Research Article Optimal Configuration of Virtual Links for Avionics Network Systems

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1 Iteratioal Joural of Aerospace Egieerig Volume 205, Article ID , 9 pages Research Article Optimal Cofiguratio of Virtual Liks for Avioics Network Systems Dogha A, Kyog Hoo Kim, ad Ki-Il Kim Departmet of Iformatics, Research Ceter for Aerospace Parts Techology, Gyeogsag Natioal Uiversity, Jiju-daero 50, Jiju 660-0, Republic of Korea Correspodece should be addressed to Kyog Hoo Kim; khkim@gu.ac.kr Received 28 Jue 205; Accepted 8 October 205 Academic Editor: Lida L. Vahala Copyright 205 Dogha A et al. This is a ope access article distributed uder the Creative Commos Attributio Licese, which permits urestricted use, distributio, ad reproductio i ay medium, provided the origial work is properly cited. As the badwidth ad scalability costraits become importat desig cocers i airbore etworks, a ew techology, called Avioics Full Duplex Switched Etheret (), has bee itroduced ad stadardized as a part i ARNIC 664. However, sice previous research iterests for are maily bouded for aalyzig the respose time where flows iformatio is give, cofiguratio problem for both Maximum Trasmissio Uit (MTU) ad Badwidth Allocatio Gap (BAG) over virtual liks i etworks has ot bee addressed yet eve though it has great impact o required badwidth. Thus, i this paper, we preset two cofiguratio approaches to set MTU ad BAG values o virtual liks efficietly while meetig the requiremet of. The first is to search available feasible cofiguratio (MTU, BAG) pairs to satisfy applicatio requiremets as well as switch costraits, ad the secod is to get a optimal pair to miimize required badwidth through well-kow brach-ad-boud algorithm. We aalyze the complexity of the proposed algorithm ad the evaluate the proposed algorithm by simulatio. Fially, we prove that the proposed schemes are superior to geeral approach i the aspects of speed ad required badwidth i etworks.. Itroductio Due to icreasig demads i Aircraft Data Networks (ADNs), such as high available badwidth, miimum wirig to reduce the weight, ad low developmet cost, typical commuicatios techologies are expected to be replaced by ew oe.iotherwords,sicearnic429,mil-std-553,ad ARNIC 629 caot accommodate the metioed demads completely, a ew techology, called Avioics Full Duplex Switched Etheret (), has bee implemeted ad the stadardizedforewadn[ 3].Asaewtechologyfor ADN, reliable ad determiistic property as well as implemetatiocostshouldbecosidered.asaresult,was itroduced ad recetly deployed i data etworks o the Airbus 380 aircraft. I the poit of techical issue, the follows origial Etheret for compatibility ad scalability properties ad exteds it to esure determiistic behavior ad high reliability. I order to comply with the striget requiremets of ADNs as well as esurig them, two ew fuctios areitroducedadimplemetedi.oeistraffic cotrol by guarateeig the badwidth of each applicatio, ad the other is duplicated trasmissio for reliability alog dual redudat chaels. While the former aims to boud the jitter ad trasmit latecy withi the deadlie, the latter trasmits the same data stream over disjoit etworks cocurretly. To achieve this goal, virtual liks are itroduced ad created for each (source, destiatio) pair i. By cotrollig these virtual liks, determiistic behaviors are completely guarateed. Thus, determiig flows for the same virtual lik ad its properties become the etwork desiger s great task whe it comes to cofigurig etworks. Two parameters of virtual liks i AFDEX etworks are importat i terms of real-time requiremets: BAG (Badwidth Allocatio Gap) ad MTU (Maximum Trasfer Uit). BAG is the time duratio or period betwee two cosecutive frames, where the value of BAG is ad 28 msec i a form of power of 2. MTU is the size of message i each frame. Thus, the cofiguratio problem is to determie these two parameters of each virtual lik without missig the deadlie.

