🔙 Quay lại trang tải sách pdf ebook Giáo trình báo hiệu và đồng bộ trong mạng viễn thông Ebooks Nhóm Zalo s o g iA o d u c vA dA o t a o hA nOi • • • KS. NGUYfeN THI THU THUY (Chu bien) g i A o TRINH BAO HIEU VA Dtf NG BO TRONG MANG VllN THONG m (Dung trong cac trtfdng THCN) n h A x u A t b an h A n 6i - 2007 n h A x u a t b a n h A n Oi 4 - TONG DUY TAN, QUAN HOAN KlfiM, HA N0I Dign thoai: (04)8.252916. Fax: (04)9.289143_______ g iA o t r i n h BAO HIF.U VA DONG B$ TRONG MANG VllN THONG NHA XUAT BAN HA NOl - 2007 Chiu trach nhifim xu£t ban: NGUYEN KHAC OANH Bien tip: TRUONG DUC HUNG Bla: TRAN QUANG Truth bay - Ky thuat vi ti'nh: THU Hll^N Sua ban in: DONG VAN In 850 cu6'n, khd 17x24cm tai Cfmg ty c6 phan in KHKT. Quyfi't dmh xuat ban s6: 160 - 2007/CXB/467GT - 27/HN. S6 313/CXB ca'p ngay 2/3/2007. In xong va n6p luu chi£u quy III/2007. Lcfi gidi thieu A T uoc ta dang buoc vao thcri ky cong nghiep hoa, hien 1 V dai hoa nham di(a Viet Nam tro thanh nuac cong nghiep van minh, hien dai. Trong su nghiep each mang to Ion do, cong tac dao tao nhan luc luon giu vai trd quan trong. Bao cao Chinh tri cua Ban Chap hanh Trung UOng Dang Cong san Viet Nam tai Dai hoi Dang toan quoc Ian thu IX da chi ro: “Phat trien giao due va dao tao la mot trong nhffng dong lire quan trong thuc day sir nghiep cong nghiep hoa, hien dai hoa, la dieu kien de phat trien nguon lire con ngirdi - yeu to co ban de phat trien xa h6i, tang trudng kinh te nhanh va ben virng”. Quan triet chu truong, Nghi quyet cua Dang va Nha m(dc va nhan thifc dung ddn ve tarn quan trong cua chucmg trinh, giao trinh doi vai viec nang cao chat luong dao tao, theo de nglii cua Set Giao due va Dao tao Ha Noi, ngay 231912003, ■> Uy ban nhan ddn thanh pho Ha Noi da ra Quyet dinh so 5620/QD-UB cho phep So Giao due va Dao tao thuc hien de an bien soan chucmg trinh, giao trinh trong cac trudng Trung hoc chuyen nghiep (THCN) Ha Noi. Quyet dinh nay the hien su quan tarn sau sac cua Thanh uy, UBND thanh pho trong viec nang cao chat luong dao tao va phat trien nguon nhan life Thu do. Tren co so chucmg trinh khung cua Bo Giao due va Dao tao ban hanh va nhung kinh nghiem rut ra tit thuc te dao tao, So Giao due va Dao tao da chi dao cac truong THCN to chuc bien soan chucmg trinh, giao trinh mot each khoa hoc, he 3 thong va cap nliat nhung kien tlnfc thuc tien phii lurp vcn doi tuong hoc sinh THCN Ha Noi. Bo giao trinh nay la tai lieu giang day va hoc tap trong cac trudng THCN d Ha Noi, dong then la tai lieu tham khdo huu ich cho cac trudng co dao tao cac nganh ky thuat - nghiep vu va dong dao ban doc quan tam den van de hudng nghiep, day nghe. Viec to chuc bien soan bo chucmg trinh, giao trinh nay la mot trong nhieu hoat dong thiet thuc cua nganh giao due va dao tao Tlui do de ky niem “50 ndm gidi pliong Thu do ”, “50 ndm thanh lap nganh ” va hudng tdi ky niem “1000 ndm Thang Long - Ha Noi". Sd Giao due va Dao tao Ha Noi chan thanh cam on Thanh uy, UBND, cac so, ban, nganh cua Thanh pho, Vu Giao due chuyen nghiep Bo Giao due va Dao tao, cac nha khoa hoc, cac chuyen gia ddu nganh, cac giang vien, cac nha quan ly, cac nha doanh nghiep da tao dieu kien giup do, dong gop y kien, tham gia Hoi dong phan bien, Hoi dong tham dinh va Hoi dong nghiem thu cac chucmg trinh, giao trinh. Day la Ian ddu tien So Giao due va Dao tao Ha Noi to chuc bien soan chuong trinh, giao trinh. Du da h it sue co gdng nhung chac chdn kliong tranh khoi thieu sot, bat cap. Cluing toi mong nhan duoc nhung y kien dong gop cua ban doc de tifng buoc hoan thien bo giao trinh trong cac Ian tai ban sau. GlAM DOC S6 giA o DUC VA DAO TAO 4 Ldi noi dau T Tien nay, mang ludi viin thong dang duoc quan tam va phat trien rat L i mqnh d Viet Nam nham dap icng nhitng nhu cau phat trien kinh te, xd lioi, chinli tri, an ninh quoc phdng va phuc vu thong tin cho moi tang Idp trong xd hoi. Su phat trien do ddi hoi thdi gian thiet lap cupc goi cung nhu chat luong cac dicli vu vien thong ngay cang phai dupe nang cao. De co dupe dieu nay, can phai co ra c bien phap quy hoach nhuquy hoach dinli tuyen, quy hoach bao hieu, quy hoach dong bo... Tit khi dupe dita vdo dp dung trong cong nghe vien thong ky thuat so da dan ddn khang dinh dupe vi tri va vai trd trong cong nghe vien tliong liien dai. Viec dp dung ky thuat so vdo cong nghe vien thong gop phdn day manh su phat trien cua mang, nang cao chat lupng pliuc vu, gop phdn m o rpng them cac dicli vu cung cap cho klidch hang nham dap itng nhu cau cua khacli hang trong moi mat hoat dong cua xd hoi. Tntoc su phat trien nhanh va manh cua mang vien thong citng voi su phat trien cua ky thuat so, cac ky thuat lien quan den mang so cung dupe nghien citu, trong do phai ke den ky thuat dong bo mang va ke hoach phat trien mang bao liieu. O Viet Nam nliUng ndm gan day, ciing voi sit phat trien cua mang luoi vien thong, mang bao hieu va dong bo cung dang co nhung buoc phat trien dang ke. De tiep can voi kien thuc co ban cua mang bao liieu va dong bo, ddc biet giup cac hoc sinh lie ky thuat vien vien thong co kien thuc co ban ve cac hudng phat trien cua mang bao hieu va mang dong bo vien thong, duoc So Giao due va Dao tao Ha Noi cho phep, cluing tdi da bien soan giao trinh Bao hieu va dong bo trong mang vien thong dua tlieo de cuong mon hoc Bao hieu va dong bo trong mang vien thong cliing cho nganh ky thuat vien vien thong da duoc So duyet. Noi dung chinli duoc de cap bao gom: Phdn I: Bao hieu trong mang vien tliong. Chuong 1: Dai cuoiig ve bao liieu. Chuong 2: Bao hieu kinh ket hop - CAS. Chuong 3: Bao liieu kinh cluing - CCS. Phdn II: Dong bo trong mang vien thong. Chuong I : Tong quan ve ky thuat dong bo mang. Chuong 2: Dong bo trong cac tdng dai. Chuong 3: Mang dong bo vien thong Viet Nam. Voi chuong trinh dao tao trung cap, giao trinh se trang bi cho cac ky thuat vien viin thong nhung kien thilrc co ban, can thiet ve cau true mang bao hieu, mang dong bo vien thong, cac ky thuat dong bo mang va thuc te ve van de bao liieu va dong bo trong mang vien thong Viet Nam. Mong rang cuon giao trinh nay phdn ndo se giiip cho cac ky thuat vien co the tiep can duoc voi thuc te trong cac ky thuc tap cung nhu sau khi tot nghiep; dong thdi cung co the Id tdi lieu tham khao cho cac doc gia muon di sau vdo nghien cifu mang bao liieu va mang dong bo. Cac noi dung trong giao trinh duoc de cap tuong doi day dii va phii hop cho chuong trinh trung cap. Mac dii da rat co gang, tuy nhien giao trinh kho tranli khoi sai sot, cluing tdi rat mong nhan duoc y kien dong gop cua doc gia. Tac gia 6 Phan I bAo hieu trong mang ■ ■ viIn thong 7 Chtfcfng 1 DAI CLfONG vfi BAO HlfiU • • Muc tieu Phan rich qua trinh phat trien cua mang bao hieu, cac churc nang cua bao hieu, cac thanh phan cua bao hieu va phan loai bao hieu. Noi dung tong quat Chuang nay cung cap cac kien thurc ve he thong bao hieu, mot so cac khai niem lien quan den bao hieu, vai tro cua bao hieu, cac nhom chuc nang cua bao hieu, phan loai bao hieu. Sau khi hoc xong chuang nay, hoc sinh ndm duoc vai tro, dac diem, churc nang cua bao hieu. Phan tich cac thanh phan cua mang bao hieu, cac he thong bao hieu trong mang vi£n thong. Phan tich he thong bao hieu va so sanh giua cac he thong bao hieu nhu bao hieu dan tan, da tan, bao hieu trong bang, bao hieu ngoai bang... I. DINH NGHlA VA VAI TRO CUA BAO HIEU 1. Ojnh nghTa ve bao hieu Trong cuoc song thuang ngay ta gap nhieu cach thuc va cac he thong bao hieu khac nhau. Do la cac he thong bao hieu trong giao thong, trong dieu khien tir dong... 0 vi^n thong, bao hieu (Signalling) la mot phuang tien hay mot he thong de chuyen cac thong tin va cac lenh tir diem nay den diem khac trong mang, dung de dieu khien xu ly goi va quan ly mang. Cung co the dinh nghTa bao hieu la nhung goi so lieu, tin turc (co dac trung khong phai la tieng noi) dirac sir dung de hinh thanh duong truven. dieu khien dirong truyen cung nhu trao dcii thong tin dieu khien gitra cac mang vai nhau. Vi du: Cac tin hieu de’ thiet lap, giam sat duang ket noi giua thue bao nav vai thue bao khac trong cung mot dai hoac giua cac dai khac nhau. 9 Tong dai A T6ng dai B Thue bao Hinh 1.1. Mo lunli mang (lien thoai Cac thong tin - cac lenh nay co lien quan den viec to churc. thiet lap. giam sat quan ly va giai phong mot cuoc goi. Co the dinh nghTa bao hieu la nhung tin hieu chi dan de: - Thiet lap. - Giam sat (Quan ly). - Giai phong mot cuoc goi. Nhu vay, tren mang ngoai tin hieu trao d6i thong tin giua cac cuoc goi con co cac tin hieu ve bao hieu. Cac tin hieu nay tham chi cung duoc xir ly, to chuc theo nhieu phuong phap khac nhau, theo nhung cong nghe khac nhau til don gian den phurc tap, tir analog den digital... Can hieu ring bao hieu cung to churc nhu mot he thong thur hai song song voi he thong lien lac co san. Truac khi tim hieu tong quat \ i cac phuong phap va tieu chuain cua bao hieu, mot van de quan trong can duoc lam ro la tim hieu \6 mot so cac tin hieu bao hieu co ban. 2. Vai net ve cac tin hieu bao hieu co ban Cac tin hieu bao hieu co ban la nhirng tin hieu duoc tao ra hoac nhan ve 6 may thue bao. Do cac tfnh nang ky thuat cua tung the he may, co cac dang tin hieu bao hieu co ban la cac xung hay cac tone sau: 2.1. Bao hieu tuong tir va bao hieu so Theo truyen thong, cac PABX tong dai co quan da dau noi boi cac ducmg day trung ke tuang tu dan gian de truyen cac thong tin trong bang tan thoai. Hien nay, cac he thong thong tin tuong tu khong con su dung rong rai nhu trudc kia, trong rat nhieu truang hcrp, chung da duoc thay the bai cac phuong tien so toe do cao va gia thanh re han. Bao hieu so la mot trong nhung kieu bao hieu dien thoai ph6 bien nhat de su dung lien ket va cung cap dich vu cua cac mang hien nay. 10 2.2. Bao hieu dong dien mot chieu (DC) Kieu bao hieu nay sir dung dong dien mot chieu (DC) de bao hieu tori tong dai hoac he thong chuyen mach. Bao hieu DC chi ra trang thai thay doi boi viec khoa hoac ngat dong mot chieu DC. Cac tong dai sir dung mot bo giam sat dong de xac nhan sir thay d6i trang thai. Bao hieu DC duoc sir dung trong hai loai bao hieu sau: 2.2.1. M ach vdng thue bao Day la mot dang rat don gian cua bao hieu DC giua thue bao va tong dai ket cuoi. Khi thue bao nhac to hop, tiep diem nhac/dat cua may dien thoai kin mach mot chieu, dong DC se duoc chuyen qua duong day hoac mach vong giua thue bao va tong dai ket cuoi. Mach duong day thue bao trong tong dai duoc lap dat bo giam sat dong se phat hien ra yeu cau dau noi. Khi thue bao dat to hop, tiep diem nhac, dat t6 hop se ho mach mot chieu. Tuong tu nhu trong trang thai nhac to hop, su thay d6i trang thai dong mot chieu DC tu trang thai ho mach sang trang thai km mach se bao hieu tdi tong dai ket cuoi rang cuoc goi da ngat. Trong trudng hop nay, tren cung mot doi day duoc dung de cap cho ca duong truyen thoai va bao hieu. 2.2.2. N han va truyen (E&M) Day la mot dang bao hieu trung ke su dung kieu dong mot chieu DC de xac nhan sir thay doi trang thai cua trung ke tuong tu hoac tie - line. Trong kieu bao hieu E&M, hai day - mot goi la day E va mot goi la day M duoc dung de! bao hieu. Hoan toan co the xac dinh duoc dau la day E va dau la day M qua viec dat vao do dien ap da't (ground) hoac mot dien ap duong. Cac xung dong mot chieu nay xuat hien khi thong bao chon cac dia chi cua may thue bao bj goi. Thuc chat la cac xung cua cac con so may quay so. Do ca'u tao cua may, ung voi m6i so quay cho mot so luong xung tuong ung voi tieu chuan: - Do rong xung: 40ms. - Khoang cach giua cac xung: 60ms. Chung duoc hinh thanh tu nguon mot chieu (DC) cua tong dai noi hat cap cho may thue bao va sir chap nhan nha dia so luc quay v&. Dang tin hieu DC nay duoc minh hoa 6 hinh 1.2. 