SATELLITE-ATM NETWORKING AND CALL PERFORMANCE EVALUATION FOR MULTIMEDIA BROADBAND SERVICES

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1 EUROPEAN COOPERATION IN COST 252 TD (98) 38 THE FIELD OF SCIENTIFIC Veice, Italy, 6 November 998 AND TECHNICAL RESEARCH EURO - COST SOURCE: TASK: KEYWORDS: SRU (Uiversity of Surrey) WG2 MULTIMEDIA, S-, CALL PERFORMANCE SATELLITE- NETWORKING AND CALL PERFORMANCE EVALUATION FOR MULTIMEDIA BROADBAND SERVICES I. Mertzais, G. Sfikas, R. Tafazolli, B. G. Evas Cetre for Commuicatio Systems Research (CCSR), Uiversity of Surrey, Guildford, Surrey, GU2 5XH, U.K. Tel: ++44(0) , Fax:++44(0) , {I.Mertzais, G.Sfikas}@ee.surrey.ac.uk Abstract I this paper, we idetify the protocol referece model that best satisfies the requiremets of a itegrated solutio of the future broadbad satellite etworks with the Broadbad-Itegrated Services Digital Network (B-ISDN). I additio, the Coectio Admissio (CAC) mechaism that eeds to be implemeted to satisfy certai Grade Of Service (GoS) ad Quality Of Service 2 (QoS) criteria is discussed. A ew methodology for the call performace evaluatio of the Available Bit Rate (ABR) service class i a satellite Asychroous Trasfer Mode () etwork is proposed. Results at call level for differet mix of service classes are preseted usig both aalytical ad simulatio models. The simulatio model was developed usig OPNET modeller ad it was used to record statistics that caot be easily obtaied by aalysis. Defied as the call blockig probability 2 Defied i terms of Cell Loss Rate (CLR) ad Cell Delay Variatio (CDV)

2 . INTRODUCTION s are foresee as beig complemetary to the future fixed or terrestrial mobile etworks i order to provide coverage to remote users. O the oe had, curret work i the Europea ACTS (Advaced Commuicatios Techologies ad Services) [] projects such as SECOMS 3, ASSET 4, WISDOM 5 ad ACCORD 6 [2] cosider rates up to 2 Mbps for the satellite segmet ad iclude ew geeratio multi-spot beam satellites with advaced o-board processig capabilities. O the other had, targetig at high data rate multimedia services maily to fixed ad possibly portable user termials a large umber of Ka-bad (30/20 GHz) proposals exist such as: SPACEWAY, ASTROLINK [3], CYBERSTAR [4], TELEDESIC [5], N-STAR [6], WEST [7] ad EUROSKYWAY [8]. As suggested i [9], a ew modified versio of the protocol layer (kow as - layer, S-) is required. This proposal has bee further exploited ad a highly itegrated broadbad - etwork sceario is preseted. The rest of the paper is orgaised as follows: I the followig two sectios the satellite etwork architecture ad the protocol stacks are discussed. Sectio four presets the resource maagemet block diagram ad the mappig of the layer services to the (MAC) layer oes. The methodology that has bee developed is explaied i sectio five, alog with the assumptios made. The paper cocludes with the calculatio of the ad MAC layer resources as fuctios of the offered load, for two differet cases. 2. BROADBAND SATELLITE NETWORK ARCHITECTURE The satellite costellatio is the iitial parameter that affects the desig of a global etwork ifrastructure. Most of the proposed systems, cocetrate o the Geostatioary Orbit (GEO). For example: i Europe EUROSKYWAY by Aleia Aerospazio (Italy) ad WEST (GEO compoet) by Matra Marcoi Space (Frace/UK), i the Uited States ASTROLINK by Lockheed Marti, SPACEWAY by Hughes ad CYBERSTAR (GEO compoet) by Loral Space ad i Japa N-STAR by NTT. The o-geo systems are: TELEDESIC that proposed to use 288 Low Earth Orbit satellites (LEO) ad CELESTRI (LEO 63) which was recetly merged with the TELEDESIC proposal. At the same time, there are proposals based o hybrid costellatio approach usig GEO ad o-geo compoets; e.g. WEST ad CYBERSTAR. As far as the satellite groud etwork is cocered, the umber ad the locatio of the Lad Earth Statios (LES) depeds o the costellatio parameters ad o the provisio of Iter- Liks (ISLs) as well as the feeder lik badwidth requiremets. Aother parameter that iflueces the selectio of the satellite etwork architecture, is the