2 2 Iteratioal Joural of Aerospace Egieerig I [4], they provided several algorithms ad itegerliear programmig formulatio i order to solve the trasmissio parameters of virtual liks as well as data routig over liks i the AFDEX etworks. They provided optimal solutios to miimize reserved badwidth as well as actually cosumed badwidth, respectively. I [5], modelig method for frame maagemet was itroduced to ascertai the reliability properties of desig. Aother importat property of, reliability through redudat trasmissios, was aalyzed by formal method i [6]. Aother related work is to aalyze the system metric such as respose time of etworks. I [], they applied etwork calculus, queuig etworks simulatio ad model checkig ito evaluatig boudig ed-to-ed delays o etworks. I [8], they showed that Trajectory approach which aalyzes the worst-case delays throughout message flows outperforms the etwork calculus method uder idustrial cofiguratio. I [9], they obtai worst-case latecy ad output jitter for the etwork messages by defiig a realtime model for a commuicatios etwork based o. Aother approach i [0] is performace evaluatio system through simulatio with popular NS-2 ad aalysis of impact of several system parameters such as schedulig algorithm. Sicemostofexistigresearchworkhasassumedthe precofigured etworks i advace, cofiguratio problem should be metioed prior to deploymet. To achieve this goal,ithispaper,wefocusotwomaiproblems:(i) fidig feasible BAG ad MTU parameters of virtual liks i a switch for give virtual liks of messages ad (ii) providig a optimal solutio i feasible pairs to miimize the total badwidth. We defie two problems formallyadthesolvetheproblemsusigthebrach-adboud techique. While our earlier work [] oly provided a algorithm to solve the first problem, this paper improves ad exteds it to iclude optimal solutio for the purpose of miimizig the total badwidth. Fially, complexity of the proposed scheme ad experimetal results through diverse simulatio scearios are give to demostrate the suitability of the proposed scheme. The rest of this paper is orgaized as follows. The system model ad the problem defiitio are provided i Sectio 2. The solutio of a feasible cofiguratio problem is dealt with i Sectios 3 ad 4, while the optimal algorithm is provided i Sectio 5. Performace evaluatios are show i Sectio 6. Fially, coclusio ad further work followed i Sectio. 2. System Model ad Problem Defiitio 2.. System Model. I this paper, we assume that a avioics system is composed of may computig or sesig uits ad etwork switches to coect other computig uits. Thus, a message is uiquely defied by UDP source ad destiatio ports, as show i Figure. Sie we focus o real-time messages, a message flow f i is defied by (l i, p i ), where l i is the payload of the message i bytes ad p i is Message Trasmit Cycle (MTC) of the message i msec. That is, a message of l i bytes is geerated every p i time uits ad is delivered to the destiatio applicatio. The basic commuicatio uit i AFDEX etworks is defied as a virtual lik (VL). For example, Figure shows three virtual liks amog LRUs. These virtual liks sharig physical liks are scheduled i etwork switches. Furthermore, multiple applicatios trasmit real-time messages throughout a commo virtual lik if their source ad destiatio uits are the same. I the example of Figure, two applicatio messages are shared i the virtual lik VL 3. There are two importat parameters i a virtual lik. The first is Badwidth Allocatio Gap (BAG) to specify a periodic frame. I switches, a BAG is defied by a value of 2 k msec, where k = 0,,...,.AsallBAGsare2 k msec, virtual liks are multiplexed i switches. The secod parameter is Maximum Trasfer Uit (MTU) of the message i bytes at each frame. Payloads of applicatios i a virtual lik are trasmitted withi maximum