framework for network coding in challenged wireless networ

Alaeddine El Fawal

David Cavin

Jean-yves Le Boudec

Kave Salamatian

Yoav Sasson

Network coding is an area that has emerged in 2000, and has since then attracted an increasing interest, as it promises to have a significant impact in both the theory and practice of networks. To evaluate its performance in realistic situation, we developed a network coding based framework for challenged wireless networks where disconnection and reconnection is frequent as in PANs (Personal Area Networks) or vehicular networks, resulting in a new appelation for these scenarios as Delay Tolerant networks (DTN). For living in such hostile environment our development complies with several constraints as portability, flexibility, genericity, etc. Moreover to reduce the development effort using our framework, a single implementation might be used as standalone as well as inside a simulation environment

El Fawal, Alaeddine

Salamatian, Kave

Cavin, David

Sasson, Yoav

Le Boudec, Jean-Yves

Infoscience - École polytechnique fédérale de Lausanne

A framework for network coding in challenged wirelessnetworkAlaeddine El Fawal, Kave Salamatian, David Cavin, Yoav Sasson and Jean-Yves Le BoudecSchool of Computer and Communication SciencesEcole Polytechnique Fe´de´rale de Lausanne (EPFL){alaeddine.elfawal, kave.salamatian, david.cavin, yoav.sasson, jean-yves.leboudec}@epfl.chI. INTRODUCTIONToday Internet architecture and protocols operate poorly in en-vironment characterized by uncertain networking conditions, highmobility and frequent network partition. A lot of interest have beenattracted during the past couple of years to practical situationswhere disconnection and reconnection is frequent as in PANs(Personal Area Networks) or vehicular networks, resulting in a newappelation for these scenarios as Delay Tolerant networks (DTN).These problems are aggravated by heterogenity in used appliances(PDAs, laptop, etc.), difference in user behaviours (highly mobile vs.static users), power consumption constraints that results in puttingcommunication appliance in ”off-line” state as well as various levelof collaboration (collaborative vs. selfish users). As a scenario ofinterest, we might think of a wireless network that is divided intodisconnected island of connected users. Nodes circulating betweengroups transport information that are to be transferred. Underthese challenging situations classical routing based approaches arenot anymore effective and new forwarding paradigms should bedevelopped.Network coding is an area that has emerged in 2000 [1], and hassince then attracted an increasing interest, as it promises to have asignificant impact in both the theory and practice of networks. Wecan broadly define network coding as allowing intermediate nodesin a network to not only forward but also process the incominginformation flows. Linear Network coding processing/forwardingapproach consists in choosing a subset of received packets andforwarding a linear combination of chosen packets with randomcoefficients. Because of the intrinsic broadcast property of wirelessnetworks this linear combination might be received at severalreceivers resulting in new linear combinations when they are mixedwith other packets. At destination, multiple linear combination arereceived through different paths resulting in a system of linear equa-tions; if the number of independent equations exceed the number ofcombined packet the system of linear equation could be invertedleading to the initial packets. This is to compare with classicalrouting approach where only packets that validate a routing criteriaare forwarded or flooding where each single packet is forwardedindifferently. Network coding is attractive for challenged networksbecause of its inherent unsynchronized operation: each node decidesto forward a random linear combination without needing any globalinformation about the topology or destination placement. Moreoverforwarding a random combination reduces highly the probability ofsending redundant packets that is the Achille heel of the floodingapproach. Finally Network Coding has been proven to reach Min-cut Max-Flow optimality at least in lossless network with directedgraphs in adding to the theoretical attractiveness of the approach.Up to now, all the above properties have been exhibited in theory.To the best of our knowledge only two implementation of networkcoding have been reported : one is the avalanche system by microsoft[2] for content diffusion over P2P networks and the second one isthe COPS system developped at MIT in the context of wirelessmesh networks [3]. These implementations have been designed fordifferent communication scenarios than the one we are interestedin. Evaluation