OSI Model. SS7 Protocol Model. Application TCAP. Presentation Session Transport. ISDN-UP Null SCCP. Network. MTP Level 3 MTP Level 2 MTP Level 1

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1 Direte Event Simulation of CCS7 DAP Benjamin, AE Krzeinki and S Staven Department of Computer Siene Univerity of Stellenboh 7600 Stellenboh, South Afria fbenj,aek,taveng@.un.a.za ABSTRACT: Complex imulation model are omputational expenive. Parallel and ditributed imulation oer a method for imulating large ytem. A ditributed direte event imulator i being developed to model ITU-T Common Channel Signalling Sytem No. 7 (CCS7) network. The ditributed omputing environment onit of a olletion of networked miro-kernel upporting interproe ommuniation whih allow proee to exhange information independent of their phyial loation. The DCE allow a dynamially alable imulator to be implemented on a network of worktation. Introdution The performane of teleommuniation network an be evaluated uing analytial model, uing imulation and by taking meaurement of the network. In the pat the rt two approahe had a major limitation in term of their alability. However advane in hardware, oftware and algorithm for ditributed ytem have allowed imulation model to beome an attrative evaluation method. Thi paper i organized a follow. Setion introdue the bai terminology for deribing a CCS7 network. Setion 3 preent a brief motivation for ditributed imulation. Setion 4 deribe the imulator. Setion 5 deribe a mall CCS7 network to be imulated. Setion 6 deribe a queueing network model of the CCS7 network. Setion 7 preent ome of the performane meaure of the network. Thi work i upported by a grant from the Telkom SA Teletra Initiative Programme. CCS7 The ITU-T Common Channel Signalling Sytem No. 7 (CCS7) i a paket-withed network whih arrie all ignalling meage independently of the underlying teleommuniation network that it upport. Digital telephone exhange rely on CCS7 to failitate ommuniation between exhange, whih allow the eparation of ignalling element from the bearer element in the network. The reult i improved performane and the ability upport new ervie. A CCS7 network onit of two type of node alled ignalling point (SP) and ignalling tranfer point (STP), interonneted by ignalling link. SP are node where ignalling meage originate and terminate or in whih proeing of the meage take plae at an appliation level. STP are paket withe whih determine the next node to whih a meage i to be routed, elet appropriate ignalling link and aure delivery of the meage in proper equene. Figure how the truture of the CCS7 protool and how it relate to the OSI layered model. The Network Servie Part (NSP) of the CCS7 network onit of a Meage Tranfer Part (MTP) and a Signalling Connetion Control Part (SCCP) and orrepond to the Network/Data Link/Phyial layer tak in the OSI model. The NSP provide for reliable tranfer of meage between appliation part of CCS7. The ISDN Uer Part (ISUP) provide the ignalling funtion needed to upport the bai bearer ervie, a well a upplementary ervie, for withed voie and non-voie appliation in an ISDN environment. Prior to the ISUP, the Telephone Uer Part (TUP) wa peied to provide ignalling funtion to upport ontrol of telephone all on national and international onnetion. ISUP provide all of the funtionality of the TUP,

2 OSI Model Appliation Preentation Seion Tranport Network Data Link Phyial SS7 Protool Model OMAP ASE TCAP ISDN-UP Null SCCP MTP Level 3 MTP Level MTP Level everal omputer. A onurrent program onit of everal equential proee that ooperate to perform a pei tak []. The proee ommuniate with eah other in order to oordinate their ativitie. Communiation between proee i done by aeing data in hared memory or by tranferring data in meage. The main reaon to write ditributed appliation are: to ahieve high peed through parallelim OMAP = Operation Maintenane and Adminitration Part ASE = Appliation Servie Element TCAP = Tranation Capabilitie Appliation Part ISDN-UP = ISDN Uer Part SCCP = Signaling Connetion Control Part MTP = Meage Tranfer Part Figure : CCS7 protool arhiteture plu many enhanement for non-voie all and advaned ISDN and Intelligent Network (IN). The Tranation Capability Appliation Part (TCAP) provide appliation-layer protool that allow an appliation at one node to invoke the exeution of proedure in another node and exhange the reult of uh an invoation. There are no layer in the CCS7 protool that orrepond to the OSI Preentation, Seion and Tranport layer. Other uer of TCAP are the Operation, Maintenane, and Adminitration Part (OMAP) and the Mobile Appliation Part (MAP). OMAP provide the appliation protool and proedure to monitor, oordinate, and ontrol the network reoure that make ommuniation baed on CCS7 poible. MAP provide the ignalling apabilitie needed to upport mobile apabilitie in a mobile network. 