HETEREGENEOUS INTELLIGENT FILTERING IN TACTICALWIRELESS MOBILE NETWORKS

J. Tyler Barton', Ta Chen', Ibrahim Hokelek\ Vikram Kaul I, Raj Rajendran',

Sunil Samtani', David Shur'", Aristides Staikos'' Shery Thomas2

'Appl ied Research, Te lcord ia Techn ologies, Inc.Piscataway, NJ 08854

3Contact author: dshur@research.telcordia.com

2U.S. Army CERDEC,Fort Monmouth, NJ 07703

ABSTRACTIn this paper', we propose a novel approach, which istermed Heterogeneous Intelligent Filtering (HIF), forintelligent control and application data filtering in multi­domain heterogeneous networks. HIF creates intelligentgateways to rapidly and autonomously adapt the flow ofinformation content to the changing mission needs andnetwork characteristics. HIF employs a MANETManagement Protocol (termed MMP) which enables anovel light-weight publish/subscribe mechanism.Interoperability is provided with upper echelon networksrunning legacy directory and session announcementprotocols. MANET users can discover multicastinformation sourced in the backbone network andsubscribe to only subset ofthe information that they need.HIF enables the MANET nodes to avoid being swampedby too much data - extraneous information not needed bythe end-user is filtered by the HIF agents. Adaptation istriggered by QoS messages derived from ongoingapplicationperformance and network monitoring.

We have implemented HIF in a laboratory testbed usingthe MANE emulation system, and successfullydemonstrated it 's publish/subscribe and filteringcapabilities for real-time multimedia and tacticalsituational awareness applications. The experimentsconfirmed our conjecture that if adaptive and intelligentcontent filtering is performed, the end-user performance(and packet loss and latency) becomes significantly andconsistently better during the periods when MANETnodes are subjected to overload conditions.

INTRODUCTION

Because of the highly mobile nature of and terrainsensitivity in tactical MANETs, the bandwidth availableto mobile nodes within the MANET may be limited andvary over time. Typically, tactical MANETs areinterconnected via a quasi-static upper-echelon backbone

4 Prepared through the PILSNER program. The U.S. Government isauthorized to reproduce and distribute reprints for Governmentpurposes notwithstanding any copyright notation thereon.

Copyright (c) 2009 Telcordia Technologies. All rights reserved.

978-1-4244-5239-2/09/$26.00 ©2009 IEEE

network (QSN) that is generally relatively stationary andhas higher bandwidth compared with MANETs. Theconnectivity between two heterogeneous networks isusually provided through one or more gateways . Duringthe periods where the available bandwidth is low,MANET nodes may be unable to handle the informationload sourced from or distributed via the QSN. Thedifference may be dramatic - for example a node in aQSN may be able to handle a multimegabit/s video feedwhile the MANET node may only be able to handleorders of magnitude smaller bandwidth.

Alternative data coding techniques such as multi­description/multilayer coding and transcoding on the flycan be employed for the MANET. In multilayer coding,nodes may receive a subset of the layers according totheir capabilities/needs and network conditions. A nodelooking for low bandwidth may receive only lower layersand thereby reduce the load, while a node wishing for thehighest quality may receive all the layers. Significantwork has been carried out on encoding, transcoding, andmulti-description/multilayer encoding in the context ofvoice and video streaming (see for example [1]).However, this approach is only applicable to contentproduced according to multi-layer techniques, whichhave not been widely adopted . Furthermore, it has beenshown that there is an extra overhead for generatingcontent in this format [1].

The alternative technique of creating different versions ofthe content encoded at different qualities and rates isrelatively straightforward. The MANET node subscribesto the lower bandwidth version while the QSN usersubscribes to the high bandwidth. However, multipleversions of the content must be produced and sourcedinto the network and hence the bandwidth used by theextra versions is wasted. This inefficiency is particularlyan issue if the source is located in a bandwidth limitedMANET. In transcoding, data filtering, and compressionon-the-fly, an intermediate node or proxy transforms theoriginal data/multimedia stream into a lower bandwidthversion before transmitting it to downstream nodes. Thisapproach increases efficiency in terms of bandwidthusage as the redundancy of the multiple versions isavoided . In the past, transcoding was viewed as

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computationally expensive, while being recognized asbandwidth efficient. We believe that transcoding hasbecome more tractable as computing power/unit cost hascontinued to decrease, while transcoding software hasbecome more efficient. Furthermore, the applicationbandwidth required for tactical MANETs is generallylower for the aforementioned reasons, so that thecomputational requirements are lessened. For theremainder of our discussion we will focus on transcoding,although architecturally neither of the other two methodsdiscussed is precluded.