in realistic situation of highly dynamic networks ofnetwork coding based forwarding paradigms was missing. It wastherefore very hard to evaluate the complexity of the decoding stepto see if network coding is a viable solution for such challengedneworks. Our development effort have been targeted toward fillingthis gap.Before dealing with forwarding paradigms, one has to definea software and system framework for implementing applicationsin challenged networking conditions. For living in such hostileenvironment a software framework has to comply with severalconstraints as portability, flexibility, genericity, etc. Moreover toreduce the development effort using a framework where a singleimplementation might be used as standalone as well as inside asimulation environment is highly desirable. The FRANC (FRame-work for Ad hoc Network Communication) Framework [4] has beendevelopped to take up this challenge.As the developped software is released under a fully open sourceGNU licence1 [5], and because of the inherent properties of theFRANC framework we hope it to be used by the whole com-munity for testing, simulating and evaluating new communicationparadigms for challenged Mobile Wireless networks.II. FRANC FRAMEWORKFRANC [4] is a lightweight framework tailored to implement anddeploy real ad-hoc network applications. Ultimately, the real-lifedeployment of MANET applications is not only complementaryto simulation but indispensable to fully evaluate their performanceunder realistic settings. FRANC is implemented in Java and thusrequires the presence of a Java virtual machine (JVM) to run. Themost noticeable benefit is the direct portability of the framework.Whenever a JVM exists for a particular device and operating system,then FRANC can be executed independently from the underlyingplatform. The other important strengths of FRANC are the flexibilityand the modularity of the protocol stack composition and the abilityto transparently execute the same code on top of a simulatednetwork.Recycled msg poollocalcomm.multihopcomm.local broadcastlayerroutingdispatcherapplicationNeighborsmsgmsgmsgmsgJAVA virtual machineServicesFig. 1. FRANC architecture1Up to our knowledge, no other implementation of Network Coding isavailable for free access.Figure 1 depicts the general architecture of FRANC . It consistsof three main components, (1) the protocol stack, (2) the servicesand (3) the recycled message pool. The protocol stack is composedof a set of ordered layers which defines the application executedon a node. Layers are chosen off-the-shelf and their composition isspecified by the user in the configuration file at start-up. Addition-ally, to weaken the rigid structure of the stack, FRANC implements amechanism, we call service, that allows to share portions of code byexecuting them aside the protocol stack. This is, for example, usefulto avoid unnecessary duplication of identical features like neighbordetection. With respect to message handling, FRANC compensatesthe high computing cost of standard Java object serialization (espe-cially on portable devices) with a more flexible user-defined messageserialization. Additionally, unused references to messages either senton the network or whose treatment in the stack has completed, arerecycled in a message pool and made available for new messagecreation.A. Integration with Jist/Swans simulatorSimulation capabilities remain desirable as a preliminary and cost-effective step to evaluate an application before its deployment. Thisis particularly true for large networks or complex mobility patterns.To this means, we have integrated FRANC with Jist/Swans [6], aJava-based simulation runtime for mobile ad-hoc networks devel-oped at Cornell University. The benefit of this integration is thecapability of either deploying or simulating the same code seam-lessly, without any modification. To this means, the FRANC stack isexecuted independently of Jist and only the networking operationsare delegated to the simulator.III. NETWORK CODING IMPLEMENTATION FEATURESOur aim was to define a framework where the researcher inter-ested only in forwarding paradigm could focus on a specific partwithout dealing with applicative and physical layer concerns. TheFRANC framework is an excellent answer to this demand. We haveimplemented Network coding as a layer in the FRANC architecture(Fig. 1) seating between the dispatcher and the physical layer.Because of the modular structure of FRANC one could replaceNetwork Coding with more traditional approaches as Flooding,AODV routing or any new forwarding scheme by just changingsome line in the FRANC application stack description file definedin XML.In the forthcoming we will describe the features of our imple-mentation of network coding.1) Random Linear Network