MTU bytes i a sigle frame. If the size of a payload is greater tha the MTU, it is fragmeted ito multiple frames. Therefore, a virtual lik VL i is defied by (BAG i,mtu i, F i ) as follows: (i) BAG i : Badwidth Allocatio Gap or period of VL i i avalueof2 k msec where,,...,. (ii) MTU i : maximum trasfer uit or message size of VL i i bytes. (iii) F i : a set of message flows i VL i,wherethejth message flow is deoted as f i,j =(l i,j,p i,j ) Problem Defiitio. For a give virtual lik VL i,mtu ad BAG are cofigured so as to meet all the real-time requiremets of message flows i the lik. If the payload of amessageisgreaterthathemtusize,itistrasmitted i multiple fragmeted packets. Sice all BAGs of VLs are harmoic, the schedulability aalysis is easily derived by utilizatio aalysis. Thus, () tells the message costrait of VL i with i messages to guaratee the real-time requiremet of all message flows i the lik [2]: i j= l i,j /MTU i p i,j BAG i. () Let us assume that the system has N VLs o a switch with B badwidth i bps. Each VL i is cofigured with (MTU i,bag i ), so that MTU i bytes are trasmitted every BAG i msec. I additio, each VL message requires the overhead of 6 bytes as show i Figure 2. Sice the total badwidth of VLs should ot exceed the etwork badwidth, the followig badwidth costrait should be met: i= 8 MTU i +6 BAG i 0 3 B. (2) The last costrait of virtual lik schedulig is about jitter. The maximum allowed jitter o each virtual lik i

3 Iteratioal Joural of Aerospace Egieerig 3 port LRU Partitio Partitio 2 port port port IP 0 UDP IP 20 UDP IP 0 UDP IP 20 UDP MAC 0 VL VL 3 VL 2 LRU 2 switch LRU 3 MAC MAC 3 MAC 2 IP UDP IP 3 UDP 2 IP 3 UDP 2 IP 2 UDP port port port port Partitio Partitio Figure : A example of virtual liks i a switch. Preamble bytes SFD byte MAC destiatio 6 bytes MAC source 6 bytes Type IPv4 2 bytes IP header 20 bytes UDP header 8 bytes payload bytes Paddig 0 6 bytes SN byte FCS 4 bytes IFG 2 bytes Overhead (50 bytes) payload Overhead ( bytes) Figure 2: The frame structure ad its overhead. the ARINC 664 specificatio requires 500 μsec [2]. Thus, the followig equatio tells the jitter costrait, where 40 μsec is the typical techological jitter i hardware level to trasmit a Etheret frame: i= (6 + MTU i) 500. (3) B I this paper, we defie two problems related to cofiguratio of virtual liks of a switch. The first problem is to fid a feasible cofiguratio of BAG ad MTU pairs of virtual liks, which satisfies three costraits of (), (2), ad (3). This is useful ad importat whe a admiistrator fids a feasible cofiguratio of a give set of real-time messages i the switch. The followig tells the formal defiitio of the problem. Defiitio. For a give set of virtual liks V = {VL i i =,...,N}, the problem of -CONF is to determie (BAG i,mtu i ) of each VL i so as to satisfy three costraits of (), (2), ad (3), where BAG i {, 2, 4, 8, 6, 32, 64, 28} ad MTU i {,2,...,4}. The secod oe is to fid a optimal cofiguratio of virtual liks for the purpose of miimizig the total badwidth. The badwidth remaiig after reservig real-time flows is geerally used for o-real-time etwork traffic. Thus, it is importat to fid a cofiguratio with the least badwidth as

4 4 Iteratioal Joural of Aerospace Egieerig Algorithm Fid Feasible BAG MTU (VL i ) () N step (2) for each message f i,j i VL i do (3) frag l i,j /( l i,j /p i,j ) (4) while frag do (3) m l i,j /frag (5) N step N step {m} (6) frag frag () edwhile (8) edfor (9) for k from 0 to do (0) MTU i,k 0 () MTU i,k the least m N step s.t. i j= ( l i,j/m /p i,j ) /2 k (2) edfor Algorithm : Algorithm of feasible BAG ad MTU pairs of a VL. log as the cofiguratio is feasible. The followig tells the secod problem defiitio. Defiitio 2. For a give set of virtual liks V = {VL i i =,...,N},theproblemof-BOPT is to fid (BAG i, MTU i ) of each VL i so as to miimize the total badwidth ad satisfy three costraits of (), (2), ad (3), where BAG i {, 2, 4, 8, 6, 32, 64, 28} ad MTU i {,2,...,4}. We solve both problems of -CONF ad - BOPT i two steps. The first step is to fid the list of (BAG i, MTU i ) which guaratees the schedulability of message flows i VL i. Each (BAG i,mtu i )shouldbeselectedsuchthatit satisfies the costrait of () (i Sectio 3). The, we fid the solutio of give virtual liks with cosideratio of two costraits of (2) ad (3) (i Sectios 4 ad 5). 