depedecy o the terrestrial etwork ifrastructure. The satellite liks, are essetial for iter-statio sigallig whe there is o terrestrial ifrastructure deployed. For example, most GEO systems do ot eed groud statio itercoectio through terrestrial liks, whereas o-geo systems require oly a few satellite liks to the LESs whe ISLs are used, otherwise they are highly depedet o a fast backboe etwork. I GEO systems, ISLs are cosidered maily to hadle the traffic betwee differet regios of the earth ad to bypass the terrestrial liks whereas i most o-geo costellatios ISLs are essetial i order to reduce the umber of LESs. I a typical broadbad satellite system (see Figure ) the followig etwork etities are cosidered: User Termials (UT): Several differet protocol stadards such as: User Network Iterface (-UNI), Frame Relay UNI (FR-UNI), Narrowbad Itegrated Services Digital Network (N- ISDN) Basic Rate Iterface (BRI), N-ISDN Primary Rate Iterfaces (PRI), Trasmissio 3 EHF Commuicatios for Mobile Multimedia Services 4 ACTS Switchig Ed-to-ed Trials 5 Widebad Demostratio Of Multimedia 6 ACTS Broadbad Commuicatio Joit Trials ad Demostratio 2

3 Protocol / Iteret Protocol (TCP/IP). They are coected to the Adaptatio Uit (SAU) through oe of the supported stadard iterfaces. Adaptatio Uit (SAU): This is a o-stadard, specially desiged uit, resposible to provide access to the satellite etwork. It performs all the ecessary user termial protocol adaptatios to the satellite protocol platform. The SAU also icludes all the physical layer fuctios such as chael codig, modulatio/demodulatio, the Radio Frequecy (RF) parts ad the atea sectio. A set of differet types of termial with a variety of trasmissio capabilities ISL ISL O-Board Switchig UP lik processor DOWN lik processor O-board ler Telemetry & Trackig Commad system Coverage Areas Adaptatio Uit Sigle User Eviroemet TTC SAU User Termial GTW ISDN Multi User Eviroemet SAU Adaptatio Uit NCS Network Statio IWU GaTeWay Statio B-ISDN PSTN Iteret Frame-Relay Figure : etwork architecture ad coectivity with the fixed etworks. is usually offered by a satellite etwork. Startig from miimum trasmissio rates of 6 Kbps of eve less, they ca cope with maximum trasmissio rates of 44Kbps or 384Kbps for persoal type user termials, or eve 2,048Kbps ad higher for fixed type termials with larger ateas. All of the supported termials, share the same the access scheme ad protocols stacks. Payload (P/L): Full o-board satellite sigal re-geeratio is assumed i most of the future broadbad satellite systems. The o-board satellite processig uits perform multiplexig, demultiplexig, chael codig/decodig ad like switchig usig a multi-spot beam cofiguratio. The o-board satellite switch icludes oly part of the fuctios that a groud switch would perform. Most of the power hugry processig operatios such as the call set-up sigallig or the Coectio Admissio are performed o the groud. Gateway statios (GTW): These are the Lad Earth Statios (LES) that provide coectivity to the exteral etworks. Most of the future proposed broadbad satellite systems support itercoectio to the fixed B-ISDN, Frame Relay, N-ISDN, PSTN ad Iteret, via the proper iterworkig uits at the gateway. The level of iterworkig betwee the GTWs ad the terrestrial etworks depeds o the type of traffic that the satellite etwork carries. The SAU provides a access iterface very similar to the stadard -UNI, therefore the required iterworkig at the termial or at the GTW sides is miimised. The sigallig protocols for call ad coectio cotrol ca be reused (based o the ITU-T Q.293 stadard) ad the traffic ad etwork maagemet fuctios ca share commo characteristics. All service classes ca be supported ad directly mapped ito the satellite air iterface through the SAU. Fially, the 3

