICOCA to:

• Hybrid, state-of-the-art cooperative caching

protocol for MANETs

• Implementation of protocols using J-Sim simulation library

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Evaluation setting (2/2)

• Measured quantities

• number of hits (local, remote and global)

• residual energy level of the sensor nodes

• average latency for getting the requested data

• the number of packets dropped

• Present here only results for number of hits

• A small number of global hits

• less network congestion, fewer collisions and packet drops

• Large number of remote hits  effectiveness of

cooperation

• Large number of local hits ≠ effective cooperation

• the cost of global hits vanishes the benefits of local hits

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Cache vs hits (MB files & uniform access) in a dense WMSN (d = 7)

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Cache vs hits (MB files & uniform access) in a very dense WMSN (d = 10)

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Cache vs hits (KB files & Zipfian access) in a dense WMSN (d = 7)

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Cache vs hits (KB files & Zipfian access) in a very dense WMSN (d = 10)

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Summary

• Wireless Multimedia Sensor Networks (WMSNs)

• Unique features of WMSNs call for protocol

designs that provide application-level QoS

• Cooperative caching protocol, NICoCa ,

suitable for WMSNs

• NICOCA evaluation with J-Sim and comparison

to the state-of-the-art protocol

• NICOCA can:

50%

cooperation) at an average percentage of 40%

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Important references

1 I Akyildiz, T Melodia, and K R Chowdhury A

survey of wireless multimedia sensor

networks Computer Networks, 51:921-960, 2007

2 Y Diao, D Ganesan, G Mathur, and P Shenoy

Rethinking data management for

storage-centric sensor networks Proceedings of the

Conference on Innovative Data Systems

Research (CIDR), pp 22-31, 2007

3 S Nath and A Kansal FlashDB: Dynamic

self-tuning database for NAND flash Proceedings

of the ACM International Conference on

Information Processing in Sensor Networks

(IPSN), pp 410-419, 2007

4 L Yin and G Cao Supporting cooperative

caching in ad hoc networks IEEE Transactions

on Mobile Computing, 5(1):77-89, 2006

Thank you

for your attention!

Any questions?