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CHUONG 3 C C K THUT CO BN TRONG TRUYN S LIU

N?i dung. Tn hi?u v d? li?uTruy?n d?n d? li?uC?u trc knh truy?n Tu?n t?Song songC?u trc truy?n B?t d?ng b??ng b?Cc phuong ki?m tra v pht hi?n l?iC?u hnh Giao ti?p V.24/EIA-232-FNn thng tin Phn h?p knh (Multiplexing)ADSL. Thu?t ng?. Thnh ph?n trong m hnh truy?n d? li?u

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CHUONG 3 C C K THUT CO BN TRONG TRUYN S LIU

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    1. CHUONG 3 CC K? THU?T CO B?N TRONG TRUY?N S? LI?U anhph@cse.hcmut.edu.vn

    2. N?i dung Tn hi?u v d? li?u Truy?n d?n d? li?u C?u trc knh truy?n Tu?n t? Song song C?u trc truy?n B?t d?ng b? ?ng b? Cc phuong ki?m tra v pht hi?n l?i C?u hnh Giao ti?p V.24/EIA-232-F Nn thng tin Phn h?p knh (Multiplexing) ADSL

    3. Thu?t ng? Thnh ph?n trong m hnh truy?n d? li?u (du?i gc d? v?t l) Thi?t b? Thi?t b? pht (Transmitter) Thi?t b? thu (Receiver) Mi tru?ng truy?n (Medium) K?t n?i K?t n?i tr?c ti?p (Direct link) Khng c?n cc thi?t b? trung gian K?t n?i di?m-di?m (Point-to-point) K?t n?i tr?c ti?p Ch? c 2 thi?t b? dng chung k?t n?i K?t n?i nhi?u di?m (Multi-point) = 2 thi?t b? dng chung k?t n?i

    4. Ch? d? truy?n Simplex mode Khng dng r?ng ri v khng th? g?i ngu?c l?i l?i ho?c tn hi?u di?u khi?n cho bn pht Television, teletext, radio Half-duplex mode B? dm Full-duplex mode i?n tho?i

    5. Truy?n d?n d? li?u D? li?u Th?c th? mang thng tin Analog Cc gi tr? lin t?c trong m?t vi th?i kho?ng e.g. m thanh, video Digital Cc gi tr? r?i r?c e.g. van b?n, s? nguyn Tn hi?u Bi?u di?n di?n ho?c di?n t? c?a d? li?u Analog Bi?n lin t?c Mi tru?ng lin t?c (wire, fiber optic, space) Bang thng ti?ng ni 100Hz t?i 7kHz Bang thng di?n tho?i 300Hz t?i 3400Hz Digital Dng 2 thnh ph?n m?t chi?u Truy?n d?n Trao d?i d? li?u thng qua vi?c x? l v lan truy?n tn hi?u

    6. Tn hi?u mi?n th?i gian Tn hi?u lin t?c Thay d?i lin t?c theo th?i gian Tn hi?u r?i r?c Thay d?i t?ng m?c theo th?i gian Tn hi?u chu k? M?u l?p l?i theo th?i gian Tn hi?u khng tu?n hon M?u khng l?p l?i theo th?i gian

    7. Tn hi?u analog Ba d?c di?m chnh c?a tn hi?u analog bao g?m Bin d? (Amplitute) T?n s? (Frequency) Pha (Phase) Bin d? c?a tn hi?u analog o d? m?nh c?a tn hi?u, don v?: decibel (dB) hay volts. Bin d? cng l?n, tn hi?u cng c cu?ng d? m?nh. Tn hi?u ti?ng ni - t? hello. Ti?ng ni (speech) l m?t tn hi?u r?t ph?c t?p. Ti?ng ni ch?a hng ngn t? h?p khc nhau c?a nhi?u tn hi?u.

    8. T?n s? c?a tn hi?u analog T?c d? thay d?i c?a tn hi?u trong m?t giy, don v? Hz hay s? chu k? trong m?t giy (cycles per second) Tn hi?u c t?n s? 30Hz ~ thay d?i 30 l?n trong m?t giy. M?t chu k? l s? di chuy?n sng c?a tn hi?u t? di?m ngu?n b?t d?u cho d?n khi quay tr? v? l?i di?m ngu?n d.

    9. Pha c?a tn hi?u analog T?c d? thay d?i quan h? c?a tn hi?u d?i v?i th?i gian, du?c m t? theo d? (degree) S? d?ch pha x?y ra khi chu k? c?a tn hi?u chua k?t thc, v m?t chu k? m?i c?a tn hi?u b?t d?u tru?c khi chu k? tru?c d chua hon t?t Tai ngu?i khng c?m nh?n du?c s? d?ch pha Tn hi?u mang d? li?u b? ?nh hu?ng b?i s? d?ch pha V d? cc m?i n?i khng hon h?o s? gy ra d?ch pha

    10. Tn hi?u mi?n t?n s?

    11. Thnh ph?n c?a ti?ng ni T?m t?n s? c kh? nang nghe 20Hz 20kHz Ti?ng ni 100Hz 7kHz D? dng chuy?n sang d?ng tn hi?u di?n t? d? truy?n d?n Cc t?n s? v?i m lu?ng khc nhau du?c chuy?n thnh t?n s? di?n t? v?i di?n p khc nhau T?m t?n s? gi?i h?n cho knh tho?i 300 3400Hz

    12. Tn hi?u s? (digital) Tn hi?u s? bao g?m ch? hai tr?ng thi, du?c di?n t? v?i hai tr?ng thi ON hay OFF ho?c l 0 hay 1 Tn hi?u s? yu c?u kh? nang bang thng l?n hon tn hi?u analog.

