Đệm trong chuyển mạch gói quang

;<br /> <br /> <br /> <br /> <br /> DEM,TRONG<br /> CHUYEN MACH<br /> GOI Q U A N G<br /> s«Kl4i». irtw-ini^<br /> <br /> -UM,<br /> *J*<br /> '**3«4<br /> <br /> <br /> <br /> <br /> ThS. Nguyen Thj Thu Nga<br /> MO DAU<br /> Ky thuat ghep kenh quang theo budc sdng da tao quang. Bii bao niy se trinh biy vi cie phuong thuc<br /> ra dugc bang tin trayin din rpng Idn den hang dem trong chuyen mach gdi quang. Chuyen mach<br /> Tb, Tuy nhien vdi he thdng trayin din niy thi cie gdi quang cd 3 ehuc nang ca bin: chuyen mach,<br /> ehuyin mach dien tit khdng thi theo kip dugc. dem vi xit ly mio diu. Chuyin mach thue hien<br /> Chuyen mach quang li mdt giii phap hua hen chuyen gdi den diu ra phii hgp dua tren thdng tin<br /> nhim giam khoing cich glQa tdc dp trayen din va chira trong tieu di gdi. Khi cd nhieu gdi trong cung<br /> tdc dp chuyen mach trong mang toin quang raong mot khe thdi gian tren eac diu vio khic rihau cung<br /> lai. Chuyin mach quang bao gom ehuyin mach mudn den mdt diu ra thi xiy ra tranh chip. Xu ly<br /> kenh quang, chuyin mach gdi quang vi chuyen tieu di thuc hien viee dpe thdng tin vi dich eiia gdi<br /> mach burst quang. Chuyin mach gdi quang gidng ddng thdi cap nhit thdng tin mdi qua mdi nut.<br /> nhu chuyen mach gdi nhung thuc hien trong miin Trong ehuyin mach gdi quang khi cd xiy ra tranh<br /> chap gdi thi cd 3 each di giii quyit dd li: thuc<br /> hien trong miin thdi gian bing each dem, thue hien<br /> trong miin tin sd bing each chuyen doi budc sdng<br /> hoac thuc hien trong miin khdng gian bing each<br /> doi hudng.<br /> <br /> <br /> DEM QUANG<br /> Dem li lira chpn dau tien khi xay ra tranh chap<br /> trong mang chuyin mach gdi quang. Tuy nhien<br /> <br /> <br /> <br /> TAP CHI CNTT&TT KY 1 (12.2009) | 27<br />  CONG NGHE V I E N THONG<br /> <br /> <br /> mang la rit Idn nen dd dii cua eic dudng day tti<br /> quang cung Idn. Tuy nhien, van chua ed cdng nghe<br /> dem nao khic cho tin hieu quang di cd the luu trQ<br /> dQ Ueu dudi dang inh sing nen cie phuong phip<br /> dem bang dudng day tii quang vin cd tinh khi thi<br /> honca.<br /> Dudng day tri quang dugc kit hgp vdi cie Unh<br /> kien quang khac nhu chuyen mach cong quang, bd<br /> ehuyin ddi budc sdng quang, bp tach ghep kenh<br /> quang vi bd khuich dai di tao ra dem. Cd hai kieu<br /> dem dugc tao ra hi dudng diy tri: dem chuyen tiep<br /> va dem quay vdng.<br /> Dem chuyen tiip, bao gdm nhiiu dudng day tri<br /> quang cd chiiu dai raong duong vdi bdi so cua thdi<br /> gian mot gdi tin T vi cie chuyin mach quang di<br /> lua chgn dudng day tri quang. Trong loai dem niy,<br /> thdi gian luu trQ cua mot gdi dan gian dugc xac dinh<br /> bing khoing thdi gian gdi dd trayin qua chiiu dai<br /> trong ehuyin mach gdi quang ta khdng the luu dem ciia sgi quang. Dem chuyen tiep dugc minh hpa o<br /> cie gdi nhu trong chuyin mach gdi dien. De thuc Hinh l.a.