4 itercoectio iterfaces with all the other public terrestrial etworks should be based o stadards for iterworkig with B-ISDN. I GEO systems the placemet ad umber of GTWs o the groud segmet deped maily o the traffic demad. A large umber of gateways is expected i geographical areas where the traffic demad is high ad these gateways are always coected with the same satellite(s). However, i o-geo systems the umber ad placemet of the gateway statios depeds o some additioal system desig characteristics such as: costellatio desig, use (or ot) of ISLs ad the overall ed-to-ed system delay budgets. For example, i a global MEO system with o iter-satellite liks, a total umber of less tha 0 gateways ca provide full coectivity to the lad masses most of the time. A LEO system will require tes to hudreds of gateways but this umber ca be reduced with the use of ISLs. Network Statio (NCS): A cetral etity, used i a GEO satellite system (usually oe per satellite) that provides overall cotrol of the satellite etwork resources ad operatios. This ode is resposible for allocatig radio resources to the LESs/GTWs accordig to a log term resource plaig scheme. The NCS is resposible for performig most of the resource maagemet, call maagemet ad user/termial mobility maagemet fuctios i additio to autheticatio, registratio, de-registratio ad billig. I some systems, these operatios are performed i more tha oe groud statios i a distributed maer. 3. SATELLITE ACCESS INTERFACE AND PROTOCOL STACKS The proposed protocol stacks for both the cotrol ad the user plae i a satellite etwork are show i Figure 2. I [9], the use of the S- layer has bee proposed for the space segmet. The ad the radio physical layers reside below the S-. The fields that are preset i the S- cell header carry essetial routig ad cotrol iformatio for the satellite segmet ad deped o the implemetatio of the o-board satellite switch. The dimesioig of the Virtual Path Idetifier (S-VPI) ad the Virtual Chael Idetifier (S-VCI) fields User Termial & Adaptatio Uit Plae Protocols Network Statio Switch User Termial & Adaptatio Uit User Plae Protocols UNI Sigallig UNI/NNI Sigallig NNI/UNI Sigallig APPLICATION Higher Layers APPLICATION Higher Layers SAAL SAAL Gateway Statio SAAL AAL Gateway Statio AAL S- S- S- S- S- S- S- Network Network Network Ed User Figure 2: based protocol referece model depeds o system parameters such as: the satellite capacity, the umber of spot-beams, the satellite termial trasmissio graularity ad the switch architecture. Sigallig for call cotrol is based o the Q.293 protocol stadard ad is termiated o the groud segmet. I the case of mobile or portable termials, future stadards by Forum or ITU-T for B-ISDN sigallig ad Itelliget Network (IN) ca be supported i a highly itegrated etwork eviromet. All the satellite specific fuctios ca be defied iside the S- layer ad cotrol messages ca be trasmitted through the F4 ad F5 Operatio ad Maiteace (OAM) cell flows. 4

5 4. RESOURCE MANAGEMENT AND CONTROL Oe of the mai areas of iterest i broadbad teletraffic egieerig is the provisio of multimedia services with QoS guaratees to a large umber of users while maitaiig high system resource utilisatio. I systems where user applicatios ca share commo etwork resources some level of coectio admissio cotrol is required i order to provide fairess ad to guaratee that the requested QoS criteria are met. I a broadbad satellite etwork a two level call acceptace cotrol algorithm must be cosidered; the first at the MAC layer ad the secod at the layer. As show i Figure 3, the resource maagemet ad cotrol fuctios are distributed betwee the space ad the groud segmet. The o-board satellite switch is resposible to provide full coectivity from ay up-lik to ay dow-lik spot beam ad it is cotrolled by the switch cotrol uit ad the Call (CC) ad the CAC uits. The physical locatio of the blocks that implemet the CC ad the CAC fuctios ca be o the groud i order to reduce the o-board processig requiremets. The up-lik ad dow-lik resource cotrol uits are resposible for the icomig ad outgoig traffic maagemet actios at the iput ad the output ports of the switch respectively. The overall etwork resource maagemet fuctio is performed by the Resource Maagemet (RM) cotroller which supervises the operatio of the MAC ad the resource maagers. 