3. Schedulable BAG ad MTU Pairs of a VL I etworks, multiple applicatios should sed their messages to a virtual lik queue i the system, so that the schedulig issue for those messages is required. Let us cosider a virtual lik VL with two message flows of f, (80, 0), f,2 (00, 2) as a example. The values of BAG ad MTU of VL are set to satisfy () i order to meet the realtime requiremet of two messages. The left side of () is show i Figure 3 as a step fuctio, while /BAG is also draw i the figure for differet BAG values. For a give BAG i, there exist may MTUs which satisfy (). For example, whe BAG =,allmtuscabeusedif MTU, as show i Figure 3. Sice a loger MTU size requires more badwidth ad jitter, the smallest value should be selected. Thus, MTU of the example VL is bytes whe BAG is msec. Similarly, MTUs of VL for BAGs with 2 msec ad 4 msec are give by 40 bytes ad 00 bytes i each, as show i Figure 3. WhetheMTUsizeisgreaterthathemaximumpayload size of messages, the required utilizatio is ot chaged. For example, the lower boud of the utilizatio of VL is give by about at MTU = 00. This implies that there is o MTU which guaratees the schedulability of two messages if Utilizatio /MTU /MTU 2 / (BAG =) /2 (BAG =2) /4 (BAG =4) /8 (BAG =8) MTU Figure 3: A example of feasible BAG ad MTU of a virtual lik. BAG is greater tha or equal to 8 msec. Therefore, the feasible solutios (BAG,MTU )ofvl aregiveby(,),(2,40), ad (4, 00). The pseudocode of Algorithm describes how to obtai the set of feasible BAG ad MTU pairs of a give virtual lik VL i. The first part of the algorithm gathers all step itegers at which the utilizatio fuctio begis a ew piecewise costat due to the ceilig fuctio. We deote the set of such step itegers as N step.foreachmessagef i,j,suchsteppoits are derived ad added ito N step (lies 8). The, for each 2 k value, we fid the miimum MTU which satisfies () (lies 9 2). We deote MTU i,k by the feasible MTU i case of BAG i =2 k foravirtuallikvl i.ifthere is o feasible MTU, the MTU i,k =0.Foragive i flows, the time complexity of Algorithm is O( i N step ) sice we have tofidadcheckthefeasibilityateachsteppoitofmessages. 4. Feasible BAG ad MTU Pairs of VLs 4.. Problem Defiitio. The problem of fidig feasible BAG ad MTU pairs of a give set of virtual liks is ot trivial. For

5 Iteratioal Joural of Aerospace Egieerig 5 Flows (f i,j ) Table : A example of virtual liks (B =Mbps). Payload (l i,j ) MTC (p i,j ) VL f, f, Feasible BAG ad MTU pairs s i,k (bag i,k, MTU i,k ) (, 5), (2, 9), (4, ), (8, 34), (6, 6), (32, 200) VL 2 f 2, (, 6), (2, 2), (4, 25), (8, 50), (6, 00), (32, 200) f 2, example, let us cosider the example of two virtual liks of Table where the etwork speed (B) isgivebymbps.for each virtual lik, the feasible BAG ad MTU pairs are derived by Algorithm, as show i the last colum of Table. Now, a ew problem arises about selectig appropriate BAG ad MTU pairs of two virtual liks so as to meet both costraits of (2) ad (3). There are some tradeoffs amog feasible BAG ad MTU pairs of a virtual lik VL i. Solutios with smaller BAG provide less jitter due to smaller MTU size, while they require more badwidth due to overhead of fragmetatio. For example, if we select (, 5) ad(, 6) as (BAG, MTU) of two VLs of Table, it does ot meet