3 Motivation Computing failitie typially onit of powerful time-haring erver aeed via worktation on a loal area network. Many of thee worktation are often idle. Thee idle worktation an be utilied by uing them a a multiomputer [9]. A multiomputer i a ditributed hardware arhiteture oniting of multiple omputer onneted via a network. Single appliation an be peeded up by implementing them a onurrent program running on to ahieve high reliability through repliation ome appliation are inherently ditributed beaue they exeute on phyially ditributed omputer. A imulation i well uited for implementation a a ditributed program. By parallelizing an algorithm, one may gain ubtantial performane benet by utilizing the latent proeing power of many worktation onneted on a network. Direte event imulation operate on a ytem of omponent (phyial proee) that interat by direte ation. Thee direte ation an be embodied a meage paed between the variou omponent. 4 Simulator 4. Hardware platform The Hybrid mirokernel [4, 5] wa developed at the Univerity of Stellenboh for implementing lienterver appliation. The kernel exeute on Intel 80x86 proeor (x 3). The kernel upport ditributed appliation and a ditributed programming upport environment run at uer level on the kernel [8]. The kernel upport a worktation operating ytem and other appliation onurrently. Eah mahine in thi Ditributed Compute Environment (DCE) periodially report in to the DCE Manager. Figure how a typial etup of the DCE Manager. It ontain the following information: the name of the worktation, available memory, CPU utilization, uptime (DD+HH:MM) and idle time (HH:MM). Uer an deny the ue of their mahine in the DCE environment. When a proe i to be reated on a mahine, a query i made to the DCE Manager. If the mahine i uable then

3 Agent Free CPU Uptime Idle Agent Free CPU Uptime Idle Lab0 Lab0 Lab03 Lab04 Lab05 Lab06 Lab07 Lab08 Lab0 Lab Lab3 Lab4 Lab0 Lab 430K 500K K 800K 500K K K 00+0:4 00+0: :47 0+4: : : :35 +6:30 0+:9 0+:56 0+6: : : :3 0:4 0:44 :58 3:58 0:59 0:45 0:46 **:4 35:30 **:07 64:5 0:07 0:43 0:36 Lab 500K Lab33 500K aterix 6864K bart 5388K loet 544K durnik 56K evinrude 5904K hairy 4040K magrat 6300K obelix 608K roebud 6784K zoe 3900K zue 3908K : :5 00+0:00 0+8: :44 0+8: :45 0+3:6 0+:4 0+4:03 0+0: :6 00+8:0 **:4 **:46 00:09 00:07 00:00 66:48 00:00 0:30 0: 00:9 :43 00:06 00:00 Figure : DCE Manager the DCE Manager return the information needed to tart the proe on the remote mahine. Hybrid make ue of meage paing to enable proe ynhronization. VMTP [3] wa implemented to upport reliable interproe ommuniation, thu failitating the tranparent exhange of information between proee, regardle of their phyial loation. Hybrid mahine are alo able to ommuniate with other mahine uing the TCP/IP protool uite. 4. Software platform The Oberon language [0] wa deigned to erve a an implementation tool for the Oberon ytem [3], an eient, onie operating ytem founded on objet-oriented programming. The Oberon language i a modet extenion, and a trongly treamlined deendant of Modula-. The Oberon language i dened in term of few, fundamental programming onept, it i rigorouly trutured, and it i eiently implemented on everal modern omputer arhiteture. The primary benet of uing Oberon i the proviion for type extenion on the bai of etablihed, well-undertood notation of data type and proedure. The Oberon ytem ha a Graphial Uer Interfae (GUI) management ytem (Figure 3) named Gadget. It allow the run-time ontrution of uer interfae from building blok alled gadget. The ytem provide a bai et of often ued gadget. The uer ombine gadget at runtime to build omplex gadget from impler one. Gadget at a funtionally independent unit that an be ued in any environment, allowing them to be integrated in eah other, or into text, drawing