A Cross-Layer Cross-Overlay Architecture for Proactive Adaptive Processing in Mesh Networks

Transcription

1 1 A Cross-Layer Cross- Architecture for Proactive Adaptive Processig i Mesh Networks Dilip Krishaswamy, Hsie-Po Shiag, Joh Vicete, Vidya Govida, W. Steve Coer, Sajay Rugta, Wiso Cha, Kai Miao Itel Corporatio, 1900 Prairie City Road, Folsom CA 95630, USA Abstract The dyamic characteristics of wireless mesh etwork eviromets make delay-sesitive multimedia applicatios processig i such etworks a very challegig task. Cross-layer optimizatios are commoly desiged to esure that applicatio requiremets are met. Improved timeliess of delivery ad precisio of iformatio as acquired by a decisio-etity ca help i effective maagemet of resources ad strategies i the mesh etwork to achieve better applicatio availability, stability, ad performace. I this paper, a iformatio exchage ad database architecture is preseted to allow regular updates ad access of cross-layer parameters through distributed database services over a overlay etwork. The architecture provides cross-layer cross-overlay iformatio to eable proactive decisio makig ad adaptatio with distributed optimizatio for trasmissio of delay ad badwidth sesitive applicatio flows i mesh etworks. Distributed multi-flow routig optimizatio over heterogeeous wired + wireless-mesh etworks with the suggested iformatio-exchage architecture is also explored. I. INTRODUCTION I recet years, wireless mesh etworks [1] have become icreasigly popular ad the demads for effective support for ed-to-ed QoS maagemet of multimedia applicatios over such etworks with dyamically varyig coditios have also icreased. Cetralized cross-layer solutios are becomig less promisig due to the limitatios of scalability, cotrol iformatio gatherig, ad implemetatio complexity. It is essetial to have distributed solutios with timely ad accurate iformatio exchage for these delay-sesitive applicatios. Figure 1 shows the geeral distributed cotrol that ca be possible i a mesh etwork ode with cross-layer cross-overlay iformatio exchage i the etwork. I the distributed architecture, decisios are made based o iformatio available from multiple sources. The iformatio sources could iclude the followig: (a) upper protocol layer requiremets, icludig applicatio Dilip Krishaswamy is with the Mobility Group at Itel Corporatio. Hsie-Po Shiag is a visitig researcher at Itel Corporatio ad a PhD cadidate at the Uiversity of Califoria, Los Ageles, CA, USA. Joh Vicete, Sajay Rugta, Wiso Cha, ad Kai Miao are with the Iformatio Techology Research Group at Itel Corporatio. Joh Vicete is a PhD cadidate at Columbia Uiversity, New York, NY, USA. Vidya Govida is with the Digital Eterprise Group at Itel Corporatio. W. Steve Coer is with the Corporate Techology Group at Itel Corporatio statistics, badwidth requiremets, priority categories, legth of data packets, packet arrival rate, impact metric of losig a specific packet, ad the deadlie for receivig a useful packet, (b) the iformatio from lower layers i the protocol stack that provide parameters that decide the operatios of trasmissio, such as routig decisios, trasmissio opportuity (TXOP) of cotetio-less medium access cotrol (MAC), retrasmissio limits, ad physical layer modulatio ad codig schemes (MCS), ad, (c) the etwork eviromet that is usually captured by desigig a set of good parameters to be moitored ad exchaged amog etwork odes, such as expected delay, auto-regressive badwidth predictio, or roud-time average queue size, ad iformatio related to iterferece ad cogestio i the etwork. Based o the iformatio above, itelliget decisio-makig ad cotrol mechaisms ca be desiged to optimize strategies such as routig paths for flows or trasmissio opportuities that eed to be assiged to differet flows. Such optimizatio techiques ca maximize a certai utility fuctio joitly cosiderig the service availability, stability, ad applicatio performace. The cotrol mechaisms ca operate at differet time-scales some cotrol mechaisms ca operate at loger time-scales such as durig applicatio layer sessio maagemet, while other cotrol mechaisms may operate at lower time-scales such as o a per packet basis. Figure 1. Distributed cotrol with cross-layer cross-overlay iformatio exchage We deploy a lightweight iformatio exchage service o a overlay etwork to provide support for regular asychroous ifrequet updates about etwork coditios usig Distributed Virtual Machies (Ds). This has several advatages.