    13. Tn hi?u s? (digital) Cc v?n d? khi s? d?ng knh tho?i (voice channel) trong vi?c truy?n tn hi?u s? M?t tn hi?u s? l m?t t? h?p c?a cc tn hi?u khc. ?c bi?t, tn hi?u s? c th? du?c bi?u di?n nhu sau Signal = f + f3 + f5 +f7 +f9 +f11 +f13 ....f? Do d m?t tn hi?u s? g?m 1 t?n s? co b?n (f), c?ng thm t?n s? 3f (hi t?n b?c 3), c?ng thm t?n s? 5f (hi t?n b?c 5), N?u bin d? c?a t?n s? f, f3, f5, l a, a3, a5, th a = 3a3 = 5a5 ? g?i tn hi?u s? qua knh truy?n tho?i, bang thng c?a knh truy?n ph?i cho php t?n s? co b?n f, t?n s? 3f v t?n s? 5f di qua m khng ?nh hu?ng nhi?u d?n cc t?n s? ny y l yu c?u t?i thi?u d? bn nh?n nh?n dng du?c tn hi?u s?

    14. Tn hi?u s? (digital) Truy?n 1 tn hi?u s? nh? phn t?c d? 2400bps trn knh tho?i c bang thng 3.1kHz T?n s? co b?n: 1200Hz (thng thu?ng b?ng t?c d? bit) Ch? c t?n s? co b?n di qua m khng b? thay d?i

    15. D? li?u v tn hi?u Thu?ng dng tn hi?u s? cho d? li?u s? v tn hi?u analog cho d? li?u analog C th? dng tn hi?u analog d? mang d? li?u s? Modem C th? dng tn hi?u s? d? mang d? li?u analog Compact Disc audio

    16. Truy?n d?n Truy?n d?n analog Khng quan tm d?n n?i dung d? li?u du?c truy?n (s? ho?c tuong t?) Suy gi?m khi truy?n xa Dng b? khu?ch d?i (amplifier) d? truy?n d? li?u di xa Khu?ch d?i c? tn hi?u l?n nhi?u

    17. Analog data/Analog Signal G?i bnh thu?ng ho?c m ha vo ph?n ph? khc Analog data/Digital Signal M ha dng b? codec d? t?o ra chu?i bit s? Digital Data/Analog Signal u?c m ha dng modem d? t?o ra t/h tuong t? Digital Data/Digital Signal Bi?u di?n tr?c ti?p d? li?u ho?c m ha d? t?o ra t/h s? c d?c tnh mong mu?n Analog Signal/Analog Transmission Lan truy?n thng qua cc b? khu?ch d?i, x? l t/h nhu nhau b?t k? d? li?u l s? ho?c tuong t? Analog Signal/Digital Transmission Gi? s? t/h bi?u di?n d? li?u s?, lan truy?n qua cc b? repeater Digital Signal/Analog Transmission Khng dng Digital Signal/Digital Data T/h l chu?i nh? phn lan truy?n qua cc b? repeater D? li?u, tn hi?u v truy?n d?n

    18. Truy?n d?n s? Uu di?m Cng ngh? s? Cng ngh? LSI/VLSI lm gi?m gi thnh Ton v?n d? li?u Nhi?u v suy gi?m tn hi?u khng b? tch luy b?i cc repeater Truy?n kho?ng cch xa hon trn cc du?ng truy?n km ch?t lu?ng Hi?u qu? knh truy?n TDM > FDM B?o m?t Cc k? thu?t m ha d? b?o m?t d? li?u d? p d?ng Tch h?p D? li?u s? v analog du?c x? l tuong t? nhau

    19. Digital ? Digital Tn hi?u s? Xung di?n p r?i r?c, khng lin t?c M?i xung l m?t ph?n t? tn hi?u D? li?u nh? phn du?c m ha thnh cc ph?n t? tn hi?u

    20. Thu?t ng? Unipolar T?t c? cc ph?n t? tn hi?u c cng d?u Polar M?t tr?ng thi logic du?c bi?u di?n b?ng m?c di?n p duong, tr?ng thi logic khc du?c bi?u di?n b?ng m?c di?n p m T?c d? d? li?u (data rate) T?c d? truy?n d?n d? li?u theo bps (bit per second) ? r?ng (chi?u di 1 bit) Th?i gian (thi?t b? pht) dng d? truy?n 1 bit T?c d? di?u ch? T?c d? m?c tn hi?u thay d?i on v? l baud = s? ph?n t? tn hi?u trong 1 giy Mark v Space Tuong ?ng v?i 1 v 0 nh? phn

    21. Di?n gi?i tn hi?u C?n bi?t ?nh th?i c?a cc bit (khi no chng b?t d?u v k?t thc) M?c tn hi?u Y?u t? ?nh hu?ng d?n vi?c di?n gi?i tn hi?u T? s? SNR T?c d? d? li?u Bang thng

    22. Polar Encoding

    23. Nonreturn to zero (NRZ) Nonreturn to Zero-Level (NRZ-L) 2 m?c di?n p khc nhau cho bit 1 v bit 0 i?n p khng thay d?i (khng c transition) khi khng c s? thay d?i tn hi?u i?n p thay d?i (c transition) khi c s? thay d?i tn hi?u (t? 0?1 ho?c t? 1?0) Nonreturn to Zero Inverted (NRZI) NRZI cho cc bit 1 D? li?u du?c m ha can c? vo vi?c c hay khng s? thay d?i tn hi?u ? d?u th?i kho?ng bit. Bit 1: du?c m ha b?ng s? thay d?i di?n p (c transition) Bit 0: du?c m ha b?ng s? khng thay d?i di?n p (khng c transition)