11 (mure thaip) Hinh 1.2. Xnng dong DC bien dien con so 2 Thong thirong tieu chuan duoc thong nhat do nhu cau cau tao dia so cua cac nha san xuat: 50 1 1 xung 50 2 2 xung 50 3 3 xung SoO___ 10 xung Cac con so dia chi nay duoc giri den tong dai gan nhat. Tong dai co nhiem vu thu nhan, xir ly va giri den thue bao bi goi. 2.3. Bao hieu trong bang va bao hieu ngoai bang Bao hieu trong bang sir dung tone (am hieu) thay cho bao hieu DC. Cac tone nay duoc truyen tren cung mot phuong tien nhu dien thoai, vi vay no nam trong bang tan thoai tir 0 - 4KHz. Cac tone nay gom co don tan, da tan (MF), va da tan ket hop (DTMF) nhu mo ta dudi day: 2.3.1. Don tan Dang tone nay duoc sir dung cho cac trung ke lien dai co hai trang thai: dat to hop hoac r6i, nhac to hop hoac ban. Vi vay, khong co tone the hien khi co dau noi. Khi mot trong hai thue bao dat to hop. tin hieu tan so 260Hz se duoc truyen tren mach de bao hieu tdi tong dai tham gia ket noi trang thai ngat dau noi cua thue bao. Doi khi. tone don tan duoc sir dung de chong lai su vi pham cac dich vu dudng dai tir cac nha cung cap dich vu. Ngudi sir dung dich vu gian lan dat vao dudng day cua ho mot “hop xanh” de sir dung vdi muc dich giri tin hieu 2600Hz tdi cac tdng dai nhu la mot bao hieu xoa hudng di. Cac tong dai trung gian chap nhan duoc con so bi goi va tin tudng rang tdng dai noi 12 hat muon tra cudc phi cho cuoc goi do. Vide truy cap tdi tong dai trung gian thudng duoc thuc hien bdi viec quay so 0 va se truyen di tdi tdng dai ke tiep tren dudng trung ke trudc khi ngudi dieu hanh tra Idi. Mot vai nha cung cap dich vu tham chi muon phong toa hoat dong nay bang cach cai thien mure do bao ve. 2.3.2. MF Loai tone nay duoc su dung d cac trung ke lien dai de xac nhan cac sir kien nhu la: bao chiem, giai phong, tra ldi va xac nhan, truyen thong tin nhu so chii goi. Bao hieu MF su dung mot td hop tan so' de bao hieu qua mang. Cac tan so nay dac trung doi vdi tirng he thd'ng va se duoc de cap ky hon trong cac muc CAS, R 1, R2 d phan sau. Bao hieu MF sir dung cung mot phuong tien nhu tuyen dudng thoai, vi vay no se co hieu xuat thap hon so vdi he thong bao hieu kenh chung (CCS) nhu la bao hieu so 7. 2.3.3. DTMF Day la mot dang dia chi duoc sir dung de truyen cac chu so dia chi tir thue bao tdi tong dai ket cuoi. Su phat trien cua bao hieu DTMF se thay the cac bo dao dong dung transitor trong may dien thoai bang ban phim va cac bo dao dong da tan ket hop. Cac tone DTMF xac nhan cac con so tir 0 den 9 va cac ky hieu * va #. Khi thue bao nhan mot trong cac phim nay, bo dao dong se giri hai tone ddng thdi. Cac con so se duoc the hien bdi mot td hop hai tan so nha't djnh: Mot d trong nhom tan so thap (697, 770, 852, 941 Hz) va mot d trong nhom tan so cao (1290, 1336, 1477, 1633Hz). Nhu vay, co the tao ra 16 to hop con so. Tuy nhien, thudng chi co 12 con so duoc the hien tren ban phim cua mot may dien thoai thong thudng. Td hop ciia hai tan sd xuat hien khi chii goi la may an phim. Do CCITT khuyen nghi, cac may dien thoai an phim deu ca'u tao cac con so dia chi theo mdt tieu chudn thong nhat tir mot ma tran don gian theo hang va cot. Nhu vay, mdi sd' la td hop cua 2 tan so theo hang va cot tuong ung: So 1: td hop cua 697 va 1209Hz. Sd 2: td hop cua 697 va 1336Hz. Sd 3: td h<^> ciia 697 va 1477Hz. Mdi td hop do deu xuat hien khi ta “nhan” sd va duoc truyen len dudng thue bao tdi tdng dai. Tdng dai nhan duoc se phan tich va xac nhan chu sd dia chi. V iec xir ly cac thong tin dia chi va thong bao di cac noi tuy thuoc cac he thdng bao hieu duoc irng dung tren mang va tren cac tong dai. 13 Tuy cac loai bao hieu (mach vong thue bao hay lien dai ) va cac c6ng ngh£ bao hieu khac nhau ma co cac cach thuc khac nhau. Bang tone cua no nhu hinh 1.3. 697 --------- 1I d L J L ± J 770 --------- 4h i 0 H 852 7............... 18 1...........G D ......- t u 941 (Hz)# D 1209 1336 1477 Hinh 1.3. Bang tone may an phim 2.4. Bao hieu tiep vong va bao hieu tiep dat 1633 (Hz) Co hai phuong phap pho bien nhat cho cac bao hieu ket cudi la bao hieu tiep vong va bao hieu tiep dat. 2.4.1. Bao hieu tiep vdng Day la mot phuong phap bao hieu don gian nha't va kern thong minh nhat trong hai kieu bao hieu. No cung la mot dang pho bien nhat cua bao hieu mach vong thue bao. Thu tuc bao hieu hoat dong co ban nhu bao hieu giua thue bao va tdng dai ket cuoi, do do tao ra cac khoi tao mach vong cho cuoc goi va ngat cho mot tien trinh ket thuc cuoc goi. Bao hieu tiep vong khong thong dung trong cac he thong bao hieu cua tong dai PBX va no co mot diem han che quan trong, khi trang thai doi dau (glare) xay ra. Glare xay ra khi thue bao chu goi va bi goi cung muon chiem duong tai mot thdi diem, va thudng xuyen co ket qua la 2 thue bao deu duoc dau noi ma ho khong nhan tha'y. M6t nguoi nha'c may len va nghi rang minh se nghe duoc am moi quay so, nhung nguoi do khong biet rang thuc chat cuoc goi cua minh da duoc dau noi, va chu goi lai khong phai la minh. 14 2.4.2. Bao hieu tiep dat Thu tuc bao hieu nay khac vdi bao hieu tiep vong, no cung cap sir xac nhan chac chan cua ket noi va ngat ket noi. Cac ky thuat phat hien dong duoc sir dung tai m6i dau cuoi trung ke, cho phep tdng dai thoa thuan trung nao se bi chiem trudc khi trung ke do thuc sir bj chiem. Dang bao hieu nay giam toi thieu hieu urng glare va vdi gia thanh tuong tir nhu bao hieu tiep vong. Nhu vay, phuong phap bao hieu tiep dat duoc ua chudng hon trong cac he thong PBX. 2.5. Cac tone bao hieu chuan mang tin khac nhau Dudng day thue bao ngoai churc nang tao tuyen va truyen cac tin hieu dia chi con co nhiem vu truyen tai cac tone (am bao) khac. Khi nha'c td hop, cong tac nhac dat td hop dong mach va truyen di mot tin hieu yeu cau quay so' (yeu cau cuoc goi). d trang thai binh thudng, tdng dai gan nha't se giri den mot am mdi quay so. Do la mot tin hieu 425Hz duoc truyen ve lien tuc ma d tai nghe ta van nhan bie't. Sau khi quay so neu truyen noi binh thudng, se co tin hieu rung chuong giri den may bi goi. Tuong irng d phfa chii goi ta co the nhan duoc tin hieu hoi am chuong. Mdi quay so -------------------------------------------------------------- 425Hz Chuong/ hoi am chuong ls_____ ° ’5s ______ls 425Hz 2.25s 0,75s 2,25s425Hz 0.25s Ban ................................................................................................... 425Hz 75 ms 1,5s 75 ms Nghiep vu ----- ----- 425Hz Tone dac biet________ 1800 ________ _________ 1800Hz _______ 1400 _________ _______ 1400Hz _____ 950 ______ ______ 950Hz Hinh 1.4. Cac tone (dm bao). 15 Neu doi phirong ban hay tac nghen duong truyen, chu goi co the nhan biet qua tone bao giri lai cung 6 425Hz va tieu chuain thdi gian co va khong co tone nhu hinh 1.4. Chu y 1: Trir tone dac biet co tan so thay doi cao dan 6 3 muc: 950Hz, 1400Hz va 1800Hz, cac tone con lai deu la 425Hz. Chu y 2: Cac net ve dam la tuong urng vdi thdi han co tone hinh sin. Chu y 3: Tieu chuan thdi gian cu the: - Tone mdi quay sd: Gan nhu lien tuc. - Tone hoi am chuong va chudng: Co tone Is: nghi 5s. - Bao ban: co 0,25s: nghi 0,2s. - Tac nghen: co 2,25s: nghi 0,75s. - Xam nhap nghiep vu: co 75ms: nghi 1,5s. - Tone dac biet: 3 tone lien tuc 0,75s: nghi Is. Ngoai ra, ta con co cac tone bao khac cho nghiep vu hay sir co dac biet. 2.6. Cac loai bao hieu AC khac Thuc ra bao hieu xoay chieu la rat thong dung vi bao hieu DC khong the di xa duoc. Do do, cac tdng dai thudng co cac bo giao tiep de bien ddi cac tin hieu bao hieu DC thanh tin hieu bao hieu AC. Cac tin hieu AC co the truyen d trong bang, ngoai bang va AC tan thap. - Cac tan sd trong bang thudng dung tir 2000Hz + 3000Hz, noi nang luong tieng noi tap trung ft. Nhuoc diem ciia bao hieu trong bang la de dung nham nen can co cac giai phong dac biet nhu dung bo loc, bo tre de cho tin hieu bao hieu di qua ri6ng biet de dang. - Bao hieu ngoai bang thudng dung cac tan sd 3700Hz hoac 3825Hz. Uu diem cua bao hieu ngoai bang la co the thuc hien duoc sir giam sat lien tuc du co tieng noi hay khong co tie'ng noi. Mot uu diem nua la khong bi tac dong nham nhu loai bao hieu trong bang. Nhuoc diem ciia bao hieu ngoai bang la ky thuat phirc tap hon, kinh phi ton kern hon. - Bao hieu AC tan thap. Thuc chat cung la bao hieu ngoai bang vdi cac tan so bao hieu nho hon 300Hz. Cac tan sd ciia tin hieu bao hieu co the dung: 50Hz, 80 - 135Hz hoac 200Hz. 16 Dac diem cua bao hieu AC tan thap la don gian nhung cu ly bi han che va chat luong kern do suy hao va meo. 2.7. CAS va CCS Hien nay, he thong bao hieu kenh lien ket CAS ton tai trong rat nhieu mang. He thong CAS da duoc phat trien bdi nhieu nha cung cap thiet bi khac nhau, vi vay no ton tai nhieu phien ban va bien the khac nhau. Mang vien thong hien nay yeu cau hieu qua hon trong cong tac bao hieu, vi vay phuong phap bao hieu chuyen sang bao hieu kenh chung CCS. CCS su dung mot lien ket chung de mang thong tin bao hieu cho mot so cac trung ke. Kieu bao hieu nay kinh te hon, thdi gian dau noi nhanh hon va mem deo hon he thong CAS. 3. Vai tro cua bao hieu Bao hieu lien quan chat che den ky thuat mang noi chung va den cac nut (node) hay cac tong dai noi rieng. Bao hieu se tac dong den cac tdng dai SPC va tao ra cac hoat dong linh hoat, dap ung cac loai hinh dich vu khac nhau. Bao hieu giup cho cac co sd d dir lieu va cac nut “thong minh” trong mang trao doi cac thong tin dau noi va giam sat cuoc goi. Bao hieu se trao ddi, thong bao nhung thong tin ve nguyen vong, nhu cau cua dich vu, nhung trang thai, tinh trang ciia he thong vien thong, nhung con sd dia chi dau noi tren pham vi toan mang, nhung thong tin ve cuoc phi... Tom lai, co the noi bao hieu la mot he thong than kinh trung uong ciia co the mang, no phoi hop va dieu khien cac chuc nang ciia cac bo phan trong mang vien thong. II. PHAN LOAI HE THONG BAo HIEU Sir phat trien ciia bao hieu gfin lien vdi sir phat trien ciia mang vien thong. Mang vi^n thong trai qua nhieu giai doan phat trien khac nhau, cong nghe vien thong luon thay ddi va ngay cang hien dai hon. Vi vay, kha nang va nhu cau dich vu vien thong ngay cang phong phu nen bao hieu cung xuat hien va ton tai qua nhieu he thong va cong nghe khac nhau. Co the neu ra cac he thong bao hieu: - He thong bao hieu tirong tu (E&M). - He thong bao hieu da tan R 1 (Bfic My). 17 - He thong bao hieu da tan R2 - Da tan bat buoc d cac nude chau Au, A, chau Dai Duong, chau Phi va Trung Nam My. - Cac he thong bao hieu so 4 va so 5 cho cac duong vien thong quoc te cap bien va ve tinh. - Bao hieu kenh ket hop (CAS) hay bao hieu kenh chung (CCS). Hien nay, he thong bao hieu kenh lien ket CAS t6n tai trong rat nhieu mang. He thong CAS mang thong tin ve cac kenh trung ke tren chinh cac trung ke do. He thong CAS da duoc phat trie’n bdi nhieu nha cung cap cac dich vu khac nhau, vi vay phuong phap bao hieu chuyen sang he thong bao hieu kenh chung nhu CCS. CCS sir dung mot lien ket chung de mang cac thong tin bao hieu cho mot sd cac trung ke. Kieu bao hieu nay kinh te hon, thdi gian dau noi nhanh hon va mem deo hon he thong CAS. The he dau tien ciia he thong bao hieu kenh chung la he thong bao hieu SS6. the he thur hai la he thong SS7 duoc trinh bay trong chuang 3. Noi tom lai, co the phan chia ra cac loai bao hieu khac nhau. Thong thudng bao hieu duoc chia thanh hai loai: 1. Bao hieu dudng thue bao hay bao hieu mach vong thue bao La bao hieu giua tong dai noi hat den thue bao va nguac lai. Bao hieu giua thue bao vdi tong dai co chuc nang dieu khien viec thiet lap va giai toa dudng ket noi; giam sat dudng ket noi va cung cap cac thong tin can thiet cho thue bao. Neu ai da tirng dung dien thoai, hay de y den tirng thao tac va cac tin hieu hay cac am bao (tone) xuat hien trong qua trinh thiet lap hay giai toa mot cuoc goi (a call). Hinh ve 1.5 se minh hoa cu the cac tien trinh sau. - Khi thue bao chii goi co nhu cau dich vu va nhac to hop. mot tin hieu duoc giri tdi tong dai bao cho biet co nhu cau dich vu. Do chi'nh la tin hieu nha'c to hop (hook off). - Tdng dai co thiet bi thu va nhan, biet duoc tin hieu nhac td hop sau do giri tin hieu mdi quay sd cho thue bao chu goi. - Thue bao chu goi quay (nhan) sd ciia thue bao bi goi. Do la cac thong tin dia chi ciia thue bao bi goi. Cac chu sd co the duoc phat di bang 2 cach: Tin hieu xung thap phan hoac tin hieu luong am da tan (DTMF). Tin hieu xung thap phan: Tin hieu nay duoc tao ra tir cac may dien thoai dung dia quay sd hoac an phim dung phuong thuc phat xung (pulse). Mdi chur 18 so (dia chi) duoc dac trirng bdi mot loat xung tuong umg, ngoai trCr so 0 la 10 xung. Day la qua trinh lam dong ngat lien tuc mach vong duong day thue bao theo nhip xung (thudng ty le dong ngat la 1:2). Phuong thuc nay doi hoi phai co thdi gian dung giira hai chu sd lien tiep khoang vai tram ms de cho phep tong dai phan biet duoc cac chu so ke tiep. Tdc do truyen xung toi da la 11 xung/ giay. Do do phuong thuc nay cham va tin hieu dia chi khong phat duoc trong giai doan thoai. Tin hieu DTMF (Dual Multi Frequency): Phuong thuc