2 2 (a) It provides more efficiet iformatio exchage capability ad distributed iformatio availability betwee odes. Due to the broadcast ature of the wireless eviromet, the required iformatio is more easily obtaiable from a distributed database rather tha to request directly from the sources. (b) The iformatio exchage service is ifrequet ad lightweight i ature, ad therefore the overhead associated with this service is small. (c) It eables scalability with maagemet capabilities for clusterig odes, with a scalable iformatio exchage etwork service i the applicatio layer. (d) Overall, it provides the ability to perform proactive adaptive processig for multiple flows i the etwork, based o requiremets of the flows ad the dyamic coditios i the etwork, alog with optimizatio at differet layers i the protocol stack such as rate adaptatio at the applicatio layer, routig optimizatio at the etwork layer, or optimizatio for trasmissio strategies at the MAC/PHY layers. The cross-layer cross-overlay architecture will be described i detail, with a discussio of multi-flow joit optimizatio routig algorithms. The paper is orgaized as follows. Sectio II illustrates the cross-layer cross-overlay architecture. Sectio III describes the database system deployed i the architecture. I Sectio IV, we preset a routig algorithm based o extracted iformatio from the database architecture for cross-layer optimizatio. I Sectio V, the architecture is exteded to heterogeeous etworks ad optimizatio for a multi-hop VoIP applicatio over a heterogeeous etwork usig the cross-layer cross-overlay architecture is discussed. Sectio VI cocludes the paper. II. THE CROSS-LAYER CROSS-OVERLAY ARCHITECTURE The high-level system architecture for the cross-layer cross-overlay iformatio exchage architecture for delay sesitive applicatios i wireless mesh etworks is depicted i Figure 2. The architecture based o the OverMesh research platform architecture that was recetly proposed [2] which eables a ovel wireless mesh iteretworkig system ad realizes etwork cetric computig. Computatioal overlays i OverMesh provide the facility to deploy distributed services across mobile mesh odes. The platform eables developmet ad deploymet of cocurret distributed experimets o wireless mesh etworks. Based o this research platform, a cross-layer searchig algorithm, which combies traditioal overlay searchig with ad hoc etwork routig so that a physically short searchig route is facilitated, was itroduced i [3]. The otio of a Distributed Network Iformatio Base (DNIB) with DNIB-SAs (DNIB-Service Agets) at each ode was itroduced i [4] for iformatio storage ad exchage i a wireless etwork. This paper provides additioal architectural isight ito the ature of such databases, the mechaism of iformatio exchage betwee odes, ad addresses how a problem such as multi-flow routig optimizatio over heterogeous etworks (hybrid wireless etworks (WiMAX + WLAN) with wireless+wired+wireless ed-to-ed paths) ca take advatage of such architectural features. The followig are key properties of OverMesh [2]: - Ifrastructure-free: a decetralized edge/access system with a aggressive covergece strategy for ode computatio, etwork processig ad storage. Ay physical ode may be capable of supportig switchig or routig fuctios, alog with cliet or compute fuctios; - Network virtualizatio: based pricipally o a robust D overlay strategy, the use of computatioal service overlays would eable a computatioal model for provisioig ad maagig etwork structure, services ad resources; - Emerget cotrol ad maageability: to achieve the same resiliece see i today s decetralized iteretworkig systems, it allows for alterative learig ad iferece techiques to off-load huma-depedecy o operatioal maagemet ad provisioig to discover, predict ad adapt distributed etwork state; - Cooperative ad adaptive ed-to-ed cotrol: to support a horizotal (ed-to-ed) ad vertical (ode-level) systems orietatio to scale ad adapt wireless commuicatios, It provides for tighter layer itegratio ad automatio of applicatio-to-etwork cotrol ad maagemet through cross-layer facilities. OverMesh research is primarily focused o scalig mesh etworks, realizig overlay service architectures, resource ad resiliecy maagemet ad ed-ed optimizatio challeges through self-orgaizig ad cross layer services, respectively. OpeDHT VoIP Applic. Prestadard s Dist. DB LOCAL DB CROSS LAYER/OVERLAY Figure 2. System diagram of curret cross-layer cross-overlay iformatio exchage architecture The curret OverMesh research prototype leverages [5] to provisio light weight virtual machies, or VServer, o selected set of OverMesh odes. is a distributed service platform i the applicatio layer with services i the virtual machies (s) such as a OpeDHT distributed hash-table directory lookup service [6], a VoIP applicatio service, ad a distributed database service. Each OverMesh ode ca have multiple virtual machies that participate i differet slices [5]. These slices form the differet overlay etworks the ca cooperate ad collaborate to provide specific services or perform specific tasks. Curret implemetatio requires a admiistrator to explicitly select the