<br /> Men luu dem eic gdi trong chuyen mach gdi quang<br /> Dem quay vdng, bao gdm dudng diy tri quang cd<br /> ta phii tiin hanh dem qiiang. Dem quang ed the<br /> thdi gian ed thi thay doi duge va mot ehuyin mach<br /> thuc hien bing mdt trong cae cich sau:<br /> quang 1 xN. Dudng diy tri quang ed do dii bing<br /> - Dem bing dudng day trd khoing thdi gian eua mdt gdi tin. Thdi gian tri cua<br /> - Dem bing phuong phap dung linh kien bin din<br /> chim lugng tit<br /> J^.<br /> - Dem bing phuong phip sit dung bd nhd<br /> quang.<br /> jni.<br /> JOI<br /> a) Dem chuyen tiep<br /> Hien tai, cac he thdng dem quang chit yiu sit dung<br /> phuong phip dung dudng day tri, cac phuong phap<br /> dem bing linh kien ban din chim lugng tu vi sit<br /> diing bd nhd quang vin cdn dang nghien cim trong<br /> phdng thi nghiem.<br /> Oem bang dUdng day t r e<br /> <br /> Dem bing dudng diy tii quang dugc tao thanh<br /> tii cac sgi quang. Dp dai sgi quang li khoing cich<br /> mi anh sang trayin dugc trong khoing thdi gian<br /> tri yeu ciu. Vi yeu cau tai cie diim node trong sudt b. Dim quay vdng<br /> ve tdc dp; mat khic tdc dp inh sang trayin tren H inh 1: Cau tao ca ban cua dem bang dwing day tr§<br /> <br /> <br /> <br /> <br /> 28 TAP CHI CNTT&TT KY 1 ( 1 2 . 2 0 0 9 )<br />  CONG NGHE V I E N THONG<br /> <br /> <br /> da gii su ring suy hao tren dudng diy tri co tiie bd<br /> gdi dugc xic dinh bing sd vdng lap cua gdi ttong<br /> qua. De chimg minh gia tiiuyit biy gia sii tiiiit ke<br /> vdng. Su suy giam cdng suit arih sang ttong qui<br /> dem dugc 250 gdi tin hoat ddng 6 toe dp lOGbit/s.<br /> trinh trayin trong vdng lap duge bii lai bing each<br /> Niu te bao dugc dem la ATM till bd dem phii luu<br /> dung mdt bp khuich dai quang. Nhiiu do phit xa<br /> 53x8x250 = 106.000 bit. Niu moi bit keo dii 0,1ns<br /> tir phit tir bp khuich dai quang dupe khueeh dai se<br /> thi dp tri la 10,6ns, nhu vay dp dai dudng day tri<br /> tich luy vi lim suy giam chit lupng cua tin hieu,<br /> li 2,12km. Vdi suy hao quang tiidng thudng thi mil<br /> do dd gidi ban sd lan lap cue dai. Khdi diiu chinh<br /> dudng diy tre nhu vay la cd the bd qua.<br /> thdi gian tre quang trong dem quay vdng dugc dieu<br /> khiin bing bp chuyen doi budc sdng hoac bp dich De khic phuc han che cua phuong phip dem bing<br /> budc sdng. Hinh 1 .b la kiiu dem quay vdng. dudng day tri quang ngudi ta dua ra mot phuong<br /> phip dem khic dung linh kien ban dan cham lugng<br /> Dem chuyen tiep cd cau tao don giin va di thuc<br /> hien hon. Tuy nhien, trong mang quang tiiuc te, tit.