nhu mang hinh ludi khdng day do phai doi mat voi cac yen diem noi tai aia mang va moi tnrong hoat dong nhu su bat dn dmh aia hen ket chat luong duong din va suy giam hieu nang mang Bai bao nay torn luoc cac dac diem chat luong dich vu. chit luong trai nghiem cua luong da phuang tien va tiep can xuyen lop nhim giai quyet muc tieu thoa man yeu cau ngudi dung va nang cao hieu nang mang Qua do rat ra mot so danh gia ve kha nang va xu huong phat tnen cua cac giai phap hien nay
Nguyen Thanh Tra
1. G I O I THIEU
Trayen taong da lop khflng ddy la mflt Imh vuc phdt tadn rdt mato me ttong mflt sd nam gan ddy do phdt huy tdi da tito di dflng ciia nguoi su dung ttong vide phto phdi cac ngi dung da phuong tidn [1]. Tidp cdn mang Mto lufli khflng day WMN (Wireless Mesh Network) duge eoi la 0ai phap men chdt cho eae mang tmy todp voi su ho tto cua da dtog logi hito cong nghd tou: Bluetooth, WlFi, WIMAX, v.v... Mflt edu tnie mang WMN dien hito dugc mfl ta trong Hito 1.
Ngoai cdc muto loi ve khd ntog mo rflng vmg phu, 0 a mdto tadn khai mdp vd hd ttg truy todp
Intemet mpi liic, moi noi, WMN buflc phai ddi mdt vol van de cung edp chat luong dieh vu cho eac ludng da phuong Uen ngay eang 0 a tang tii phia nguoi su dung. Viee dam bao QoS (Quahty of Seviee]
cho cac luflng luu luong da phuong tidn vd tdi uu Meu nang mang se la dieu kien taen ehdt eho su phat taen eua cac toa khai tadc mgng. Dieu nay dde biet khfl khdn doi vfli eac mang traydn thflng da buflc khong day tou WMN kM QoS can cfl eac co ehd dieu khidn mfli, todm khdc phuc mot loai eac ydu diem nfli tgi ma WMN d m g ddi mat nhu su bdt dn dmh cua hdn kdt, chdt lumg dutog ddn va cde
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Hinh 1 Mang hinh lubi khong day dien hinh
tac dflng nMdu a t o huong ngMem ttong toi Meu ndng mang, v.v... Nhdm tiep can van dd chat luong dich vu QoS va ehdt luong ttai ngMem eua ngufli dimg QoE [Quality ol Experience) ttong mang V\/MN, hutog tidp cdn xuyen lop da va dang la mgt giai phap moi efl nMdu ky vong tau hut idt nMdu cdc toa nghien cto Men nay.
2 . V A N D E D A M B A O Q o S T R O N G W M N Su phd bien cua cflng nghd va cac uu diem ttong tndn khai la cac dieu kien thiic ddy chito cho su phat taen cua eac 0ai phdp mang WMN su dung cho tray toap Intemet. Tuy nMen, viee hfl tto QoS trong Mch ban nay la khong don 0 a n dfli vol WMN vi ba ly do cltoh: Thii todt, WMN phdi dam bao duoc dung luong cao toam chuyen tiep luu luong tich luy nguoi dmg. Thir hai, su da dang cua cde yeu cdu QoS gflm rat nMdu taam sd tou: Do tte, mflng luong, ti Id tdn mdt gfli tm, v.v... Cudi cmg, cae vdn dd ttdn lufln ddn toi bai toto toi uu toan cue vol nMdu taam sd bien dflng do chito mfli tratog
WMN tao ra tou: Vtog phu, luu luong m m g vd tat nguydn mang, v.v... Dd dap tog duge eae doi hdi dfl, mgt loat cdc ky muat dam bdo QoS mfli da duoc dd xudt gdm ky tauat da anten, 0 a o tauc didu kMen lop tray toap phuang tien mfli, eae co chd dato trafle va du phflng tai nguydn, eo ehd dieu kMdn chap todn va dmh tuydn, v.v...