4. Mappig service classes ito the air iterface Space Segmet U p l i k B e a m U p l i k B e a m MAC Service Classses Class 0 Class Class i Class 0 Class Class i C i C i Up-lik Resource I Ports N X N switchig module N Out Ports N O-Board Switch Service Classses CBR rt-vbr rt-vbr ABR UBR CBR rt-vbr rt-vbr ABR UBR C out C out Dow-lik Resource D o w - li k B e a m D o w - li k B e a m Groud Segmet MAC Resource Maager CC & CAC RM ler Resource Maager Figure 3: Resource Maagemet ad block diagrams The flexibility i desigig a MAC scheme for a GEO satellite system, is limited maily by the log propagatio delay. Therefore, i most of the proposed schemes at least a miimum up-lik badwidth reservatio takes place for most of the supported service classes. All services ca be classified at the MAC layer accordig to the umber of slots that are assiged i the up-lik directio i additio to the time period for which the resources are allocated (i.e. permaet, semi-permaet, o demad). For bi-directioal services each lik is set-up idepedet from each other but i our study we did ot 5

6 take the forward traffic requiremets ito cosideratio. A Multi Frequecy Time Divisio Multiple (MF-TDMA) access scheme is cosidered i our study. Five distict service categories have bee specified by the Forum [3] to accommodate all the differet applicatios: Costat Bit Rate (CBR), rt-vbr (real-time Variable Bit Rate), rt-vbr (o-real time VBR), Uspecified Bit Rate (UBR) ad Available Bit Rate (ABR). We assume that all service classes except the UBR share the same pool of up-lik resources. This is because UBR is the oly service that a hybrid approach which combies both radom access ad a reservatio based resource allocatio algorithm should be used, if we wish to provide a certai level of QoS. Durig the call set-up phase, the CBR, rt-vbr ad rt-vbr services are assiged a fixed umber of up-lik slots which remai costat for the duratio of the call. Therefore, some multiplexig gai ca be achieved oly at the layer by limitig the available resources at the switch output queues. For the ABR service, a more flexible access scheme is proposed. A ABR call is accepted or blocked at the MAC layer accordig to its Iitial Cell Rate (ICR), or Miimum Cell Rate (MCR) requiremets. After the call is accepted, all the slots that remai free i the up-lik directio ca be shared amog all ABR users i order to satisfy the istataeous requiremets for icreased badwidth. If we wat to maitai certai call blockig rates for all the supported service classes at the MAC layer, the available slots which are shared amog all ABR services should be used i such away, that does ot affect the ew call blockig rate of ay service type. The determiatio of the call blockig probabilities of N differet service classes each oe requestig for costat rate of c i from a shared lik of capacity C ca be performed with some widely used multi-rate models if a complete sharig admissio policy is assumed. Each service class is characterised by a arrival process which is assumed to be Poisso with mea call arrival rate λ i ad call holdig times followig a geeral distributio with mea call holdig times µ i. The aalysis of multi-rate models is well preseted i existig literature ad product form solutios for the state probabilities ca be foud i [0, ]. However, the solutio to this problem becomes itractable as the umber of states ad service classes icreases. Therefore, a recursive solutio that was give to this problem by [2] simplifies the calculatios for a large umber of service classes ad system states. Both the uormalised probability P u (m) of m occupied badwidth uits ad the ormalised probability P(m) are give by: P u : m = 0 ( m) = 0 : m < 0 N λ i Pu( m mi ) mi : 0 < m M m i= µ i ( ) = ( ) M P m Pu m Pu ( m) () m= 0 where M = C/dc, m i = c i /dc ad dc represets the greatest commo divisor of c i.. The blockig probability per class ca be calculated from: P bi = M P( m) m= M mi + (2) 5. CALL PERFORMANCE EVALUATION Each coectio i a etwork is associated with a set of traffic parameters i additio to a set of egotiated ad o-egotiated QoS parameters [3]. Durig the call establishmet phase, oe importat etwork operatio is the evaluatio of the QoS impact of the ew call o the accepted calls that share commo resources. CAC is the etwork fuctio that decides if a ew call should be accepted or ot. A ew call ca be blocked if there are ot eough resources either at the MAC or at the layer. Aalytical models ca be very complex whe cosiderig multi-rate services at both call ad cell level ad a simulatio model that rus at cell level will require extremely log processig period to produce accurate results at call level. Therefore, a hybrid approach was take 6