nay su dung hai bo 4 tan so nam trong bang tan tieng noi. An mot phim tao ra mot tin hieu gdm 2 tan sd, mdi tan sd cho mdi nhom. Vi vay, no duoc goi la DTMF. Tin hieu nay duoc phat di ngay sau khi phim duoc an. Tan sd cao nha't la 1633Hz hien nay chua duoc dung. Thue bao chii goi Nha'c t6 hop (1) _ Mdi quay sd Cac con sd (3) Thue bao bi goi (2) Hoi am chudng (4) Dong chudng Tra ldi (nhac to hop)(5) Cat hdi am chudng (6) Cat dong chudng (7) Hdi thoai (8) Dat to hop Dat td hop (9) *— Hinh 1.5. Lkoc do bao hieu dudng thue bao 19 Bang phuong phap nay, thdi gian quay sd se giam di ra't nhieu vi nhu 10 chu sd co the phat di trong mot giay. Mat khac, khi sir dung tan sd trong bang tan tieng noi, thong tin dja chi co the duoc phat di trong giai doan dam thoai de thiet lap cuoc goi khac. Viec lira chon cac tan sd nay dam bao yeu cau la chong duoc sir phong tao dia chi theo am thanh khi noi chuyen. - Tdng dai nhan biet duoc cac thong tin do va td churc da'u noi bang cach gui mot trong cac tin hieu sau den thue bao chu goi: + Tin hieu hoi am chudng neu thue bao bi goi roi, khi do thue bao chu goi se nhan duoc tin hieu hdi am chudng ra't ro. Tin hieu chudng co tan so 20, 25 hoac 50Hz, dien ap 60V den 85V. + Tin hieu bao ban neu thue bao bi goi ban. + Mot thong bao de’ bao cuoc goi bi that bai khac vdi trudng hop thue bao bi goi ban. - Thue bao bi goi nhac td hop tra ldi, tdng tro dudng day giam xuong thap, tdng dai phat hien viec nay. - Tdng dai cat tin hieu rung chudng va hoi am chudng. Phi'a chu goi biet doi tac cua minh da tiep nhan cuoc goi. - Hai ben tien hanh dam thoai. - Neu thue bao chu goi dat td hop trudc thi tin hieu dat td hop (Hook on) duoc bao den tdng dai. - Hoan toan tuong tu ddi vdi thue bao bi goi du dat td hop sau hay trudc. Khi do cuoc goi da duoc cat, d loai bao hieu nay ta co the du doan nhung tin hieu can trao doi giua cac thue bao chu goi, thue bao bi goi den tdng dai noi hat va nguoc lai. 2. Bao hieu lien dai hay con goi la bao hieu giua cac tong dai vdi nhau O hinh 1.6. cac tin hieu duoc trao doi giua hai nut qua dudng day trung ke. Do la qua trinh bao hieu xay ra giua hai tdng dai A va tdng dai B hoac qua cac tdng dai khac hay cac hudng khac. Loai bao hieu nay chi lien quan den cac thong tin trao doi giua cac tdng dai. Bao hieu lien dai co the’ duoc phat qua mdi mach trung ke lien dai. Cac tin hieu nay gom cac tin hieu bao hieu dudng (Line Siznalling) va cac tin hieu bao hieu ghi phat (Register Siznalling). Hinh 1.6 mo ta tien trinh bao hieu lien dai. 20 Noi dung co ban cua no la nhung thong tin giam sat trang thai duong va nhung thong tin dia chi trao d6i giua 2 t6ng dai. Cac buoc nhu sau: - Khi thue bao chu goi can goi: Tong dai A se phat tin hieu chiem. - Tin hieu xac nhan chiem. - Cac thong tin ve dia chi. - Thue bao goi tra loi. - Hoi thoai. - Xoa nguoc. - Xoa thuan. Bao hieu lien dai co the phan lam hai loai: - Bao hieu kenh rieng (hay bao hieu kenh lien ket) CAS (Channel Associated Signalling). - Bao hieu kenh chung CCS (Common Channel Signalling). Chi tiet ve nhung loai tin hieu nay duoc trinh bay o phan sau. 21 Mo phone ve sir phan chia bao hieu co the trinh bay bang cau true nhu hinh 1.7. Hinh 1.7. Phdn chia he thong bao hieu. Ngoai ra, tren duong day thue bao con xuat hien cac tin hieu khac: - Nguon mot chieu: Do tong dai cap cho thue bao, thudng co dien ap la 48V. - Nguon thu: Duoc cung cap bat chap tinh trang cua thue bao. - Cac am hieu trong trudng hop su dung cac dich vu dac biet. - Cac thong bao trong cac trudng hop: May bi khoa do thieu cuoc. goi sai sd hay so khong co trong danh ba, tuyen noi bi nghen hay ban. Tren day la su mo phong tdng quat ve cac loai tin hieu bao hieu. noi dung chi tiet duoc de cap d chuong 2 va 3. III. CAC NHOM CHUC NANG CUA BAO HIEU Mot cach tdng quat, co the phan ra cac nhom chuc nang cua bao hieu nhu sau: 1. Churc nang giam sat Thuat ngu giam sat trong trudng hop nay duoc dung theo y nghTa cua cac dac tmh ddi. Do la trang thai: - Co tra ldi/khong tra ldi. - Ban/rd i. - San sang/khong san sang. 22 - Binh thudng/khong binh thudng. - Duy tri/giai toa. Nhu vay, cac tin hieu giam sat duoc dung de xem xet cac dac tfnh san co cua cac thiet bj tren mang cung nhu cua thue bao. Chung cung duoc xem xet va trao doi ve cac trang thai cua cac thiet bi. Co the noi, bao hieu giam sat duoc dung de cung cap cac dieu kien va phuong tien de thiet lap cuoc goi. Do la viec khdi tao cuoc goi, bat dau hoac giai phong tuyen noi, bat dau va ket thuc tinh cudfc. 2. Churc nang tim chon Nhom chuc nang tim chon chinh la churc nang dia chi. Cac chuc nang nay lien quan den thu tuc dau noi: - Bao hieu ve dia chi - cac con so, ma sd. - Dinh tuyen, dinh vi tri va cap chiing cho thue bao bi goi. - Thong bao kha nang tiep nhan con sd . - Thong bao gui cac con sd tiep theo trong qua trinh tim dia chi. Churc nang tim chon co lien quan den thdi gian dau noi mot cuoc goi ma true tiep la thdi gian tr£ quay sd (PDD - Post Dialling Delay). Thdi gian tr£ quay sd la khoang thdi gian tu khi thue bao chu goi hoan thanh quay sd den khi nhan duoc hdi am chudng con goi la thdi gian thiet lap cuoc goi. Bao gom: Thdi gian xir ly tai cac tong dai va thdi gian truyen bao hieu cua cac tong dai (chu yeu la thdi gian truyen bao hieu cua cac tcing dai). Duong nhien PDD phu thuoc vao kha nang xir ly bao hieu giua cac tdng dai, turc la kha nang tim chon cua he thong bao hieu. Nhu vay, co nghTa la cac he thong bao hieu khac nhau se co thdi gian tr6 quay sd khac nhau. PDD la mot tieu chuain rat quan trong. Can PDD cang nho cang tot de thdi gian thiet lap cuoc goi cang nhanh, hieu qua xam nhap vao mang cang cao. 3. Cac churc nang van hanh va quan ly Hai chuc nang tren chi lien quan den qua trinh xir ly va thiet lap cuoc goi. Chuc nang thu ba nay nham sir dung mang ludi tdi uu nhat. Cac chirc nang hay cac tin hieu quan ly co ban la: - Nhan biet va van chuyen cac thong tin ve trang thai tac nghen trong mang. 23 - Thong bao ve cac thiet bi, cac trung ke dang bao duong hay binh thudng. - Cung cap cac thong tin vd cuoc phi. - Cac thong tin danh gia ve viec dong chinh canh bao cua cac tong dai. Tom lai. cac churc nang quan ly ngay cang phong phu va phurc tap. Do la cac churc nang duoc md rong bao trum len toan bo mang va phu hop tinh hinh phat trien cua mang. IV. CAC YEU CAU DOI v O l HE THONG BAO HIEU Yeu cau tong quat cua he thong bao hieu la cac tdng dai deu hieu duoc ban tin hay cac thong tin bao hieu giua chung va co toe do xu ly nhanh. Co the neu cac yeu cau cu the sau: - Toe do bao hieu nhanh de giam thieu thdi gian thiet lap cuoc goi hay thdi gian trd sau quay sd. - Tranh khong anh hudng hay giao thoa giua thong tin thoai va bao hieu. - Co do tin cay cao, rung chudng dung thue bao, khong lac dia chi. - Thdi gian cung cap cac tin hieu “mdi” hay “bao” phai nhanh nhat. - Thdi gian chuyen cac con sd dia chi giua cac tdng dai phai nhanh nhat. - Thdi gian quay sd nhanh nhat (tuy thuoc vao ky thuat may dien thoai). Noi chung. cac yeu to co lien quan den cac yeu cau hay cac chi lieu tren la: - Kfch cd. pham vi cua mang va cac tdng dai. - Sd thue bao so vdi dung luong hay kha nang chuyen mach cua cac tdng dai. - Kieu goi sd cua cac may dien thoai. - Toe do truyen dan cua mang. - Cac kieu he thong bao hieu. Cau hoi on tap chudng 1 1. Cho biet vai tro va chifc nang cua bao hieu? 2. Phan loai he thong bao hieu? 3. The nao la bao hieu giCra thue bao va tong dai? Hay phan tich mo hinh cua bao hieu nay? 4. The nao la bao hieu giua cac tong dai? Hay phan tich mo hinh cua bao hieu nay7 5. Hay phan tich cac yeu cau doi vdi he thong bao hieu? 24 Chu’dng 2 bA o h i £ u k £ n h k £ t H O P - C A S • • M uc tieu - Phan tich dac diem , sir phat trien, pham vi urng dung bao hieu kenh rieng (ket hop) - CAS. - Tim hieu bao hieu ma da tan MFC - R2 ve dac tfnh, cau true cac tin hieu duong, tin hieu ghi phat va cac kieu truyen thong tin bao hieu. Noi dung tong quat - Gidi thieu chung ve CAS, cac dac tfnh chung cua CAS, phan loai CAS, bao hieu R2, cac tin hieu bao hieu duong hudng di va hudng v£ cho ca hai phuong an tuong tu va sd. Cac tin hieu bao hieu ghi phat hudng di va ve. - Chuong 2 cung cap kien thuc ve he thong bao hieu kenh ket hop hay con goi la he thong bao hieu kenh rieng - CAS. Trong noi dung nay can ndm duoc dac diem mo hinh he thong bao hieu kenh rieng, uu nhuoc diem cua CAS, mot sd loai bao hieu kenh rieng nhu bao hieu MF he thong Bell, bao hieu N°5, va dac biet la bao hieu R2. I. DAC DIEM CHUNG VA S1/ PHAT TRIEN CUA BAO HIEU KENH KET HOP - CAS 1. Khai niem va mo hinh bao hieu kenh ket hop - CAS Bao hieu kenh ket hop (Channel Associated Signalling) la he thong bao hieu dung de truyen di cac tin hieu bao hieu giua cac tdng dai ma trong do cac kenh bao hieu duoc truyen tren cung dudng trung ke truyen tin hieu thoai. No con duoc goi la bao hieu kenh rieng vi cac kenh bao hieu duoc truyen doc lap vdi nhau tren cac dudng trung ke rieng biet, mdi mot kenh thoai su dung rieng mot trung ke de truyen tin hieu thoai va tin hieu bao hieu. 25 Tom lai, goi la kenh ket hop vi 6 day bao hieu nam trong kenh tieng. giong nhu bao hieu trong bang hoac bao hieu co lien quan chat che den mdt kenh tieng. Con goi la kenh rieng la do m6i cuoc goi can cung cap rieng mGt he thong tin hieu bao hieu ma khong the dung chung cho nhidu cuoc goi. NghTa la: - Tren duong thong thoai: Thong tin bao hieu va thoai duoc chia se liru luong tren cung mot kenh, thong tin bao hieu se duoc truyen trong khoang thai gian khong phat tin hieu thoai. Noi cach khac, viec truyen thong tin bao hieu se duoc gidi han cho den khi thue bao bi goi nhac may tra ldi. Vi du: Cac tin hieu bao hieu trong bang. Tai cac tdng dai chuyen tiep day la nguyen tac hoat dong cung nhu yeu cau ket noi cho nhieu kenh luu luong. Khi co yeu cau ket noi, thong tin bao hieu se duoc thiet lap tren mot kenh trong mot khoang thdi gian nhat dinh, neu co yeu cau ket noi tiep theo thi thong tin bao hieu bat dau duoc thiet lap tren kenh ke tiep. Dieu nay se gay ra viec tang tong thdi gian thiet lap cuoc goi tu thdi diem ngudn den dich. - Tren kenh lien ket: Thong tin bao hieu co the duoc chuyen giao trong mot kenh bao hieu rieng biet. Vi du: Trong he thong PCM30, cac tin hieu dudng day duoc chuyen giao d khe thdi gian TS16. May dien Dau cuoi Dau cuoi thoai CAS CAS Cac truns ke SIGl SIGl 1r r SIG SIG 2 SIGn SIGn SIG: Thiet bi bao hieu Hinh 2.1. He thong bao hieu CAS 26 May dien thoai Ro rang d loai CAS kenh bao hieu ket hop dn dinh vdi mot kenh tieng xac dinh. 2. Tong quan chung ve CAS CAS ton tai nhieu bien the khac nhau va hoat dong tren cac trung ke lien ket tuong tu va so khac nhau. Tren duong trung ke tuong tir gom ca hai kieu 2 day va 4 day, tren cac duong trung ke so nhu chuan El cua chau Au va chuan T1 cua Bdc My. Diem quan trong can phai thao lu$n trong he thong bao hieu CAS la bao hieu giam sat va bao hieu dia chi qua cac phuong tien trung ke tuong tu va so. He thong Bell dung bao hieu MF trong bang de bao hieu dia chi. De bao hieu trang thai giam sat he thong Bell su dung ky thuat don tan cho dudng trung ke tuong tu va bit a/b cho cac trung ke sd. CCITT N"5 da hoach dinh cho cac trung ke tuong tu sir dung cac tin hieu MF de bao hieu giam sat va bao hieu dia chi. Bo giam sat tone trong bang duoc sir dung de phat hien va giao tiep vdi cac tin hieu da tan MF. Mot sd khai niem can duoc hieu trudc khi di sau vao mot sd loai bao hieu CAS nhu: Khi cuoc goi xuat phat tu tdng dai A sang tdng dai B, tdng dai A duoc coi la tdng dai goi di va tdng dai B duoc coi la tdng dai goi den. Cac trung ke mot hudng la cac trung ke tren do chi cho phep tdng dai A hoac tdng dai B khdi tao cuoc goi. Ca hai tdng dai chi co the khdi tao cuoc goi neu trung ke do la trung ke hai hudng. Chiem trung ke kep co the xay ra khi ca hai tdng dai deu muon chiem mot dudng trung ke vao mot thdi diem, tuy nhien khi xay ra hien tuong do, cac ky thuat nhu la sir dung bo dem thdi gian de phat hien va giai quyet van de. Ba nhom tin hieu bao hieu duoc the hien trong cac he thong bao hieu lien dai sir dung kieu bao hieu kenh lien ket la: ™ Bao hieu giam sat - Cac bao hieu nay the hien trang thai sir kien xay ra tren dudng trung ke va mang tmh dac trung ddi vdi cac he thong CAS. Bao hieu gom: Chiem dudng. nhay (wink) va tra ldi (chung con duoc goi la bao hieu