    24. Nonreturn to Zero (NRZ) M ha sai phn D? li?u du?c bi?u di?n b?ng vi?c thay d?i tn hi?u (thay v b?ng m?c tn hi?u) Nh?n bi?t s? thay d?i d? dng hon so v?i nh?n bi?t m?c Trong cc h? th?ng truy?n d?n ph?c t?p, c?m gic c?c tnh d? dng b? m?t Uu v nhu?c di?m c?a m ha NRZ Uu D? dng n?m b?t Bang thng dng hi?u qu? Nhu?c C thnh ph?n m?t chi?u Thi?u kh? nang d?ng b? Dng trong vi?c ghi bang t? t dng trong vi?c truy?n tn hi?u

    25. Multilevel Binary Dng nhi?u hon 2 m?c Bipolar-AMI (Alternate Mark Inversion) Bit-0 du?c bi?u di?n b?ng khng c tn hi?u Bit-1 du?c bi?u di?n b?ng xung duong hay xung m Cc xung 1 thay d?i c?c tnh xen k? Khng m?t d?ng b? khi d? li?u l m?t dy 1 di (dy 0 v?n b? v?n d? d?ng b?) Khng c thnh ph?n m?t chi?u Bang thng th?p Pht hi?n l?i d? dng Pseudoternary 1 du?c bi?u di?n b?ng khng c tn hi?u 0 du?c bi?u di?n b?ng xung duong m xen k? nhau Khng c uu di?m v nhu?c di?m so v?i bipolar-AMI

    26. Trade Off Khng hi?u qu? b?ng NRZ M?i ph?n t? t/h ch? bi?u di?n 1 bit H? th?ng 3 m?c c th? bi?u di?n log23 = 1.58 bit B? thu ph?i c kh? nang phn bi?t 3 m?c (+A, -A, 0) C?n thm kho?ng 3dB cng su?t d? d?t du?c cng xc su?t bit l?i Multilevel Binary

    27. Biphase Manchester Thay d?i ? gi?a th?i kho?ng bit Thay d?i du?c dng nhu tn hi?u d?ng b? d? li?u L?H bi?u di?n 1 H?L bi?u di?n 0 Dng trong IEEE 802.3

    28. Biphase Differential Manchester Thay d?i gi?a th?i kho?ng bit ch? dng cho d?ng b? Thay d?i d?u th?i kho?ng bi?u di?n 0 Khng c thay d?i ? d?u th?i kho?ng bi?u di?n 1 Dng trong IEEE 802.5

    29. Biphase Uu v nhu?c di?m Nhu?c di?m T?i thi?u c 1 thay d?i trong th?i kho?ng 1 bit v c th? c 2 T?c d? di?u ch? t?i da b?ng 2 l?n NRZ C?n bang thng r?ng hon Uu di?m ?ng b? d?a vo s? thay d?i ? gi?a th?i kho?ng bit (self clocking) Khng c thnh ph?n m?t chi?u Pht hi?n l?i Khi thi?u s? thay d?i mong d?i

    30. Biphase

    31. Polar Encoding

    32. Bi t?p

    33. Bi t?p

    34. Bi t?p

    35. Bi t?p

    36. Bi t?p

    37. Bi t?p

    38. Bi t?p

    39. Bi t?p

    40. Scrambling Dng k? thu?t scrambling d? thay th? cc chu?i t?o ra h?ng s? di?n p Chu?i thay th? Ph?i t?o ra d? s? thay d?i tn hi?u, dng cho vi?c d?ng b? ha Ph?i du?c nh?n di?n b?i b? thu v thay th? tr? l?i chu?i ban d?u Cng d? di nhu chu?i ban d?u Khng c thnh ph?n m?t chi?u Khng t?o ra chu?i di cc tn hi?u m?c 0 Khng gi?m t?c d? d? li?u C kh? nang pht hi?n l?i

    41. B8ZS B8ZS (Bipolar With 8 Zeros Substitution) D?a trn bipolar-AMI N?u c 8 s? 0 lin ti?p v xung di?n p cu?i cng tru?c d l duong, m thnh 000+0+ N?u c 8 s? 0 lin ti?p v xung di?n p cu?i cng tru?c d l m, m thnh 000+0+ Gy ra 2 vi ph?m m AMI C th? l?m l?n v?i tc d?ng gy ra b?i nhi?u B? thu pht hi?n v di?n gi?i chng thnh 8 s? 0 lin ti?p

    42. B8ZS

    43. HDB3 HDB3 (High Density Bipolar 3 Zeros) D?a trn bipolar-AMI Chu?i 4 s? 0 lin ti?p du?c thay th? theo quy lu?t nhu sau

    44. HDB3

    45. Bi t?p

    46. Bi t?p

    47. Bi t?p

    48. Bi t?p

    49. So snh cc phuong php m ha Ph? tn hi?u Vi?c thi?u thnh ph?n t?n s? cao lm gi?m yu c?u v? bang thng T?p trung cng su?t ? gi?a bang thng ?ng b? ?ng b? b? thu v b? pht Tn hi?u d?ng b? ngo?i vi Co ch? d?ng b? d?a trn tn hi?u Kh? nang pht hi?n l?i C th? du?c tch h?p trong co ch? m ha Nhi?u v kh? nang mi?n nhi?m Vi m t?t hon cc m khc ? ph?c t?p v chi ph T?c d? tn hi?u cao hon (v do d t?c d? d? li?u cao hon) d?n t?i chi ph cao Vi m di h?i t?c d? tn hi?u cao hon t?c d? d? li?u

    50. ?ng d?ng Dng d? truy?n d? li?u s? trn m?ng di?n tho?i cng c?ng 300Hz ? 3400Hz Thi?t b? MODEM (MOdulator-DEMulator) K? thu?t i?u bin: Amplitude-Shift Keying (ASK) i?u t?n: Frequency-Shift Keying (FSK) i?u pha: Phase-Shift Keying (PSK) Digital ? Analog