7 that combies a call level simulatio of multi-rate, multi-class services ad icorporates look-up tables that provide the resource utilisatio statistics for differet service classes. These tables ca be geerated by usig proper aalytical or simulated traffic source modellig techiques depedig o the service type. 5. CBR Service A fixed umber of up-lik slots are allocated for a CBR call; this umber correspods to the source Peak Cell Rate (PCR). No multiplexig gai ca be performed at the MAC layer from termials that share the same up-lik resources due to the real time costraits. However, depedig o the activity of the source, multiplexig gai ca be achieved at the layer. For the simulatio it was assumed that voice traffic was supported over the CBR service. Each source was modelled as a ON-OFF process with egative expoetial call holdig time ad the the aalysis preseted i [4] was used to obtai the utilisatio of the allocated resources as a fuctio of the umber of users, for differet QoS (expressed i terms of CLR ad maximum queuig delay, at the switch). 5.2 rt-vbr The rt-vbr service is iteded for o real time applicatios that have bursty traffic characteristics ad characterised i terms of PCR, Sustaiable Cell Rate (SCR) ad Maximum Burst Size (MBS). For the cells that are trasferred withi the traffic cotract, the applicatio expects low CLR. To simplify our calculatios we assume that the MAC resources are allocated i a similar way to the CBR service (circuit switch allocatio usig the SCR istead of the PCR). No multiplexig gai ca be obtaied at the level, sice detailed traffic sources for this service have ot bee implemeted. The SCR is also used at the layer to allocate () resources to each user. The user is resposible for maagig its ow trasmissio rate depedig o the termial buffer size. 5.3 rt-vbr Real-time VBR services are also treated similar to the CBR service at the MAC layer. However, the umber of the allocated up-lik slots is related to the SCR ad ot to the PCR. For the simulatio it was assumed that video traffic was supported over the rt-vbr service. The traffic was modelled as i [5]. Similar to CBR, the resource utilisatio was calculated as a fuctio of the umber of users ad the expected QoS, i order to cosider the multiplexig gai at the switch. 5.4 ABR Service Durig the coectio set-up phase, the followig traffic parameters are egotiated for the ABR service types: the Iitial Cell Rate (ICR), the Miimum Cell Rate (MCR) ad the Peak Cell Rate (PCR). A ABR source is allowed to trasmit cells at a Allowed Cell Rate (ACR), which varies over time depedig o the etwork cogestio status. The mechaism to chage the source ACR is based o the trasmissio of RM cells that traverse ed-to-ed from the source to destiatio (forward directio) ad are looped back to the origiatig source i the backward directio. The cotets of the RM cells ca be chaged by the destiatio or the itermediate odes by alterig the Cogestio Idicatio (CI) bit ad the Explicit Rate (ER) fields ad the source ACR is adjusted accordig to these fields. The etwork cogestio idicatio mechaism depeds o the switch architecture ad ca be Explicit Forward Cogestio Idicatio (EFCI)-based switch or ER-based switch. A set of time-out mechaism exists i this type of flow cotrol to overcome the problems arisig from erroeous cells. The efficiet operatio of a rate-based cogestio cotrol mechaism depeds o the careful switch buffer dimesioig procedure i order to avoid cell loss. I geeral, ER based switches perform better tha the EFCI but are harder to be implemeted. For log ed-toed cotrol loops such as those that are icluded i a GEO satellite etwork, it is suggested that smaller cotrol segmets should be cosidered (at least two segmets must be created; oe for the radio part ad oe for the fixed part of a coectio. I this paper, oly the radio parts of all coectios were cosidered ad o particular algorithm (either at the MAC or at the layer) that supports badwidth o demad for ABR services has bee take ito accout. Therefore, the 7