dudng day). ™ Bao hieu dja chi hay bao hieu thanh ghi - Cac bao hieu nay the hien cac con sd da quay di hoac con sd thue bao bj goi, trong mot vai trudng hop no con mang cac thong tin khac. 27 ™ Tone va thong diep thong bao - Cac tone nay nha h6i am chuong. tone bao ban va thong diep thong bao nhu “Cac con so ban da quay chua dung”. Them mot khai niem duoc dua ra trudc khi nghien cuu chi tiet he thong CAS la mach dich vu. Cac mach dich vu duoc sir dung rong rai trong cac he thong tdng dai de gui va nhan dia chi bao hieu va tone, cung nhu dong vai tro cua may thong bao phat ra cac thong diep. 3. Gidi thieu tong quat ve mot so loai bao hieu kenh ket hop - CAS Co nhieu he thong CAS duoc su dung khac nhau: - Bao hieu MF he thong Bell. - Bao hieu xung thap phan mot tan so thoai: 1VF (Voice Frequency). - Bao hieu don tan SF (Single Frequency). - Bao hieu 2 tan so thoai 2VF (CCITT so4). - Bao hieu xung da tan MFP (vf du nhu CCITT R1 hoac sd 5). - Bao hieu da tan cudng buc MFC R2. Phuong thuc bao hieu don tan duoc su dung chu yeu cho churc nang giam sat. Vf du, thong bao trang thai roi hoac ban cua trung ke bing cach phat mot am don tan, thudng dung tan sd 2600Hz len trung ke rdi, dieu nay co nghla la khi khong co am hieu. trung ke d trang thai ban. Bao liieu da tan duoc sir dung rong rai cho chuc nang tim chon, bang cach sir dung 2 trong 5 hoac 6 tan sd nim trong bang tan kenh thoai (300 - 3400 Hz). He thong bao hieu CAS duoc ung dung rong rai nhat hien nay la he thong bao hieu da tan ma R2 chuan CCITT. Cac he thong bao hieu nay deu phat tin hieu d dang xung (Pulse) hoac tone va ket hop cua cac tan sd tone. 4. Phan loai cac tin hieu bao hieu kenh ket hop - CAS 4.1. Co sd phan chia tin hieu bao hieu CAS Dac diem ndi bat ciia CAS la ddi vdi mdi kenh thoai co 1 dudng tin hieu bao hieu rieng. Du d tren dudng thong thoai (trong bang) hay tren kenh lien ket (PCM-TS16). CAS van bi han che ve tdc do va dung luong. Bao hieu kenh lien ket - CAS giua cac tdng dai thudng duoc chia thanh bao hieu dudng day va bao hieu thanh ghi hay con goi la bao hieu dia chi. Trong hinh 2.2 chung ta se xem xet ly do cua su phan chia nay: - Cac tin hieu chiem kenh, tin hieu tra ldi va tin hieu xoa chi mang thong v • c c tin ve trang thai cua thue bao. 28 - Nguac lai, thong tin dia chi mang mot lirang thong tin dang ke. - Cac thong tin dia chi duac truyen chi mot lan tai mot thai diem nao do trong thu tuc thiet lap cuoc goi, trong khi cac tin hieu ve trang thai nhac to hcrp cua thue bao co the duac truyen vao bat cur thai diem nao. Tong dai Tong dai Day chinh la nhung diem quyet dinh phan chia bao hieu kenh ket hop - CAS thanh bao hieu dudng day va thanh ghi. Qua trinh gui cac tin hieu dia chi duac goi la bao hieu thanh ghi do cac sd cua thue bao bi goi duac liru tru trong cac thanh ghi, qua trinh bao hieu xay ra giua cac thanh ghi cua cac tdng dai. Vi thong tin dia chi chi duac truyen khi thiet lap cuoc goi, sau do thanh ghi duac gi;ii phong. Dieu nay co nghTa la cung mot thanh ghi co the phuc vu cho nhieu kenh. thanh ghi la tai nguyen chung sir dung trong viec thiet lap cuoc goi trong tdng dai. Khi mot cuoc goi duac thiet lap, no se duac cap phat mot thanh ghi de truyen dia chi. Qua trinh truyen trang thai nhac to hap cua thue bao duac goi la bao hieu dudng day. Mdi ket noi can co thiet bi truyen cac tin hieu dudng day tai nhune thdi diem nao do trong suot tien trinh cuoc goi. Cac tin hieu dudng day duac sir dung de giam sat ket noi trudc, trong va sau khi thiet lap cuoc goi. 29 Bang 2.1 the hien viec so sanh giCra bao hieu thanh ghi va bao hieu dudng day v£ cac tieu chi nhu luong thong tin, toe do truyen. thdi gian truyen va sd thiet bi su dung. Tieu chi' Bao hieu dudng day Bao hieu thanh ghi Luong thong tin ft Nhieu Toe do truyen Thap Cao Thdi gian truyen Dai Ngdn Sd thiet bi sir dung Lon Nho Being 2.1. So sanh giua cac tin hieu thanh ghi va cac tin hieu dudng day 4.2. Khai quat ve bao hieu dudng day va bao hieu dja chi (bao hieu thanh ghi) Du la kieu tuong tu hay kieu sd thi bao hieu CAS cung dupe chia lam hai loai tin hieu bao hieu. do la: - Bao hieu dudng day (Line Signalling) hay bao hieu giam sat: gom cac tin hieu nhu tin hieu chiem dung, giam sat, giai phong... - Bao hieu thanh ghi hay bao hieu dia chi (Register Signalling): gom cac tin hieu co lien quan den chuc nang tim chon, chuc nang khai thac. 4.2.1. Dao hieu duong hay bao hieu dudng day (bao hieu giam sat) thuc liien chuc nang giam sat cuoc goi. Bao liieu dudng co the la bao hieu kieu tuong tu hoac kieu sd Cac tin hieu trong bao hieu dudng duoc phan chia theo hudng di va hudng ve. Hudng di gom cac tin hieu: - Tin hieu chie'm dudng. - Tin hieu giai phong hudng di. Hudng ve gom cac tin hieu sau: - Tin hieu xac nhan chiem. - Tin hieu tra ldi. - Tin hieu giai phong hudng ve. - Tin hieu khoa. Cac he thong truyen dan tuong tu hoac truyen d&n sd deu co cac phuong an thich ung nhu co tone khi roi hoac cac bit lua chon cho tirng hudns. Ton tai 2 phuong an bao hieu dudng day. do la: - Phuong an Analog dung cho he thong truyen din tuong tu. - Phuong an Digital dung cho he thong truyen dan so. 30 Chi tie't ve cac phuong an nay se duac de cap chi tiet a phan bao hieu R2. 4.2.2. Bao hieu thanh ghi (bao hieu dia chi) thuc hien chuc nang dieu kliien thiet lap cuoc goi 4.2.2.1. Khdi quat chung ve bao liieu thanh ghi (bao liieu dia chi) Bao hieu thanh ghi su dung he thong ma da tan (MFC) voi sir cung cap so luong day dii cac tin hieu theo ca hai chieu nen no cho phep trao doi mot so luong Ion thong tin giua cac thanh ghi. M6i ma da tan la to hop cua 2 trong 6 tan so a bang 2.2. Hudng di 1380 1500 1620 1740 1860 1980 Hz Hudng ve 1140 1020 900 780 660 540 Hz Bang 2.2. Cac tan so tao ma dR2. Bao hieu thanh ghi de trao doi cac thong tin can thiet cho qua trinh thiet lap cuoc goi. Cac thong tin do la thue bao bi goi, so thue bao chu goi, loai thue bao, cac ma vung, quoc gia, quoc te... Bao hieu ghi phat duoc tien hanh d giai doan giua cua qua trinh thiet lap cuoc goi. Khi thuc hien chuyen mach mot cuoc goi co lien quan den nhieu tong dai, can phai chuyen cac thong tin ve con so giua cac tong dai do de ket cuoi cuoc goi chinh xac den thue bao mong muon. Thdng tin ve con so duac chuyen theo hudng di, nhung de dieu khien qua trinh thiet lap goi, con can phai chuyen mot so cac tin hieu bao hieu theo hudng nguoc lai. Ta co the phan biet bao hieu dudng va bao hieu thanh ghi nhu trong hinh sau: Hinh 2.3. Cac tin liieu ghi phat duoc mang tren kenli tieng Cac tin hieu trong hudng di gom: - Tliong tin con sd dia chi bj goi. 31 - Thuoc ti'nh thue bao chu goi - Thong tin thong bao ket thuc giri dia chi bi goi. - Thong tin ve con so cua thue bao chu goi cho tfnh cuoc chi tiet. Cac tin hieu hudng ve g6m: - Tin hieu thong bao tong dai bi goi san sang nhan cac con so dia chi cua thue bao bi goi - do la tin hieu PTS. - Cac tin hieu dieu khien: Xac nhan kieu cua thong tin. - Thong tin ket thuc qua trinh tim chon: Thong tin nay dd giai phong thanh ghi va thiet lap tuyen thoai. D6ng thdi no con dua ra cac thdng tin ve trang thai td hop cua thue bao bi goi. - Thdng tin tinh cudc: Chuyen cac thdng tin can thiet de phan tich ti'nh cudc (cho cac cuoc goi quoc te nhat dinh). Thdng tin dia chi mang mot luu luong tin ldn, va de co dupe qua trinh thiet lap goi nhanh thi phai phat trien cac he thdng bao hieu thanh ghi. Thuc te chung ta co vai he thdng chinh vi cac he thdng nay re va d6 dang dap ung vdi cac phuong thuc truyen dan dang tdn tai. Bao hieu nav dupe truyen ngay tren kenh thoai ma no bao hieu thdng qua viec nhan va giri cac td hop ma da tan. 4.2.2.2. Cac kieu truyen tin hieu bao liieu thanh ghi hay tin hieu bao liieu dia chi Thuc te viec bao hieu khong chi xay ra giua 2 tdng dai vdi nhau ma co the di6n ra qua nhieu tdng dai khac nhau cho mot cuoc goi. Do do. co cac phuong thuc co ban de chuyen cac thdng tin dia chi giua cac tdng dai nhu sau: + Kieu tirng chang (Link - by - Link). + Kieu thdng suot (End - to - End). + Kieu hdn hop (Mixed). * Phuong thuc bao hieu tieng dicing (Link- by- Link). Bao hieu tirng chang: 0 dang nay cac thdng tin dia chi can thiet cho viec dinh tuyen cuoc goi dupe trao ddi day dii qua tirng chang mot ke tir ngav sau tdng dai xuat phat. Cu nhu vay. tir tdng dai thu 2 den tdng dai thu 3... cho den chang cuoi ciing. Phuong thuc link - by - link co the chia ra cac giai doan theo tirng cap mot giua cac tdng dai tir tdng dai gan nhat den cac tdng dai sau no. 32 Khi do, cac thong tin chi dupe bdt dan qua tirng khu vuc dinh tuyen va khu vuc quan ly (ma viing, ma trung ke...). 6 tong dai ket cuoi, chi can nhan mot phan dia chi cua thue bao B (so thue bao cua may le). Phuong phap nay co uu diem la viec quan ly va tfnh cudc dupe tan dung tdi da nhat la d cac buu dien tinh, de dang phat hien cac tin hieu (nhidu, meo do tr6, meo do nhi6u... chi tren mot lien ket). Nhung nhupc diem cua no cung kha trdm trong la keo dai thdi gian chiem dung thanh ghi trong cac tong dai trung gian. Dieu do dan den viec keo dai thdi gian thiet lap cuoc goi, ddi khi dSn den ton that cuoc goi va hieu qua cua mang thap. Hinh 2.4. Bao hieu tieng chang. * Phuong thuc bao hieu xuyen suot hay diem tdi diem (End-to-End) Bao hieu xuyen suot: Bao hieu dia chi xuyen suot thi cac thdng tin can thiet cho viec dinh tuyen dupe phat ra tir thanh ghi (tdng dai) xuat phat (goi ra - out going) tdi thdng cac thanh ghi goi vao (transit). Trong bao hieu theo nguyen tdc diem noi diem, cac thanh ghi cua tdng dai qua giang chi nhan cac sd du de djnh tuyen, thanh ghi ciia tdng dai xuat phat cuoc goi se lam viec trong suot thdi gian thiet lap cuoc goi, no can dupe chuan bi de giri mot phan thdng tin dja chi khi co yeu cau bang cac tin hieu hudng ve. Thanh ghi qua giang giai phong khdi ket noi khi ket noi dupe phat trien len phia trudc tir tdng dai qua giang do. 33 Vi du minh hoa: Hinh 2.5. Bao hieu xuyen suot Nhu- hinh ve 2.5 minh hoa: 0 phuong phap nay chi tdng dai cuoi cung hay ket cuoi tdng dai 4 mdi can den con so dia chi thue bao bi goi B: 3456. Cac tdng dai trudc no khong can nhung thdng tin ay. Mdi tdng dai chi din nhung con sd rieng cua no de’ dinh hudng cho cuoc goi. Nhu vay. cac tdng dai trung gian chi can lupng thdng tin rat ft. Dieu do co nghTa la phuong thuc nay co nhieu uu diem dang quan tarn: - Tdi thieu hoa thdi gian giu cac dia chi d tdng dai trung gian. Do do. se giam dupe thdi gian can thiet lap cuoc goi, sir dung co hieu qua cac thiet bi tren mang. - Tranh phai nhan. luu tru, truyen lai cac tin hieu khong can thiet d cac tdng dai qua giang, tang tdc do bao hieu. - Cac thanh ghi cua tdng dai qua giang lam viec don gian hon do chi xir ly mot phSn thdng tin dia chi. - Giam thdi gian chiem cac thanh ghi ciia cac tdng dai qua giang. - Giam lupng tre sau khi quay sd do cac thanh ghi dupe giai phong sdm hon, thdng mach hon. 34 * Ket qua hai phuong thuc tren ta co mot phuong thuc thu 3: Bao hieu lidn lu/p Hinh 2.6. Bao hieu lion hop Ngoai 2 kieu co ban tren, co the dat ra cac chuong trinh h6n hcfp (Mixed) giua xuyen suot va tirng chang tren toan bo tuyen noi. Phuong thuc nay chi thuc hien tot khi cac tong dai co kha nang phoi hop giao tiep giua hai he thong bao hieu. Tom lai, nhung khai niem mot dau ve bao hieu dudng day hay bao hieu giam sat va bao hieu ghi phat hay bao hieu dia chi giup ta lam quen vdi cac loai hinh thuc hay cac chuc nang bao hieu co ban cua he thdng bao hieu kenh rieng CAS. Phan tiep theo se phan tich cu the ve mot sd he thong bao hieu CAS, dac biet la he thdng bao hieu R2 dang duoc coi nhu mot kieu bao hieu truyen thdng tren mang vi£n thdng hien hanh. 5. Uu, nhUdc diem cua bao hieu kenh rieng CAS * Uu diem: Thong tin bao hieu cua cac kenh duoc truyen rieng biet nhau, vi vay hu hong tren mot kenh bao hieu nao do se khong anh hudng den cac kenh khac. 35 * Nhuoc diem: - Toe do bao hieu cham (2kb/s). - Hieu suat sir dung kenh bao hieu khong cao do kenh bao hieu danh c6 dinh cho kenh thoai ngay ca luc kenh thoai khong c£n den bao hieu va ca khi kenh khong dupe sir dung. - Dung lupng thong tin han che. - Thiet bj bao hieu co cau true phan bo. - No khong thuc hien dupe cac churc nang phirc tap. CAS thuc chat co toe do cham va chi dap urng voi cac mang co dung lupng thap va cac loai hinh dich vu con ngheo nan (chi sir dung trong PSTN). II. HE THONG BAO HIEU SO 2 (R2 CUA CCITT) 1. Gidi thieu ve R2 Bao hieu R2 la he thong CAS theo kieu ma da tan cuong che (MFC). No la he thong bao hieu kenh lien ket dupe phat trien trong nhung nam 60 cua the ky XX va hien nay van con dupe sir dung tai chau Au, chau My La Tinh, Uc, va chau A. Bao hieu R2 co mot vai phien ban quoc gia va co duy nhat phien ban quoc te goi la CCITT-R2. Bao hieu R2 hoat dong tren cac he thong trung ke so va tuong tir 2 day cung nhu 4 day, he thong nay khong hoat dong cung voi thiet bi trung ke h6 tro TASI hoac cac lien ket ve tinh. Bao hieu R2 kha thfch hop voi cac trung ke quoc te ngSn. Mot trong nhung khfa canh khac biet ciia he thong nay so voi he thong R1 la thanh ghi hoac bao hieu thanh ghi ciia no. O Viet Nam cung sir dung chii yeu la bao hieu R2 tren toan mang vi£n thong. Hien nay, bao hieu R2 cho phep thiet lap cuoc goi tuong doi nhanh, tin cay va co the cung cap cac thong tin cho nhieu dich vu gia tang tren mang. 2. Bao hieu dudng day hay bao hieu giam sat d R2 2.1. Cac loai tin hieu duong huong di * Tin hieu bao chiem: La tin hieu giri di luc bat dau cuoc goi nham thiet lap lai trang thai mach vao tir trang thai r6i sang trang thai bj chiem. Khi do tong dai goi vao co the nhan dinh dupe cac tin hieu thanh ghi tiep theo. 36 * Tin hi£u xoa thuan (giai phong hudng di): La tin hieu gui di de ket thuc cuoc goi, nham giai phong tdng dai bj goi va cac khdi chuyen mach dang giur mach cho cuoc goi. Tm hieu xoa thuan dupe gui di khi: - Thue bao chu goi dat may hay mot cong viec khac tuong tu ddi vdi che do tu dong. - Khi nhan dupe tin hieu xoa ngupc (Clear back), sau thdi gian time out neu thue bao chu goi khong dat may thi tong dai chu goi se gui tin hieu xoa thuan. 