    51. i?u bin (ASK) Dng 2 bin d? khc nhau c?a sng mang d? bi?u di?n 0 v 1 (thng thu?ng m?t bin d? b?ng 0) S? d?ng m?t t?n s? sng mang duy nh?t Phuong php ny ch? ph h?p trong truy?n s? li?u t?c d? th?p (~1200bps trn knh truy?n tho?i) T?n s? c?a tn hi?u sng mang du?c dng ph? thu?c vo chu?n giao ti?p dang du?c s? d?ng K? thu?t du?c dng trong cp quang

    52. i?u bin (ASK)

    53. i?u bin (ASK)

    54. i?u t?n (FSK) Binary FSK (BFSK) S? d?ng hai t?n s? sng mang: t?n s? cao tuong ?ng m?c 1, t?n s? th?p tuong ?ng m?c 0. t l?i hon so v?i ASK u?c s? d?ng truy?n d? li?u t?c d? 1200bps hay th?p hon trn m?ng di?n tho?i C th? dng t?n s? cao (3-30MHz) d? truy?n trn sng radio ho?c cp d?ng tr?c

    55. i?u t?n (FSK) Binary FSK (BFSK)

    56. i?u t?n (FSK) Multiple (FSK) Dng nhi?u hon 2 t?n s? Bang thng du?c dng hi?u qu? hon Kh? nang l?i nhi?u hon M?i ph?n t? tn hi?u bi?u di?n nhi?u hon 1 bit d? li?u

    57. i?u pha (PSK) S? d?ng m?t t?n s? sng mang v thay d?i pha c?a sng mang ny PSK vi phn (differential PSK) thay d?i pha tuong d?i so v?i sng tru?c d (thay v so v?i sng tham chi?u c? d?nh) Cho php m ha nhi?u bit trn m?i thay d?i tn hi?u sng mang (Phase Amplitude Modulation) Phuong php ny thu?ng du?c dng trong truy?n d? li?u ? t?c d? 2400bps (2 bits per phase change - CCITT V.26) ho?c 4800bps (3 bits encoding per phase change - CCITT V.27) ho?c 9600bps (4 bits encoding per phase/amplitude change) T?ng qut cho m ha NRZ-L

    58. i?u pha (PSK)

    59. i?u pha (PSK) Quadrature PSK (QPSK) M-ary PSK H? th?ng 64 v 256 tr?ng thi C?i thi?n t?c d? d? li?u v?i bang thng khng d?i Tang kh? nang ti?m ?n l?i

    60. Hi?u su?t Bang thng Bang thng ASK v PSK lin quan tr?c ti?p v?i t?c d? bit BT = (1+r)R Bang thng FSK c quan h? v?i t?c d? d? li?u d?i v?i cc t?n s? th?p, c quan h? v?i d? d?ch chuy?n c?a cc t?n s? di?u ch? d?i v?i t?n s? cao BT = 2?F + (1+r)R Tn hi?u nhi?u m?c BT = (1+r)R/m = (1+r)R/log2M Trong tru?ng h?p c l?i, t?c d? l?i c?a PSK v QPSK cao hon kho?ng 3dB so v?i ASK v FSK

    61. Quadrature Amplitude Modulation (QAM) QAM du?c dng trong ADSL v m?t s? h? th?ng wireless K?t h?p gi?a ASK v PSK M? r?ng logic c?a QPSK G?i d?ng th?i 2 tn hi?u khc nhau cng t?n s? mang Dng 2 b?n sao c?a sng mang, m?t ci du?c d?ch di 90 M?i sng mang l ASK d du?c di?u ch? 2 tn hi?u d?c l?p trn cng mi tru?ng Gi?i di?u ch? v k?t h?p cho d? li?u nh? phn ban d?u

    62. Digital ? Analog

    63. Analog ? Digital ?ng d?ng Dng d? truy?n d? li?u tuong t? trn m?ng truy?n d? li?u s? T?n d?ng cc uu di?m c?a truy?n d?n s? (thi?t b? r?, dng repeater, TDM, ) S? ha D? li?u s? c th? truy?n dng NRZ-L hay cc lo?i m khc Thi?t b? CODEC (COder-DECoder) K? thu?t i?u ch? xung m: Pulse Code Modulation (PCM) i?u ch? Delta: Delta Modulation (DM)

    64. i?u ch? xung m (PCM) L thuy?t l?y m?u N?u tn hi?u f(t) du?c l?y m?u d?u v?i t?c d? l?y m?u cao hon t?i thi?u 2 l?n t?n s? tn hi?u cao nh?t, th cc m?u thu du?c ch?a d? thng tin c?a tn hi?u ban d?u. T/h f(t) c th? du?c ti t?o, dng b? l?c thng th?p Cng th?c Nyquist: N >= 2f N: t?c d? l?y m?u f: t?n s? c?a tn hi?u du?c l?y m?u D? li?u ti?ng ni Gi?i h?n t?n s? <4000Hz T?c d? l?y m?u c?n thi?t 8000 m?u/giy

    65. i?u ch? xung m (PCM) PAM (Pulse Amplitude Modulation) Cc xung du?c l?y m?u ? t?n s? R=2B Lu?ng t? ha cc xung PAM Xc d?nh gi tr? c?a di?m du?c l?y m?u, roi vo kho?ng no th l?y gi tr? kho?ng d Ty thu?c vo cc m?c lu?ng t? 2n (n l s? bit c?n thi?t d? s? ha 1 xung) M ha d? li?u Th?c hi?n cc thao tc m ha thng tin tru?c khi truy?n di