ytem, page layout heme' et. Another ad- Figure 3: Gadget GUI vantage i that uer interfae are ontruted independently of the appliation. Thi allow uer to modify and utomie the interfae, or to extrat ueful omponent from other appliation. The Oberon ytem ha been ported to Hybrid together with the Gadget environment. Programmer an add their own funtionality to the ytem by building new gadget, or extending exiting gadget uing objet-oriented tehnique. Uer or programmer an take ontrol of their own gadget uing either the Oberon programming language or a imple ript faility. The Gadget ytem provide a powerful imaging model that help to redue the burden of programming graphial appliation. 4.3 Management platform The Oberon GUI i being ued to develop the graphial front-end to the imulator. It make the prototyping of the uer interfae impler without the need to ontinually rewrite large amount of ode. Thi graphial front-end erve a a Management Station olleting information from variou node in the network, diplaying thee tatiti (load of the node, number of all per time unit, available node, failed node and ongeted node) in an eaily undertandable format. Figure 4 how a mall etion of the management interfae. In order to tranparently utilize the latent proeing power in the multiomputer network, the

4 aterix zoe Node Server v.0 Start Monitor Stop Monitor Add Node Kill Node Get Stat Lab09 Lab Lab3 Lab5 Lab6 Lab9 Lab Lab3 Lab5 aterix zoe Idle? Avaliable Node vmtat In Ue On 6 Node Server v.0 Stating monitor Started node aterix Started node zoe Started node Lab5 Killed node Lab5 zoe aterix 5 Figure 4: Management Station 4 3 uer of the ative worktation mut be unaware of the imulator. For thi reaon all ontrol and querie to proee on the worktation are initiated from a remote mahine. In thi way one an ongure and maintain tatiti of the entire network from one entral mahine. When the imulator i initially tarted, it read in a onguration le. Thi onguration le i ued to etup the CCS7 network and default value for the omponent in thi imulated CCS7 network. One thi i omplete the imulated CCS7 network i now fully uer ongurable. The uer i preented with a lit of available node of the multiomputer and the relative peed of eah node. Apart from being able to alter the initial onguration le the uer i alo able to re-dimenion the imulated CCS7 network (remove or add STP', SP', and ignalling link) via a imple drag and drop interfae. To failitate the eay reonguration of the node in the imulated CCS7 network a mehanim i provided whereby the uer only ha to lik on a node, to be preented with a lit of poible onguration option (node failure, node ongetion, and hanging the apability of a node). A typial etup for the imulator would be to imulate one CCS7 node per multiomputer node. In thi way eah mahine i reponible for the proeing overhead of one node. The diadvantage i the penalty inurred in the form of tranmiion overhead of the ynhronization meage. The maximum onurreny of a imulation an be ahieved when one imulation element i aigned to eah node []. Figure 5: The CCS7 Network The heduler of eah node mut be ynhronized in order to enure the orret equene of event over the ditributed imulator. A entral Time Server [] determine the orret equene of ation for the node in the network. 5 CCS7 Network Figure 5 how the onguration of a mall CCS7 network [6] oniting of ix ignalling region and ix fully interonneted STP. Eah ignalling region ontain everal SP, repreented by the retangle, and eah SP i onneted to two STP, repreented by the irle. Beaue the network i mall, it lend itelf well to analyti modelling tehnique to ompute performane meaure. Thi i not the ae for real CCS7 network beaue they are large and omplex. The paket in the network are routed aording to a hortet path algorithm whih ue the hortet path between adjaent ignalling region. Average and wort ae end-to-end paket delay are ued to ompare the performane of the network under normal and fault ondition. The latter our when the STP fail; up to three failure are invetigated. Figure 6 how the enario for one and three STP failure of whih ome reult will be preented in Setion 7. Time ynhronization i an important implementation onideration when building a ditributed appliation. One of the hief omponent of the node in the imulated CCS7 network i the heduler.

