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<ul><li> 1. HC VIN CNG NGH BU CHNH VIN THNG TNG QUAN V VIN THNG (Dng cho sinh vin h o to i hc t xa) Lu hnh ni b H NI - 2007 </li></ul><p> 2. HC VIN CNG NGH BU CHNH VIN THNG TNG QUANG V VIN THNG Bin son : Ths. Nguyn Vn t Ths. Nguyn Th Thu Hng Ks. L S t Ks. L Hi Chu 3. TNG QUAN V VIN THNG M s : 411TQV260 Chu trch nhim bn tho TRUNG TM O TO BU CHNH VIN THNG 1 (Ti liu ny c ban hnh theo Quyt nh s: /Q-TTT1 ngy ca Gim c Hc vin Cng ngh Bu chnh Vin thng) 4. LI NI U Trong nhng nm qua, h tng vin thng pht trin nhanh v c cng ngh v cht lng cung cp dch v. Vin thng tri qua mt qu trnh pht trin lu di vi nhiu bc ngot trong pht trin cng ngh v pht trin mng li. Vit Nam cng nh cc nc trn th gii, hin nay c rt nhiu nh khai thc vin thng khc nhau vi s a dng ca cng ngh v cu hnh mng cng nh cc dch v cung cp. c c ci nhn tng quan v vin thng ni chung, nm bt nhng kin thc c bn v vin thng v cng nm trong chng trnh o to ca h i hc t xa ca Hc vin Cng ngh Bu chnh Vin thng, cun ti liu Tng quan v vin thng c cc ging vin B mn Mng Vin thng, Khoa Vin thng I bin son. Ti liu gm 6 chng, trnh by nhng kin thc c bn v lch s pht trin ca vin thng, cc dch v vin thng, cc k thut c bn v truyn dn v chuyn mch trong vin thng cng vn bo hiu v ng b mng. Chng 1- Gii thiu chung: chng ny cung cp cho hc vin cch nhn tng quan v mng vin thng; qu trnh pht trin ca vin thng trong qu kh, hin ti v xu hng pht trin trong tng lai cng nh cc khi nim c bn trong vin thng c cp gip ngi c bc u hiu v vin thng ni chung v c s tip cn vi h thng vin thng phc tp. Chng 2- Dch v vin thng: chng ny cp n cc vn lin quan n dch v vin thng nh khi nim, cch thc phn loi dch v vin thng, cc yu t nh hng n cht lng dch v v cht lng mng, ng thi gii thiu v cc loi hnh dch v vin thng c bn v cc dch v mi trn th gii v Vit Nam, nhu cu v xu hng pht trin dch v vin thng. Chng 3- Cc mng vin thng: chng ny gii thiu s hnh thnh v pht trin ca cc mng vin thng: cc mng mng in thoi, cc loi mng v cng ngh mng truyn s liu, mng my tnh, Internet. Chng ny cn gii thiu nhng khi nim cn bn v cc phn t to nn mng vin thng, v quan im phn tng giao thc v cc phng thc chuyn giao thng tin qua cc mng c bn. Chng 4- Cc vn truyn dn v ghp knh. Chng 4 trnh by cc ni dung lin quan n truyn dn; khi nim v ghp knh v cc k thut ghp knh c s dng trong mng vin thng. Chng 5- Cc vn v chuyn mch v nh tuyn. Chng ny trnh by cc khi nim v chuyn mch knh, k thut chuyn mch thi gian v khng gian, s kt hp cc k thut trong cc h thng chuyn mch; K thut chuyn mch gi, nhng khi nim v nh tuyn v s phn loi chng cng c cp. Chng 6- Bo hiu v ng b trong mng vin thng: Chng ny a ra cc khi nim v cc k thut c bn v bo hiu; vai tr v cc gii php ng b mng v ng b trong mng vin thng Vit Nam (ca VNPT). 5. 