<br /> dem cin phii ed dp siu dem nhit dinh di trinh D e m bang phu'dng phap dung linh kien ban<br /> <br /> mit gdi. De tao dem chuyen tiip cin phii cd mdt d i n cham lu'dng tu'<br /> <br /> lupng Idn cac dudng diy tri va cd thi lim cho dem Cie thiet hi quang dua tren vat Ueu bin din<br /> trd nen cdng kinh. Ddi vdi dem quay vdng, thdi gian chim lugng tu ngiy cing dugc quan tim trong viin<br /> tri dugc xic dinh bing chiiu dai eua vdng lap va sd thdng. Cac du in nghien cim ve xu ly tin hieu quang<br /> vdng lap. Vi viy, mdt dudng day tri don ed thi tao dua tren bin din chim lugng tu cho cae img dung<br /> ra dugc thdi gian tri Idn bing cich ting sd vdng lap khic nhau nhu: lip tin hieu quang da budc sdng,<br /> va nhd the ta da giim duge kich thudc bg lap. Dem bg dem quang. Dem bang phuong phap dung linh<br /> quay vdng cd tinh linh boat cao nhung yeu ciu he kien ban dan chim lugng tu su dung dng din sdng<br /> thdng dieu khiin phuc tap hon. cham lugng tit lam mdi tmdng trayen sdng thay vi<br /> Dem bing phuong phip dung diy tri cd mdt vii su dung dudng diy tri quang. Tdc dp nhdm eua<br /> ban chi. Thu nhat li khd diiu chinh thdi gian tri. tin hieu trong dng din sdng se giim xudng khi cd<br /> Khi gdi dugc gui din diy tri thi khdng thi khdi phuc mot ngudn sing manh dugc bom ddng thdi vao mdi<br /> lai dugc den khi nd din diu ra ben kia. Vi du, de luu tradng trayin sdng. Kit qua md phdng chi ra ring<br /> dem mot gdi phuong phap niy cd the giam dugc tdc dp nhdm<br /> cd thdi gian vdi he so 55 va su glim tdc dp nhdm cd thi diiu<br /> 1 ,646irs chinh dugc bing cich thay ddi ning lugng bom<br /> can mdt vio. Hon nua, dem theo phuong phip niy cd the<br /> doan day li tich hgp dugc. Vi vay day li mdt phuong phip hap<br /> 330m, kich din de thue hien dem quang trong mot chip quang.<br /> thudc niy Tuy nhien, eic kit qua nghien cim sit dung phuong<br /> la qui Idn phip niy vin chua dugc xuit bin.<br /> de dua vao D e m b i n g phu'dng phap sii dung bo nhd<br /> mdt mach quang<br /> quang tich Dem quang bing phuong phip bp nhd quang li<br /> hpp, Mac sir dung tinh phi rayin cua bp khueeh dai quang<br /> du d diy ta bin din kit hgp vdi dudng day tri quang. Bp dem<br /> <br /> <br /> <br /> TAP CHI CNTT&TT KY 1 ( 1 2 . 2 0 0 9 ) 29<br />  CONG NGHE V I E N THONG<br /> <br /> <br /> vio ttang tiiii luu lupng, Anh sing UentiicCWtiibd<br /> phin dinh quang dugc dua din chuyen mach dinh<br /> <br /> <br /> M<br /> •^ Chuyen doi<br /> birffc (Ong<br /> £m m tuyin theo budc sdng. Do dd bd phin dinh quang<br /> diiu khiin budc sdng eua inh sing Uen tiic CW va<br /> cung li dieu khiin viee dmh rayin gdi, Cac kit qui<br /> da chi ra ring khdng can thiit phii nhin biit vi xu<br /> phan kenli<br /> ly cac tieu de di thuc hien dem.