2.2. Cac tin hieu dudng hudng ve * Tin hieu nay chi dung trong bao hieu dudng day sd. No dupe tdng dai bj goi phat ve sau khi nhan dupe tin hieu bao chie'm. Khi do tdng dai goi ra xac nhan mach vao da chuyen tir trang thai rdi sang trang thai chie'm. * Tin hieu tra ldi: Tin hieu nay dupe gui cho tdng dai chu goi khi thue bao goi nhac may. Tin hieu tra ldi con dung de tfnh cudc cho thue bao chu goi. * Tm hieu xoa ngupc: La tin hieu gui den tdng dai goi ra khi thue bao bj goi dat may. No con thuc hien tfnh nang giam sat. * Tm hieu canh phong - xoa: La tin hieu gui ve tdng dai goi ra sau khi nhan dupe tin hieu xoa thuan de xac djnh san sang phuc hoi cac khdi chuyen mach sang trang thai rdi. Tm hieu nay con bao ve viec chiem mach tiep theo. * Tin hieu khoa: La tm hieu dupe giri tren cac mach rdi ve tdng dai chu goi de gay nen trang thai ban, earn viec chiem mach tiep theo. 2.3. Cac phuong phap bao hieu dudng hay bao hieu giam sat Ton tai 2 phuong an bao hieu dudng, do la: - Phuong an Analog dung cho he thong truyen dan tuong tu. - Phuong an Digital dung cho he thdng truyen dan sd. 2.3.1. Bao hieu duong day hay bao hieu giam sat tren duong trung ke tuoiig tu Dac trung d dang nay la: Co am hieu (tone) khi rdi va khong co am hieu khi ban lien tuc trong ca 2 hudng, su dung mot tan sd ngoai bang la 3825Hz. Ddi vdi mdi hudng truyen can co mot kenh bao hieu ngoai bang. Khi d trang thai rdi thi mdi tone dupe truyen lien tuc d muc thap theo 2 hudng thdng qua cac kenh bao hieu. Am hieu hudng di se bj xoa khi co tin hieu chiem va tone hudng ve se bj xoa khi thue bao bj goi tra ldi. 37 Cuoc goi dupe giai phong khi am hieu hudng di dupe phuc h6i va viec phuc hoi tone hudng di se dan den viec phuc hdi tone hudng ve. Trong trudng hop thue bao bi goi dat may trudc thi tone hudng ve dupe phuc hdi d&u tien. Tiep do tone hudng di dupe phuc hdi neu thue bao chu dat may hoac sau mot khoang thdi gian nao do ke tir khi co am bao hieu hudng ve. Hudng Kieu bao hieu Trang thai Hudng di Chie'm Bat tone sang tat tone Hudng di Xoa hudng di Tat tone sang bat tone Hudng ve Tra ldi Bat tone sang tat tone Hudng ve Xoa hudng ve Tat tone sang bat tone Hudng ve Giai phong phong ve Tat tone sang bat tone Hudng ve Khoa trung ke' Tat tone sang bat tone Bang 2.3. Cac bao liieu hudng di, hudng ve va cac trang thdi chuyen doi cac tin hieu dudng trong phucmg an Analog. Chu y: - Thdi gian can thiet de chuyen trang thai tu co sang khong co tone: 40 ± 7ms. - Thdi gian nhd nhat de nhan biet co tan sd am hieu hudng di va mat am hieu d hudng ve, ky hieu la T l= 250 ± 50ms. - Thdi gian de giai phong mach dien ky hieu la T2= 450 ± 90ms. Gia tri T1 va T2 neu tren dupe sir dung toi uu cho cac tuyen truyen dan mat dat ke ca cac tuyen cap tha bien, vdi thdi gian tre truyen dan mot chieu cue dai la 30ms. Con ddi vdi kenh truyen dan ve tinh T l= (1000 ± 200)ms, T2 = (1600 ± 320)ms ung vdi dieu kien ve thdi gian tre truyen dan mot chieu cue dai la 270 ± 20ms. Co the hie’u cac trang thai d dieu kien binh thudng sau: - Chiem: Tai dau cuoi phfa ra tone bi xoa theo hudng di. Neu viec chiem xay ra ngay sau khi xoa tone thi can phai duy tri ft nhat 100ms de dam bao chac chan dau cuoi da nhan ra trang thai mat tone. - Tra ldi: Dau cuoi phfa vao tone dupe xoa tren hudng ve. Cac chang lien quan cung dung bao hieu tuong tu den tdng dai goi ra thi trang thai khong co tone can phai thiet lap ngay tren chang. Neu chang lien ket khong sir dung bao hieu tuong tu thi viec ghep noi giua cac mang bao hieu phai tuan theo nhung thu tuc, tieu chuan nha't dinh. 38 - Xoa hudng v6: Dau cuoi vao tone dupe phuc hdi tren hudng ve. Quy trinh xay ra tren cac chang lien ket cung keo theo nhu nguyen tac neu tren theo trang thai co tone. - Xoa hudng di: Dau cuoi phfa ra tone dupe phuc hdi d hudng di. Khi dudng lien lac d hudng di dupe giai phong va lan lupt dupe canh phong - xoa bat dau ngay khi trang thai bao hieu thay doi dupe cong nhan tai dau cuoi phfa vao. 6 tdng dai goi ra mach van bi khoa cho den khi tuan tu canh phong khoa ket thuc. - Khoa va khong khoa: Cac mach cua tdng dai goi ra bi khoa khi khong co tone d hudng ve. Su khdi phuc tone d hudng ve kern theo co tone d hudng di se phuc hdi mach ve trang thai rdi... Cac trang thai muon chuyen doi dut khoat va tin cay thi bo phat tin hieu can lam viec dn dinh ve tan sd va mure. Cac kenh bao hieu phai tranh dupe sir anh hudng cua kenh thoai. Bo thu nhan tone phai co do nhay tot de phan biet dupe trang thai co hoac khong co tone. Dac biet may thu phai co do dn djnh va kha nang chong nhi£u. Bao hieu R2 quoc gia co mot vai dang tuy thuoc vao cac quoc gia. Phien ban R2 quoc gia dupe sir dung phd bien nhat la su dung xung bao hieu giam sat. Vf du cac tin hieu bao hieu dudng hay bao hieu giam sat dupe chi ra tren bang 2.4. Hudng Kieu bao hieu Chu ky xung theo ms Hudng di Chiem 150 Hudng di Xoa hudng di 600 Hudng ve Tra ldi 150 Hudng ve Xoa hudng ve 600 Hudng ve Giai phong phong ve 600 Hudng ve Khoa trung ke Lien tuc Bang 2.4. Vi du ve cac tin hieu bao hieu dudng hay bao hieu giam sat R2. 2.3.2. Bao hieu dudng day hay bao hieu giam sat tren du&ng trung ke so Trong he thdng truyen dan sir dung ky thuat dieu che xung ma (PCM) tin hieu tieng va cac thdng tin khac dupe truyen trong dang ma hoa vdi tan sd ldn hon hoac bang 2 lan tan sd ldn nhat ciia kenh tieng can truyen, ta goi la 39 tan so lay mau (8000Hz) va tai ddu thu tin hieu tieng duoc khdi phuc lai tu cac tin tuc da ma hoa nay. Voi tan so lay mau 8000Hz va 8 bit dupe sir dung de ma hoa cho mot mau, mdi kenh PCM se co toe do 64Kb/s. Neu he thong truyen dan g6m N khe thdi gian thi toe do cua he thdng se la 64N kb/s x N, cung co thd la sd lupng kenh tieng trong he thdng PCM, nhung trong mot sd he thdng mdt hoac vai khe thdi gian dupe su dung rieng cho muc dich dieu khien. Bao hieu R2 hoat dong tren dudng trung ke El. El co 32 khe thdi gian, danh sd tir khe TS0 tdi TS31, trong do TS1- TS15 va TS17- TS31 dupe sir dung de mang thdng tin thoai ma hoa theo ky thuat PCM vdi toe do 64 kb/s tren khe thdi gian. Nhu trong phan trudc ta da thay, bao hieu dudng theo phuong an Analog chi co hai bien trang thai co the co trong mdi hudng la co tone va khong co tone. Giai phap nay cung co the ung dung cho he thdng Digital bang viec sir dung mot kenh bao hieu (1 bit). Sir dung he thdng bao hieu vdi hai trang thai thdi gian nay la mot van de can thiet ddi vdi nhung yeu cau khac nhau va ddi vdi viec xac dinh thu tu thich hop trong chuyen doi tin hieu. De don gian hoa cac thiet bi dau cuoi bao hieu, trong he thdng PCM 30, he thdng bao hieu dudng cho phep sir dung 4 bit bao hieu cho 1 kenh tieng. Co the hinh dung: O Analog dung hai trang thai co hoac khong co tone cho cac hudng di, hudng ve, thi d Digital co the dung cac bit trang thai cho tirng hudng. Ve nguyen ly co the dung cac sd lupng bit khac nhau de bao hieu cho mot kenh tieng. Cac kha nang co the chon: - 4 bit bao hieu cho 1 viing tieng: abed. - 3 bit cho mot kenh tieng: a b c 1. - 2 bit cho mot kenh tieng: a b 0 1. - 1 bit cho mot kenh tieng: a 1 0 1. Trong trudng hop bao hieu CCITT R2 chi co bit a va bit b duoc sir dung. Bit c = 0 va bit d = 1. Trang thai rdi dupe xac dinh khi bit a = 1 va bit b = 0. Bao hieu dupe thuc hien lien tuc. Ddi vdi cac trung ke 2 hudng, luat giam sat cho bao hieu hudng di va hudng ve khac nhau ddi vdi tirng cuoc goi. Bang 2.5 minh hoa bao hieu giam sat R2, trang thai chuyen ddi va hudng sir dung tren cac dudng trung ke sd. :'40 C) he thong bao hieu ma da tdn R2 nguoi ta dung 2 trong 4 bit cho tirng hudng. - 2 bit cho hudng di: af va bf. - 2 bit cho hudng ve: ab va bb. Y nghTa cua cac bit bao hieu d di6u kien binh thudng nhu sau: + af xac dinh chi ra trang thai ciia dudng va may thue bao chu goi va trang thai thiet bi bao hieu goi ra. + bf cho biet thdng tin canh bao trong truyen tin hieu hudng di. + ab cho biet trang thai cua dudng va may thue bao bi goi. + bb cho biet thiet bi bao hieu vao rdi hay ban. Bao hieu dudng day kieu sd dupe truyen theo phuong thurc tirng chang. Hudng Kieu bao hieu Chuyen doi trang thai Hudng di Chiem a,b: 1,0 sang 0,0 Hudng di Xoa hudng di a,b: 0,0 sang 1,0 Hudng ve Tra ldi a,b: 1,0 sang 1,1 Hudng ve Xoa hudng ve a,b: 1,1 sang 0,1 Hudng ve Giai phong phong ve a,b: 0,1 sang 1,1 Hudng ve Khoa trung ke a,b: 0,1 sang 1,0 Being 2.5. Bao hieu giam sat tren cac dudng trung ke so. Trong thuc te con chia thanh 2 trudng hop: - Bao hieu dudng day co sir dung xung tfnh cudc. - Bao hieu dudng day khong sir dung xung tinh cudc. Hien nay, tren mang vidn thdng Viet Nam dang khuyen nghi sir dung bao hieu dudng day khong co xung cudc. Nhung yeu cau cac tong dai phai co kha nang chuyen doi co xung cudc khi can. Trong phuong an Digital, tin hieu dudng dupe truyen d khe thdi gian 16 (TS16) ciia td churc khung PCM 30/32 kenh thoai. Trong khuon dang sieu khung SF gom 16 khung dupe danh sd tir khung 0 tdi khung 15. TS16 ciia khung 0 dupe sir dung cho thdng tin sdp xep khung, cac TS16 ciia cac khung con lai sir dung de bao hieu cho cac kenh tren dudng trung ke. Bon bit trang thai trong TS16 dupe sir dung cho bao hieu la cac bit a, b, c va d. Mdi TS16 cua khung 125fis gom 8 bit dupe chia thanh 2 nhom (mdi nhom 4 bit) de mang tin tuc bao hieu dudng cho 2 kenh thoai tuong urng trong cac khung PCM. 41 Thi du nhu TS16 cua khung 1 dung bao hieu cho kenh thoai thu nhat va thoai thur 16 (TS17). Tuong tu. TS16 cua khung 16: Kenh 16 va 17... nhu hinh 2.7. 0 16 31 Khung 0 Da khung 0 0 16 16 a b c d a b c d 31 31 Khung Khung 15 Tir ma 8 bit Hinh 2.7. Mo phong da killing cho bao liieu Khao sat hinh 2.7 mo phong to chuc da khung trong do co tir 8 bit ciia TS 16 danh cho bao hieu tir khung thu 1 den khung thu 15. Con khung thu 0 (hay khung thu 16 cua da khung) dupe dung cho dong bo da khung voi tir ma la 0 0 0 0 x e x x- tir 8 bit vdi chu giai nhu tren. Cho den TS16 cua khung thu 15 se bao hieu cho cac kenh thoai 15 va kenh 30. Ta van biet cac TSO cua cac khung dung de dong bo khung va TS16 cua khung 0 dung de dong bo da khung. Ta co the tham khao bang phan bo bao hieu TS16 cho cac kenh thoai. Khung thu abed abed 0 0 0 0 0 x e x x 1 Kenh 1 Kenh 16 (TS17) 2 Kenh 2 Kenh 17 3 Kenh 3 Kenh 18 - - - 14 Kenh 14 Kenh 29 15 Kenh 15 Kenh 30 Bang 2.6. Pluin bo cac kenh bao liieu trong TS16 cua lie thdng PCM 30. 