3 3 OverMesh odes for a give slice at a web cosole hosted o a cetral server. This cetral server also coordiates the allocatio of resources ad the creatio of virtual machies o each OverMesh ode. I OverMesh, the challege is to decetralize this fuctio, ad allow the odes to itelligetly form sub-groups of odes to accomplish tasks over a distributed etwork. A pre-stadard implemetatio of IEEE s [7] is adopted for mesh odes. The s mesh implemetatio provides layer 2.5 routig itegrated o the MAC ad PHY s routig uses MAC addresses rather tha IP addresses to maitai trasparecy with the IP layer ad existig etwork ifrastructure. The default routig protocol is a variat of the ad-hoc o-demad distace vector (AODV) routig protocol [8] modified to eable route idetificatio based o performace metrics rather tha hop-cout. The protocol uses a airtime metric similar to ETT, derived from hop-by-hop MAC statistics, that is iteded to idetify routes that miimize the ed-to-ed amout of time spet trasmittig or retrasmittig a message across a multi-hop path, typically resultig i higher throughput routes tha whe usig hop-cout as a metric. The iformatio exchage service allows itegratio of better decisio-makig i the etwork. A multi-flow routig optimizatio problem is solved as a example showig the beefit of such service for delay-sesitive ad badwidthsesitive applicatios. As show i Figure 3, the iformatio related to cross-layer parameters are exchaged over the applicatio overlay etwork as a distributed database service. The iformatio is associated with the local database iformatio to ehace the implemeted operatios i the s protocol stacks. It is possible that cliet odes with limited capabilities ca obtai the global iformatio from the distributed database through iformatio query mechaisms from their more-capable eighbors. For heterogeeous etworks such as wireless+wired+wireless etworks ad/or hybrid WiMAX+WLAN wireless etworks, applicatio-layer overlay services ca exted across differet etworks usig differet wireless protocols. Local iformatio updated may be limited to a specific etwork-type such as a s etwork, while global iformatio stored ca spa differet etworks. The curret s stadard is targetig relatively small mesh deploymets of up to 32 odes i a etwork [7]. s ca help i iformatio exchage i small-scale etworks, ad also i larger-scale etworks or heterogeous/hybrid etworks to eable ed-to-ed flow optimizatio ad applicatio adaptatio i such etworks. I summary, with the cross-layer cross-overlay architecture, decisios are made joitly accordig to the latest local ad global iformatio. A geeral optimizatio problem that is solved at ay give time t ca be formulated as: maximize F g ( t'), h ( t ''), (1) ( ) app local global where g local (t ) represets the collectio of local iformatio gathered at time t (where t t ) directly from the eighborig eviromet i the viciity of a ode, ad h global (t ) represets the collectio of global iformatio gathered at time t through the overlay etwork, where i geeral t t t (sice global iformatio is exchaged i a slower maer). Iformatio exchage Iformatio query Iformatio exchage overlay etwork Distributed Database Service o Iformatio query Figure 3. Iformatio exchage usig the overlay etwork. The objective fuctio F app may be differet for various applicatios. For example, voice applicatios are sesitive to the delay metrics, while video applicatios may eed to cosider both delay metrics ad available badwidth. I the ext sectio, the database system adopted i the cross-layer cross-overlay architecture is itroduced. IIII. A DISTRIBUTED NETWORK INFORMATION BASE FOR THE CROSS-LAYER CROSS OVERLAY ARCHITECTURE I the cross-layer cross overlay architecture, local ad global etwork iformatio ca be stored at each ode i a Distributed Network Iformatio Base (DNIB) [4] at each ode, with query maagemet for retrieval of iformatio. A DNIB Service Aget (DNIB-SA), as illustrated i Figure 5, will be available at each ode to respod to requests for iformatio from a eighborig ode i the etwork. The DNIB-SA will respod with iformatio available from the DNIB cotet locally available at the ode, ad, if ecessary, the aget will forward the request to oe or more eighborig ode(s), util ed-to-ed iformatio betwee two ed poits ivolved i the commuicatio is obtaied. Some of the tasks that DNIB-SAs ca perform (but ot limited to) are listed below [4]. DNIB-SAs ca (a) respod to requests from eighborig odes, (b) moitor coditios o active liks i active routes ad forward iformatio about dyamic variatios i lik quality to odes i the local routig table at a ode, with iformatio to be propagated quickly to edpoits i a commuicatio path to eable real-time adaptatio, (c) chage

4 4 policies that ca relate to routig, QoS, or security as eeded, ad i additio, depedig o local, global or ed-ed situatios, the policies could relate to chagig flow trasport parameters or chagig moitorig requiremets, (d) chage etwork cofiguratio ad eable localized route modificatios whe required by collaboratig with DNIB-SAs i a sub-etwork to cofigure a alterate route whe coditios o a lik degrade, (e) propagate ed-to-ed iformatio to edpoits for a ewly cofigured route. These services provided by the DNIB-SAs ca be eabled through the system overlay architecture. Figure 4: DNIB ad DNIB-SAs distributed cofiguratio The DNIB ca cosist of two databases a global database with global iformatio across the overlay ifrastructure, ad a local database with eighborig iformatio. Although the two databases reside o differet protocol layers (see Figure 2), they ca exist physically i the same database system at a ode (machie). I the curret setup, the database system is built usig MySQL. The etries of each table are idetified with a attribute idicatig local/global iformatio. The iformatio exchage mechaisms that update the databases are differet for these two kids of etries. Iformatio exchage mechaisms ca be global or local with differet update frequecies listed below: (1) Global iformatio update, with frequecy freq. G Not all the odes i the etwork may have iformatio that pertais to global database iformatio. The iformatio sources for global iformatio exchage are the capable odes that have the PLANETLAB istalled o the overlay etworks, which costatly exchage iformatio through the overlay applicatio virtual machies. Iformatio i the global database at a ode ca be populated by local database iformatio regardig lik coditios, or through iformatio messages propagated through the overlay etwork. Oly the etries with a global attribute are exchaged durig global iformatio updates. For scalability, oe ca iclude architectural optios such as proactive propagatio of such iformatio, or propagatio of such iformatio