Mflt kMa cato khac eua van de dam bao QoS ttong WMN hen quan tfli bdi toto tMet kd chito la humg tiep can 0 a i quyet. Phan Ito eae tidp can hd tto QoS Men nay dua trdn Udp cto phdn lop. Tidp can phto lop da rdt taato cflng ttong eac mang may tito kM phat huy duoe kha nang mo' rflng va tito mem ddo ttong kdt ndi traydn mflng. Tuy nhien, cdc ky mudt tdi su d m g tan sd rtadm tdi uu tai nguydn, tito ndng phdt quang ba thong ta, su bidn dflng cua chdt luto9 hdn ket vd toat la su sai khac cua cae khung mfli gian cua cdc giao tauc tten eae lop khde toau da ddn tfli Mdu ntog cua toto he mflng thdp do khflng tdi mi. Vi du, vide ldp lich tai ldp mdu kMdn ttuy todp phumg tien MAC (Medium
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Access Conttol) se dan ddn su a t o hutog toidu tdng vd a t o hutog toi Mdu ntog lop Vat ly do 0am ty Id to Mdu/nMeu va cudi ctog ldm 0am Mdu nang toan he tadng. Viec tdi uu dung luong cue bo taflng qua giai phap ldp lieh cung cfl tad tao ra cac diem nghen ed chai mfli trong mang.
Them vao dfl, vide ddto 0 a khflng cMto xac cae tde dflng se anh huong ngMem ttong toi ede dich vu ydu eau QoS dang tdn tai.
Nhtog han chd cua tidp cdn phdn lop da nay sito su phdt taen tiep can
xuydn lop ttong mang WMN. Trong do, viec ket hop tfll uu didu khidn giiia hai hoae toidu lop cfl the ttog dtog kd Mdu ndng mang. KM dfl, viec tauc Mdn dam bao QoS se dugc bd sung boi cae eo chd dam bao QoS trdn ttog lop. Vi du nhu: Tai Iflp MAC:
Md rflng vd eai tMdn kJ taudt dieu kMen tray todp tou chudn 802.1 le [2]. Tai lop mgng: mo iflng giao miic dinh Myen vfli cde tham sfl hd tro QoS tir Iflp MAC hoae Iflp Vdt ly. Tai lop m g dung: Hfl ttg phdn phdi nOi dung da phumg tidn mflng qua cae pMdn tuong tMch ttang taai mang. Mot mdeh tairc Ito toat cua eac giai phap dam bao QoS ttong WMN la tMdu gial phap dam bao miic ehdt luong cho eae m g dung tuong tog voi su chap toan ciia ngufli dtog. Cae eo chd do lumg traydn tadng cM phan anh dugc mot phan ciia khia cato QoS chit khong tae quto ly duge toto bfl va tir dau cudi toi ddu cudi.
Didu nay cho tady cac hoat dflng dieu kMen va cac mam sd QoS khflng thd hien duoc miic dfl hai long eua ngufli su dmg. VI vay, mflt tiep can dua tten dde trang cam xiie, toto mire vd each phan tog cua nguoi sii dung dieh vu da duge dd xuat boi [3] todm giai quyet mflt sd han ehe trdn.
3. CHAT Ll/ONG TRAI NGHIEM QoE Chdt luong trai nghiem QoE dang tao ra mot hd data 0 a vd quan ly moi cho cac dich vu da phuong tien va duoc dac biet chii y ttong WMN. Thay vi do luong cae tham so QoS cua ludng da phuong tidn dua tten chap toto ngufli dmg, QoE tidp cto tix khia cato chu quan vd cam todn cua eon ngufli.
QoE dua ra mot phdn lop nguoi dmg mfli mang tinh ehat trim tuong voi su bd sung todn tauc nguoi dmg. Do dd, QoE duoc coi la su mo rang ciia van dd cung cdp QoS ttdn quan didm nguoi dmg qua cac hoat dflng eai tMdn mdt phdng didu kMen.
Hoat dflng do lutog eua QoE todm dato gia mfli tramg mtog dap m g tou tad nao traoc nhtog yeu cau eua nguoi dtog. Kieh b t o khd dung, cde ydu cau, phuong phap danh gia va uoc lugng tiong cac he mflng da phuong tien da duoc ngMen cim boi mot loat cac toflm lam vide Ito tou td chirc hen minh vidn mong qude te ITU-T [4], Vien ngMfln cim vidn taflng chdu Au ETSI [5] va toflm chuyen 0 a chat Iugng video VQEG [6]. Cac de xudt dam bao QoE tten se eho phep taen khai cac dieh vu nhgy cam vol QoS/QoE vd cung edp ludn tauydt mfli dd
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I) b) c) d) Hinh 2: Tbidt kS xuyen \t3p long va ch$t
phdt trien cde 0ao tauc, phuang phdp ddnh 0d, mam sd vd eac tidp cdn phii hgp hon vfli mfli tradng mang da d m g hifln tai.