    66. i?u ch? xung m (PCM)

    67. i?u ch? xung m

    68. Non-linear coding M?c lu?ng t? khng d?u Gi?m mo tn hi?u Companding (compressing-expanding)

    69. i?u ch? Delta (DM) Tn hi?u tuong t? du?c x?p x? b?i hm b?c thang (staircase) Hnh vi nh? phn i ln hay xu?ng 1 m?c (?) t?i m?i th?i kho?ng l?y m?u Hi?u su?t ? ti t?o ti?ng ni t?t PCM - 128 m?c (7 bit) Bang thng tho?i 4khz C?n 8000 x 7 = 56kbps d?i v?i PCM K? thu?t nn d? li?u c th? c?i thi?n thm V d?: k? thu?t m xen khung (interframe coding) cho video

    70. i?u ch? Delta (DM)

    71. i?u ch? Delta (DM)

    72. Analog ? Analog ?ng d?ng Dng d? di?u ch? d? li?u tuong t?: thay d?i t?n s? truy?n (t?n s? cao hon truy?n d?n t?t hon) Dng cho FDM K? thu?t i?u ch? bin: Amplitude Modulation (AM) i?u ch? gc (Angle Modulation) i?u ch? t?n s?: Frequency Modulation (FM) i?u ch? pha: Phase Modulation (PM)

    73. i?u ch? bin (AM) Bin d? c?a sng mang du?c thay d?i b?i bin d? c?a tn hi?u du?c truy?n di s(t) = [1+nax(t)]cos(2?fct) T?o ra t/h 2 bn (DSBTC), trong d ch? c?n c m?t bn na<1 t/h bao l b?n sao c?a t/h ban d?u na >1 t/h bao c?t tr?c th?i gian (thng tin b? m?t) Pt = Pc(1+ na2/2) Pt v Pc cng su?t t/h du?c truy?n di v t/h sng mang na ch? s? di?u ch?, t? s? bin d? t/h du?c truy?n v sng mang SSB v DSBSC Uu di?m D? hi?n th?c (di?u ch? v gi?i di?u ch?) D? bi?n d?i tn hi?u sang cc gi?i bang t?n khc nhau Khuy?t di?m D? b? ?nh hu?ng c?a nhi?u Khng s? d?ng hi?u qu? nang lu?ng

    74. i?u ch? bin (AM)

    75. i?u ch? t?n s? (FM)

    76. i?u ch? gc s(t) = Accos[2?fct + ?(t)] Phuong php di?u t?n s? (FM) Tn hi?u du?c truy?n di thay d?i thnh ph?n t?n s? c?a sng mang t? l? v?i bin d? v t?n s? c?a tn hi?u truy?n di ?(t) = nfm(t) Uu di?m Kh b? ?nh hu?ng c?a nhi?u S? d?ng hi?u qu? nang lu?ng Khuy?t di?m Tn hi?u du?c di?u ch? yu c?u bang thng r?ng hon nhi?u tn hi?u truy?n di ban d?u (d? li?u) Hi?n th?c m?ch di?u ch? v gi?i di?u ch? ph?c t?p hon so v?i phuong php di?u bin

    77. i?u ch? gc

    78. i?u ch? gc Phuong php di?u ch? pha (PM) ?(t) = npm(t) Tn hi?u truy?n di khng ?nh hu?ng d?n thnh ph?n bin d? v t?n s? m ch? lm thay d?i pha c?a sng mang Ph? t?n s? c?a tn hi?u du?c di?u ch? theo phuong php di?u pha tuong t? nhu phuong php di?u t?n ? phuong php di?u pha cung c cc d?c di?m tuong t? phuong php di?u t?n Tuy nhin, c hai l do phuong php di?u pha du?c d? ch?p nh?n hon ?i v?i bn nh?n: t?n s? c?a tn hi?u nh?n du?c l c? d?nh, ch? c pha thay d?i nn ch? c?n thi?t k? b? l?c t?n s? ch? cho m?t t?n s? duy nh?t thay v nhi?u t?n s? nhu trong phuong php di?u t?n ? gi?m chi ph thi?t k? v hi?n th?c m?ch Trong tru?ng h?p tn hi?u di?u ch? ch? nh?n m?t s? gi tr? (nhu tn hi?u s?), m?ch di?u ch? v gi?i di?u ch? hi?n th?c theo phuong php di?u pha du?c don gi?n r?t nhi?u

    79. Hi?u su?t Bang thng AM BT = 2B FM&PM BT = 2(?+1)B FM&PM c?n bang thng l?n hon so v?i AM

    80. C?u trc knh truy?n M d? li?u Baudot (Emile Baudot) 5 bit (32 m) dng 2 m 5 bit (letter & figure) d? m h?t cc k t?, ch? s? v d?u ASCII (American Standard Code for Information Interchange) 7 bit (128 m), bao g?m cc k t? ch? thu?ng v hoa, cc k t? ch? s?, cc k t? d?u ch?m cu v cc k t? d?c bi?t. Ph? bi?n nh?t hi?n nay du?c s? d?ng trong giao ti?p d? li?u tu?n t?. EBCDIC (Extended Binary Coded Decimal Interchange Code) 8 bit u?c dng trong cc h? th?ng my tnh IBM Unicode 16 ho?c 32 bit H?a h?n du?c s? d?ng r?ng ri trong tuong lai