8 simulatio model was used maily to produce statistics that express the resources that remai free to be used by the ABR services at both the MAC ad the layers as a fuctio of the total offered load uder differet traffic scearios. 5.5 Traffic Scearios ad simulatio approach A simulatio model was implemeted i OPNET modeller i order to evaluate the performace of multi-class, multi-rate services. Four differet service classes were idetified. Each service class is characterised by a umber of up-lik slots that are requested by the MAC layer ad a rate which is used for the layer resource utilisatio calculatios. The mai objective of this work is the evaluatio of the resources that are available to be used by the ABR service. Therefore, all ABR services that are accepted at the MAC layer have o resource limitatio at the layer (i.e. their rate is always zero) ad there is o ew call blockig at the layer for ay service. However, calls that caot be admitted at MAC layer are blocked ad cleared from the system. The Service Class MAC Slots parameters Service Class Traffic Sceario Class 0 PCR=, activity factor=0.4 Class 2 4 MCR=2 MCR=4 CBR, Voice, CLR=0E-3, 30ms max queuig delay Mea Call Arrival Rate (λ i ) system capacity, for the simulatio scearios preseted i Table, was set to C = 00 up-lik slots. Two differet traffic scearios were simulated. I traffic sceario I all service classes (0,,2,3) cotribute equally to the total offered load. I traffic sceario II, the cotributio of each service class is 20%, 40%, 20% ad 20% of the total offered load. New calls are geerated accordig to a Poisso distributio; the call duratio follows egative expoetial distributio with average value (all the other parameters are ormalised to this value). ABR ABR I & II I II Variable Variable Variable Class 2 4 SCR=4 rt-vbr, Data I & II Variable Class 3 0 PCR=0, SCR=4, MBS=300 cells rt-vbr, Video, CLR=0E- 5, 30ms max queuig delay at each layer (MAC ad ) I & II Table : Simulatio service scearios, defiitio of classes ad parameters. Variable 6. SIMULATION RESULTS AND DISCUSSION The call blockig probability as a fuctio of the offered load is preseted i Figure 4 ad 7 for traffic scearios I ad II respectively. As expected, the service classes that request for a higher umber of MAC slots experiece higher call blockig rates. The simulatio results are i full agreemet with those obtaied by aalysis (see equatios ad 2) therefore, the simulatio model was used to record very useful statistics that caot be easily provided by aalysis. As show i Figure 7, the service classes ad 2 (traffic sceario II) experiece the same call blockig rate although they represet differet service classes (ABR ad rt-vbr). Therefore, if there is oadmissio cotrol applied by the etwork, the traffic from differet service classes is regulated oly by the MAC layer. However, from the resource utilisatio statistics that are plotted i Figure 5 ad Figure 8 for both traffic scearios, it is clearly show that differet admissio cotrol policies are applicable at the layer. 8