the badwidth costrait of (2). O the cotrary, if (2, 9) ad(2, 2) are selected as (BAG, MTU) of two VLs, this cofiguratio does ot meet the jitter costrait of (3). The selectio of (, 5)ad(2, 2)ofVL ad VL 2 satisfies both costraits so that all messages i VLs meet their real-time requiremets. Let us assume that MTU i,k is derived from Algorithm for each i ad k. Ad, let us deote it by X ik = { if BAG ad MTU of VL i are set as 2 k ad MTU i,k i each, { 0 otherwise. { (4) The, the problem of -CONF cabestatedasthe followig liear iteger problem with 8biary variables ad three costraits: to fid X ik subject to i= i= ( ( X ik = X ik MTU i,k +6 ) B 2 k 8000 X ik (6+MTU i,k )) 460 B Algorithm. For give N virtual liks, the exhaustive search of the problem -CONF takes O(8 N ) sice each virtual lik might have maximum eight solutios. I this paper, we provide a ehaced brach-ad-boud algorithm proposed i [] i order to fid a feasible solutio for give N virtual liks with their feasible BAG ad MTU pairs derived byalgorithm.i[],weusedthecumulativebadwidth ad jitter for the pruig coditio. I this work, however, we defie the boud fuctios of badwidth ad jitter for theremaiiglevelsithesearchtreeiordertofid the pruig ode as early as possible. The followig is the pruig coditio ad brach-ad-boud strategy of the proposed algorithm. (i) Pruig Coditio. The pruig coditio is two costraits of (2) ad (3). The algorithm examies whether (5) the solutios i the subset satisfy both costraits by usig the boud fuctio of miimum values of remaiig levels. The algorithm stops the search of the subset which already violates oe of two costraits. (ii) Brach-ad-Boud Strategy. The algorithm searches a feasible solutio i a leaf ode i depth-first-search (DFS) maer. This algorithm fids a feasible solutio whe it reaches ay leaf ode i the search tree. Algorithm 2 fids the set of feasible BAG ad MTU pairs of each virtual lik by callig the fuctio Fid Feasible BAG MTU ( ) proposed i Algorithm (lies, 2). Let us deote σ i by the set of feasible BAG ad MTU pairs (s i,k )ofvirtualliki. The,theboudsofbadwidth ad jitter i virtual lik i are foud by selectig the miimum values (lies 4 ). The fuctio EDFS BadB i Algorithm 2 is the recursive implemetatio at level i i the search tree. Two values of B prev ad J prev are two bouds of badwidth ad jitter of subsolutios from VL i to VL N.Foreachs i,k =(bag i,k, MTU i,k ), two costrais of (2) ad (3) are checked icludig a ew solutio of VL i (lies 4 6). If either of the two costraits is ot satisfied, it is prued. Otherwise, the depth-first-search is cotiued with two updated boud values (lie ). Whe the search reaches a leaf ode, the fuctio returs true (lie 2). The retur value of callig EDFS BadB is true; thefialsolutios is updated as to iclude s i,k (lie 9) ad the fuctio returs true. Thus, the problem of -CONF is solved by Algorithm 2. If the retur value of DFS BadB (B 0, J 0,, S) istrue, a feasible solutio is stored

6 6 Iteratioal Joural of Aerospace Egieerig Algorithm Fid Feasible Cofiguratios (V) / V={VL i i=,...,n} / () for i from to N do (2) call Fid Feasible BAG MTU (VL i ) (3) S (4) for i from to N do (5) B i mi si,k σ i {(MTU i,k + 6)/bag i,k } (6) J i mi si,k σ i {MTU i,k + 6} () edfor (8) B 0 N i= B i (9) J 0 N i= J i (0) result EDFS BadB (B 0,J 0,,S) () retur S Fuctio EDFS BadB (B prev,j prev,i,s) (2) if i=n+the retur true (3) for each s i,k of VL i do (4) B curr B prev B i +(MTU i,k + 6)/bag i,k (5) J curr J prev J i + MTU i,k +6 (6) if B curr B/8000 ad J curr 460 B the () result EDFS BadB (B curr,j curr,i+,s) (8) if result = true the (9) S S {s i,k } (20) retur true (2) edif (22) edif (23) edfor (24) retur false Algorithm2:Theproposedalgorithmfor-CONF. i S. Otherwise, the empty set is retured, which implies o feasible cofiguratio is foud for a give