    81. M Baudot

    82. M ASCII

    83. C?u trc knh truy?n Song song (Parallel) M?i bit dng m?t du?ng truy?n ring. N?u c 8 bits du?c truy?n d?ng th?i s? yu c?u 8 du?ng truy?n d?c l?p ? truy?n d? li?u trn m?t du?ng truy?n song song, m?t knh truy?n ring du?c dng d? thng bo cho bn nh?n bi?t khi no d? li?u c s?n (clock signal) C?n thm m?t knh truy?n khc d? bn nh?n bo cho bn g?i bi?t l d s?n sng d? nh?n d? li?u k? ti?p

    84. C?u trc knh truy?n Tu?n t? (Serial) T?t c? cc bit d?u du?c truy?n trn cng m?t du?ng truy?n, bit ny ti?p theo sau bit kia Khng c?n cc du?ng truy?n ring cho tn hi?u d?ng b? v tn hi?u b?t tay (cc tn hi?u ny du?c m ha vo d? li?u truy?n di) 2 cch truy?n B?t d?ng b?: m?i k t? du?c d?ng b? b?i start v stop bit ?ng b?: m?i kh?i k t? du?c d?ng b? dng c?

    85. Truy?n b?t d?ng b? D? li?u du?c truy?n theo k t? (5 ? 8 bits) Ch? c?n gi? d?ng b? trong m?t k t? Ti d?ng b? cho m?i k t? m?i Hnh vi ?i v?i dng d? li?u d?u, kho?ng cch gi?a cc k t? l d?ng nh?t (chi?u di c?a ph?n t? stop) ? tr?ng thi r?nh, b? thu pht hi?n s? chuy?n 1 ? 0 L?y m?u 7 kho?ng k? ti?p (chi?u di k t?) ?i vi?c chuy?n 1 ? 0 cho k t? k? ti?p Hi?u su?t on gi?n R? Ph t?n 2 ho?c 3 bit cho m?t k t? (~20%) Thch h?p cho d? li?u v?i kho?ng tr?ng gi?a cc k t? l?n (d? li?u nh?p t? bn phm)

    86. Truy?n b?t d?ng b?

    87. Truy?n b?t d?ng b? ?ng b? bit Chuy?n d?i 1 byte thng tin thnh/t? chu?i bit PISO SIPO Clock thu?ng m?t d?ng b? B? thu thu?ng dng clock g?p N l?n clock c?a b? pht

    88. Truy?n b?t d?ng b?

    89. Truy?n b?t d?ng b? ?ng b? k t? (character synchronization): dng start v stop bit

    90. Truy?n b?t d?ng b? khung ?ng b? khung (frame synchronization): dng cc k t? di?u khi?n (STX, ETX, DLE)

    91. Truy?n b?t d?ng b? - t?c d? xung clock

    92. Truy?n b?t d?ng b? - t?c d? xung clock

    93. Truy?n b?t d?ng b? - t?c d? xung clock

    94. Truy?n d?ng b? Truy?n khng c?n start/stop Ph?i c tn hi?u d?ng b? ?ng b? bit (bit synchronization): s? d?ng cc phuong php sau Clock encoding and extraction (Timestamp) Tch h?p thng tin d?ng b? (clock) vo trong d? li?u truy?n ?u nh?n s? tch thng tin d?ng b? d?a vo d? li?u nh?n du?c RZ, Manchester (NRZ signaling), differential Manchester Digital Phase-Lock-Loop Dng m?t du?ng tn hi?u d?ng b? ring bi?t S? d?ng m?t ngu?n clock ?n d?nh du?c gi? d?ng b? v?i d? li?u d?n t?i noi nh?n M ha thng tin ph?i d?m b?o c s? thay d?i bit trong m?t kho?ng th?i gian d? d? ngu?n clock du?c ti d?ng b? C?n s? d?ng cc phuong php m ha nh? phn (AMI, HDB3, B8ZS) Thch h?p khi truy?n m?t kho?ng cch ng?n Tn hi?u d?ng b? d? b? suy gi?m trn du?ng truy?n

    95. M ha v tch d? li?u d?ng b?

    96. Digital Phase Lock Loop

    97. Truy?n d?ng b? ?ng b? khung (frame synchronization): s? d?ng cc phuong php sau Character-oriented synchronous transmission Dng cc k t? di?u khi?n : SYN, STX, ETX, DLE. Bit-orienter synchronous transmission Dng cc m?u bit di?u khi?n (flag byte or flag pattern) ? bit stuffing problem Hi?u qu? (ph t?n th?p) hon so v?i truy?n b?t d?ng b?

    98. L?i

    99. i?u khi?n l?i Mi tru?ng truy?n d?n b? nhi?u (di?n, t?, ) ? d? li?u nh?n c l?i 2 cch kh?c ph?c khi pht hi?n c l?i Forward error control: thng tin s?a sai du?c thm vo cc k t? ho?c cc frame truy?n di, d? bn nh?n c th? pht hi?n khi no c l?i v l?i n?m ? du d? s?a (c kh? nang s?a l?i) Feedback (backward) error control: thng tin s?a sai du?c thm vo cc k t? ho?c cc frame truy?n di ch? d? d? pht hi?n khi no c l?i (khng c kh? nang s?a l?i). Co ch? yu c?u truy?n l?i k t?/frame sai du?c dng trong tru?ng h?p ny Co ch? pht hi?n l?i BER: xc su?t 1 bit don b? l?i trong m?t th?i kho?ng nh?t d?nh Phn lo?i l?i Single-bit error nhi?u tr?ng Burst error: chu?i cc bit lin ti?p b? l?i nhi?u xung, suy gi?m (khi truy?n v tuy?n)

    100. Qu trnh pht hi?n sai

    101. Parity Bit parity Parity ch?n: (N + P) ph?i l m?t s? ch?n Parity l?: (N + P) ph?i l m?t s? l? N: t?ng s? bit 1 c trong d? li?u c?n ki?m tra l?i P: gi tr? c?a bit parity, l 0 hay 1 sao cho t?ng s? bit 1 (N+P) lun l m?t s? ch?n (l?) ty theo phuong php parity ch?n hay l? tuong ?ng

    102. Parity ?c di?m Ch? d du?c l?i sai m?t s? l? bit, khng d du?c l?i sai m?t s? ch?n bit Khng s?a du?c l?i Hi?u su?t truy?n thng tin km, do s? bit thm vo d? d tm l?i chi?m t? l? l?n so v?i d? li?u truy?n di.