to oly a limited umber of hops with further propagatio doe oly o request from a eighborig ode. The iformatio source is recorded for each etry i the database to idetify the ode that provides the iformatio. (2) Local iformatio updates with frequecy freq. L The local database has etries with a local attribute set, ad they are updated costatly whe the ode gathers the eighborig iformatio by sedig hello messages to the eighbors. (3) Local to- Global iformatio syc frequecy freq. S The Local-to-Global sychroizatio frequecy is represeted as freq. It should be oted that the sychroizatio is oly S meaigful whe freqg < freqs freq. If oe sets L freqs = freq, the if a local iformatio etry is updated, L the the correspodig etry i the global database at the collocated ode (machie) is updated to keep the global database curret with the latest iformatio. For example, local lik-layer iformatio could be updated more frequetly o the order of 10s of millisecods (for example every 20ms) while the global iformatio may be trasmitted less frequetly through the overlay etwork o the order of a few 100s of millisecods (e.g. approximately every 300ms for example). Trasmissio duratios for packet data trasmissio are much smaller time-scales such as a few 100s of microsecods to a few millisecods (e.g. trasmissio opportuities for high-data rate video aggregated packet trasmissios could last about 2ms over a give lik). This esures that frequecies of updates ad etwork iformatio propagatio are ifrequet ad lightweight, relative to the amout of time take by applicatio data packets i the etwork. It should be oted that there is o eed for updates to happe at specific times oly, with a sychroized clock. There is o eed for sychroizatio for iformatio propagatio i the etwork. Iformatio is propagated wheever possible at a approximate frequecy of update for global ad local iformatio suggested by freqg, freqs, freq parameters. Distributed optimizatio i L the etwork ca be performed based o the latest iformatio available. A ode performig a optimizatio uses whatever iformatio it has, which could be curret or delayed depedig o propagatio delays i the etwork. If there is a possibility that there are multiple sources for the same iformatio arrivig over the distributed etwork, a loosely sychroous value of time ca be used to tag messages (such as a etwork with a loosely sychroized start time ad coarse-grai updates to a local time couter (e.g. the couter could icremet locally o each ode every 100ms)). This ca help to keep the latest message regardig some specific iformatio i the database, while igorig old updates arrivig i a delayed fashio from other sources. I the example problem discussed i the paper, distributed dyamic routig optimizatio is accomplished usig the data available through iformatio exchage mechaisms i the cross-layer cross-overlay architecture. Figure 5 illustrates the database desiged for the cross-layer cross-overlay architecture. The Flow, Path, Lik, Node, ad Network-card etities are

5 5 show. These etity tables cotai the flow-level, path-level, lik-level, ode-level, ad etwork-card-level iformatio respectively. The coectios betwee the tables are as follows: a. Each flow i the Flow Table ca have multiple routes/paths i the path Table, which are composed by several liks i the Lik table. Each flow i the Flow Table is associated with two odes i the Node Table idicatig the source ode ad the destiatio ode. This is idicated by the [M:2] cardiality i the relatioship betwee a Flow ad Node etities. Multiple flows may exist, ad multiple paths are possible for each flow, idicated by the [M:N] cardiality of the relatioship betwee the flow ad path tables. Each flow may have differet requiremets such as Ed-to-Ed delay ad Ed-to-Ed badwidth. The curret effective ed-to-ed delay ad badwidth that is allocated to each flow is also stored based o latest available iformatio for the flow. b. Each path i the Path table cotais the list of the liks associated with the path. The Path table provides the path betwee the source ad destiatio odes associated with a give flow. Paths ca cotai oe or more liks, ad each lik may be associated with multiple paths, idicated by the [M:N] cardiality o the relatioship betwee the Path ad Lik tables. c. Each lik i the Lik Table is associated with MAC addresses associated with the two odes at the ed-poits of the lik, idicatig the trasmitter ad the receiver of the lik coectio. Each lik may support a differet protocol ad may operate i a differet frequecy chael. It is importat to keep track of relevat curret iformatio about the lik such as curret MCS scheme, average umber of retrasmissio, ad delay, badwidth, ad utilizatio metrics associated with the lik. Differet metric values related to specific lik betwee two odes ca be stored for differet etwork protocols such as or e ad/or for differet chaels that may be used for the lik commuicatio. d. Each ode i the Node Table cotais iformatio about the ode, icludig iformatio about multiple etwork cards with multiple radios, ad MAC Addresses associated with them. e. Each etwork card withi a ode is represeted as a NetworkCard table, ad if a etwork card supports multiple protocols, the the etwork card etity is replicated for each protocol that is supported. f. The delay metric is expaded further. It is possible that differet delay metrics ca be associated with each lik which ca be stored i a Delay Table. A delay value has a type to idetify what kid of delay this value represets for, such as ETT, ETX, RTT, or etwork pig delay, based o differet metrics that oe may choose to use, ad the routig algorithms that oe may choose from [8,9,10,11,12,13,14]. Iformatio about a approximate time-stamp associated with the metric ad whether the iformatio is obtaied local lik layer measuremets or through the overlay architecture is also stored. Figure 5: DNIB database desig Give a flow with a source-destiatio pair, for delay-based