set of virtual liks. 5. Optimal Solutio of BAG ad MTU Pairs for Reducig Badwidth I this sectio, we focus o fidig a optimal cofiguratio of virtual liks i terms of the used badwidth of the cofiguratio. It is importat to miimize the total badwidth of virtual liks for real-time traffic because we ca use the remaiig badwidth for o-real-time etwork traffic i avioics systems. The problem of -CONF fids a feasible solutio which satisfies three costraits of switch as soo as possible, so that it does ot miimize the badwidth. However, -BOPT fids a feasible solutio which miimizes the total badwidth, so that the problem is rewritte as follows: to miimize 8000 subject to i= ( X ik MTU i,k +6 ) 2 k (6) X ik = () i= i= ( ( X ik MTU i,k +6 ) B 2 k 8000 (8) X ik (6 + MTU i,k )) 460 B 8. (9) For example, there are two feasible cofiguratios i Table : {(, 5), (2, 2)} ad {(2, 9), (, 6)} uder the badwidth costrait of Mbps. The first cofiguratio requires 892 kbps, while the secod oe uses 888 kbps. Thus, i this case, {(2, 9), (, 6)} is the optimal cofiguratio of two virtual liks. I order to solve the problem, we provide a brach-adboudalgorithm.theboudfuctioisthesameasoe i Algorithm 2, so that we use the miimum badwidth adjitterforboudvaluesofeachode.thus,thepruig coditio is two costraits of (8) ad (9) usig the boud fuctios. The brach strategy is differet from DFS. Sice thealgorithmfidsaoptimalsolutioassooaspossible, we select a ode with the miimum badwidth boud fuctio ad brach its child odes. The pseudocode of this is show i Algorithm 3. Sice the brach-ad-boud techique searches all possible cases i the worst-case, the time complexity of Algorithm 3 is O(2 N ) for give N virtual liks. I Algorithm 3, a ode has four data: ode.level for the ode level, ode.b for the badwidth boud, ode.j for the jitter boud, ad ode.s for the selected cofiguratio from theroottotheode.weuseapriority-queueformaagig live odes i the order of badwidth boud. The fuctio isert ode i Q (i, B, J, S) makesaodewithfourdata ad iserts it ito the priority queue. The, the fuctio get first i Q ( ) returs the miimum-badwidth ode i curretly live odes i the queue. Whe the algorithm reaches a leaf ode (lie 2), it fids a optimal solutio ad returs the cofiguratio (lie 3). The brach strategy is implemeted by the priority queue. The fuctio call of get first i Q () selects such ode to brach amog live odes. For all child odes of the selected ode, the boud fuctios of badwidth ad jitter are updated (lies 6-). The pruig coditio is checked i lie 8. If a ew child ode is ot prued, it is added i the priority queue (lie 9). The algorithm repeats this procedure utilitfidsaoptimalsolutioorthereisoliveodeithe queue. If there is o feasible cofiguratio for virtual liks, it returs the empty set for otifyig o feasible solutio (lie 22). 6. Performace Evaluatios I this sectio, we show performace evaluatio of the proposed algorithm. First, we evaluate the executio time of the proposed algorithms compared with the brute-force search ad the previous work []. I the experimets, we geerate five virtual liks with two message flows i each virtual lik. The payload of a message is radomly geerated from 20 to 80 bytes. The MTC or period of a message is

7 Iteratioal Joural of Aerospace Egieerig Algorithm Fid Miimum Badwidth Cofiguratio (V) () for i from to N do (2) call Fid Feasible BAG MTU (VL i ) (3) for i from to N do (4) B i log si,k σ i {(MTU i,k + 6)/bag i,k } (5) J i log si,k σ i {MTU i,k + 6} (6) edfor () B 0 N i= B i (8) J 0 N i= J i (9) isert ode i Q (0, B 0,J 0, ); (0) while is empty Q ()=false do () ode get first i Q (); (2) if ode.level = N the (3) retur ode.s; (4) i ode.level + (5) for each s i,k of VL i do (6) B curr ode.b B i +(MTU i,k + 6)/bag i,k () J curr ode.j J i + MTU i,k +6 (8) if B curr B/8000 ad J curr 460 