42 Chu y d bang 2.6 thi: - Kenh 1 d&n kenh 30 la cac kenh thoai cua td churc khung 30/32 kenh thoai. - 0 0 0 0 la tir d6ng bo da khung. - e la tin hieu xac nhan d6ng bo da khung: e = 0 khong co canh bao, e = 1 co canh bao. - x la cac bit dir phong, thudng cho x = 0. Theo khuyen nghi cua CCITT - Q422 ma bao hieu dudng day tren dudng trung ke PCM trong dieu kien binh thudng nhu bang 2.7 sau: Chu y: - Thdi gian cSn thiet cho chuyen trang thai tir 0 sang 1 va nguoc lai la 20 ± 10ms. - Sai sd thdi gian khi truyen dong thdi cac ma bao hieu trong 1 hudng khong vuot qua 2ms. Mat khac, bang 2.7 la sir mo ta cac trang thai bao hieu d dieu kien binh thudng. Neu co ldi xay ra, cac trang thai se trd nen khac thudng. Ta co the tham khao cac bang ma sau day, ke ca phfa goi ra (out going) va dau bi goi (in coming) khi cac ma sd nhan duoc d hai phia do khong chmh xac. Ma bao hieu trong khe thdi gian 16 Trang thai mach Hudng bao hieu Hudng di Hudng ve af bf ab bb Rdi/Giai phong Hudng di Hudng ve 1 0 1 0 Chiem dung Hudng di 0 0 1 0 Xac nhan chiem Hudng ve 0 0 1 1 Tra ldi Hudng ve 0 0 0 1 Giai phong hudng ve Hudng ve 0 0 1 1 Giai phong hudng di Hudng di 1 0 0 1 Canh phong nha Hudng ve 1 0 1 0 Khoa mach Hudng ve 1 0 1 1 Bang 2.7. Cac tin hieu dieting trong phifcnig dn Digital Bang 2.8 mo ta trang thai bao hieu d dau goi ra (out going) co sir co khac thudng (KT). 43 Cac chu thich co ban cua bang 2.8: - (1): O trang thai nay dau goi ra phai ngan chan viec chiem mach phuc vu cho cuoc goi mdi va co the dua ra mot canh bao den bo xir ly tucmg iimg. - (2): Sau khi giri tin hieu chiem mot khoang thdi gian 100 - 200ms ddi vdi tuyen truy6n dan mat da't hoac sau 1 - 2 s ddi vdi tuyen truyen dan qua ve tinh ma chu goi khong nhan dupe tin hieu cong nhan chiem thi canh bao hoac thdng tin tac nghen se dupe giri tren hudng ve hoac co gang thiet lap lai cuoc goi. Trong suot thdi gian nay mach goi ra phai chong lai sir chiem mach cho cuoc goi mdi. Sau thdi gian chd dpi (time out) vupt quy dinh phai giri tin hieu giai toa hudng di de ket thuc cuoc goi bat binh thudng nay. Trang thai binh thudng d phia ra Ma giri ab = 0, bb = 1 ab = 0, bb = 1 Via thu ab = 1, bb = 0 ab = 1, bb = 1 Rdiaf = 1 bf = 0KT (1) KT (1) Rdi Khoa bf = 0KT (2) KT (2)Chiem Chiemaf = 0 Xac nhan chiemaf = 0 (2)Xac nhan chiem bf = 0KT (3) Tra ldi KT (3) Xac nhan chiem Tra ldi C3 <4_ II o o -OKT (4) Tra ldi KT (4) Xoa nguoc <*-c II Xoa ngupcaf = 0 l_bf = 0KT (4) Tra ldi KT (4) Xoa ngupc Xoa thuanaf = 1 bf = 0KT (1)Xoa thuan Khoa f 1 KT(1) Xoa - Rdi Xoa thuan | bf = 0KT (1) Rdi Khoa Bang 2.8. Dau goi ra khac thu&ng. - (3): Trong trudng hop bb = 0. sau khi nhan dupe tin hieu cong nhan chiem 1- 2s ma chua co tin hieu tra ldi canh bao hoac thdng tin tac nghen dupe giri ve hoac co gang thiet lap lai cuoc goi. Dau goi ra phai chdng lai sir chiem mach cho cuoc goi mdi. Khi bb chuvein sang trang thai 1 thi sau 1- 2s 44 chu goi phai giri tin hieu xoa thuan de ket thuc viec thiet lap cuoc goi bat binh thudng nay. - (4): Neu nhan duac bb = 0 trong khi di6n bien cuoc goi dang d trang thai tra ldi hoac trang thai giai toa theo hudng v6 thi cac hoat dong trung gian tiep theo khong c£n thiet ntra. Khi nhan duac tin hi6u giai toa tir thiet bi phfa trudc gui den thi tin hieu xoa thuan khong cdn gui di ngay ma phai chd den khi bb = 1 va thdi gian chd dai nay cung duac quy dinh trudc. Neu qua thdi han chd kenh se bi khoa. Bang 2.9 mo ta cac trang thai co ldi hay bat binh thudng cua cac ma nhan duac d d5u bi goi (in coming). Trang thai binh thudng a d3u bi goi Ma giri af = 0, bf = 1 Ma thu af = 0, bf = 1 af = 1, bf = 0 af = 1, bf = 1 Rdiab = 1 bb = 0Chiem Ldi (1) RdiLdi (1) ab = 1 Cong nhan chiem bb = 1Cong nhan chiem Ldi (2) Xoa thuanLdi (2) Tra ldiab = 0 bb = 1Tra ldi Ldi (3) Xoa thuanLdi (3) Xoa nguacab = 1 bb = 1Xoa ngugc Ldi (4) Xoa thuanLdi (4) ab = 0 Xoa thuan bb = 1 hoac ab = 1 bb = 1 Chiem KT (7)Ldi (7) Xoa thuan (7)Ldi (7) Khoaab = 1 bb = 1 Chiem KT (7) Ldi (6) KhoaLdi (6) Bang 2.9. Ma ldi a ddu vao. Cac chu thfch ca ban cua bang 2.9: - (1): Neu d trang thai rdi hay giai phong ma bf = 1 thi bb phai chuyen thanh 1. 45 - (2): Trong trudng hap nay thiet bi dem thai gian chd d(ri se hoat dong. Theo quy dinh Q 1 18, neu qua time out se giai toa ket noi tren kenh bi I6i. Neu co tin hieu tra lai khong duac giri di tren dudng day phfa trudc cho den khi af = 0, bf = 0. - (3): Trong trudng hap nay tong dai se khong lam gi cho den khi nhan duac tin hieu giai toa theo hudng ve va den luc nay giai toa se duoc tien hanh ngay tuc thi. - (4): 6 trang thai nay, tuyen thdng tin phai duac giai phong ngay. - (5): Trong trudng hap nay khong can thiet phai co hoat dong nao. Nhung viec giai toa se di6n ra nhanh han neu dau bi goi (phia in coming) duoc linh hoat tra ldi bang viec gui ab = 0; bb = 1. - (6): Trong trudng hap nay tdng dai se khong thuc hien mot hoat dong nao. - (7): Sau khi tin hieu xoa thuan duac cong nhan va den khi ma ab = 1, bb = 1 duac gui, tat ca cac tin hieu duac gui trong hudng di se duac bo qua. Tom lai, thuc te co the’ xay ra cac trang thai khac thudng (KT) hoac co l6i dudng truyen. Can co cac giai phap phong ngira va giai toa dac biet, bao ve chong anh hudng cua ldi va ddi khi gap ldi dudng truyen can khoa mach, ngung ngay viec thu nhan bao hieu de’ tranh thu sai ma cang nhanh cang tot. (G. 734 khuyen nghi < 3ms). 3. Bao hieu thanh ghi hay bao hieu dja chi d R2 Khai niem v i bao hieu dia chi trong R2 co sir khac biet ra't nhd ddi vdi cac he thdng bao hieu CAS da de cap d tren. Trong trudng hap bao hieu R2. tdng dai duac coi la cac thanh ghi va bao hieu giua cac tong dai duac goi la bao hieu lien thanh ghi. Bao hieu lien thanh ghi su dung tin hieu MF trong bang tren hudng di va hudng v& de truyen con sd bi goi, sd chu goi va mot sd dac tinh cua thue bao chu goi. Trong trudng hap nay, bao hieu la bat buoc bdi vi cac thanh ghi trong cac tdng dai goi di va goi den giu cac bao hieu cho den khi nhan duac xac nhan tra ldi. Bao hieu thanh ghi thuc chat la su trao ddi cac td hap ma da tan (MFC) theo hai hudng giua cac tdng dai. Cac td hop ma da tan duac phat va thu bdi cac thiet bi bao hieu da tan, cac thiet bi da tan nay ket hap vdi thanh ghi goi ra (out going) va thanh ghi goi vao (in coming) de dieu khie-n thiet bi chuyen mach. 46 To hap ma da tan la to hap cua 2 trong 6 tan so theo hai hudng. Khuyen nghj Q 411 cua CCITT da trinh bay cac td hap MFC nhu bang 2.2. So luong t. cac ma da t^n tuy thuoc sd luong tan sd bao hieu duac su dung. O trudng hap dung 6 tan sd nhu Q 411 thi co tdi 15 td hap ma. Vdi sd luong nay, hien tai la du cho viec bao hieu d cac mang quoc te va quoc gia. Tat nhien giam luong cac ma da tan se co lai theo quan diem kinh te. tiet kiem thiet bi nhung han che cac kha nang md rong djch vu cho khach hang. Sd luong ma da tan co the giam bdt cho cac mang quoc gia, sd tan sd hudng di va hudng ve cung co the thay ddi va khong nhat thiet phai bang nhau cho ca hai hudng. Bao hieu trong cac thanh ghi trong R2 MFC duoc sir dung d Viet Nam la kieu bao hieu bi khong che, cac tan sd chuain duoc chon phu hap vdi khuyen nghi Q 411 cua CCITT- sach xanh. Mdi tm hieu trong thanh ghi la td hap cua 2 trong 6 tan sd trong bang, duac phan lam 2 hudng di va ve (theo bang 2.2). Cac tan sd trong hudng di gom: 1380, 1500, 1620, 1740, 1860, 1980 (Hz). Cac tan sd trong hudng ve gom: 1140, 1020, 900, 780, 660, 540 (Hz). Cac tin hieu hudng di duac phan lam 2 nhom: Nhom I va nhom II. + Cac tm hieu nhom I chu yeu mang cac thdng tin ve dia chi cua thue bao bi goi, tuc la cac con sd tu 0 - 9. + Cac tin hieu nhom II mang thdng tin ve thuoc tfnh cua thue bao chu goi. Cac tin hieu hudng ve duac phan lam 2 nhom: Nhom A va nhom B. + Cac tin hieu nhom A la cac tin hieu dieu khien. + Cac tin hieu nhom B la cac thdng tin ve trang thai cua dudng thue bao bi goi. Bao hieu Cac tan sd hudng di (Hz) Cac tan sd hudng ve (Hz) Sd 1 1380 va 1500 1140 va 1020 Sd 2 1380 va 1620 1140 va 900 Sd 3 1500 va 1620 1020 va 900 Sd 4 1380 va 1740 1140 va 780 Sd 5 1500 va 1740 1020 va 780 So 6 1620 va 1740 900 va 780 So 7 1380 va 1860 1140 va 660 Sd 8 1500 va 1860 1020 va 660 Sd9 1620 va 1860 900 va 660 Sd 0 1740 va 1860 1140 va 540 47 Du phong 1380 va 1980 1020 va 540 Du phong 1500 va 1980 900 va 540 Du phong 1620 va 1980 780 va 540 Du phong 1740 va 1980 780 va 540 Ket thuc # 1860 va 1980 660 va 540 Bang 2.10. Cac tan so bao hieu thanh ghi CCITT R2 va R2 quoc gia. 3.1. Cac nhom tin hieu hirong di Khuyen nghi CCITT Q 411 da quy dinh 2 nhom y nghTa huong di: Nhom I va nhom II. Viec thay doi nhom y nghTa tir I sang II cung co the’ duoc thuc hien bang yeu cau ciia cac tin hieu A-3 hoac A-5. 3.1.1. Cac tin hieu hu&ng di nhom I (bang 2.11) To hop Tin hieu V nghTa tin hieu (a) (b) (c) 1 I - 1 Chu so 1 2 1 -2 Chu so 2 3 1 -3 Chu so 3 4 1 -4 Chu so 4 5 1 -5 Chu so 5 6 1 -6 Chu so 6 7 1 -7 Chu so 7 8 1-8 Chu so 8 9 1 - 9 Chir so 9 10 I - 10 Chu so 0 11 I - 11 Khong sir dung. 12 I - 12 Yeu cau khong duoc chap nhan. 13 I - 13 Truy nhap tori thiet bi kiem tra. Khong dung trong tuyen ve tinh. 14 I - 14 Khong dung. 15 I- 15Chi thi ket thuc xung quay so. Chi thi ket thuc dac tinh thue bao. Bang 2.11. Tin hieu huong di nhom I. Ghi chic - Cac tin hieu tu I - 1 den I - 10: Cac dia chi can thiet cho viec thiet lap cu6c goi (ma quoc gia, ma vung va cac dia chi can thiet). Cac dia chi do dirge 48 gui bang thanh ghi R2 phfa out going hay mot thanh ghi phfa ra quoc te ngay sau khi viec chiem dung kenh vira thuc hien xong hoac khi tra ldi cho mot trong huong tin hieu hudng ve: A-l; A-2; A-7; A-8. Ma quoc gia cung nhu ma vung dung de ghi R2 phfa ra quoc te tra ldi cac tin hieu, yeu cau gui cac tin hieu thdng tin ve noi xuat phat cuoc goi. - I - 11: Mang vidn thdng quoc gia Viet Nam chua dung tin hieu nay. Mot sd mang co dupe sir dung vdi y nghTa cuoc goi yeu cau dat cac bo triet am doi hudng di hoac yeu cau mot cuoc goi qua giang quoc te... - 1 - 12: Khi khong dap urng dupe yeu cau thi gui tin hieu 1-12. Ngoai ra, co the bieu thi y nghTa khong can cac bo triet am doi hoac ket hop vdi mdt sd ngdn ngu khac de tiep nhan thdng tin tdi nhung vi tri dac biet qua dinh tuyen. - I - 13: Mang quoc gia Viet Nam chua sir dung tin hieu nay. No co the dung de chi thi cuoc goi kie’m tra, tiep thdng den thiet bi kiem tra, khong dung tuyen ve tinh (thanh ghi goi ra khong lam viec vdi ve tinh). - I - 14: Mang quoc gia Viet Nam chua sir dung tin hieu nay. No co the dung vdi y nghla: + Ma quoc te se dupe giri ngay sau do. + Yeu cau bo triet am dpi. + Thanh ghi goi ra lam viec vdi ca ve tinh. - 1 - 15: Ket thuc xung quay sd. Ket thuc nhan dang dac tfnh thue bao chu goi. 3.1.2. Cac tin hieu hudng di nhom 11 (bang 2.12) Ghi chu: - Cac tin hieu nhom II la tin hieu chi thi ve dac tfnh cuoc goi va dac tfnh thue bao chii goi nham tra ldi cac tin hieu A - 3 hoac A - 5. Chung deu bieu thi cac uu tien hudng di trong mang quoc te neu co yeu cau. Chung phu hop cho tin hieu A - 5 va dieu khien thfch hop cho chuyen mach. To hop Tin hieu Ghi chu Y nghla tin hieu 1 II- 1 Cac tin hieu nay Thue bao khong uu tien. 2 II - 2 dupe sir dung Thue bao co uu tien. 3 I I -3 cho lien lac Cuoc goi tir trung tarn bao dudng. 4 I I -4 quoc gia. Cuoc goi tir trung tarn chan. 5 II - 5 Dien thoai vien. 6 I I -6 Truyen dan sd lieu trong nude. 49 7 II - 7 Cac tin hieu nay Thue bao quoc te. 8 II - 8 dupe sir dung cho Truyen dan sd li6u quoc te. 9 II -9 quoc te. Thue bao co uu tien quoc te. 10 II- 10 Dien thoai vien quoc te. 11 II - 11 Cuoc goi tu dien thoai cong cong. 12 II - 12 Thue bao chu goi khong dung hoac khong nhan dang dupe. 13 II- 13 Dung cho du trur quoc gia. 14 II- 14 Du trur quoc gia. 15 II- 15 D utruquoc gia. Being 2.12. Tin hieu hudng di nhom II. - Cac tin hieu tu II - 7 den 11-10 chi dung trong mang quoc te. Phan con lai chi dung trong mang quoc gia. Cac tin hieu nay se lam thay ddi y nghla trong thanh ghi R2 de phan biet quoc gia hay quoc te. + Voi nhung cuoc goi vao tu cac thue bao va tir dien thoai vien tin hieu II - 2 va II - 5 se duoc gui vao mang quoc gia. + Doi voi cac cuoc goi di quoc te, tong dai Gateway se thuc hien su bien d6i sau day: • Tin hieu II - 1 den II - 4 dupe chuyen thanh tin hieu II - 7. • Tin hieu II - 5 dupe chuyen thanh II - 10. • Tin hieu II - 6 dupe chuyen thanh II - 8. • Tin hieu II - 11 den 11-15 dupe chuyen thanh II - 7. 