routig optimizatio, oe ca extract the multiple possible routes from the Path Table ad sum up the correspodig delays of the liks that compose these routes to determie optimal ad alterative routes for the flow. IV. MUTLI-FLOW ROUTING OPTIMIZATION The multi-flow routig optimizatio is achieved by gatherig metrics such as ETT/ETX lik ad airtime estimates [4], delay ad badwidth demad costraits for flows, ad iformatio about the iterferece graph, ad chael allocatios to liks, from the global database ad local eighbor iformatio. Additioal statistics such as traffic loads ad cogestio may also be gathered by distributed traffic moitorig ad aalysis tools such as CoMo [15] which are complimetary to this architecture ad provide additioal isight ito the performace characteristics of differet liks, odes, ad paths withi the etwork. A joit optimizatio is performed to meet costraits for multiple flows i the etwork. Chael allocatio is assumed to be fixed prior to solvig the routig optimizatio problem. A source ode for a flow performs the joit optimizatio over all the flows, with its goal beig to determie the optimal route (or combiatio of routes) for flows origiatig from it. A flow f k is a applicatio with a fixed source ad destiatio pair. Differet applicatios ca co-exist i the etwork with multiple flows. The set of possible selected paths for flow fk is give by : 1 2 N Pathk = { pathk, pathk,..., pathk,..., pathk }, (2) assumig that there are N paths for flow f k. The selected routig graph (combiatio of paths of each flow) is give by: r RouteGraph { Path1 Path2... Pathk }. (3) Let us assume that the throughput demad of flow f k isdemad k, ad the delay deadlie requiremet is deadlie k. The ETT metrics for a certai lik i maybe differet for each flows, sice the effective packet legth Size k might be differet with applicatios: Sizek ETTki, = ETXi. (4) t ( TH ) ki, i

6 6 Here TH i represets the throughput (badwidth) over the lik i. ad t ki, is the time portio ([0,1]) of the flow f k beig distributed over lik i. Let us deote the effective throughput of a path of flow f k path k as TH path k, which is calculated from the followig relatioship: 1 pathk = max X j, TH path 1 j c k (5) pathk where Xj = ETTki,. i chaal j o pathk Iformatio about lik coditios is take from the available latest local ad global iformatio at a ode (global iformatio is delayed relative to the local iformatio). Let β k, be the portio of the flow f k beig distributed over the path path k. Let us deote the effective throughput of a flow f k through overall multiple paths with a certai routig graph r as TH kr, : overall THkr, = βk, TH path,0 βk, k 1. (6) The Joit Optimizatio Problem is: 2 overall THkr, miimize 1 r RouteGraph k demad k subject to ETT deadlie gap i pathk t 1 ki, k k ki, k overall kr, k k k, for all k TH demad, if f is a oscalable applicatio path r f (7) As coditios vary, the optimizatio problem ca be solved either i a distributed maer or i a cetralized maer, at approximately regular itervals. I a distributed optimizatio solutio, we will assume that each source ode for a flow will make idepedet decisios with regard to its preferred route for the flow, i the process of obtaiig a solutio to the joit optimizatio problem over all the flows. The solutio to the above problem is solved idepedetly at each source ode for a flow based o the latest iformatio available at the source ode, ad decisios are subsequetly take about the routes that would be used for the flows that a source ode is resposible for. Although each source ode cosiders the optimal routes for all other sources as well, it will ot force others to follow the choices it might make for other sources. It uses however uses the routig decisio it takes for the flows origiatig from it. The distributed method is based o the latest iformatio from the local ad global database of each idividual source ode, which could be slightly differet amog source odes due to the various locatios ad iformatio update frequecies. For a cetralized solutio, the multiflow routig joit-optimizatio problem ca be solved at a cetral ode usig iformatio collected through overlay mechaisms ad local updates. Subsequetly, the selected paths for the flows ca be distributed to the participatig mesh odes by iformatio trasfer egieered usig distributed overlay applicatios. Nodes will cotiue to use a previous kow solutio util a updated solutio arrives through a overlap applicatio iformatio trasfer mechaism. Flows ca be scalable or o-scalable. No-scalable flows have a fixed miimum requiremet o the allocated badwidth to the flow below which the flow becomes ifeasible. Scalable flows (such as video) may have a rage of tolerable badwidth such as badwidths lower tha a maximum demad specified may be tolerable, with some loss i quality. Whe solvig a optimizatio problem for such scalable applicatios, such a loss i a metric associated with quality (such as PSNR) should also be cosidered ito the optimizatio fuctio to miimize the impact to such a metric. For applicatios such as VoIP that have a strict ed-to-ed delay costrait but that do ot eed sigificat badwidth requiremets, oe ca focus o path costructio through the etwork ad applyig the ed-to-ed delay costrait durig path costructio. To idetify possible routes betwee a source ode ad a destiatio ode, oe ca exhaustively costruct all the possible routes that grow from the source. If the accumulated delay of a certai route (by addig the ETT values) exceeds the delay deadlie of the applicatio, the oe ca drop the route from further cosideratio. Path costructio is cotiued util the destiatio ode is reached, or whe the delay deadlie is reached. Depedig o the average degree of a ode i the mesh etwork, ad the average umber of hops required to go from a source to a destiatio, the complexity of such computatio ca be sigificat. Cosider, for istace, a etwork with size (umber of odes), ad each ode with average degree k (has