2 phn u mi chng u c phn gii thiu v ni dung ca chng v ch r nhng kin thc c bn hc vin cn nm bt sau khi hc xong chng ny. Ngoi ra, gip sinh vin cng c kin thc hc, cui mi chng u c cc cu hi n tp. Cc cu hi c a ra di dng trc nghim, gip hc vin c th t nh gi nh phn hng dn tr li cui ti liu. y l ti liu cung cp cho cc hc vin h o to i hc t xa ca Hc vin Cng ngh Bu chnh Vin thng ni ring cng nh nhng ngi c mun tm hiu, tip cn v vin thng, mt trong nhng lnh vc cng ngh hin i v rt phc tp. Trong qu trnh bin son, chng ti lun c gng a ra nhng gii thch, v d n gin d hiu, tuy nhin khng th trnh khi nhng thiu st, rt mong cc hc vin, bn c thng cm v cho nhng gp . Nhng kin ng gp xin gi v : B mn Mng vin thng- Khoa Vin thng 1- Hc vin Cng ngh Bu chnh vin thng T: 84-34-515484, bomonmangVT1@yahoo.com H Ni, thng 8 nm 2006 6. 3 CHNG 1 - GII THIU CHUNG GII THIU CHNG Mc ch ca chng 1 l cung cp cho ngi c nhng khi nim c bn nht v vin thng, v qu trnh pht trin ca vin thng trong qu kh, hin ti v xu hng pht trin trong tng lai. Phn u chng 1 cp n lch s pht trin vin thng v nhng khi nim cn bn v thng tin, tn hiu v h thng truyn thng. Vn chun ha l mt ni dung rt quan trng trong vic nghin cu, tm hiu vin thng ni chung. Chng 1 trnh by cc ni dung lin quan n vn chun ha, trong gii thiu v cc t chc chun ha khc nhau. y l cc t chc chun ha quc gia, khu vc v quc t c nh hng rt ln ti cc nh sn xut thit b vin thng, cc nh khai thc vin thng v c khch hng s dng dch v vin thng. Hc vin cn phi nm c cc khi nim c bn v thng tin, tn hiu v h thng truyn thng; lch s pht trin vin thng v cc t chc chun ha vin thng quc t. 1.1 LCH S PHT TRIN CA VIN THNG Vin thng l mt trong nhng b phn kinh doanh pht trin nhanh nht trong cc cng ngh thng tin hin i. Ch cch y vi thp k, c coi l c hiu bit c bn v vin thng, ta ch cn nm bt c cch thc hot ng ca mng in thoi l . Ngy nay, lnh vc vin thng bao gm rt nhiu cng ngh v dch v hin i. Ngoi mt vi dch v hon thin nh dch v in thoi c nh cn c rt nhiu dch v v ang bng n nh dch v in thoi di ng v Internet. S xa b nhng quy nh trong nn cng nghip vin thng lm kinh doanh tng trng mc d gi c ca cc dch v ngy cng gim. Mi trng vin thng m mi ngi phi la chn hin nay kh l phc tp. Trc y, chng ta ch c mt la chn duy nht l c dng hay khng dch v ca mt nh cung cp dch v thoi duy nht. Ngy nay, c rt nhiu nh cung cp dch v cung cp dch v ADSL hoc modem cp cho truy nhp Internet v chng ta c th la chn mt trong s nhiu nh cung cp khi mun dng dch v thoi. Vin thng l ngun ti nguyn quan trng mang tnh chin lc cho hu ht cc tp on hin i v tm quan trng ca vin thng ngy cng gia tng. Mi trng vin thng lun lun thay i ny cho ta nhiu la chn mi v chng ta cn hiu v vin thng nhiu hn v tng qut hn c th tn dng c nhng kh nng sn c ngy nay. 1.1.1 Khi nim chung v vin thng Vin thng: bao gm nhng vn lin quan n vic truyn thng tin (trao i hay qung b thng tin) gia cc i tng qua mt khong cch, ngha l bao gm bt k hot ng lin quan ti vic pht/nhn tin tc (m thanh, hnh nh, ch vit, d liu, ) qua cc 7. 