3.2. Cac nhom tin hieu huong ve Cac tin hieu a hudng ve cung tuan theo Q441 cua CCITT. Nhung tin hieu nay cung dupe phan lam 2 nhom A va B. 3.2.1. Cac tin hieu huong ve nhom A (bang 2.13) Ghi chu: - Cac tin hieu nhom A huong ve dung de tra ldi xac nhan cho cac tin hieu hudng di nhom I va trong mot sd trudng hop la de xac nhan cho cac tin hieu hudng di nhom II. Ngoai vai tro la cac tin hieu xac nhan trong thu tuc bao hieu bdt buoc. cac tin hieu nhom A con co churc nang chuv^n dua cac thdng tin bao hieu. - A - 1: Gui con sd tuy theo (n+1) khi da nhan dupe con sd n. - A - 3: Dia chi da day du. Thanh ghi bi goi khong can thu them con sd dia chi nao nua va chuyen sang nhan cac tin hieu nhom B la cac thdng tin ve trang thai cac thiet bi tdng dai goi vao hoac trang thai dudng day thue bao bi goi. 50 - A - 4: Co tac nghen d cac tuyen trung ke lien dai hoac 6 cac bo chon thdi gian trong cac tong dai. Co the xay ra trudng hop giai toa thanh ghi bao hieu R2 trong tinh trang bat binh thudng hoac do qua thdi gian chd dpi (time out) vi mot ly do nao do. - A - 5: Yeu cau goi dac tfnh thue bao chu goi (CLI: Calling Line Identity). Cau true cua CLI can phai gui: + Ddi vdi lien tinh hoac quoc te: Loai thue bao chu goi + ma viing + sd chu goi + I - 15 + Ddi vdi noi tinh: Loai thue bao chu goi + sd chu goi + I - 15 - A - 6: Tin hieu nay chi thi ring thanh ghi R2 d tdng dai phfa in coming khong can phfa out going gui them tin hieu dia chi nao nua nhung no se khong giri cac tin hieu nhom B va cuoc goi nay phai tfnh cudc khi thue bao bj goi tra ldi. - A - 7: (cung nhu A-8 va A-2): Deu khong dung cho tuyen ve tinh. - A - 9 den A - 10: Chi dung rieng cho cac mang quoc gia, khong dung cho tuyen ve tinh va co the dupe quy djnh bdi to churc quan ly ky thuat ciia tirng nude. To hop Tin hieu Y nghla tin hieu 1 A - 1 Giri con sd tiep theo. 2 A -2 Giri con sd (n-1) trudc con sd cuoi. 3 A - 3 Ket thuc dja chi chuyen sang nhan tin hieu nhom B. 4 A - 4 Tac nghen trong mang quoc gia. 5 A - 5 Giri dac tfnh va con sd thue bao chu goi. 6 A - 6 Bj goi rdi, thiet lap tfnh cudc khi co tin hieu tra ldi. 7 A - 7 Giri con sd (n-2) trudc 2 con sd cuoi. 8 A -8 Giri con sd (n-3) trudc 3 con sd cuoi. 9 A - 9 Phat lai sd bj goi tir dau. 10 A - 10 Giri cac con sd bj goi dudi dang thap phan. 11 A - 11 Du phong. 12 A - 12 Du phong. 13 A - 13 Du phong. 14 A - 14 Du phong. 15 A - 15 Tac nghen trong mang quoc te. Being 2.13. Tin hieu nhom A lur&ng ve. 51 - A - 11 den A - 14 la cac tm hieu du phong. Chung co the duoc khai thac theo cac dac tfnh yeu cau ky thuat rieng. Thi du: qua giang qudc gia. qua giang quoc te, cho qua ve tinh hay khong cho qua ve tinh... - A - 15: Bieu thi tac nghen quoc te do tuyen trung ke hay cac tdng dai quoc te hoac thanh ghi bi xoa bat thudng do chd dpi qua hdi gian quy dinh... 3.2.2. Cac tin hieu nhom ve hu&ng B Td hop Tin hieu Y nghTa tin hieu 1 B- 1 Thue bao rdi/yeu ciu nhan dang cuoc goi pha rdi. 2 B - 2Giri tone dac biet thdng bao thue bao bi goi da di chuyen hoac thay doi. 3 B- 3 Dudng day thue bao ban. 4 B - 4 Tac nghen. 5 B - 5 Sd thue bao khong co trong danh ba. 6 B - 6 Dudng day thue bao bi goi rdi, tfnh cudc. 7 B - 7 Dudng day thue bao bi goi rdi, khong tfnh cudc. 8 B- 8 Dudng day thue bao bi goi co su co. 9 B - 9 Dudng day thue bao bi chan. 10 B - 10 Du tru cho mang quoc gia. 11 B - 11 Du tru cho mang quoc gia. 12 B -12 Dir tru cho mang quoc gia. 13 B - 13 Du tru cho mang quoc gia. 14 B - 14 Du tru cho mang quoc gia. 15 B - 15 Tac nghen trong mang quoc te. Bang 2.14. Cac tin hieu nhom B hu&ng ve. Bat ky mot tin hieu nhom B nao cung deu tra ldi xac nhan cho mot tin hieu nhom II cua hudng di va luon luon di sau tin hieu day dii A - 3, bieu thi thanh ghi R2 phfa vao da nhan dii toan bo tin hieu hudng di nhom I. Ngoai cac chuc nang xac nhan trong thu tuc cudng che do, cac tin hieu hudng di nhom B con chura cac thdng tin ve tinh trang ciia thiet bi chuyen mach trong tdng dai phfa thu (In coming) hoac thong tin ve trang thai dudng day thue bao bi goi. Clui tliich: - B - 1: Tdng dai chua thue bao bi goi yeu cau tdng dai A (chua thue bao chu goi) giri dac tfnh thue bao chu goi (CLI). Neu tdng dai phfa A khong dap ung dupe thi: 52 + Tong dai A giri: Loai thue bao chu goi + I - 12 (tu choi). + Tdng dai B giri: A - 3, B - 1 cho tdng dai A. Neu tdng dai A dap urng dupe yeu ciu cua tdng dai B thi: + Tdng dai A gui cau true CLI di. + Tdng dai B gui cho tdng dai A bao hieu A - 3, B - 1. Chu y: • Trong ca hai trudng hop neu tren, deu dung che do xoa tu dong, khong co sir can thiep cua dien thoai vien. • Doi vdi cac tdng dai Tandem do tfnh chat quan ly cudc nen khi Tandem da hdi A - 5 thi cac tdng dai phai gui dupe ma gia dung cau true CLI va phai the hien dung noi cuoc goi xuat phat. - B - 2: Mang y nghTa: + Trang thai dudng day bi goi khong phu hop vdi mot trong cac bao hieu nhom B hien co. + Trang thai dudng day bi goi khong dan den thiet lap cuoc goi. + Khi thue bao bi goi da thay ddi. Sau khi da nhan dupe tin hieu B - 2 thanh ghi R2 ra xoa bo hudng di va giri tone dac biet hoac thdng bao tdi “ thue bao chii goi”. - B - 3: Khi dudng day thue bao bi goi lay tin hieu B - 3 dupe giri di, thanh ghi ra se dupe giai phong va am bao ban dupe giri ve thue bao chii goi. - B - 4: Neu xay ra tic nghen sau khi chuyen tu bao hieu nhom A sang nhom B thi B - 4 dupe giri di thay cho A - 4. Cuoc goi dupe giai phong va thdng tin tic nghen dupe chuyen di. - B - 5: Cho biet thue bao bi goi khong co trong danh ba, thanh ghi R2 ra xoa cuoc goi va tone dac biet hoac thdng bao dupe giri ve thue bao chii goi. - B - 6: Dudng day thue bao bi goi rdi va co tinh cudc. - B - 7: Dudng day thue bao bi goi rdi va khong tmh cudc khi thue bao tra ldi. Tin hieu nay cho phep thuc hien cac cuoc goi khong tfnh cudc ma khong can phai truyen cac thdng bao khong tfnh cudc nao khac tren dudng day. - B - 8: Dudng day thue bao dang co sir co do hu hong hay m ic ldi gi do. - B - 9 den B - 15: Cac tin hieu nay danh rieng cho cac mang quoc gia, y nghTa ciia chung phai dupe chi dinh tuong hop vdi cac tone bao dac biet va ngan ngira viec giri cac tin hieu nay ra mang qudc te. 4. LiTdc do thu tuc mot cuoc goi theo bao hieu R2 Dira tren cac trinh tir ciia qua trinh thuc hien mot cuoc goi va cac nhom tin hieu theo cac hudng. ta co the hinh thanh cac lupc do tien trinh mot cuoc goi theo bao hieu MFC R2. Mot cuoc goi co the hoan thanh da'u noi, co the khong thanh do cac nguyen nhan khac nhau nhu ban hay tic nghen, co the do dac tfnh rieng cua cuoc goi (cua dich vu)... Do do, co the dat ra cac bai tap khac nhau va tu trinh bay. Thue bao B Ill ------------------------------------► B-3 •4------------------------------------- Hinh 2.8. Vi du bao liieu cho mot cuoc goi 54 III. CAC THIET BI BAO HlfiU MA DA TAN BAT BU0C - MFC Thiet bi bao hieu da tin la cac ket c&u d ca hai dau cho phep gui hay phat (Sender) va nhan hay thu (Receiver) cac to hop ma da tan lin nhau va lam viec theo giao thuc hay thu tuc bit buoc (Compelled Control). Cac thiet bi nay co cac chuc nang co ban nhu sau: - Nhan cac td hop ma da tin (cac bo thu ma - Code Receiver). - Phat cac td hop ma da tan (cac bo phat ma - Code Sender). - Bao ve chong nhi6u. - Van chuyen cac tin hieu den va di tir cac thanh ghi Cac ket cau nay dupe xem nhu la mot don vi chuc nang rieng, va co the goi la thiet bi bao hieu da tan. Thu tuc- co cau bao hieu ma da tan 6 Viet Nam cung nhu d hau het cac mang d cac qudc gia khac deu ap dung bao hieu khong che hay cudng buc da tan (Multi Frequency Compelled - MFC). Cudng buc co nghTa la tin hieu hudng di dupe phat lien tuc cho den khi nhan dupe tin hieu di£u khien tir tdng dai ddi phuong. He thdng bao hieu dupe mo phong nhu hinh ve 2.9. Thuc ra bo phat ma CS (Code Sender) cung bao gom mot may phat va mot thiet bi thu (S va R). Bo thu ma CR (Code Receiver) cung gom 2 bo phan thu va phat (R va S). CS CR Hinh 2.9. He tliong bao liieu MFC. O bo phat ma -CS. may phat S dung de tao cac tin hieu dia chi va truyen tdi ddi phuong. may thu R d bo thu ma - CR se nhan dupe cac tin hieu do. 6 phfa ngugc lai, may thu ma - CR se thu tin hieu dia chi bing may thu R va tao ra cac tin hieu difeu khien cho may thu R d bo phat ma CS bing bo phat S. Thu tuc cudng buc da tan dupe mo phong 6 hinh ve 2.10. CS CR S R R S b -----------------------► > f g ----------------------------------------------------------------► Hinh 2.10. Tliu tuc cudng buc da tan Bieu do hinh 2.10 dupe van hanh nhu sau: a. Mot tin hieu lien tuc gom 2 tan so dupe phat di tu bo phat ma - CS do may phat S dam nhiem. b. May thu ma - CR xac nhan 2 tan so tone tao thanh tin hieu va lenh cho may phat S dua ra mot tin hieu didu khien. c. Bo thu ma - CR giri di mot tin hieu dieu khien cung gom 2 tan so den bo phat ma - CS. d. Bo phat ma - CS xac nhan tin hieu dieu khien tao tu 2 tan so thu duoc va lenh cho ngirng ngay viec phat tin hieu dau tien (a). Luc nay, chi con lai tin hieu dieu khien (C). e. Bo thu ma - CR nhan thay tin hieu ban dau tir CS da bi ngirng. no giri lenh cho bo phat S ciia chinh no ngirng phat tin hieu dieu khiem. Thuc ra CR biet ring CS da nhan dupe tin hieu dieu khien. Tai thdi diem nav. dudng day khong co tin hieu nao. hoan toan yen tinh. 56 f. Bo CS da nhan biet tin hieu dieu khien bi ngirng va no chuan bj dS phat tiep tin hieu tiep theo. g. Tin hieu tiep theo (thur 2) dupe gui tiep tir CS va qua trinh cur nhu vay den tin hieu cuoi cung. Ro rang thu tuc cua bao hieu ma da tin R2 la hoan toan cudng che. Nhu the do tin cay se cao tuy co do phurc tap. Thuc te co the dung ket noi 4 day hoac 2 day nen hinh thanh cac thiet bj da tan 4 day va thiet bj da tan 2 day. Tren hinh ve 2.1 la va 2.1 lb mo phong cac cau true do. 4 day a) Hinh 2.11. Cac so do 4 day va 2 day. Thiet bj bao hieu da tan 4 day la thiet bj dupe ket noi den duong thong thoai bdi 2 ddi day. Nhu vay, phan thdng thoai cung cau true vdi kieu 4 day. Tren hinh ve dieim A la cira ra va diem B la cira vao cua thiet bj. Thiet bi da tan 2 day la thiet bj dirpc ket ndi mot ddi day de nhan va gui cac td hop ma da tan. Tren hinh ve ta thay cac bo may phat S va thu R deu dua vao khdi ket hop hay phan hop (Coupling Device). Diem C la cua chung cho ca ra va vao. IV. MOT SO HE THONG BAO HIEU KENH RIENG (CAS) KHAC 1. He thong bao hieu MF he thong Bell Muc nay giai thieu he thdng bao hieu MF dupe phat trien bdi Bell tu nam 1950. He thong van con dupe sir dung trong mang noi hat d My va gan giong nhu he thdng bao hieu R1 dupe mo ta trong khuyen nghj Q.310 va Q.332 cua ITU-T. Vdi bao hieu MF he thdng Bell, co the su dung cho trung ke mot hudng va trung ke hai hudng, bao hieu dja chi va giam sat dupe thiet ke theo kieu link by-link. Bao hieu giam sat dupe thiet lap qua tone don tan cho cac dudn° trun° 57 ke tuong tu va bao hieu bit bit cho cac duong trung ke so. Cac thong tin dia chi dupe giri qua tone da tan. 1.1. Bao hieu giam sat Cac bao hieu giam sat dupe truyen lien tuc bdi cac tong dai ket cuoi dei xac dinh trang thai duong trung ke. No dupe goi la bao hieu hai trang thai lien tuc. Cac trang thai co the khac nhau vdi cac diem ket cuoi trung ke khac nhau. Bao hieu MF dupe sir dung de xac nhan trang thai nhac td hop hoac trang thai dat td hop, nhu liet ke trong bang 2.15 dudi day: Hudng Kieu bao hieu Trang thai chuyen doi Di Chiem dudng Dat td hop sang nhac td hop Di Xoa hudng di Nhac td hop sang dat td hop Ve Tra ldi Dat td hop sang nhac td hop va Xoa hudng ve Nhac td hop sang dat td hop Ve San sang nhan (wink) Xung nhac td hop, 120-290 ms Bang 2.15. Cac bao hieu giam sat. Hoat dong bao hieu giam sat khong khac nhau nhieu ddi vdi dudng trung ke tuong tu va dudng trung ke sd. 1.1.1. Cac trung ke tuong tu Tone don tan 2600 Hz duoc sir dung de xac dinh trang thai trung ke tuong tu giua 2 tdng dai. Tone nay dupe dua vao bang tan thoai chuyen qua dudng trung ke va se ngit khi mot cuoc goi dang xir ly hoac thiet lap xong. Vi vay, trang thai dat td hop hay rdi dupe the hien khi co tone nay va trang thai nhac td hop hay ban khi khong co tone nay bien mat tren dudng trung ke. Cac tin hieu giam sat theo phuong phap don tan duoc mo ta tren hinh 2.12. Bao hieu thuan Nhac td hop Gac td hpp Bao hieu ngupc Nhac td hop Gac td hop" Trung ke dang dung Chiem Dia chi bao hieu Xir ly ngan 120-290 ms Xoa thuan Xoa ngupc Hinh 2.12. Bao hieu giam sat huong di va huong ve cho mot cuoc goi. 58 Trong hinh 2.12, gia thiet ring tdng dai A gui bao hieu huong di va tong dai B gui tin hieu hudng ve. Tdng dai A gui tin hieu chiem hudng di hoac tin hieu nhac may tdi tdng dai B tren trung ke dupe chon. Sau