<br /> Hinh 2: Cau tao cua mot chuyen mach quang dinh Hinh 3 trinh biy phuong phip dem quang ca bin,<br /> tuyen theo buPc song Chimg ta gia su ring eic gdi cung din dong thdi vi<br /> gom 2 khdi ehuc nang ca b i n : mdt bp p h i n dinh gdi 1 cd do uu tien cao hon gdi 2, Cdng suit quang<br /> quang v i mdt chuyen mach quang. cua gdi 1 trade tien dugc chia thanh 2 phin: phan<br /> Khdi chire nang thu nhat tiong dem li chuyin thu nhat tmyin qua node true tiip vi khdng hi tri,<br /> mach quang. Day cd thi li chuyin mach khdng Phin kia duge bom vio OTF boat dpng nhu mdt bd<br /> gian, chuyen mach phan chia theo budc sdng hoac phan dinh quang di quyit dinh niu cd tranh chap<br /> bat ky loai chuyen mach nio khac. 6 diy, ta chpn gdi xiy ra. Neu cd tranh chap, gdi 2 se bi lim tri va<br /> loai chuyin mach dinh tuyin theo budc sdng vi nd di ra khoi dem sau gdi 1.<br /> cho phep tich hpp quang. OTF ed ciu tao dua tren laser ghep ddi. Hoat ddng<br /> Chuyen mach dinh rayen theo budc sdng bao gom cua OTF raong tu nhu mdt bg nhd quang kieu flip-<br /> mdt bd ehuyin ddi budc sdng vi mot bp tich kenh flop. Mdt he thdng 2 laser ghep ndi ed thi ed 2 trang<br /> quang nhu trong Hinh 2. Bp chuyen ddi budc sdng thii. 6 trang thii 1, anh sing cd budc sdng A,l tu bd<br /> ed the chuyen tin hieu tu mdt budc sdng niy den phit laser 1 trpi hon inh sang cd budc sdng X2 tir<br /> mdt budc sdng khic trong miin quang bing cich laser 2. Do dd, >L1 li budc sdng uu thi tai dau ra ciia<br /> dua vio bd chuyen doi budc sdng ddng thdi 2 tia OTF. Nguge lai, d trang thii 2, inh sing tii laser 2<br /> sing. Mdt tia sing li sdng anh sing lien tue CW cd trdi ban laser 1, X2 ehiim uu thi. Ddng trong SOA<br /> budc sdng li Xi, vi mdt tia sang khac li gdi dQ lieu dugc dinh thien bat ddi ximg nen he thdng d trang<br /> da dugc diiu chi bien dp va khuich dai vdi budc thai I niu khdng ed budc sdng tu ben ngoii dugc<br /> sdng Xp. Sau khi da ehuyin doi buoc sdng thdng tin dua vio. Di chuyen trang thii, hire xa tii laser phat<br /> da diiu chi trong gdi tai budc sdng Xp dugc chuyin uu thi duge lim tit bdi anh sang dugc bom vio<br /> sang budc sdng Xi. Bp tach kenh quang dugc dung (khdng cung budc sdng vdi laser ehiim uu thi). Do<br /> de dinh tuyin gdi din cong ra xic dinh, dita vio dd, laser 2 tra thanh laser uu the. Tuy nhien, su<br /> budc sdng cua gdi. Bdi vay, gdi tin cd budc sdng Xi<br /> dugc dinh tuyin den cong ra i. Viec dinh tuyin gdi<br /> tin duge quyet dinh bdi buoc sdng ciia inh sang lien<br /> tuc. Do dd chi can dieu chinh budc sdng cua anh<br /> sing Uen tuc nay ta cd the chuyin mach gdi tin din<br /> eic cong ra khic nhau.<br /> Khdi ehuc ning thu hai ttong dem la khoi phan<br /> dinh quang OTF, Vai trd ciia nd li giii quyit tranh Mai trutmg<br /> ITP quang<br /> chap gdi vi diiu khien chuyin mach quang, Bp<br /> phan dinh quang phit ra anh sing Uen tuc CW dua Hinh 3: So do dem quang sir dung ham ngioig OTF<br /> <br /> <br /> <br /> <br /> 30 TAP CHI CNTT&TT KY 1 ( 1 2 . 