B the (9) isert ode i Q (i, B curr,j curr,ode.s {s i,k }); (20) edfor (2) edwhile (22) retur Algorithm 3: The Bouded BFS BadB algorithm Normalized executio time Normalized executio time ~60 60~0 0~60 60~20 20~260 MTC 0~60 60~0 0~60 60~20 20~260 MTC Brute-force DFS EDFS (a) -CONF Brute-force B-DFS EBFS (b) -BOPT Figure 4: Normalized executio times of algorithms. radomly selected amog five differet itervals, as show i Figure 4. The etwork badwidth is set as 6 Mbps. ForeachcaseofFigure4,wegeerate5000radomsets of five virtual liks ad measure the average executio time of algorithms. Figure 4(a) shows the ormalized executio times of the brute-force search, DFS i [], ad EDFS i this paper for solvig -CONF. Similarly, Figure 4(b) shows the performace of the proposed algorithm EBFS compared to the brute-force search ad the modified versio of DFS [] for solvig -BOPT. As show i Figure 4, the proposed algorithms ru much faster tha the exhaustive search algorithm due to the brachad-boud techique. Let us ote that the y-axis i Figure 4 is log-scale value. Table 2 shows the average umber of BAG ad MTU pairs per virtual lik. As the MTCs become larger, the umber of possible solutios of each virtual lik is icreased, which requires more executio time, as show i Figure 4. Sice we use boud fuctios for badwidth ad jitter, the proposed oes are faster tha the previous algorithm i [].

8 8 Iteratioal Joural of Aerospace Egieerig Normalized badwidth ~60 60~0 0~60 60~20 20~260 Normalized executio time MTC Brute-force B-DFS EBFS Number of VLs Figure 5: Badwidth compariso. Table 2: The average umber of BAG ad MTU pairs per VL. BF DFS EDFS (a) -CONF MTC BAG ad MTU pairs per VL Next, we compared the badwidth reserved by the solutios of -BOPT with feasible solutios of -CONF. AsshowiFigure5,theproposedalgorithmfor- BOPT reduces much badwidth, so that the remaiig badwidth ca be used for other o-real-time etwork traffic. We also aalyzed the effect of algorithm executio times i terms of the umber of virtual liks. I Figure 6, we icreased the umber of virtual liks from to 6, where each virtual lik icludes two messages. As show i Figure 6, the executio time of brute-force search icreases expoetially sice the search space is O(2 N ).Letusotethaty-axis i Figure 6 is log-scale. Although the time complexity of the proposed algorithm is O(2 N ),bothedfs ad EBFS are much faster tha the previous algorithms i []. This is maily becauseweuseefficietboudfuctiosithealgorithms. The executio time of EBFS i case of 6 virtual liks is decreased sice the algorithm decides that there is o solutio i the upper-layer of solutio trees. Normalized executio time BF B-DFS EBFS Number of VLs (b) -BOPT Figure 6: Normalized executio times with respect to the umber of virtual liks.. Coclusios I this paper, we provided a efficiet algorithm to fid feasible cofiguratio of a switch for the purpose of meetig the real-time requiremets of all messages i avioics. Two importat parameters of BAG ad MTU of virtual liks are cosidered i the cofiguratio problem. The proposed algorithm is based o brach-ad-boud techique so that the simulatio results show that it is faster tha the exhaustive search algorithm of the previous work. We also provide a optimal solutio of the problem for the purpose of reducig the total badwidth of cofiguratio. Throughout simulatios, we showed that the algorithm rus fastadreducesmuchbadwidthcomparedwiththealgorithmtofidafeasibleset.theproposedalgorithmisuseful whe the remaiig badwidth for real-time traffic is used for other etwork traffic. Sice the etwork cofiguratio becomes a importat issue i avioics systems, we will ivestigate may problems based o the results of this paper. For example, we will exted the problem ito multiple switches or discuss the routig issues through the etworks.