k eighbors). Assume that the ed-to-ed delay metric results i a average path legth of h. The umber of cosidered routes from a source to a destiatio i the h exhaustive approach could be as high as Ok ( ) i the worst case. A sample pseudo code for such path costructio is provided i Appedix A. Alteratively, oe could use heuristic techiques to idetify multiple paths betwee a source ad a destiatio that meet the delay costrait, by applyig Dijkstra algorithm betwee itermediate odes, ad the extedig the path obtaied by the Dijkstra algorithm to iclude the source ad the destiatio i the ed-to-ed route. Thus, oe ca itetioally force the selected routes to flow through a set of predetermied odes, ad use the Dijkstra algorithm to fid the shortest delay path betwee two itermediate odes. We call the set of these predetermied odes as a Multi-path Middle-ode Set (MMS). Note that we ca have multiple MMS s i the etwork. We give a example usig pseudo code for a two-mms case, oe MMS as the eighbors of the source (SourceMMS) ad the other MMS as the eighbors of the destiatio (DestiatioMMS). The Dijkstra algorithm is applied to fid routes betwee odes

7 7 i the SourceMMS to the odes i the DestiatioMMS. The paths obtaied are exteded to iclude the source ad the destiatio to obtai the complete ed-to-ed route. Routes which exceed the ed-to-ed delay costrait are dropped durig such costructio. I this example, assumig that 2 Dijkstra s algorithm has complexity O(( 2) ) (source ad destiatio odes are excluded i a -ode graph), the complexity of executio for the path costructio for such a 2 2 two-mms graph is Ok ( ( 2) ) (this assumes a average degree of k for the source ad destiatio odes). Appedix B icludes pseudo-code for such a path costructio algorithm. Whe applicatios are cosidered that require sigificat badwidth demad costraits, oe should cosider elimiatig paths that do ot provide the ed-to-ed throughput that is desired. After possible routes for a flow are obtaied, oe ca cosider the possibility of joit optimizatio of the flows such that the throughput demads ad delay costraits of all flows are satisfied, startig with the satisfactory paths that were idetified for each flow. Appedix C has pseudo-code for a possible implemetatio of the multi-flow optimizatio, by cosiderig the impact to the delays due to the possibility of overlap betwee the multiple paths selected for each flow.. Figure 6 shows a example problem solved i a matlab simulatio eviromet. Two VoIP applicatio flows are cosidered ad optimized simulateously oe from SourceA to DestiatioA ad oe flow from SourceB to DestiatioB for a mesh etwork with mesh odes located as show i Figure 6. Figure 7 shows multi-path optios for the two flows. The simulatios were performed to compare the ed-to-ed flow packet loss rate with traditioal layer 2.5 reactive mesh routig protocol ad the multi-path routig with proactive adaptatio that is suggested i the paper. Traditioal reactive mesh routig establishes a route ad a ew route is chose oly whe a existig route fails. Multi-path routig with proactive adaptatio selects multiple possible routes from a source to a destiatio with partial flow allocatio to each path, with alterative routes maitaied to allow for faster route switchig. Usig multiple paths for the same flow provides better resiliecy. Additioally, faster proactive adaptatio with alterate routes maitaied based o lik coditios helps i reducig the ed-to-ed flow packet loss rate. The packet error rate over the liks was varied with a probability i the rage Figure 8 shows that the ed-to-ed flow packet-loss-rate decreases as the ed-to-ed delay limit is icreased for each applicatio flow. For applicatio flow B, there is ot much differece i the packet loss rate values betwee reactive ad multi-path proactive adaptatio. However, for applicatio A, better results (more graceful degradatio i packet loss rate as ed-to-ed applicatio delay deadlie is reduced) are achieved with the multi-path proactive adaptatio. Figure 9 shows results from experimetatio with worser lik coditio variatios the lik packet error rates varyig from 0.05 to 0.3. I this case, it ca be see that ed-to-ed flow packet error rates start icreasig for larger ed-to-ed flow delay limits, as oe would expect. Figure 6: Routig Optimizatio example for two flows Figure 7: Multi-path optios for two flows Figure 8: Ed-to-Ed Flow Packet Loss Rate vs Applicatio Ed-to-Ed Delay (good chael PER variatio from 0.05 to 0.15) Figure 9: Ed-to-Ed Flow Packet Loss Rate vs Applicatio Deadlie (good chael PER variatio from 0.05 to 0.30) V. EXTENSION OF THE CROSS-LAYER CROSS-OVERLAY ARCHITECTURE TO HETEROGENEOUS MESH NETWORKS I the discussio i the previous sectio, it should be oted that a pre-stadard s implemetatio was cosidered. However, the cross-layer cross-overlay architecture proposed

8 8 for mesh etworks (such as s) ca be exteded for ed-to-ed optimizatio over heterogeeous etworks as well. For example it is coceivable that a ode ca have a radio ad a e radio, ad it may receive iformatio over the radio iterface ad forward it over the e iterface. A typical s mesh etwork caot support rages beyod 100 meters ad mobile devices movig at vehicular speed. Multi-hop relay WiMAX mesh etworkig ca offer sigificat beefits by extedig the coverage of a BS, ad extedig the rage of WiMAX "path" to reach a locatio. WiMAX Relay Statios (RS) ca be Fixed, Nomadic or Mobile. Frequecy coversio ca be supported to support radios/devices operatig at differet frequecies, which ca provide better spectrum utilizatio. I additio, the use of multi-radio, multi-chael, multi-protocol capabilities with MIMO techologies, ad use of techiques such as etwork codig ad co-operative diversity ca provide improvemets i badwidths alog with the icreased rage provided by WiMAX. Cosiderig all these factors, the j stadard (this is work i progress) evisos a multi-hop WiMAX etwork beyod BS-based etwork ad WiFi s mesh, capable