The Heterogeneous Intelligent Filtering (HIF) concept isbased on the idea of network-based data transformation,and data filtering through agents distributed in thenetwork. Deployment of HIF filters are taken place at thepoints in the network where discontinuities in networkcapability occur. Thus the gateways of the tacticalMANETs are key locations for HIF. In the limit, HIFfilters may be deployed on every node in the MANET. Inthis work, we focus on gateway-based filters; distributedfilters will be considered in subsequent studies. There hasbeen little work on this topic in the literature. Somerelated work includes content-based multicast for data forpersonalization purposes has been done [3], and alsocontent dissemination filtering of routing updates [4].Adaptation of voice and video media content has alsobeen previously described in the context of wirednetworks with differences types of access (see forexample [9] and [10]). In [11] adaptation of proxies in amobile environment was considered, and it wasconcluded that protocol filtering was preferable toapplication filtering. We differ from [11] by focusing onapplication filtering because in important cases such as[6], effective filtering needs to be based on applicationattributes such as geographical coordinates, roles andpriorities.

W ireless LOS MNM

Wireless LOS

Figure 1: HIF agents in MANET intemetworking

OVERALL ARCHITECTURE

Figure 1 depicts a typical MANET intemetworkingscenario, where tactical MANETs are connected to anupper echelon quasi-static backbone network (QSN).Although QSN is mobile, it is called quasi-static relativeto degree of the mobility of MANETs. Figure 1 showssources of multicast data originating from both the

backbone and edge MANETs. A specialized agent calledan Inter-domain Multicast Filter (ldMF) runs on gatewaynodes connecting the QSN to the MANET. The IdMFagent performs the HIF function as it forwards data fromthe backbone to receivers in the MANET. The MNMagents (which have a subset of the functionality of theIdMF agents) within the MANET may also performfurther HIF filtering if needed. Due the constraints on theMANET nodes, filtering may operate primarily in thecontrol plane (e.g., flow-based filtering).

ARCHITECTURAL COMPONENTS

Application Gateway

A tactical MANET is expected to have significantvariations in available bandwidth, packet loss, and userdemands as a function of time. For real-time services, atraditional approach for handling varying user demand isthrough admission control. Unfortunately there aretactical scenarios for which this approach does not work.Consider an example where the resourceslbandwidth arefully allocated to existing real-time flows. Suppose a newflow is required to be sent into the system. One option isto terminate one or more of existing flows, which wouldfree up some capacity for the new flow. The problem ishow to choose which flows to drop. If prioritymechanisms are available they can be used, but unlessthere is only one flow in the priority class to be dropped,a choice still needs to be made. The HIF mechanism weare proposing may be used in conjunction with priorityschemes or not. In HIF, adaptation takes place by data­reducing existing flows so that they consume lessbandwidth. By adaptively decreasing the demand on thesystem, we can allow new flows to enter the systemwithout having to remove flows already in the system.

The application gateway contains the functionality of theIdMF agent, where the data adaptation takes place.Application data is received by the agent, transformed,and re-multicast into the tactical MANET. The originalapplication data is not forwarded into the MANET. TheIdMF has a set of filter components, each of which isdesigned for a particular data transformation operation.An application or application class may employ aparticular group of filter components, while otherapplications may employ different filter sets. Note thateach IdMF instance performs filtering only on the(relatively few) flows that are forwarded into theassociated MANET. Flows that are not forwarded intothe MANET are blocked by IP multicast groupmembership methods. Hence the IdMF processing load islargely independent of the number of interconnectedMANETs, and the total number of flows.