4 phng tin truyn thng (hu tuyn nh ng dy kim loi, cp quang hoc v tuyn hoc cc h thng in t khc). Hnh 1.1 l lc phn loi vin thng. Vin thng chim phn ch o trong truyn thng. Truyn thng l vic truyn thng tin t mt im ti mt im khc, gm c truyn thng c hc (bu chnh) v truyn thng in (vin thng) bi v n pht trin t dng c hc (my mc) sang dng in/quang v ngy cng s dng nhng h thng in/quang phc tp hn. Vin thng n hng Song hng Truyn thanh Truyn hnh Truyn hnh v tuyn Truyn hnh cp in bo Telex in thoi c nh in thoi di ng Truyn d liu Th in t Truyn hnh hi ngh Hnh 1.1: Vin thng T phn truyn thng c hc (th t, bo ch) ang c xu hng gim trong khi t phn truyn thng in/quang, c bit l truyn song hng, li gia tng v s chim th phn ch o trong tng lai. V vy, ngy nay nhng tp on bo ch cng ang tp trung v hng ti truyn thng in/quang, coi l c hi kinh doanh tng lai ca mnh. 1.1.2 Cc giai on pht trin vin thng Vin thng tri qua nhiu giai on lch s khc nhau. Hnh 1.2 cho ta nhng mc lch s pht trin quan trng trong vin thng, ch yu nhn mnh vo s pht trin v m rng ca cc h thng v dch v vin thng (chi tit hn v cc dch v c gii thiu trong Chng 2). C th phn s pht trin ca vin thng qua bn giai on chnh. Giai on th nht ko di khong 90 nm t khi in thoi ra i v pht trin. Giai on th hai l giai on xut hin chuyn mch SPC, truyn dn s v thng tin v tinh. Giai on th 3 l giai on pht trin c trng ca cc mng d liu v cng ngh chuyn mch gi. Giai on th 4 xut hin cng vn lin kt mng truyn thng. Phn tip theo trnh by nhng mc thi gian ng nh i theo nhng s kin ni bt lin quan ti vin thng (xem Ph lc 1 bit thm chi tit). - 1838-1866 in bo (telegraph): Samuel Morse hon thin h thng in bo ca chnh mnh; in bo l dch v vin thng u tin xut hin nm 1844. 8. 5 - 1876-1899 in thoi (telephony): Alexander Graham Bell pht minh ra in thoi (1876); xut hin tng i in thoi u tin vi 8 ng dy; Almond Strowger sng ch ra tng i c in kiu tng nc (step by step, 1887). - 1920-1928 Carson, Nyquist, Johnson v Hartley gii thiu l thuyt truyn dn. - 1923-1938 Truyn hnh (Television): H thng c hnh nh c thc hin; bt u nhng th nghim v thc nghim qung b. - 1937 Alec Reeves hnh thnh khi nim iu xung m (PCM). - 1938-1945 Cc h thng radar v viba pht trin trong i chin th gii ln th 2; FM c s dng rng khp trong truyn thng qun s. - 1948-1950 C.E. Shannon pht hnh cc bi bo nn tng v l thuyt thng tin. WAN: Mng din rng LAN: Mng ni ht WLAN: LAN khng dy WWW: World Wide Web ADSL: ng dy thu bao s bt i xng ISDN: Mng s tch hp a dch v AM: iu ch theo bin FM: iu ch theo tn s IP: Giao thc Internet CS: Chuyn mch knh PS: Chuyn gi VoD: Truyn video theo yu cu TV: Truyn hnh Hnh 1.2: S pht trin ca cc h thng v dch v vin thng - 1950 Ghp knh phn chia theo thi gian (TDM) c p dng vo in thoi. - 1953 Cc chun Tivi mu c cng b M. - 1955 J. R. Pierce xut cc h thng truyn thng v tinh. - 1962-1966 Dch v truyn d liu c thng mi; PCM chng t s thch hp cho truyn thoi v TV; l thuyt truyn dn s c pht trin. - 1965 Mariner IV truyn nhng bc nh t Sao Ha v Tri t. - 1976 Ethernet LAN do Metcalfe v Broggs (Xerox) sng ch. - 19701975 Chun PCM c CCITT trin khai. - 19801983 Khi ng ca Internet ton cu da trn giao thc TCP/IP. - 19801985 Cc mng di ng t bo hin i cung cp dch v; NMT Bc u, AMPS M, m hnh tham chiu OSI c T chc chun ha quc t (ISO) nh ngha. - 1989 Tim Berners-Lee (CERN) c ban u cho vn kin kt ni Web trn WWW (World Wide Web). 9. 