9 0 0 Traffic Sceario I Blockig Probability Resource Utilisatio(Normalised) MAC (Classes 0,,2,3) (Classes 0,2,3) (Class 0, CBR) (Class 3, rt VBR) (Class 2, rt VBR) 0 4 Class 0, CBR Class, ABR Class 2, rt VBR Class 3, rt VBR Simulatio Figure 4: Call blockig rates, sceario I Figure 5: Resource Utilisatio, sceario I Traffic Sceario I 0 0 Traffic Sceario II Resource Utilisatio(Normalised) Blockig Probability MAC resources available for ABR Used resources (Classes 0,2,3) Total Resousrces (Upper Boud, All Classes) Class 0, CBR Class, ABR Class 2, rt VBR Class 3, rt VBR Simulatio Figure 6: ABR Res. Availability, sceario I Figure 7: Call blockig rates, sceario II Traffic Sceario II Resource Utilisatio(Normalised) MAC (Classes 0,,2,3) (Classes 0,2,3) (Class 0, CBR) (Class 3, rt VBR) (Class 2, rt VBR) Resource Utilisatio(Normalised) MAC resources available for ABR Used resources (Classes 0,2,3) Total Resousrces (Upper Boud, All Classes) Figure 8: Resource Utilisatio, sceario II Figure 9: : ABR Res. Availability, sceario II Traffic Sceario I, Total offered Load = 0.72 Available MAC Reources for ABR Services (Normalised) Traffic Sceario I Traffic Sceario II Propability(X) X = Resources Utilisatio (excludig ABR) Figure 0: ABR Res. Availability at MAC layer 9 Figure : resource utilisatio, classes (0,2,3)

10 Sice the fuctio that calculates the resource utilisatio for the ABR service at the layer was ukow, the resource utilisatio statistics from all the service classes excludig the ABR were collected ad preseted i Figure 6 ad Figure 9 for traffic scearios I ad II respectively. By addig these graphs to the graphs that represet the resources that are available at the MAC layer for the ABR services (see Figure 0) the upper bouds of the total resource utilisatio are clearly show. These values are ormalised to the overall MAC resources. The Probability Desity Fuctio (PDF) of the resource utilisatio excludig the ABR services is show i Figure (traffic sceario I, total offered load = 0.72). From these results, we ca easily plot the PDFs of the ABR resource availability at the layer for differet values of the overall resources. I fact, ay coectio admissio cotrol algorithm that is applied to the ABR service will try to restrict the switch capacity requiremets by takig ito accout the maximum multiplexig gai that ca be achieved. I ay case, the overall switch capacity should be less tha the upper boud values show i Figure 6 ad Figure 9 for the traffic scearios I & II. 7. SUMMARY I this paper, a overview of the etwork aspects of the future - etworks is give, cocetratig o the resource maagemet ad the traffic cotrol issues. A block diagram of the cotrol fuctios that are distributed betwee the space ad the groud segmet is preseted alog with the mappig of the layer services to the MAC layer service classes. I additio, a ew methodology for evaluatig the performace of multi-rate, multi-class services is described. It calculates the call blockig probability per service class at the MAC layer ad the resources utilisatio. Assumig a MAC layer that supports badwidth o demad, all the available resources ca be allocated to the ABR service without affectig the GoS of the rest of the service classes. Simulatio results are preseted for two traffic scearios. Future work icludes the additio of a traffic model for the rt-vbr service i order to iclude the additioal multiplexig gai at the layer. 8. REFERENCES [] [2] [3] E.Elizodo, F.Gargioe, R.Gobbi ad K.Shockey, ASTROLINK system overview, Secod Kabad Utilizatio Coferece ad Iteratioal Workshop o SCGI, Florece, Italy, 24,26 September 996. [4] R. G. Leamo et all, CYBERSTAR, 3 rd Ka-bad Utilisatio Coferece, Sorreto, Italy, 5-8 September 997. [5] [6] T.Otsu K.Okada Y.Fukuyo M. Miomo, Ka-Bad Commuicatio Systems Operatig through NTT s Commuicatio N-STAR, 3 rd Ka-bad Utilisatio Coferece, Sorreto, Italy, 5-8 September 997. [7] B. Le Stradic, M.Vaissiere, N. Boudier, O. Bowles, The WEST Project: Exploitig the Ka-bad Spectrum to Develop the Global Iformatio Ifrastructure, 3 rd Ka-bad Utilisatio Coferece, Sorreto, Italy, 5-8 September 997. [8] G. Losquadro, The EUROSKYWAY System for Iteractive Multimedia Operatig with Feed- Back Aided Traffic Maagemet, 7 th AIAA Iteratioal Commuicatios Systems Coferece ad Exhibit, Yokohama, Japa, February 998. [9] I. Mertzais., R. Tafazolli, B.G. Evas: Protocol Architecture Scearios for ad B-ISDN Network Itegratio, 3 rd Ka Bad Utilisatio Coferece, Sorreto, Italy, September 997 0

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