Dynamic AdaptationAs discussed above, the performance of the MANETdegrades dynamically due to user mobility, peculiarities

2

Figure 2 Multicast Interworking architecture betweenMANET clouds and backbone networks

Robustness and LatencyThe introduction of compression and/or data reductiontechniques can have an impact on latency. The additionallatency depends on the filtering employed, withtranscoding adding more latency than the filtering of timeseries data. For streaming applications the additionallatency has little impact on the utility of the data.Regarding robustness, compressed data may have higherinformation content than uncompressed data. Datasampling and aggregation techniques concentrateinformation into a smaller number of packets. Hence theloss of a packet may have a greater negative impact onuser perceived quality than without data reductiontechniques being applied. Furthermore certain data ismore loss sensitive than other data. For example, datathat pertains to the management or operation of theapplication may be more critical as loss of such data may

of wireless medium, terrain effects, etc. In this caseapplication content adaptation allows both the bandwidthof the application to be reduced, and the packet lossresilience to be increased in response to the varyingnetwork performance. The adaptation needs to bemanaged carefully to balance the tradeoff between speedof adaptation and stability. Each application is defined tohave a (small) discrete number of instance classes, wherethe class is defined by the bandwidth requirement andpacket loss resilience requirement for that instance. Basedon the network conditions one of the instance classes isselected. The adaptation is fairly coarse grained, andadaptation decisions are constrained to take placerelatively infrequently (0(10)'s of seconds apart), and inresponse to significant discrete changes in performance(e.g., available bandwidth changes of >10%, packet losschanges of >5%) . Bandwidth and loss estimates may benoisy and the adaptation must be resilient to the noise inthe estimates. For stability, a hysteresis control isemployed, i.e., the criteria for adaptation for "up"­adaptation (higher bandwidth/lower loss) is morestringent that the criteria for "down"-adaptation. In thefuture, we are also planning to examine the use ofpredictive adaptation, based on predictions of futurevalues of network metrics.

cause the application to malfunction, whereas the loss ofother data (e.g., position information or image data) maynot be as critical, merely leading to distortion or atemporary error. The critical data needs an enhancedprotection against loss, and the content adaptationmechanisms mentioned above must support resilience ofthis application critical data. Possible techniques includeon demand retransmission, periodic rebroadcast, andenhanced FEe based redundancy for the critical data. Allof these approaches will be studied.

Routing Gateway

Another important consideration is the dissemination ofmulticast data in the MANET at the network layer, andhow this relates to the application performance. In thepast, it has been assumed that different aspects of theapplication data may be transported on different multicastgroups (e.g., multi-layer encoding). This has thedisadvantage of coupling the application to the networklayer, so that changes in the application structure mayrequire changes to multicast routing rules. We prefer todecouple the application from the network layer byutilizing a single multicast group for application datatransport, and performing filtering operations at theapplication layer. This also allows us to take advantageof light-weight multicast routing protocols such as SMF(see below).

In wired media, PIM-SM is a widely used and efficientmulticast routing protocol. For the tactical MANET,Simplified Multicast Forwarding (SMF) is an emergingstandard which avoids the use of distribution trees, andhas good redundancy properties that provides robustnessto topology changes. In order to interwork QSN andMANET networks, PIM-SM and SMF need to beinterconnected in an efficient way. One issue is that thetraditional group membership protocol (lGMP) is notappropriate as it assumes that multicast routers and hostsare on the same subnet. In MANETs, the gateway routermay not be within the range of the multicast groupmember issuing an IGMP join request, and similarly anIGMP query message issued by a gateway router may notbe received by a multi-hop away group member. Eitherthe basic IGMP propagation mechanism must bemodified, or an alternative group management algorithmdeveloped. A second issue is the design of a suitableSMF relay-set in order to reduce the packet duplicates,and to limit the scope of the multicast data dissemination.

There has been little work on the interconnection ofMANET multicast routing protocols and QSN routingprotocols with the recent exception of [2] and [12]. [12]focuses on IPv6, and the MDP protocol, while [2] focuseson IPv4 and the IGMP protocol. Our approach is similarto [2], except that in [2] the IGMP protocol is modified topropagate throughout the MANET. We instead subsumethe IGMP functionality inside a specific MANET

MANET

MMP

Mobile BackboneNetwork

PIM Sparse Mode

PIM Rout ing Domain

MMP

MANET

3

The MMP protocol will support the publishing of thisdataset throughout the MANET. MMP will also supportsubscription so that each agent will have knowledge of allauthorized-for sessions within the MANET. The MMPprotocol will also support on-demand queries for sessiondata.

communications, the session initiation protocol (SIP) isused. For video/audio multicasts, the sessionannouncement protocol (SAP) is used. The SessionDescription protocol (SDP) is often used in conjunctionwith SAP, SIP, RTSP and HTTP. To support all of thesesession control protocols in the MANET would beexcessively burdensome and complicate the coordinationof resources across sessions controlled by differentcontrol protocols. Therefore the IdMF agent will alsoinclude a module that will adapt the key meta­information from the aforementioned control protocols,and form a local dataset of available sessions and meta­information for use by the MMP protocol. This isillustrated in Figure 3.

