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Компьютеры, Программирование Компьютеры и периферийные устройства
Evaluating the GPRS Radio Interface for Different Quality of Service Profiles |
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Крючки с поводками Mikado SSH Fudo "SB Chinu", №4BN, поводок 0,22 мм. Abs rac . his paper prese s a discre e-eve simula or for he Ge eral Packe Radio Service (GPRS) o he IP level. GPRS is a s a dard o packe da a i GSM sys ems ha will become commercially available by he e d of his year. he simula or focuses o he commu ica io over he radio i erface, because i is o e of he ce ral aspec s of GPRS. We s udy he correla io of GSM a dGPRS users by a s a ic a d dy amic cha el alloca io scheme. I co ras o previous work, our approach represe s he mobili y of users hrough arrival ra es of ew GSM a d GPRS users as well as ha dover ra es of GSM a d GPRS users from eighbori g cells. Fur hermore, we co sider users wi h differe QoS profiles modeled by a weigh ed fair queuei g scheme. he simula or co siders a cell clus er comprisi g seve hexago al cells. We provide curves for average carried raffic a d packe loss probabili ies for differe cha el alloca io schemes a d packe priori ies as well as curves for average hroughpu per GPRS user. A de ailed compariso be wee s a ic a d dy amic cha el alloca io schemes is provided.1 I roduc io he Ge eral Packe Radio Service (GPRS) is a s a dard from he Europea elecommu ica io s S a dards I s i u e (E SI) o packe da a i GSM sys ems . By addi g GPRS fu c io ali y o he exis i g GSM e work, opera ors ca give heir subscribers resource-efficie wireless access o ex er al I er e pro ocol-bases e works, such as he I er e a d corpora e i ra e s. he basic idea of GPRS is o provide a packe -swi ched bearer service i a GSM e work. As impressively demo s ra ed by he I er e , packe -swi ched e works make more efficie use of he resources for burs y da a applica io s a d provide more flexibili y i ge eral. I previous work, several a aly ical models have bee developed o s udy da a services i a GSM e work. Ajmo e Marsa e al. s udied mul imedia services i a GSM e work by providi g more ha o e cha el for da a services . Boucherie a d Li je s developed a a aly ical model based o Markov chai a alysis o s udy he performa ce of GPRS u der a give GSM call charac eris ic . For a aly ical rac abili y, hey assumed expo e ially dis ribu ed arrival imes for packe s a d expo e ial packe ra sfer imes, respec ively. O he o her ha d, discre e-eve simula io based s udies of GPRS were co duc ed. Meyer e al. focused o he performa ce of CP over GPRS u der several carrier o i erfere ce co di io s a d codi g schemes of da a . Fur hermore, hey provided a de ailed impleme a io of he GPRS pro ocol s ack . Malomsoky e al. developed a simula io based GPRS e work dime sio i g ool . S uckma e al. s udied he correla io of GSM a d GPRS users wi h he simula or GPRSim . his paper describes a discre e-eve simula or for GPRS o he IP level. he simula or is developed usi g he simula io package CSIM a d co siders a cellclus er comprisi g of seve hexago al cells. he prese ed performa ce s udies were co duc ed for he i ermos cell of he seve cell clus er. he simula or focuses o he commu ica io over he radio i erface, because his is o e of he ce ral aspec s of GPRS. I fac , he air i erface mai ly de ermi es he performa ce of GPRS.
We s udied he correla io of GSM a d GPRS users by a s a ic a d dy amic cha el alloca io scheme. A firs approach of modeli g dy amic cha el alloca io was i roduced by Bia chi e al. a d is k ow as Dy amic Cha el S eali g (DCS) . he basic DCS co cep is o emporarily assig he raffic cha els dedica ed o circui -swi ched co ec io s bu u used because s a is ical raffic fluc ua io s. his ca be do e a o expe se i erms of radio resource, a d wi h o impac o circui swi ched services performa ce if he cha el alloca io o packe -swi ched services is permi ed o ly for idle raffic cha els, a d he s ole cha els are immedia ely released whe reques ed by he circui -swi ched service. I co ras o he models developed i , our approach addi io ally represe s he mobili y of users hrough arrival ra es of ew GSM a d GPRS users as well as ha dover ra es of GSM a d GPRS users from eighbori g cells. Fur hermore, we co sider users wi h differe QoS profiles modeled by a weigh ed fair queuei g scheme accordi g o . he remai der of he paper is orga ized as follows. Sec io 2 describes he basic GPRS e work archi ec ure, he radio i erface, a d differe QoS profiles, which will be co sidered i he simula or. I Sec io 3 we describe he sof ware archi ec ure of he GPRS simula or, de ails abou he mobili y of GSM a d GPRS users, he way we modeled quali y of service profiles, a d he workload model we used. Resul s of he simula io s udies are prese ed i Sec io 4. We provide curves for average carried raffic a d packe loss probabili ies for differe cha el alloca io schemes a d packe priori ies as well as curves for average hroughpu per GPRS user.3 he Simula io Model We co sider a clus er comprisi g of sever hexadiago al cells i a i egra ed GSM/GPRS e work, servi g circui -swi ched voice a d packe -swi ched da a calls. he performa ce s udies prese ed i Sec io 4 were co duc ed for he i ermos cell of he seve cell clus er. We assume ha GSM a d GPRS calls arrive i each cell accordi g o wo mu ually i depe de Poisso processes, wi h arrival ra es GSM a d GPRS, respec ively. GSM calls are ha dled circui -swi ched, so ha o e physical cha el is exclusively dedica ed o he correspo di g mobile s a io . Af er he arrival of a GPRS call, a GPRS sessio begi s. Duri g his ime a GPRS user alloca es o physical cha el exclusively. I s ead he radio i erface is scheduled amo g differe GPRS users by he Base S a io Co roller (BSC). Every GPRS user receives packe s accordi g o a specified workload model. he amou of ime ha a mobile s a io wi h a o goi g call remai s wi hi he area covered by he same BSC is called dwell ime. If he call is s ill ac ive af er he dwell ime, a ha dover oward a adjace cell akes place. he call dura io is defi ed as he amou of ime ha he call will be ac ive, assumi g i comple es wi hou bei g forced o ermi a e due o ha dover failure. We assume he dwell ime o be a expo e ially dis ribu ed ra dom variable wi h mea 1/h,GSM for GSM calls a d 1/h,GPRS for GPRS calls. he call dura io s are also expo e ially dis ribu ed wi h mea values 1/GSM a d 1/GPRS for GSM a d GPRS calls, respec ively.