    103. Block Sum Check Block Sum Check (BSC): s? d?ng parity hng v c?t Khng s?a du?c sai, ch? s?a du?c sai khi s? bit sai trong d? li?u l m?t D tm du?c t?t c? cc l?i sai m?t s? l? bit v h?u h?t cc l?i sai m?t s? ch?n bit. Khng d du?c l?i sai m?t s? ch?n bit x?y ra d?ng th?i trn c? hng v c?t.

    104. Block Sum Check Bi?n th? Dng t?ng b 1 (1s-complement sum) thay cho t?ng modulo 2 (2-modulo sum) Cc k t? trong block du?c truy?n du?c coi nhu cc s? nh? phn khng d?u T?t hon phuong php modulo 2

    105. Cyclic Redundancy Check Nguyn l k-bit message Bn pht t?o ra chu?i n bit FCS (Frame Check Sequence) sao cho frame g?i di (k+n bit) chia h?t cho 1 s? xc d?nh tru?c Bn thu chia frame nh?n du?c cho cng 1 s? v n?u khng c ph?n du th c kh? nang khng c l?i S? h?c modulo 2 Exlusive-or

    106. Cyclic Redundancy Check Xc d?nh FCS T: frame du?c truy?n (k+n bit) M: message d? li?u c?n truy?n (k bit d?u c?a T) F: FCS (n bit sau c?a T) P: s? chia du?c xc d?nh tru?c (n+1 bit) Ki?m tra

    107. Cyclic Redundancy Check Cch khc d? xc d?nh FCS: da th?c M = 111101 ? M(x) = X5 + X4 + X3 + X2 + 1 P = 1101 ? P = X3 + X2 + 1 ? FCS c 3 bits (n = 3) D? li?u d?ch tri n bits: 2nM(x) = X8 + X7 + X6 + X5 + X3

    108. Cyclic Redundancy Check

    109. Cyclic Redundancy Check P Di hon 1 bit so v?i FCS mong mu?n u?c ch?n ty thu?c vo lo?i l?i mong mu?n pht hi?n Yu c?u t?i thi?u: msb v lsb ph?i l 1 Bi?u di?n l?i Error=ngh?ch d?o bit (i.e. exclusive-or c?a bit d v?i 1) Tr = T + E T: frame du?c truy?n Tr: frame nh?n du?c E: error pattern v?i 1 t?i nh?ng v? tr l?i x?y ra Error khng b? pht hi?n iff Tr chia h?t cho P (i.e. iff E chia h?t cho P) Cc l?i du?c pht hi?n T?t c? cc l?i bit don T?t c? cc l?i kp n?u P c t nh?t 3 ton h?ng M?t s? l? l?i b?t k? n?u P ch?a 1 th?a s? (X+1) B?t k? l?i chm no m chi?u di c?a chm nh? hon chi?u di FCS H?u h?t cc l?i chm l?n hon

    110. Cyclic Redundancy Check 4 P du?c s? d?ng r?ng ri CRC-12 = X12 + X11 + X3 + X2 + X + 1 12-bit FCS 6-bit characters CRC-16 = X16 + X15 + X2 + 1 16-bit FCS 8-bit characters US CRC-CCITT = X16 + X12 + X5 +1 Europe CRC-32 = X32 + X26 + X23 + X22 + X16 + X12 + X11 + X10 + X8 + X7 + X5 + X4 + X2 + X + 1 32-bit FCS Point-point synchronous transmission, DoD apps

    111. Cyclic Redundancy Check

    112. Cyclic Redundancy Check

    113. S?a l?i S?a cc l?i du?c pht hi?n thng thu?ng yu c?u truy?n l?i kh?i d? li?u Khng thch h?p cho cc ?ng d?ng trao d?i d? li?u khng dy BER cao Truy?n l?i nhi?u Th?i gian tr? truy?n l?n hon nhi?u so v?i th?i gian truy?n d? li?u (vd truy?n v? tinh) Kh?i d? li?u du?c truy?n l?i b? l?i v nhi?u kh?i d? li?u khc ti?p theo C?n thi?t ph?i s?a l?i d?a vo cc d? li?u nh?n du?c

    114. Qu trnh s?a sai

    115. Qu trnh s?a sai M?i kh?i d? li?u k bit du?c nh x? vo kh?i n bit (n>k) T? m Codeword Forward error correction (FEC) encoder Codeword du?c truy?n di Chu?i bit nh?n du?c tuong t? nhu chu?i du?c truy?n di, nhung c ch?a l?i Codeword du?c g?i t?i b? gi?i m FEC N?u khng c l?i, trch xu?t kh?i d? li?u ban d?u M?t vi m?u l?i c th? du?c pht hi?n v s?a l?i M?t vi m?u l?i c th? du?c pht hi?n nhung khng s?a du?c M?t vi m?u l?i c th? khng du?c pht hi?n (t x?y ra) FEC trch xu?t kh?i d? li?u sai