Management Protocol (MMP), which is used to manageinter-agent communication. The MMP includes somefunctionality similar to IGMP, Le., it supports group joinand leave announcements and also on-demand groupquery and response messaging. The MMP protocol runsover a well-known multicast group and is distributedthroughout the MANET to all nodes via SMF, therebyensuring that all nodes in the MANET including theIdMF nodes are able to correctly determine which nodesare members of which groups at all times. The MMPfunctionality is supported in the MANET nodes through asimplified version of the IdMF agent (referred to as anMNM agent) which runs on gateway nodes. MMP alsohas additional functionality relating to applicationmanagement as will be described below.

For unicast routing, we employ the well-known OLSRprotocol. To interconnect PIM-SM domain of the QSNnetwork with the SMF domains of tactical MANETs, weemploy an IGMP-MMP gateway as part of the IdMF. TheIGMP-MMP gateway maps from the IGMP to the MMPprotocol and vice versa. The multicast routingarchitecture is depicted in Figure 2.

MANET Backbone Network

Scoping

In traditional multicast, a scoping process is used to limitthe dissemination of data flows/multicast groups tospecific groups of users independent of their joinrequests. There are two mechanisms that have been usedfor scoping: TTL based scoping and administrativescoping. In TTL based scoping, each routing nodedecrements the TTL field in the IP packet and onlyforwards packets whose TTL values greater than zero. Inadministrative scoping, certain multicast address rangesare designated as administratively scoped addresses.Routers may employ rules to check multicast addressesagainst configured forwarding and only forward based onthose rules. Both mechanisms operate at the granularityof the multicast group, and therefore different scopesrequire different groups. In addition to these mechanisms,we use a finer grained mechanism in the MNM and IdMFagents, which will forward based on user authorizationlevels in the tactical MANET. This will allow us to scopedata within the same group based on user authorizationlevels which will be set through configuration andcommunicated through the MMP protocol.

MMP PROTOCOLWe have discussed above the need for the MMP toprovide multicast group management functionality. TheMMP also serves other important purposes, which wenow describe. In multi-media communication there is aneed for session management and control. There aremany protocols used for this purpose in wired networks,depending on the application. For example for web basedtraffic, it is HTTP. For streaming multimedia, the realtime streaming protocol (RTSP) is often used. For voice

MMP

MNM IdMF

• MMP - MANET Management • SAP - sessi on announcement protocolProtocol

• SIP - sess ion initiation protocol

• RTSP - rea l time streaming protocol

Figure 3 Consolidation of multimedia controlprotocols.

The MMP protocol also includes the ability to publishMANET performance metric information announcementswithin the MANET. As the agent learns of availablebandwidth, packet loss, and latency through themonitoring of the application (e.g., via RTCP reports), orby active probes within the MANET, it will announcethese metrics within the MANET. The IdMF will also beable to query for QoS Reports on an on-demand basis.This QoS information will be used by IdMF and MNMagents as input to the content adaptation process. Thebasic MMP message types are depicted in Figure 4.

AGENT ARCHITECTURE

Existing approaches to the data reduction problem havetended to proceed on per application basis, or possibly onper application class basis (e.g., layered encoding). It ishighly desirable to develop a strategy and architecturethat comprehensively supports all applications underconsideration.

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IMPLEMENTATION AND PERFORMANCEIn order to demonstrate the HIF proof of concept, wehave implemented and tested the HIF system and MMPprotocols in a laboratory testbed using the MANEemulation package [8]. As depicted in Figure 5, a 5-nodering topology is used for our experiments, where a