Cde tidp cto ddto gid chdt lumg ludng da phuong tidn dugc cMa m d t o hai logi: (1) dua vdo ddc tito khach quan/chu quan vd (ii) dua vdo mfl hito taam ehidu [7]. Theo hutog Udp eto (i), cdc kdt qua ngMen cto dd xudt dd dugc cM ra trong [8-9] cho thdy taam so khdeh quan rdt khfl tauc Mfln ttong mfli traflng da phuong tidn mfli gian muc, taam sfl khdcdi quan dua ttdn cdc mfl hito toto hge dd uflc dito vol cam nhdn ngudi su d m g dugc tmh toto mflng qua Ifli bito phuong trung bito chi md Mdn duge su khae toau 0il:a to Meu toto dugc vd to Mdu mam khao. Vi tad khflng phdn a t o ddy dii dugc tito chat cua hd thi gide eon nguoi (vfli ludng video).
Mflt vdi eai tMdn va bidn md cua phuang phdp ndy da duge phdt taen mflng qua cdc mam sd mfli tou:
Tham sd cM thi tuong quan cau true SSIM (Stractural Similary todex Metae), taam sd chat lumg video VQM (Video Quahty Metac) vd taam sd chat lumg a t o dflng MPQM (Moving PlcUire Quality Metnc).
Tidp cdn (li) tap trung chii yeu vao chat lumg ludng Video dua ttdn mdt ttong ba mfl Mto taam cMdu:
Tham cMdu ddy du FR (Full Reference), taam cMdu nit ggn RR (Reduce Reference) vd khflng tham cMdu NR (No Reference). Mfl Itoh RR sii d m g cdc taam sd SSIM va MPQM dd ddto 0 a ede ttai ngMflm ngogi
mydn. Trong kM do chdt lumg ludng Video tirue Mydn dugc ddnh 0 d qua RR vd NR vol mdt sd mam sd VQM dd giam dfl phiic tap ttah toto.
4. TIEP CAN XUYEN LOP H d TRQ QoS Van dd h6 ttg QoS/QoE cho tog d m g da phuang tidn trong mgng WMN la mgt vi du rmto chtog su cdn tMdt eua tidp edn xuyen lop eho mtog WMN.
Trong mmg khflng ddy tou WMN, khdi nidm hdn kdt khflng cfln mang gid tri mudn todt tou ttong eae mmg ed dinh khi dudng truydn ddn 0 u a hai node khong chi ddnh ritog eho hai node. Dung lugng vd chdt luong cua Uen kdt lufln bidn dflng vd Uen quan chdo vdi cdc Uen kdt khac. Sv phu muflc ldn toau dd phd vfl' su p h t o tdch 0tta ede ldp. Vi vay, ngodi vide ddm bdo tgp tham sd QoS/QoE cua ludng luu Iugng ttdn ttog ldp, su phdi hgp tdi uu cdc mam sd vd taudt toto 0\m cdc ldp la didu kidn mdu chdt de cai thidn Mdu ntog mmg.
Cde ngMdn cto meo udp eto xuydn 16p gdn ddy eho mdy rfl ed hai kidu xu hutog tMdt kd: kdt hgp long vd kdt hgp ehdt. Hito 2 etu ra cdc vi du cua hai kidu tMdt kd ndy.
Kieu kdt hgp Idng cho taay su tdi uu khdng dua tten taflng to 0iia cdc ldp ma ehu ydu tdp tiung tai mflt ldp. Thflng muflng, mam sd 16p tadp dugc bdo cdo ten lop cao hon dd muc Mdn tito toto tdi uu. Vi
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du, Hito 2.a, ty lfl tdn mdt gfli ta tai ldp MAC hode didu Mgn keto traydn lop Vat ly dugc bdo cao ldn lop didu kMdn traydn tai TCP dd phto bidt rfl Mdn tumg tdc nghen vd tdn mdt gdi do bfl ddm. Chdt luong lidn ket tai lop Vat ly eo md Id dau vdo tito todn eho 0ao miic dito myen tai lop mang (Hito 2.b) hogc mgt lop cfl md su dtog thflng ta cua nMdu lop (Hinh 2.e). Vide su dung mflng tm xuyen lop toam ntog eao Meu ndng mang gdm hai bien md: (i) eac mam sd xuydn Iflp chito xac se ntog Mdu ntog thudt todn vd (u) thudt toan se duoc may ddi phil hgp voi mflng to toto duge. Tuy nMdn, vide may ddi muat todn tito todn cmg mutog di kem vol dfl phiie tap ttog len.