of sigificatly extedig the rage ad badwidth, yet seamlessly iteretworkig with the local mesh (802.11s based) ad with a RS resemblig a ode i the mesh etwork discussed i this paper. geeralized ode architecture for cross-layer cross-overlay iformatio exchage ad distributed optimizatio over heterogeeous etworks is show i Figure 10. Differet layers i the protocol stack implemetatio at a ode ca exchage iformatio through cross-layer mechaisms usig database implemetatios to store or retrieve data. Iformatio available about lik coditios ca be propagated from the local lik layer database to the DNIB at the applicatio layer. Database updates ca proceed asychroously with producers providig updates whe they are available. Cosumers of the database iformatio will utilize the latest available iformatio i the database wheever they eed the iformatio. The distributed virtual machies ca exchage iformatio peer-to-peer usig the uderlyig etwork ifrastructure for message commuicatio i the etwork. A key objective would be to create lightweight virtual machies so that cotrol, maagemet ad optimizatio fuctios ca be virtualized ad implemeted i a distributed maer, ad easily ivoked whe required. Additioally, applicatio services ca also be ivoked usig virtual machie implemetatios. Groups of odes egaged i a specific distributed processig task ca have a distributed virtual machie implemetatio to support that task. Differet groups of odes may be formed to process differet distributed tasks. Every ode therefore does ot have to provide support for the same. Applicatio-layer virtualizatio capabilities, alog with trasport layer ad etwork layer services are show as a sigle layer the actual implemetatio methodology to provide these capabilities may differ across platforms. The virtualizatio layer has hardware-awareess about the platform hardware resources ad costraits, ad the multi-comm multi-radio multi-chael commuicatios support available i the device, to make the most optimal utilizatio about the available commuicatios/etworkig capabilities ad system resource costraits i the device. WiFi Mesh Hotspot i Beijig Portal Node Figure 10: Geeralized Cross-Layer Cross- Architecture Over Heterogeeous Networks With differet optios for mesh etworkig providig flexibilities i rage ad performace, there is a eed for proactive adaptatio over heterogeeous mesh etworks with odes supportig multiple wireless protocols. The proposed architecture ca be exteded to such heterogeeous etworks as well. A geeralized architecture ca iclude odes with multi-radio, multi-chael, ad multi-comm-protocol capabilities, ad iformatio trasmissio ca be achieved across heterogeeous etworks. Additioally, although implemetatio is used to create distributed virtual machies, the architecture ca be geeral ad ay available virtualizatio techology ca be used to create such Ds. A VoIP peer WiMAX(opt) Wirelie / Fiber Optical Networks Broadbad Access WiMAX(opt) VoIP peer Portal Node WiFi Mesh Hotspot i Folsom Figure 11. Example of usig the cross-layer cross-overlay architecture over a heterogeeous etwork The overlay etwork ca be deployed over a heterogeeous wireless/wirelie etwork as show i Figure 11. The figure explores the applicatio of the proposed architecture for a VoIP applicatio from Beijig, Chia to Folsom, CA, USA with flow optimizatio over heterogeeous etworks i the presece of possibly additioal other flows i the etwork. The lower two layers of the cross-layer cross-overlay architecture i Figure 2 ca be differet for differet etworks such as s WiFi

9 9 Mesh, WiMAX (optioal), etc, while the upper layers icludig ad above the implemetatio layer (or other distributed virtualizatio service layer) ca provide distributed services with virtual machies across the overlay etwork. The global database provides iformatio for the routig optimizatio i (7) to obtai multiple paths that satisfy the delay costrait ad badwidth demads. The trasmissio delay betwee the broadbad access odes for the wired/optical portio (or optioally satellite liks) is assumed to be measurable ad available. Portal odes are pre-determied for each wireless mesh hotspot. The fial ed-to-ed delay that must be withi the ed-to-ed delay limit (such as 180ms) of the delay-sesitive VoIP applicatio is composed by the followig segmets: (a) the accumulated delay from the VoIP peer to the mesh portal ode i the Beijig s mesh etwork, (b) the accumulated delay from the s mesh portal through a WiMAX multi-hop relay mesh (optioal) at Beijig, (c) the ed-to-ed delay through the wired/optical lie from Beijig to Folsom, (d) the accumulated delay through the WiMAX multi-hop relay mesh (optioal) to the s mesh portal i Folsom, ad, (e) the accumulated delay from the portal ode to the VoIP peer i the Folsom s mesh. All the delay values with their types are exchaged through the distributed services provided o the overlay etwork across the heterogeeous etwork path. The routig algorithm optimizatios withi each etwork itroduced i Sectio IV ca be performed as log as the latest lik delay iformatio (such as the ETX, ETT i the pre-stadard s) is available. Reduced delay costraits ca be applied across each etwork, with routig optimizatio performed i each etwork, so that the cumulative delay across differet etworks ca meet the ed-to-ed delay requiremets for the applicatio. VI CONCLUSIONS I this paper, a cross-layer cross-overlay architecture was preseted that regularly exchages cross-layer parameters through distributed overlay services i a heterogeeous etwork architecture. A joit multi-flow routig optimizatio problem was explored with extractio of useful parameters for optimizatio from the proposed database, ad costructio of routes that satisfy the delay costrait ad the badwidth demad. By combiig the beefits of decetralizatio i both the wireless mesh ifrastructure ad the applicatio layer overlay services, the suggested cross-layer cross-overlay architecture permits