5 6 where C air and C ir are the quared oeient of variation of the la r interarrival and ervie time ditribution at entre i repetively. 5 4 (a) One STP failure 3 4 (b) Three STP failure 3 The average queue length P Q r of la r paket M in the network i Q r = i= Q ir. From Little' law, the average delay T r for la r paket in the network i T r = Q r = r and the average delay T for any paket in the network i given by T = RX RX Q r = r= r= r Figure 6: Fault ondition 6 Queueing Network Model An open queueing network i ued a performane model and the denition for it are a follow:. There are M = (6 7) + (6 ) = 54 unidiretional link, eah of whih i modeled a a ingle erver FCFS queue.. Cutomer lae are formed per region o that the number of lae i R = 6, and eah region generate tra whih form a tream of rate r, r R. The TUP/ISUP tra generated at eah region i alulated a r = C r 000 p L where C r i the number of all attempt originating from region r in Kilo Buy Hour Call Attempt, p i the perentage of ueful a well a unueful tra generating all and L i the average length of a data paket generated per all in otet. One paket per all i aumed. 3. Eah queue ha a ervie rate with parameter ir, i M. 4. The average arrival rate of la r paket in queue i i ir, i M, r R, determined by the routing algorithm. The average queue length Q ir of a GE=G= i given by [] Q ir = ir + C air + RX (? i ) u= ir iu iu C iu + C aiu The wort ae paket delay are alulated a the maximum average delay aro all route in the network. Beaue eah queue at a an independent queue, the average paket delay of a path in the network i the um of the time delay of eah queue in the path. 7 Reult SP C r Table : Call attempt in the network The tra load for the region are hown in Table in KBHCA. It i aumed that the tra generated from a SP region i equally ditributed among all ix SP region. The hortet path algorithm wa found to have the bet performane of three xed paket routing algorithm, irrepetive of the value of the variane of the interarrival and ervie time ditribution []. The average paket delay T r for the fault ondition of three STP failure (Figure 6(b)) for ignalling region,,3 and 4, a well a the average delay T for all region, i hown in Figure 7, for different value of the quared oeient of variation of the interarrival and ervie time ditribution, both indiated by C. The larger the quared oef- ient of variation, the greater the delay. Note that when C =, the analyi i idential to BCMP queueing analyi and the known BCMP reult for the network are obtained [7]. 8 Conluion The reult preented in Setion 5, 6 and 7 were obtained uing an analytial model. Thee reult

6 T r C = 0: C = :0 C = 0 [6] A. A. Lazar, K. H. Teng, and K. S. Lim. Delay Analyi of the Singapore National CCS#7 Network Under Fault and Unbalaned Loading Condition. In Pro. ICCS/ISITA '9, page 994{998, Singapore, 99. [7] A. A. Lazar, K. H. Teng, and K. S. Lim. Routing Algorithm Analyi of the Singapore National SS7 Network under Fault and Unbalaned Loading Condition. In Pro. ITC Seminar, page 99{06, Bangalore, India, SP SP SP 3 SP 4 T Figure 7: Delay (T r ) in m are now being ompared with thoe obtained from the imulator in order to validate the orret funtioning of the imulator. The analytial model ompute the teady-tate performane of a network. The imulator will ompute the tranient behavior of thee network and thu lead to a better undertanding of the network. Referene [] G.R. Andrew. Conurrent Programming: Priniple and Pratie. Benjamin/Cumming Publihing Company, 99. [] D. Benjamin. Direte Event Simulation of SS7. In Regional International Teletra Conferene, page 58{56, Pretoria, South Afria, 4 { 8 September 995. Telkom. [8] P. J. Muller. An Environment for Ditributed Programming on a Multiomputer. Mater' thei, Univerity of Stellenboh, February 994. [9] D.A. Reed and R.M. Fujimoto. Multiomputer Network: Meage-Baed Parallel Proeing. The MIT Pre, 985. [0] M. Reier and N. Wirth. Programming in Oberon: Step Beyond Paal and Modula. Addion-Weley Publihing Company, ACM Pre, New York, 99. [] S. Staven and A. Krzeinki. Maximum Entropy Method for the Performane Evaluation of SS7. In Regional International Teletra Conferene, page 8{89, Pretoria, South Afria, 4 { 8 September 995. Telkom. [] W. Su. Reative-Proe Programming and Ditribyted Direte-Even Simulation. Tehnial Report, Department of Computer Siene, Univerity of Florida, Otober 989. [3] N. Wirth and J. Gutkneht. Projet Oberon: The Deign of an Operating Sytem and Compiler. Addion-Weley Publihing Company, ACM Pre, New York, 99. [3] D.R. Cheriton. VMTP: Veratile Meage Tranfer Protool. RFC 045, Stanford Univerity, 988. [4] W. Fouhe. An Eient Kernel to Support the Client-Server Model. Mater' thei, Univerity of Stellenboh, September 99. [5] W. Fouhe and P.J.A. de Villier. A Reuable Kernel for the Developement of Control Software. Proeeding of the 6th Southern Afrian Computer Sympoium, page 83{94, 99.