6 - 19901997 H thng t bo s u tin, Global System for Mobile Communications (GSM), c thng mi v pht trin mnh trn ton th gii; S dng Internet v dch v m rng nhanh chng nh c WWW. - 19972001 Cng ng vin thng c bi b quy nh v kinh doanh pht trin nhanh chng; cc mng t bo s, c bit l GSM m rng trn ton th gii; nhng ng dng thng mi ca Internet m rng v mt phn truyn thng thoi truyn thng c chuyn t mng in thoi chuyn mch cng cng (PSTN) sang Internet; cht lng LAN c ci thin vi cng ngh Ethernet tin tin c tc ln ti tm Gigabit/s - 20012005 Truyn hnh s bt u thay th truyn hnh qung b tng t; cc h thng truy nhp bng rng m rng kh nng cung cp dch v Internet a phng tin ti mi ngi; dch v thoi tr thnh dch v truyn thng c nhn khi s xm nhp ca cc h thng t bo v PCS tng ln. - 2005 Truyn hnh s s thay th truyn hnh tng t v bt u cung cp cc dch v tng tc ngoi dch v qung b; cc h thng di ng t bo th h th 3 v cc cng ngh WLAN s cung cp cc dch v d liu tin tin cho ngi s dng di ng; cc dch v di ng ni ht s m rng, ng dng cho nhng cng ngh khng dy khong cch ngn trong nh v cng s s tng ln; mng vin thng ton cu s tin trin hng ti mt bng mng chuyn mch gi chung cho tt c cc loi dch v. 1.2 KHI NIM V THNG TIN, TN HIU V H THNG TRUYN THNG 1.2.1 Cc khi nim v thng tin, truyn thng, bn tin v ngun tin Thng tin (Information) Thng tin l cc tnh cht xc nh ca vt cht c tip nhn bi nh quan st t th gii vt cht xung quanh. C th hiu mt cch chung nht, thng tin (hay cn gi l tin tc) l s hiu bit hay tri thc, c kh nng c biu din di nhng dng thch hp cho qu trnh trao i, truyn a, lu gi hay x l. Cc dng thc thng tin c bn bao gm: ting ni, hnh nh (hnh nh tnh, hnh nh ng), d liu (k t, th). Nhng thng tin ny c thuc tnh chung l u cha ng tng trong hot ng t duy ca con ngi. Bn tin (Message) Thng tin c th hin mt dng thc nht nh c gi l bn tin. Dng th hin c th l vn bn, bn nhc, hnh v, on thoi. Mt bn tin cha ng mt lng thng tin c th, c ngun v ch xc nh cn c chuyn mt cch chnh xc, ng ch v kp thi. Ngun tin (Information source) 10. 7 Ngun tin l ni sn sinh hay cha cc bn tin cn truyn. V th, ngun tin c th l con ngi hay cc thit b thu pht m thanh, hnh nh, cc thit b lu tr v thu nhn thng tin pht i 1.2.2 S khi h thng truyn thng tin H thng truyn thng (HTTT) thc hin cc chc nng x l cn thit, bin i thng tin cn trao i thun tin cho vic lu tr, sa cha v truyn qua h thng. Hnh 1.3 cho ta s khi ca HTTT, thng tin truyn qua h thng c th l mt chiu truyn n hng (Hnh 1.3a) hoc trao i hai chiu truyn hai hng (Hnh 1.3b). Thng tin t ngun tin i ti thit b u cui (TBC) pht chuyn thnh tn hiu. Tn hiu ny c truyn qua mi trng truyn dn (knh truyn thng) ti TBC thu. Ti y, tn hiu c bin i ngc li thnh thng tin v a ti ni nhn tin. TBC pht Mi trngtruyndn TBC thu Bntin Tnhiu pht Tnhiu thu Bntin Ngun tin Nhn tin a) Truynthngmt chiu TBC pht/thu Mi trngtruyndn TBC thu/pht Bntin Tnhiu pht/thu Tnhiu thu/pht Bntin Pht/nhn tin Nhn/pht tin b) Truynthnghai chiu Hnh 1.3: M hnh h thng truyn thng HTTT do con ngi to ra da trn cc thnh tu khoa hc, lao ng sng to phc v cho nhu cu trao i thng tin ca con ngi. HTTT rt a dng, khng ngng pht trin v hon thin. Ty thuc vo tin tc, thit b u cui trong HTTT c th c cc cu to khc nhau, s dng cc phng php bin i tin