do, tdng dai B giri tin hieu wink hoac tin hieu san sang nhan sd tdi tdng dai A de dpi bao hieu dia chi hoac cac con sd tir tdng dai B giri tdi. Sau khi cac con so dupe giri di va cuoc goi dupe tra ldi, tdng dai B giri tra ldi ngupc lai hay tin h'eu nhac may tdi tdng dai A, md ra mot dudng thoai giua hai he thdng tdng dai. Trong trudng hop nay, neu thue bao chii goi gac may trudc va tin hieu xoa hudng di dupe giri tir tdng dai A sang tdng dai B. Khi thue bao bi goi gac may trudc, tin hieu xoa ngupc (hudng ve) se dupe giri di tir tdng dai B sang tdng dai A. Co hai van de can luu y d phuong phap bao hieu nay: ™ Thu nhat, he thdng MF ciia Bell khong co bao hieu hudng ve cho cac dau ndi bi hong trong qua trinh thiet lap. Vi vay, tdng dai co cuoc goi hong phai dau ndi tdi may thdng bao cho thue bao chii goi biet cuoc goi khong thanh cong khi co ldi xay ra. He thdng bao hieu se thay mat thue bao chii goi giai phong bing cach khdi tao thu tuc xoa hudng di. ™ Thu hai, he thdng MF cua Bell khong giai phong cac kieu bao hieu phong ve dang hien dien, bo dem thdi gian dupe sir dung sau khi cac trung ke dupe giai phong. Vi vay, sau khi tdng dai giai phong trung ke, no phai khdi tao mot bo dem thdi gian khoang 1 giay. Sau khi thdi han nay het, tdng dai gia thiet ring trung ke vira dupe giai phong tai dau kia ciia ket cuoi va trung ke do san sang phuc vu cho mot cuoc goi mdi. 1.1.2. Cac trung ke so Cac trung ke so thdng dung hien nay sir dung phuong tien mang El va Tl. Vdi trung ke sd, cac bit dupe bit tir cac khung dac biet va sir dung cho cac muc dich bao hieu. Vi du: Trong trung ke sd Tl co 2 kieu dinh dang khung: Sieu khung (SF) va sieu khung md rong (ESF). Bit co trong sd thap nhat dupe tach ra tir khung sd 6 va khung sd 12 ddi vdi sieu khung SF va khung sd 6, 12, 18 va 24 ddi vdi sieu khung md rong ESF. Cac bit nay dupe biet den nhu la bit Sa. Sb trona SF 59 va bit Sa, Sb. Sc va Sd trong ESF. Viec bat cac bit nav khong anh hudng tdi chat lirpng cua tin hieu thoai. Cac tin hieu bao hieu SF - Sa, Sb tuong tu nhau va cung cap hai trang thai, bao hieu giam sat lien tuc. Gia tri cua bit = 0 dupe sir dung de’ xac nhan trang thai gac may, va bit co gia tri = 1 xac djnh trang thai nhac may. 1.2. Bao hieu dja chi Bao hieu dia chi dupe sir dung de truyen cac con sd thue bao bi goi va chii goi cung nhu de xac dinh su bat dau va ket thuc ciia thdng tin dia chi. Trong phuong phap MF ciia Bell, cac bao hieu dia chi dupe td hop bdi 2 tan sd trong bang tan thoai chon tir 6 tan sd khac nhau dupe minh hoa tren bang 2.16 dudi day: Bao hieu Cac tan sd (Hz) Sd 1 700 va 900 Sd 2 700 va 1100 Sd 3 900 va 1100 Sd 4 700 va 1300 Sd 5 900 va 1300 Sd 6 1100 va 1300 So'7 700 va 1500 So 8 900 va 1500 So 9 1100 va 1500 So 0 1300 va 1500 KP (Bat dau) 1100 va 1700 ST (Ket thuc) 1500 va 1700 Being 2.16. Cac bao liieu dia clii M F ciia Bell. Day cac tin hieu dia chi dupe khdi tao bang KP hoac bang tin hieu xung bat dau va ket thuc vdi ST hoac tin hieu xung ket thuc. Hai khoang thdi gian quan trong ton tai: Do dai tin hieu KP khoang tir 90 den 110ms, va do dai tin hieu ST tir 61 tdi 75ms. Khoang lang giua hai tin hieu cung khoang tir 61 tdi 75ms. Hinh 2.13 md ta trinh tu bao hieu dia chi va bao hieu giam sat. 60 Bao hieu thuan Nha'c may Gac may Bao hieu ngirgc Nha'c may Gac may Trung ke dang dung Chiem Dia chi Tones-MF KP chu ST ; so I Xir ly ngdn Xoa thuan Xoa ngupc Hinh 2.13. Trinh tubdo hieu dia chi va giam sat. Bao hieu dia chi dung hai con so thong tin co ban. Cac ma trong thong tin nay (hoac bit I) chi thi so thue bao chu goi hoac nhan dang so tu dong (ANI) de sir dung dich vu dieu hanh he thong. (Xem trong bang 2.17). Cac ma I Thdng tin 1 = 00 Sd chu goi san sang. 1 = 02 Sd chii goi khong sin sang. I = 06 Yeu cau xac nhan may le. I = 10 Cuoc goi thu. Being 2.17. Cac md bao hieu dia chi. Cac ma thong tin dirpc giri di sau tm hieu KP va trudc khi gui cac con so cua thue bao bi goi. Ma I = 02 va 06 xac dinh rang can h6 trp dieu hanh de xir ly cac cuoc goi nav. 2. He thong bao hieu so 5 cua CCITT CCITT dira ra he thong bao hieu so 5 vao nam 1960 de’ sir dung trong mang qudc te. He thong bao hieu nay hien nay van dang su dung cho cac trung ke dirdng dai va trong mot sd trudng hop sir dung cho cac tuven lien ket xuven bien va ve tinh. He thdng bao hieu sd 5 dupe thiet ke de hoat dong qua cac dirdng trung ke tuong tir co hd trp thiet bj noi suy tieng ndi an dinh theo thdi gian TASI. TASI tuong tu nhu bo do tieng ndi tich cuc VAD. no cho phep su dung cac bang thdng thira (khoang lang hoac khoang dung trong qua trinh dam 61 thoai) de sir dung cho cac cuoc goi khac. Bao hieu dia chi va bao hieu giam sat dupe sir dung theo nguyen tic tirng chang (link- by- link) va sir dung phuong phap bao hieu trong bang. 2.1. Bao hieu giam sat Bao hieu giam sat dupe thuc hien bdi hai tan sd, chung dupe giri di rieng biet hoac theo kieu td hop. Bao hieu sd 5 ciia CCITT sir dung bao hieu giam sat bit buoc, do do tone bao hieu se ngirng khi nhan dupe xac nhan tra ldi. Hai tan sd trong bang la fl = 2400Hz va f2 = 2600Hz. Td hop ciia hai tin sd f 1 va f2 tao ra mot tin hieu da hop. Ba tin hieu mdi dupe dua ra trong bang 2.18: giai phong, nhay-ban, truydn thing. - Giai phong: Tm hieu nay dupe sir dung trong cac tdng dai bi goi de xac nhan xoa hudng di tir tdng dai goi di. No cung xac dinh cho tong dai goi di ring trung ke dang dupe sin sang cho cuoc goi den. - Nhay- ban: Tin hieu nay sir dung cho cac tong dai goi den de chi thi cho tong dai goi di ring thiet lap cuoc goi khong the chuyen tiep tdi dich. - Truyen thing: Tin hieu nay sir dung cho cac cuoc goi dich vu ciia ngudi dieu hanh. Hudng Kieu bao hieu Tan sd Hudng di Chiem fl Hudng ve Chd sd f2 Hudng di Tra ldif l Hudng ve Xac nhan f2 Hudng di Xoa ngupc f2 Hudng ve Xac nhan fl Hudng di Xoa hudng di fl vaf2 Hudng ve Giai phong fl vaf2 Hudng ve Nhay ban f2 Hudng di Xac nhan fl Hudng di Truyen thang f2 Being 2.18. Cac bao hieu va cac tan sd ciia bao hieu giam sat 62 2.2. Bao hieu dia chi Trong CCITT N°5, bao hieu dia chi dira tren td hop cua 2 tan so nhu chi ra trong bang 2.19 dudi day. Chu6i tin hieu dia chi dupe bat dau vdi KP1 doi voi cac con so quoc te va KP2 doi vdi cac con sd qudc gia. Ma 11 va 12 dupe sir dung de dau ndi tdi cac dich vu nguoi dieu hanh qudc te. Bao hieu Cac tan sd (Hz) Sd 1 700 va 900 Sd 2 700 va 1100 Sd 3 900 va 1100 Sd 4 700 va 1300 Sd 5 900 va 1300 Sd 6 1100 va 1300 Sd 7 700 va 1500 Sd 8 900 va 1500 Sd 9 1100 va 1500 Sd 0 1300 va 1500 Ma 11 700 va 1700 Ma 12 900 va 1700 KP1 1100 va 1700 KP2 1300 va 1700 ST 1500 va 1700 Bang 2.19. Cac tin liieu ciia chi CCITT N°5. 3. He thong bao hieu R1 R l cung la he thong bao hieu da tan (MF) d Bdc My va Canada da dupe CCITT cong nhan. Ma da tan R1 cung tao ra cac tin hieu la to hop ciia 2 trong sd 5 tan sd. Tan sd thu 6 de tao ra cac tin hieu chuc nang dieu khien. Vf du cac td hop ma R1 nhu bang 2.20 va y nghTa ciia chung nhu sau: R1 cung dung bao hieu ngoai bang, vdi thdng tin giam sat co f > 3,4 KHz. No co the sir dung co tone hoac khong co tone khi rdi. Thf du cac nude Bdc My da dung tone f = 3700Hz, mac dii CCITT khuyen nghi la 3825Hz. 63 Digit Cap tan so Churc nang 1 700 - 900 Con so 1 2 700- 1100 Con sd 2 3 900- 1100 Con sd 3 _ . J 4 700- 1300 Con sd 4 5 900- 1300 Con sd 5 6 1100 - 1300 Con s d 6 7 700- 1500 Con sd 7 8 900- 1500 Con sd 8 9 1100- 1500 Con sd 9 10 1300- 1500 Con sd 0 1100- 1700 Du bi 200- 1700 Ket thuc xung 700- 1700 Dieu khien nhan dong xu Bang 2.20. Cac to hop md cua R1 va y nghTa ciia cluing. 4. He thong bao hieu so 4 He thong bao hieu so 4 la he thong bao hieu tieu bieu cho loai 2VF. No dung 2 tan so: 2040 va 2400Hz tuong ung ma. Ky thuat tao ma rat don gian. No dung cac to hop co dupe cua 2 tan so tren. Thi du: Dat 2040Hz la x (0), dat 2400Hz la y (1). Tu do se co cac to hop tu 2 den 4 phan tu de tao cac tin hieu bao hieu: x - xy- xx- xxy y- yy- yx- yyxx Cu nhu vay va gan cho no cac chuc nang tin hieu. Tom lai, cac he thong CAS du theo hinh thuc nao cung con bi han che ve toe do xir ly bao hieu va dung lupng thong tin. Do do, chung chi dupe sir dung cho cac mang ca nhd hoac trong cac giai doan trudc day. Do nhu cau phat trien ciia mang vien thong ve so lupng thue bao. ve cac loai hinh dich vu cung cac phuong thuc truyen dan khac nhau. nhat la truyen dan SDH va da dich vu ISDN... He thong bao hieu kenh chung - CCS da dupe ra doi va ngay cang the hien ro vai tro ciia no tren mang. 64 Cau hoi on tap chifdng 2 1. The nao la he thong bao hieu CAS? Ve mo hinh cua he thong CAS? 2. Dac ti'nh cua bao hieu R2? 3. Hay cho biet cac loai tin hieu bao hieu di/ong hifdng di, va cac loai tin hieu bao hieu dirdng hi/6ng ve? 4. Hay cho biet cac loai tin hieu bao hieu ghi phat hi/dng di, va cac loai tin hieu bao hieu ghi phat hirdng ve? 5. Trinh bay cac kieu truyen thong tin bao hieu? 6. Pham vi Crng dung cua bao hieu R2 tren mang vien thong Viet Nam va hudng phat trien cua no? 7. So sanh giCira he thong bao hieu MF cua Bell va he thong bao hieu R1? 65 C h tfc fn g 3 BAO HlfiU KfiNH CHUNG (CCS) Muc tieu - Phan tich dac diem chung cua he thong bao hieu kenh chung - CCS. mot so loai bao hieu kenh chung, phuong phap truyen thong tin theo kieu phan lap va mo hinh OSI. - Phan tich he thong bao hieu kenh chung so 7 ve: Cau true, cac thanh phan trong bao hieu so 7, cac ban tin bao hieu so 7 va su lien quan giua mo hinh OSI va mang bao hieu so 7. - Tim hieu sir ket hop giira bao hieu R2 va bao hieu so 7 va tinh hinh ap dung bao hieu so 7 tren mang vi£n thong Viet Nam. Noi dung tong quat - Cung cap dac diem chung cua he thong bao hieu kenh chung - CCS. mot so loai bao hieu kenh chung, phuong phap truyen thong tin theo kieu phan lop va mo hinh OSI. Dac biet dua ra kien thuc v£ cau true, cac ban tin bao hieu so 7 va tinh hinh phat trien mang bao hieu so 7 tren mang vi£n thong Viet Nam. - Phan biet so sanh de rut ra cac uu diem cua bao hieu kenh chung so voi he thong bao hieu kenh rieng - CAS. - Phan tich dupe cac ban tin bao hieu so 7, co che phat hien I6i. su tuong urng giua mo hinh OSI va he thong bao hieu so 7. - Tim hieu su ton tai ciia bao hieu R2 va bao hieu so 7 tren mang vi5n thong Viet Nam va tim dupe su ket hop giua chung. I. KHAI NIEM VA CAC DAC TINH CUA CCS 1. Khai niem ve CCS Bao'hieu kenh chung la mot he thong bao hieu trong do bao hieu nim trong mot kenh tach biet vdi kenh tieng. nhung kenh bao hieu nay duoc dung chung cho mot sd lupng ldn cac kenh tieng. 66 Hay chu y nhung dinh nghTa va thuc chat cua khai niem CAS va CCS. Ban chat cua dinh nghla CCS la noi den kha nang, nang luc cua he thong bao hieu. Co the noi CCS la mot he thong bao hieu manh, mot cong nghe mdi theo ky thuat chuyen mach goi va d6 tach thfch urng vdi nhieu loai hinh dich vu khac nhau. He thong CCS ra ddi chinh la de thich hop vdi ky thuat tdng dai SPC, lam viec vdi cac luong sd lieu toe do cao. Vf du ve he thong bao hieu CCS la N°6, N°7. Hinh 3.1. So sdnlt CAS va CCS 6 bao hieu CCS. thdng tin bao hieu dupe tao thanh cac don vi tin hieu d dang cac goi sd lieu. Trong cac don vi tin hieu nay, ngoai cac thdng tin ve bao hieu eon chua chi thi v i kenh tieng, cac thdng tin dia chi, cac thdng tin dieu 67 khien I6i. Nhung iru viet cua ky thuat goi se dupe phat huy tro thanh nhung uu diem cua CCS. Cac duong bao hieu ket hop vdi cac tdng dai SPC se tro thanh mot mang chuyen mach goi cua chinh no. Hinh 3.1 mo ta he thong bao hieu CCS va CAS de tien so sanh. O cau true CCS se tao thanh dudng bao hieu rieng phuc vai cho nhieu kenh thoai giua cac thiet bj chuyen mach. O cau true CAS cac dudng bao hieu se ton tai ben canh cac dudng tieng qua cac bo bao hieu don tan va da tan. Ndi each khac, mdi dudng bao hieu chi dung cho mot ke tieng va ket hop vdi dudng tieng. 2. Cac dac tinh cua CCS - Bao hieu kenh chung la he thdng bao hieu hoan thien nhat hien nay. - Tdi uu hoa vdi mang sd sir dung cac tong dai SPC. - Thich ung cho nhieu dudng day sd co toe do khac nhau ke ca toe do cao, thich ung vdi nhidu loai mang: dien thoai, di dong, sd lieu, IDN, ISDN... - Dap ung dupe cac yeu cdu truyen tin trao doi giua cac bo xir ly bao hieu vdi mang de didu khien dau ndi, kiem tra bao dudng... - Co the neu ra mot sd dac diem ciia CCS: * Uu diem - Toe do bao hieu cao, thdi gian thiet lap mot cuoc goi lien dai dupe giam xuong dang ke (