Since no one data reduction technique will work for allapplications or media types, an architectural platform isrequired that supports plugins of data reduction filters,transcoders, and multi-layered encoders. Plugins may bebased on differing data reduction techniques and will alsodepend on differing application framing andencapsulation structures. The key design issue for theagent is to provide a general software architecture thatwill support the needs of various applications such asvoice, video, situational awareness, and data applications.Furthermore the architecture should support differentapproaches to data reduction. For example, a variety oftranscoding techniques are available for voice, video, andimage media. The techniques depend on how the originalmedia is encoded, as well as the formats use toencapsulate and frame the encoded data. For data thatconsists of a time series, a different set of data filteringtechniques can be used, such as sampling, averaging,thresholding, deviation, etc. Some techniques (e.g.,deviation based) require that the agent have access to theactual sample values, while others (such as sampling) donot. Another category of data that is supported is web­oriented content (e.g., HTML or XML). This content istypically highly compressible, and hence standardcompression techniques can be applied. Because ofsignificant differences in these filtering techniques, afiltering framework is employed where different filterlibrary or plugin components are used according to theencoding technique of the application in question. Anagent controller controls the selection and use of filters.The controller interacts with the controller of other agentsin the MANET via the MMP described above. Thisconcept is called Heterogeneous Intelligent Filtering(HIF). The HIF agent software architecture is illustratedin Figure 6. Besides support of the MMP protocol andfilter management and selection, the agent also includespolicy information used in support of the scopingfunction described above. The architecture is distributedand multiple proxies utilized.

Figure 4 MMP protocol and message types.

Nl

N3

Figure 5: Network topology

RECEIVER

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gateway serves as the source of multicast traffic enteringthe MANET. All nodes are running the SMF and OLSRprotocols for multicast and unicast forwarding,respectively. Nodes' transmission capacities are set to 5Mbps for Gateway, Nl, and Receiver while 600 Kbps forN2 and N3. There is a single receiver which can receivedata using a high bandwidth path via Nl, or a lowerbandwidth path via N2 and N3 depending on the networktopology which changes with the movement of Nl alongthe horizontal axis (other nodes are static). Note that Nl 'smovement depending on its location determines itsconnectivity to Gateway (e.g., in and out of range ofGateway).When N1 is out of range, the traffic no longer has thehigh bandwidth path available, and must follow the lowbandwidth path via N2 and N3. The low bandwidth pathmay have insufficient capacity thereby causing theapplication to suffer performance degradation. Thissituation is detected by the HIF system via low-overheadbandwidth probes [7] and the HIF system down­transcodes or filters the traffic so that the bandwidthrequired for the application is within the capability of thelow-bandwidth path.

We have conducted several experiments in the testbedusing a streaming audio source and an audio transcoder atGateway, audio client at Receiver, and a similarstreaming video source, video transcoder, and videoclient, all provided by the VLC media system. The HIFadaptation module invoked the programmatic interface toVLC in order to change the transcoding in response tonetwork conditions. We also carried out experimentsusing the C2MINCS situational awareness application[6]. For C2MINCS, we designed and coded a loadgenerator that was able to generate SA updateinformation thereby emulating an SA group whose sizes,identities, and locations were configurable. We alsocoded an adaptive HIF filtering gateway for C2MINCS

]IdMF

-orocp Membership Report-OoS Report

MNM

5

capable of time series, role and scope based filteringunder dynamic control of the HIF system. The C2MINCSgateway instance was used to filter out redundant timeseries information, and limit the forwarding of updates tothose within the scope of the emulated SA group. Due tospace limitations we give results in this paper only for theaudio streaming case.In Figure 7, we show how the available bandwidth variesdramatically depending on whether Nl in Figure 5 iswithin range of the gateway or not. The curve labeledTTL5 above shows how the hop count of traffic from thegateway to the receiver varies depending on Nl 'slocation, and serves as a marker of whether the highbandwidth path is available or not. For the lower TTLvalue, the bandwidth is consistently below 500 kbps,while for the higher TTL value, the bandwidth variesbetween 500 and 3000 Kbps. Even though the estimates(particularly the high bandwidth ones), are quite noisy,the gateway can easily discriminate between the twostates using a simple averaging of the past severalbandwidth samples.In Figure 8, we show how the packet loss as seen at thereceiver varies as a function of the topology (Le., whetherthe high bandwidth path (HBP) is available or not), andthe codec rate. We observe that from the TTL curve thatthe HBP is initially not available. At the same time, thecodec is in the high state (corresponding to 128 kbps),and we observe significant packet loss (20%-30%) at thereceiver corresponding to a highly garbled reception ofthe audio signal. The bandwidth probes shown in Figure7 detect the absence of the HBP, and the HIF adaptationmodule of the gateway switches the codec to the lowerrate (48 kbps). When this occurs, we see that the packetloss rate goes to zero, corresponding to an un-garbledreception of the transcoded audio signal. When the TTLshifts ups again, this indicates the return of node Nl andthe HBP, which is detected by the higher values of thebandwidth probe as shown in Figure 7. We observe inFigure 8 that the codec switches back to the high-ratestate, and the packet loss remains at zero, because there isadequate bandwidth available. The situation continuesuntil node Nl moves out of range again causing: thedisruption of the HBP, increase in the packet loss, loss ofintelligibility of the audio signal, decrease in thebandwidth measurements. Finally the HIF adaptationmodule switches the codec back to the low-rate stateagain, which reduces the packet loss and restoresintelligibility to the audio signal.