9 Iteratioal Joural of Aerospace Egieerig 9 Coflict of Iterests The authors declare that there is o coflict of iterests regardig the publicatio of this paper. Ackowledgmets This work was supported by Basic Sciece Research Program through the Natioal Research Foudatio of Korea (NRF) fuded by the Miistry of Sciece, ICT & Future Plaig (o. NRF-205RAAA ), ad the BK2 Plus Program (Research Team for Software Platform o Umaed Aerial Vehicle, 2A ) fuded by the Miistry of Educatio (MOE, Korea) ad Natioal Research Foudatio of Korea (NRF). Refereces [] R. L. Alea, J. P. Ossefort, K. I. Laws, A. Goforth, ad F. Figueroa, Commuicatios for itegrated modular avioics, i Proceedigs of the IEEE Aerospace Coferece, pp. 8, IEEE, Big Sky, Mot, USA, March 200. [2] Tutorial, ifokiosk/techsat TUT--EN.pdf. [3] /ARNIC 664 Tutorial, guto/afdx detailed.pdf. [4] A. Al Sheikh, O. Bru, M. Chéramy, ad P.-E. Hladik, Optimal desig of virtual liks i etworks, Real-Time Systems, vol. 49, o. 3, pp , 203. [5] I. Saha ad S. Roy, A fiite state modelig of frame maagemet usig spi, i Formal Methods: Applicatios ad Techology,vol.4346ofLecture Notes i Computer Sciece,pp , Spriger, Berli, Germay, 200. [6] J. Täubrich ad R. vo Haxlede, Formal specificatio ad aalysis of redudacy maagemet algorithms, i Computer Safety, Reliability, ad Security, vol.4680oflecture Notes i Computer Sciece, pp , Spriger, Berli, Germay, 200. [] H. Charara, J.-L. Scharbarg, J. Ermot, ad C. Fraboul, Methods for boudig ed-to-ed delays o a etwork, i Proceedigs of the 8th Euromicro Coferece o Real-Time Systems (ECRTS 06), pp , Dresde, Germay, July [8] M.Tawk,X.Liu,L.Jia,G.Zhu,Y.Savaria,adF.Hu, Optimal schedulig ad delay aalysis for ed systems, SAE Techical Paper , SAE Iteratioal, 20. [9]J.J.Gutierrez,J.C.Palecia,adM.G.Harbour, Respose time aalysis i etworks with sub-virtual liks ad prioritized switches, i XV Joradas de Tiempo Real,Satader, 202. [0] D. Sog, X. Zeg, L. Dig, ad Q. Hu, The desig ad implemetatio of the etwork simulatio system, i Proceedigs of the Iteratioal Coferece o Multimedia Techology (ICMT 0), pp. 4, Nigbo, Chia, October 200. [] D. A, H. W. Jeo, K. H. Kim, ad K. I. Kim, A feasible cofiguratio of etworks for real-time flows i avioics systems, i Proceedigs of the Iteratioal Workshop o Real- Time ad Distributed Computig i Emergig Applicatios (REACTION 3), Vacouver, Caada, Decebmer 203.

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