Coding: As explained previouslyforwarded packet in network coding are random linear com-bination of packets inside local buffers. Since coefficients andpackets used to construct a forwarded packets are unknown apriori, we need to embed these information in each encodedpacket. We have therefore constructed a specific message typecontaining an encoded payload as well as a list containingcoefficient and unique packet identifiers of packet combinedto make this packet. When a new packet containing a linearcombination is received the list of coefficient is extracted anda gaussian pivot elimination step is applied to reduce the orderof the equation. If the reduction results in the decoding of oneor several packets, the destination is checked to see if the nodeis the final destination (or if the packet is a broadcast). If itis the case the packets are forwarded to applicative layers.2) GF(28): All operations are done within GF(28) Galois Field.This ensures good performance as multiplication can be donetrough discrete logarithm tables. This lead to an improvementof a factor up to 100 in encoding and decoding.3) Contributing packet list limitation: during the course of atransmission the list containing the coefficient and the setof packet used to build an encoded packet inflates and theoverhead can become tremendous if nothing is done to limitthis number. We have therefore decided to limit the maximalnumber of packets used to encode one new encoded packet.This number is given as a parameter during the execution.4) Flooding implementation: Flooding could be considered asa subcase of network coding where the maximal number ofcontributing packets is fixed to one. We have implementedflooding through this approach to enable the coexistence ofnetwork coded and non network coded packets in the samenetwork.IV. DEMONSTRATED APPLICATIONIn the context of Mobisys 06 conference we propose to makea demonstration of our developped framework to implement adistributed Bulletin Board System (D-BBS) application. participantto the conference will be able to download the application throughan applet interface on their WIFI based PDA, laptop computer(or maybe motes) running a JVM. By running the application achat window will be opened and the user could access to theD-BBS. No configuration parameter will be needed beyond aneventual user ID. The application will be able to tackle withhighly dynamic environments and opportunistically send and receiveinformation that will be used to decode the messages sent by otherparticipants. The user will in particular be able to feel the effect ofa selfish behaviour consisting of only storing packets that have apart destinated to himself and to compare it with the cooperativebehaviour where he agrees to store packet that are not destinated tohim and use them for decoding information that are destinated tohim.We will show the interest of the approach in the a disconnectedscenario. Let’s assume that there exists several group of people thatare close to each other and are discussing together. The groupsare not in communication range of each other. We will show thatwhenever a user moves from one group to another he will act asmessage transporter and create connectivity between groups.This scenario will be shown in real as well as through simulationinside the JIST/SWANS simulation environment. Up to our knowl-edge this demonstration will be the first realistic demonstration ofnetwork coding in the context of Delay Tolerant networks.V. REQUIREMENTSThe demonstration is based on on the fact that no infrastructureis needed. We will just use one laptop generating an WIFI Adhocnetwork beaconREFERENCES[1] R. Ahlswede, N. Cai, S. R. Li, and R. W. Yeung, “Network informationflow,” IEEE Transactions on Information Theory, July 2000.[2] C. Gkantsidis and P. R. Rodriguez, “Network coding for large scalecontent distribution,” in In Proc. IEEE Infocom 2005, 2005.[3] S. Katti, D. Katabi, W. Hu, H. Rahul, and M. Medard, “Practical networkcoding for wireless environments,” in In Proc. of Allerton Conferenceon Communication, Control, and Computing, 2005.[4] D. Cavin, Y. Sasson, and A. Schiper, “Franc: A lightweight javaframework for wireless multihop communication,” EPFL-IC-LSR, Tech.Rep. LSR-REPORT-2003-016 200322, 2003.[5] [Online]. Available: http://icawww1.epfl.ch/netcod[6] R. Barr, Z. J. Haas, and R. van Renesse, “Jist: Embeddingsimulation time into a virtual machine,” in In Proc. of EuroSimCongress on Modelling and Simulation, 2004. [Online]. Available:http://jist.ece.cornell.edu

A framework for network coding in challenged wireless network

http://www.sigmobile.org/mobisys/2006/demos/Fawal.pdf

A

Abstract

Similar works

Full text

Available Versions

Infoscience - École polytechnique fédérale de Lausanne