2 0 0 9 )<br />  CONG NGHE V I E N THONG<br /> <br /> <br /> <br /> <br /> Laser 1, phit ra /-i Nhu vay, su dimg dem quang bang each sit diing<br /> him nguong da giai quyit dugc tranh chip gdi cua<br /> ISO FPF<br /> 2 gdi.<br /> Circulator ^-p<br /> <br /> 1 ^— SO.\ .50/50 KET L U A N<br /> <br /> Chuyen mach gdi quang la mot phit trien tat yiu<br /> ; 90/10 ,<br /> T { eua mang viin thdng. Di chuyin mach gdi quang<br /> sdm duge img dung thuc ti thi mdt trong cie van di<br /> can giii quyit li dem quang. Tuy nhien hien nay<br /> ; ISO ' do ban chi vi cdng nghe nen phuong phap dem<br /> ISO FPF<br /> don gian va su dung pho biin nhat trong cie du in<br /> Laser 2, phat ra).2 nghien cuu ve chuyin mach gdi quang li dem bing<br /> Hinh 4: Cau tao cua ham nguOng quang OTF dudng day tri quang kit hgp vdi mdt sd phin tit nhu<br /> bd chuyen ddi budc sdng, bd phan dinh quang, bd<br /> khdng ddi ximg eua ddng dinh thien trong SOA dim ghep/phin kenh quang di tao ra chue nang dem.<br /> bio ring he thdng quay trd lai trang thai 1 niu Cie phuong phip khic mdi dimg d mire nghien citu<br /> ngimg dua inh sing tir ben ngoii vio. vi thu nghiem, hy vpng trong raong lai khdng xa<br /> Anh sing diu ra cua OTF dugc su dimg di diiu cie phuong thue dem quang mdi se dugc sit dung<br /> khiin bd chuyin ddi budc sdng lam biin doi budc di thay thi phuong phip dem bing dudng diy tre.<br /> sdng cua gdi 2. Sau dd, phu thude vio budc sdng<br /> dugc chuyin ddi eiia gdi 2 bd tich kerih se dinh Tai lieu t h a m khao<br /> tuyin gdi 2 den mdt cdng ra hoac cong dem. Cd 3 [1]. MARTIN MAIER, 1,2008<br /> tradng hgp dau vio thdng thudng nhu sau:<br /> [2]. YONG LIU, All-Optical Buffering Based on Nonlinear Optical<br /> TriTdng hdp 1: Gdi 1 vi gdi 2 cd mat dong thdi Processing with Semiconductor Optical Amplifiers, 2004.<br /> vi tranh chip xiy ra. Do su cd mat eua gdi 1, OTF [3]. AV. TURUKHIN,* V. S. SUDARSHANAM, and M. S.<br /> hi chuyin sang trang thii 2 vi phat xa anh sing cd SHAHRIAR, Observation of Ultraslow and Stored Light Pulses in<br /> <br /> budc sdng X2. Bai viy budc sdng eua gdi 2 bay gid a Solid 2001.<br /> <br /> li X2 vi gdi dugc dinh rayin din cdng dem. Gdi 1<br /> trayin tnrc tiip qua node.<br /> TrUdng hdp 2: Cd gdi 1 nhung khdng ed gdi 2<br /> (khdng tranh chap). Gdi 1 ed the trayin true tiep<br /> qua node. Mdt phin nang lugng eua gdi 1 duge dua<br /> vao OTF de chuyen nd sang trang thai 2, phit xa<br /> anh sang cd budc sdng X2.<br /> TrUdng hdp 3: Cd gdi 2 nhung khdng cd gdi 1<br /> (khdng tranh chap). OTF phit ra inh sing ed budc<br /> sdng X\ do khdng cd gdi 1. Gdi 2 di qua cdng ra sau<br /> khi da bien ddi budc sdng.<br /> <br /> <br /> <br /> TAP CHi CNTT&TT KY 1 ( 1 2 . 2 0 0 9 ) 31<br />