5 In IP multicast, TTL controls dissemination scope (no. ofhops). We arbitrarily set the initial TTL to 64. Any valuegreater than the network diameter (here 5) will work; SMFremoves duplicate packets.

CONCLUSIONS AND FUTURE WORK6

The HIF approach to multicast information disseminationmanagement and group communications offers manybenefits to the tactical MANET environment. The IdMFprovides robust multicast routing interoperabilitybetween MANET edge networks and backbone networks.HIF offers significant improvements in the efficient useof MANET resources, by dynamically and significantlyreducing application bandwidth needs. The IdMF hidesthe complexity of the suite of multi-media controlprotocols from the MANET, and the MMP protocoloffers a single simple protocol to manage session meta­information, group management, and performance metricdissemination. Beyond the HIF capabilities described inthis document, there are a number of outstandingchallenges and extensions that need to be addressed in thefuture. The adaptation module is based on bandwidthmeasurements alone, and while the algorithm is stable,incorporation of packet loss data, latency, and othertopological data should speed up adaptation, withoutdecreasing stability. The admission control proceduresdepend on the amount of bandwidth savings possible.Therefore it is important to study the degree to whichapplication content can be compressed/bandwidth­reduced while still maintaining intelligibility. Other areasto be studied are multiple gateway coordination and loadbalancing, the cascading of MNM agents within theMANET, support for HIF over multiple domains, anddeployment considerations for red/black networks.

REFERENCES

[1] K. Taehyun and M. H. Ammar, "A comparison of heterogeneousvideo multicast schemes: Layered encoding or streamreplication", IEEE Transactions on Multimedia,. Dec. 2005.

[2] I. D. Chakeres, C. Danilov, T. R. Henderson, 1. Macker, P.Joseph, "Connecting MANET Multicast", IEEE MilitaryCommunications Conference, Oct 2007.

[3] R. Shah, Z. Ramzan, R. Jain, R. Dendukuri, and F. Anjum,"Efficient dissemination of personalized information usingcontent-based multicast", IEEE Trans. Mob. Comput. 3(4), pp.394-408, 2004.

[4] M. A. Fecko, I. Hokelek, S. Samtani, A. Staikos, "ControlledDissemination Filter (CDF) for Integrated Link SelectionAgents", International Conference on Communication SystemsSoftware and Middleware, Jan. 2007.

[5] 1. Macker, 1. Dean, and W. Chao, "Simplified multicastforwarding in mobile ad hoc networks", MILCOM 2004.

[6] K. Barry at al, "Shared Situation Awareness For NetworkedDismounted Soldiers", Ft. Belvoir Defense TechnicalInformation Center DEC 2004.

6 Disclaimer: The views and conclusions contained in this documentare those of the authors and should not be interpreted as representingthe official policies, either expressed or implied, of the Army ResearchLaboratory or the U. S. Government.

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[7] D. Shur, and A. Zelezniak, "Bandwidth and PerformanceMonitoring in Virtual Networks using Active Probes", Invitedtalk, IEEE NJ Coast Section Seminar, December 11,2002.

[8] Macker J.P., J. Weston, W. Chao. "A Low Cost IP-based MobileNetwork Emulator," IEEE Military Communications Conference(MILCOM) 2003 Proceedings, October 2003.

[9] E. Amir, S. McCanne, and H. Zhang, "An Application LevelVideo Gateway", Proc. ACM Multimedia '95, San Francisco,CA, November 1995.

[10] D. Shur, "Unicast Access to Multicast Internet ProtocolSessions", Invited paper, IEEE ICClEncom'98, Atlanta, GA, June1998.

[11] B. Zenel and D. Duchamp "A General Purpose Proxy FilteringMechanism Applied to the Mobile Environment", MOBICOM1997.

[12] L. Lanmark, Y. Lacharite, and L. Lamont, "Multicast ForwardingUsing Multiple Gateways and Hash for Duplicate PacketDetection in a Tactical MANET", IEEE MilitaryCommunications Conference (MILCOM) Proceedings, Orlando,FL,2007.

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