a ovel peer-to-peer iformatio exchage architecture i the applicatio overlay etwork (with cotrollable iformatio exchage overheads) across possibly heterogeeous wired ad wireless etworks. Future research directios iclude fidig fast routig adaptatio methods, uder dyamic etwork coditios, with exploratio of optimizatios uder differet etwork topologies ad various applicatio characteristics. ACKNOWLEDGEMENTS The authors thak Lily Yag for feedback. REFERENCES [1] I. F. Akyildiz, X. Wag, ad W. Wag, Wireless Mesh Networks: A Survey, Computer Networks Joural, vol. 47, 2005, pp [2] J. Vicete, S. Rugta, G. Dig, D. Krishaswamy, W. Cha, K. Miao, "OverMesh: Network Cetric Computig", Ivited Paper, IEEE Commuicatios Magazie, To appear [3] G. Dig, J. Vicete, S. Rugta, D. Krishaswamy, W. Cha, K. Miao, "s o Wireless Mesh Networks: Implemetatio ad Cross-Layer Searchig", To appear 9th IFIP/IEEE Iteratioal Coferece o Maagemet of Multimedia ad Mobile Networks ad Services, Dubli, [4] D. Krishaswamy, J. Vicete, "Scalable Adaptive Wireless Networks for Multimedia i the Proactive Eterprise", Itel Techology Joural, Q [5] [6] [7] IEEE Task Group s, Draft Amedmet: ESS Mesh Networkig IEEE Std s draft 0.03, July [8] Charles E. Perkis ad Elizabeth M. Royer. Ad hoc O-Demad Distace Vector Routig. I Proceedigs of the 2d IEEE Workshop o Mobile Computig Systems ad Applicatios, [9]T. Larsso ad N. Hedma, Routig protocols i wireless ad-hoc etworks - a simulatio study, Master s Thesis, LuLea Tekiska Uiversity, [10] J. Bicket, D. Aguayo, S. Biswas, R. Morris, Architecture ad evaluatio of a uplaed b mesh etwork, MobiCom 05, New York, NY, USA: ACM Press, 2005, pp [11] R. Draves, J. Padhye, ad B. Zill, Routig i multi-radio, multi-hop wireless mesh etworks, i MobiCom 04. New York, NY, USA: ACM Press, 2004, pp [12] R. Draves, J. Padhye, ad B. Zill, Compariso of routig metrics for static multi-hop wireless etworks, i SIGCOMM 04. New York, NY, USA: ACM Press, 2004, pp [13] H.P. Shiag, M. va der Schaar, Multi-user Video Streamig over Multi-hop Wireless Networks: A Distributed, Cross-layer Approach Based o Priority Queuig, submitted to IEEE JSAC. [14] Chagwe Liu, W. Steve Coer, Mark D. Yarvis, ad Xigag Guo, "Guarateed O-Demad Discovery of Node-Disjoit Paths i Ad Hoc Networks," Itel Techical Report IR-TR , Itel Corporatio, July [15] Gialuca Iaaccoe, CoMo: A ope ifrastructure for etwork moitorig, Itel Research Techical Report, February [16] WiMAX Forum White Papers, Techical Documets ad Specificatios, APPENDIX A. Pseudo code for multi-path costructio with a delay-costraied exhaustive search For each applicatio with Iput: src, dst, deadlie, apply the followig algorithm: 1. ETT getett(database); 2. N size_of_ode(ett); 3. for i = 1 to N 4. Neighbor_i CheckCoect(i); 5. ed for 6. Put src ode i the TakeSet

10 10 7. k 0; (curret route umber) 8. route_k src; 9. accum_delay_k 0; 10. while(dst ot i the TakeSet) 11. for all ode j that is NOT i the TakeSet but earest to the TakeSet 12. for all route k that exists i the TakeSet 13. Set i = LastNode(route_k) 14. if( j is i Neighbor_i ) 15. temp_delay accum_delay_k + ETT(i, j); 16. if temp_delay < deadlie 17. k k+1; 18. Add j ito route_k; 19. accum_delay_k = temp_delay; 20. ed if 21. ed if 22. ed for 23. Put ode j ito the TakeSet; 24. ed for 25. ed while 26. Output route_k that eds with dst ad the correspodig accum_delay_k; B. Pseudo code for multi-path costructio with a delay-costraied Dijkstra search betwee eighbors of the source to eighbors of the destiatio ode. For each applicatio with Iput: src, dst, deadlie, apply the followig algorithm: 1. ETT getett(database); 2. N size_of_ode(ett); 3. for i = 1 to N 4. Neighbor_i CheckCoect(i); 5. ed for 6. k 0; 7. for all ode i i the Neighbor_dst 8. for all ode j i the Neighbor_src 9. k k+1; 10. [delay_metric_k, route_k] = Dijkstra_shortest_path(i,j); // Dijkstra algorithm for the shortest path from ode i to j 11. ed for 12. ed for 13. for all route_k 14. if dst or src is i the route_k 15. drop route_k 16. else 17. oe row of output_delay_metric delay_metric_k+ ETT(src, route_k_start)+ett(route_k_ed, dst); 18. if the delay_metric_k > deadlie 19. drop route_k; 20. else 21. update route_k oe row of output_route; 22. ed if 23. ed if 24. ed for 25. Output output_route ad output_delay_metric; Subroutie for ruig Dijkstra s algorithm: [delay_metric_k, route_k] = Dijkstra_shortest_path(src,k) 1. Iitialize delay_metric for all odes 0; 2. Put src ad its earest eighbor i the TakeSet; (smallest ETT) 3. update route_earest_eighbor; 4. while( k ot i the TakeSet) 5. idex 0; for all ode i ot i the TakeSet 6. for all ode j i the TakeSet 7. if i ad j are coected 8. Temp_idex = delay_metric_j + ETT(i,j); 9. idex idex + 1; 10. ed if 11. ed for 12. [Value, idex]= mi(temp_idex); 13. delay_metric_i = Value; 14. put i ito TakeSet; 15. update route_i with idex; 16. ed for 17. ed while 18. retur delay_metric_k, ad route_k C. Pseudo code for proactive multi-flow optimizatio Iput: applicatios, deadlies, multi-routes for all distict applicatios 1. ETT getett(database); 2. N size_of_ode(ett); 3. for i = 1 to N 4. Neighbor_i CheckCoect(i); 5. ed for 6. N_lik size_of_lik(ett); 7. N_app size_of_applicatio(applicatios); 8. for all the combiatios of routes for the applicatios 9. for j= 1 to N_app 10. N_path_j umber of path for applicatio j i the combiatio; 11. ed for 12. for i= 1 to N_lik 13. for all routes i the combiatio 14. if i is i the route 15. overlap_cout_i ++; 16. ed if 17. ed for 18. ed for 19. for i = 1 to N_lik 20. update ETT_shared(i) ETT(i)*overlap_cout(i) 21. ed for 22. for all routes i the combiatio 23. for all liks i the route 24. accum_delay_route += ETT_shared(lik); 25. ed for 26. ed for 27. for j= 1 to N_app 28. delay_metric_j = max(accum_delay_route_j/n_path_j)over paths; 29. if delay_metric_j > deadlie_j 30. drop the combiatio; 31. ed if 32. ed for 33. ed for 34. Output routig combiatios, delay_metric;