Kidu tMdt kd xuydn Iflp chat cho phep eae muat toan thuflc cde lop khac nhau cung tdi im. Vi du, eae taam sd QoS/QoE duoc xae dinh Iflp MAC, co chd phto bd kdto, dumg dan dito Mydn cfl the hop todt vdo mflt giao thiic. Vide tdi uu hoa eae lop cheo toau se cho kdt qua tdt hon tMdt kd phdn Iflp Iflng.
Thdm vdo dfl, su phto hoach tdi uu 0ira cdc lop
bang each may ddi va hgp todt giao muc ctog lam ttog Mdu ntog mgng. Tuy nMdn, vto dd tdi uu chdo se dan tfli do phiie tap tang toato vd vlec hop todt giao miic se ddn toi kha ntog khflng tuong tMch vol cac mang phan ldp Mdn nay.
Trong mfli traong mang WMN tauc td, humg tidp cto xuyen lop da va dang phat tadn mato me vfli cac 0ai phdp cung edp QoS/QoE khdc toau. Mflt ttong eae 0ai phdp kha tM dfl Id su kdt hop 0ua Iflp dmh Mydn va lop MAC dd tdi uu Meu ntog mang.
Trong dfl, giao miie dito Myen duoc phat tndn tou mflt module co bto chay tren nen lop MAC (vi du ttong ehuan 802.Ue) cho phep tau map vd xii ly eac tham sd QoS/QoE tou tham sd dau vao cua tauat toan dinh tuydn. Cac taam sd a t o hutog tfli QoS tou nMdu, tdn thdt gfli ta va bdng taflng duoe phan a t o taong qua tham sd dito tuydn phan dnh ehdt luong Uen ket. Mgt sd ket qua eho mdy kha nang cai tinen Mdu ntog mang eua eac giao miic dmh tuydn hfl tro QoS duoc tang len dang kd [10- 11].
5 . KET L U A N
Voi cdc mue tieu va pham vi moi cua van de cung cap vd dam bao QoS/QoE cho trayen mflng da phuong tien trong mang WMN, cac giat phap xuyen lop da cho taay mi md ro ret ciia Uep can ddi vfli kMa cato Meu n t o g mang. Su ket hop xuydn lop giua lop dito tuydn va Iflp MAC etog vol eae eo chd dam bao QoS da va dang eho eac ket qua kha quan ban ddu ve Meu nang mang. Tuy toidn, cae giai phap QoE true Myen vd cac mfl h i t o du doto, uflc luong mam sd chdt luong xuyen lop can tiep mc cai thien nhdm ngay cang thoa man nguoi su d m g dieh vu va 0am 0 a taato khai thae thuc td.
Tai lieu t h a m khao
[1]. IAN F. AKYILDIZ, XIXONGWANG, "Wireless Mesh (Vetivorfc," chapter 4, pp.106-111, John Wiley & Sons, Ltd, 2009.
[2]. 802. lis. EEE Mesh Netv<mking, Task Crop S. Status of Project lEE 802.1 Is, accessed in March 2010, of htQjy/www.
ieee802.org/l l/Rqx)rts/tgs_nxiate.htm.
[3].T/y<AHASHI,A;HANDS,D.&BARRIAC,V. "Stano^c/(2af/on activities in the ITU for a QoE assessment of IPTV" IFFF Communication Magazine,Vol 46, No. 2, 2008.
[4]. mj-T (2010). \ntemational Teiecomnmication Union — Teiecommmication Standardization Sector, accessed in Apnl 2010, of httpy/www itu.int/nU-T/.
[5]. ETSI (2010). European Technical Committee for^ieech, Transmission, Planning, and Quality of Sen/ice, accessed in /*pril 2010, of httpL//portal.etsi.org.
[6]. VQEG (2010). Video Quality Experts Group, aciissed in April 2010, of httpy/www.lts bldrdoc.gov/vqeg/.
[7]. ROMANIAK, P.ET all "Framework for the integrated Video Quality Assessment", Institute of Technology, 2008.
[8]. BOCCA-RODRiGUEZ, et all. "Video Quality Assurance in Ivtuiti-Source Streaming Techniques", Pro. the 4th international IFIP/ACM, pp. 83-93, 2007.
[9]. KISHIGAMI, JAY "The Role of QoE on FTV Sen/ices style.
Multimedia, ISM", 9th IEEE Intemational Symposium on, pp (11- 13), 2007.
[10].\JSMA?^ASHR/^,eta\\, "An Interference and Link-Quality Aware Routing Metric for Wireless Mesh Networks,"VTC,pp.l-5, Fall 2008.
[11]. S.WAHARTE,etall "Design aid Performance Evaluation of lAR: interference-Aware Routing Metric fcf Wireless Mesh Networks.". MONET 14(5): pp.649-660, 2009.
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