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Project Status Update“Postcards from the Edge”: The Cache-and-Forward ArchitectureFIND Wireless Workshop @ BBN Sept 27, 2007

Dipankar Raychaudhuri, Sanjoy Paul, Roy YatesWINLAB, Rutgers University

{ray, sanjoy, ryates} @winlab.rutgers.edu&

Jim Kurose, U Mass, kurose@cs.umass.edu

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CNF Project: Architecture Concepts Network is optimized for efficient content delivery to mobile devices

Large storage (~TB) at each network node Single- or multi-hop wireless access with occasional disconnections Strict hop-by-hop transport (…entire file sent via reliable link protocol) “Post Offices” for opportunistic delivery to mobile clients Integration of conventional routing with retrieval of cached content

Receiver’s Post OfficeSender’s

Post OfficeReceiver

Sender

MNMN

MN

CNF NetworkRouters with

Storage

Reliable Link Layer

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CNF Project: Protocol Stack Routing protocol with integrated support of

address- and content-based modes of delivery (get “filename”, deliver ”filename” to “address”, etc.)

Support for in-network caching of content Multi-hop wireless access with disconnections and

mobility at access edge (..”postbox” concept)

Core

CNF_1 CNF_6

CNF_2

MN

SenderReceiver

MNMN

CNF_3 CNF_4CNF_5

CNC_1

Link ProtocolLink Protocol

Receiver’s Post OfficeSender’s

Post Office

Link Protocol

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CNF Project: Simulation Results – Network Topology and Simulation Parameters

GT-ITM’s transit-stub model Transit-transit links

10000Mbps bandwidth Uniform (20,23)msec delay

Transit-stub links 155Mbps bandwidth Uniform (20,23)msec delay

Stub-stub links 1000Mbps bandwidth Uniform (2,11)msec delay

15 source-destination pairs

ON State: Exponentially distributed with mean 100sec OFF State: Exponentially distributed with 3600sec An ON state is always followed by an OFF state (vice versa) Initial state of the source is ON During ON State: Fixed file size (50MB), Poisson arrivals

S

S

D

D

S

S D

D

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CNF Project: Simulation Results (1) – CNF vs. TCP Delay vs. Traffic Type & File Size

TCP outperforms CNF for “always on” traffic and at

low arrival rate

Advantage of TCP over CNF reduces for ON-OFF

traffic

Advantage of TCP over CNF for “always on” traffic is higher at smaller file size

Advantage of TCP over CNF for ON-

OFF traffic is lower at smaller file size

In-network storage in CNF serves to smooth traffic bursts

However, this must be balanced against loss of pipeline gain

Overall, CNF performs well relative to TCP except at low loads

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CNF Project: Simulation Results (2) –Delay Histograms for Alternative Content Routing/Caching Strategies

“Content Broadcast” scheme has more “low delay” file transfers compared to “Caching and Capture”

When nodes exchange “content caching” information with neighbors Average Delay in locating content reduces and the reduction is more when caching is limited to fewer nodes

Experiments Average Delay Improvement

Caching only, h=1 0.69539 22.3%

Broadcast, h=1 0.54013

Caching only, h=2 0.75455 23.8%

Broadcast, h=2 0.575

Caching only, h=max 0.92206 28.5%

Broadcast, h=Max 0.6590

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CNF Project: Status & Next Steps Basic protocol architecture done, some details being worked on

Link layer protocol Name resolution and file name resolution services Caching service protocol Routing algorithms

System level simulation studies to be completed this year (12/07) More results on caching and integrated routing protocol Addition of wireless multi-hop scenarios to network model

Started work on prototype implementation of CNF protocol on ORBIT/PlanetLab/VINI Using BBN’s DTN code base as starting point Staged implementation and evaluation of protocol modules Proof-of-concept service demos by the end of year 2 (8/08)