tc tn hiu khc nhau (v d: TBC l micro chuyn ting ni thnh tn hiu thoi, l loa chuyn tn hiu thoi thnh ting ni). Mi trng truyn dn c hai loi l hu tuyn (c dy) v v tuyn (khng dy). Mi trng truyn dn hu tuyn bao gm cc loi ng dy thng tin nh cp ng nhiu i, cp ng trc, si quang Mi trng truyn dn v tuyn l khong khng bao quanh tri t, chnh l cc tng kh quyn, tng in ly v khong khng v tr khc (khng phi chn khng). Cc HTTT u b nh hng bi nhiu, l cc dng nng lng tc ng lm thay i tn hiu truyn i trong h thng. C nhiu loi nhiu khc nhau do mi trng bn ngoi v chnh cc thit b bn trong tc ng vo h thng, in hnh l nhiu nhit (gy ra bi mch in v cc cu kin in t trong h thng), nhiu in t (st, ng dy in bn ngoi) 11. 8 1.2.3 Khi nim v tn hiu, m ha v iu ch Tn hiu (Signal) Trong HTTH n gin (Hnh 1.3), thng tin trao i c a qua cc chc nng x l cn thit. Trc ht l chc nng bin i thng tin thnh mt i lng vt l trung gian c gi l tn hiu. H thng truyn thng in t thng bao gm cc thc th chc nng x l tn hiu in v t. Nh vy, trong vin thng, tn hiu thc cht l mt dng nng lng mang theo thng tin tch ra c v truyn t ni pht n ni nhn. C nhiu quan im phn loi tn hiu khc nhau trong vin thng. Mt s quan im phn loi thng gp nh sau : - Theo c tnh hm s : Tn hiu lin tc (hay cn gi l tn hiu tng t - Analog) v tn hiu xung. Trong tn hiu xung, c mt h tn hiu quan trng l tn hiu s (Digital). Hai tn hiu tng t v s c nhng chc nng x l khc nhau: o Tn hiu tng t (analog signal), vi cc chc nng x l nh: khuch i tuyn tnh, lc, iu ch, nn gin... o Tn hiu k thut s (digital signal), vi cc chc nng x l nh: m ha, ti to, lu tr, iu ch, xo trn, nn gin, sa li... Cn nh rng, tn hiu tng t v tn hiu s c th cng ti mt thng tin v c th c chuyn i ln nhau. - Theo thng tin (ngun tin): nhn mnh ti bn cht thng tin trong tn hiu, ngi ta thng dng cc thut ng nh: tn hiu m thanh (trong c tn hiu thoi, tn hiu ca nhc ); tn hiu hnh nh (hnh nh tnh, hnh nh ng ); tn hiu d liu. - Theo nng lng mang: Tn hiu c phn chia tng ng vi dng nng lng dng mang thng tin. V d : tn hiu in, tn hiu quang - Theo vng tn s : Tng ng vi vng tn s m ph tn hiu chim gi ta c tn hiu m tn, tn hiu cao tn, tn hiu siu cao tn - Ngoi ra cn nhiu cc phn loi tn hiu khc, ty thuc vo h thng mng v cch thc truyn thng s c gii thiu hoc lm quen sau ny. Hnh 1.4 m t tn hiu thoi tng t v tn hiu thoi k thut s. Tn hiu tng t in hnh l tn hiu c bin bin thin lin tc theo thi gian. Trong Hnh 1.4(a) c v s cc gi tr trong khong i(max) i(min) u c ngha v mt mang thng tin, vi mt mc chnh xc no . Do thng tin c cha ng chnh trong dng ng sng ca hm thi gian nn h thng truyn thng tng t cn phi phn pht bo tn dng ng sng, vi mc trung thc c th. mnh ca tn hiu tng t thay i trong khong 30dB100dB ty theo cc ng dng. Do h thng tng t cn m bo tnh tuyn tnh trong mt di ng tng i ln (t tn hiu yu nht ti tn hiu mnh hn hng nghn ln) 12. 9 t i 0 i(max) i(min) (a) Tn hiu tng t 0 1 2 3 4 i t (b) Tn hiu k thut s 0 1 i t (c) Tn hiu nh phn Hnh 1.4: Tn hiu s v tn hiu tng t Hnh 1.4(b) m t tn hiu k thut s. y ch c hu hn (0;1;2;3;4) gi tr dng in c ngha v mt m ha thng tin, nhng gi tr khc khng c...</p>