o exac ly model he user behavior i he seve cell clus er, we have o co sider he ha dover flow of GSM a d GPRS users from adjace cells. A he bou dary cells of he seve cell clus er, he i e si y of he i comi g ha dover flow ca o be specified i adva ce. his is due o he ha dover ra e ou of a cell depe ds o he umber of ac ive cus omers wi hi he cell. O he o her ha d, he ha dover ra e i o he cell depe ds o he umber of cus omers i he eighbori g cells. hus, he i era ive procedure i roduced i is used o bala ce he i comi g a d ou goi g ha dover ra es, assumi g ha he i comi g ha dover ra e h GSM i i , ( ) ( ) &mi us;1 compu ed a s ep i-1. Si ce i he e d- o-e d pa h, he wireless li k is ypically he bo le eck, a d give he a icipa ed raffic asymme ry, he simula or focuses o resource co e io i he dow li k (i.e., he pa h BSC →B S →MS) of he radio i erface. Because of he a icipa ed raffic asymme ry he amou of upli k raffic, e.g. i duced by ack owledgme s, is assumed o be egligible. I he s udy we focus o he radio i erface. he fu c io ali y of he GPRS core e work is o i cluded. he arrival s ream of packe s is modeled a he IP layer. Le be he umber of physical cha els available i he cell. We evalua e he performa ce of wo ypes of radio resource shari g schemes, which specify how he cell capaci y is shared by GSM a d GPRS users: he s a ic scheme; ha is he cell capaci y of physical cha els is spli i o GPRS cha els reserved for GPRS da a ra sfer a d GSM = - GPRS cha els reserved for GSM circui -swi ched co ec io s. he dy amic scheme; ha is he physical cha els are shared by GSM a d GPRS services, wi h priori y for GSM calls; give voice calls, he remai i g - cha els are fairly shared by all packe s i ra sfer. I bo h schemes, he PDCHs are fairly shared by all packe s i ra sfer up o a maximum of 8 PDCHs per IP packe (&quo ;mul islo mode&quo ;) a d a maximum of 8 packe s per PDCH . he sof ware archi ec ure of he simula or follows he e work archi ec ure of he GPRS e work . o accura ely model he commu ica io over he radio i erface, we i clude he fu c io ali y of a BSC a d a B S. IP packe s ha arrive a he BSC are logically orga ized i wo dis i c queues. he ra sfer queue ca hold up o Q &sdo ;8 packe s ha are served accordi g o a processor shari g service discipli e, wi h he umber of physical cha els ha are po e ially available for da a ra sfer, i.e. = GPRS u der he s a ic scheme a d = u der he dy amic scheme. he processor shari g service discipli e fairly shares he available cha el capaci y over he packe s i he ra sfer queue. A arrivi g IP packe ha ca o e er he ra sfer queue immedia ely is held i a firs -come firs -served (i case of o e priori y) access queue ha ca s ore up o K packe s. he access queue models he BSC buffer i he GPRS e work. Upo ermi a io of a packe ra sfer, he IP packe a he head of he access queue is polled i o he ra sfer queue, where i immedia ely shares i he assig me of available PDCHs. For his s udy, we fix he modula io a d codi g scheme o CS-2 .
Where did you get that idea that given a problem to solve, the first thing you need is an interactive programming environment? Ingalls: ThatБЂ™s a good question. I think anything where you get immediate gratification feeds on itself by definition. Seibel: So what was that first place that you had that immediate gratification? Ingalls: There were a couple of experiences. I had a chance to work with a semi-interactive PL/I. And a friend of mine was working at an IBM where they had an interactive APL environment. I canБЂ™t remember which of those was first. I really remember the APL one. That affected me in a number of ways because of both the immediacy of interactionБЂ”seeing your results come backБЂ”and the expression evaluation, which is really different from FortranБЂ™s statement-oriented programming. You still see that now, itБЂ™s amazingБЂ”the whole C/C++/Java tradition, although it goes in an object-oriented direction, is still statement-oriented. But if itБЂ™s convenient to make expressions, it really makes the experience different
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