    116. C?u hnh du?ng truy?n C?u hnh S?p x?p v?t l cc tr?m trn mi tru?ng C?u hnh truy?n th?ng

    117. Giao ti?p Giao ti?p Thi?t b? x? l d? li?u (DTE) thu?ng khng c cc phuong ti?n pht d? li?u C?n m?t thi?t b? giao ti?p (DCE) v d?: modem, NIC, DCE pht cc bit d? li?u trn mi tru?ng truy?n d?n DCE trao d?i d? li?u v thng tin di?u khi?n v?i DTE u?c th?c hi?n thng qua m?ch trao d?i C?n m?t chu?n giao ti?p r rng ?c tnh Co kh K?t n?i i?n i?n p, d?nh th?i, m ha, Ch?c nang D? li?u, di?u khi?n, d?nh th?i, d?t, Th? t?c Chu?i cc s? ki?n

    118. Chu?n V.24/EIA232F ITU-T v.24 Ch? d?c t? ch?c nang v th? t?c Tham kh?o cc chu?n khc cho cc d?c tnh co kh v d?c tnh di?n EIA-232-F (USA) RS-232 ?c tnh co kh: ISO 2110 ?c tnh di?n: v.28 Ch?c nang: v.24 Th? t?c: v.24

    119. K?t n?i V.24/EIA232 (DTE)

    121. Local/Remote loopback testing

    122. Nghi th?c V d? modem ring b?t d?ng b? Khi modem du?c b?t ln v s?n sng, n (DCE) b?t tn hi?u DCE ready Khi DTE s?n sng g?i d? li?u, n b?t tn hi?u Request To Send C?m ch? d? nh?n d? li?u (n?u trong ch? d? truy?n half-duplex) Modem dp l?i s?n sng b?ng tn hi?u Clear To Send DTE g?i d? li?u Khi d? li?u d?n, modem g?n vo DTE s? b?t tn hi?u Line Signal Detector v g?i d? li?u cho DTE

    123. Ho?t d?ng quay s? (1)

    124. Ho?t d?ng quay s? (2)

    125. Ho?t d?ng quay s? (3)

    126. Chu?n giao ti?p EIA RS232C

    127. Trao d?i thng tin gi?a DCE v DTE Trao d?i thng tin gi?a DTE v DCE Truy?n d? li?u (DTE?DCE) B?t DTR v RTS ?i DSR ?i CTS Truy?n d? li?u Nh?n d? li?u (DCE?DTE) B?t DTR ?i DSR Nh?n d? li?u

    128. C?u hnh dy d?n k?t n?i DTE ? DTE

    129. Nn d? li?u Run-length encoding (packed decimal) Dng cho message g?m cc ch? s? M BCD thay v ASCII C th? dng 4 bit th?p d?i v?i cc thng tin d?y d?

    130. Differential encoding (relative encoding) Encoding used if differences between values is much smaller than the values themselves Original 1509 1506 1508 1510 1511 1509 1513 Encoded 1509 -3 +2 +2 +1 -2 +4 Send only the difference in magnitude Character suppresion Encoding used if 3 or more of same character found Original AAAABBCCCCCDEEEEFF Encoded A4B2C5D1EEEE4F2 Nn d? li?u

    131. Nn d? li?u Huffman encoding (Statistical Methods) ?c di?m y l m th?ng k (phuong php nn m t?i uu) M ha d?a trn xc su?t s? d?ng c?a cc k t? Nh?ng k t? du?c dng nhi?u nh?t s? c t? m ng?n nh?t Khng c tnh prefix Gi?i thu?t S?p x?p cc ngu?n tin c xc su?t gi?m d?n M?t c?p bit 0-1 du?c gn cho 2 ngu?n tin c xc su?t nh? nh?t 2 ngu?n tin ny du?c k?t h?p, t?o thnh ngu?n tin m?i c xc su?t b?ng t?ng xc su?t c?a 2 ngu?n tin thnh ph?n S?p x?p l?i cc ngu?n tin theo th? t? gi?m d?n c?a xc su?t Qu trnh trn du?c l?p l?i d?n khi 2 ngu?n tin cu?i cng du?c k?t h?p T? m cho m?i ngu?n tin du?c vi?t theo th? t? t? g?c d?n ng?n Chi?u di t? m trung bnh Lavg = ?li x pi li : chi?u di ngu?n tin Xi pi : xc su?t xu?t ngu?n tin Xi

    132. Huffman code

    133. Nn d? li?u Shannon-Fano encoding (Statistical Methods) ?c di?m M t?i uu Khng c tnh prefix Gi?i thu?t S?p x?p cc ngu?n tin theo th? t? gi?m d?n v? xc su?t Chia cc ngu?n tin thnh hai ph?n c xc su?t x?p x? nhau v gn 0 cho ph?n trn, gn 1 cho ph?n du?i L?p l?i bu?c trn cho m?i ph?n cho d?n khi ch? cn m?t ngu?n tin Ghi ra cc t? m

    134. Shannon Fano Cc ngu?n tin v xc su?t xu?t hi?n c?a cc ngu?n tin tuong ?ng X1 (30%), X2 (20%), X3 (10%), X4 (10%), X5 (20%), X6 (5%), X7 (3%), X8 (2%) Lavg = 2.0,3+2.0,2+3.0,2+3.0,1+3.0,1+4.0,05+5.0,03+5.0,02 = 2,65 bits

    135. Phn h?p knh (Multiplexing)

    136. Frequency Division Multiplexing (FDM) Phuong php ny ch? hi?n th?c du?c khi bang thng mi tru?ng truy?n l?n hon bang thng m tn hi?u du?c truy?n yu c?u Nhi?u tn hi?u c th? du?c truy?n d?ng th?i n?u m?i tn hi?u du?c di?u ch? trn m?t t?n s? sng mang Cc t?n s? sng mang khc nhau sao cho bang thng c?a cc tn hi?u du?c di?u ch? khng trng l?p nhau (guard bands) V d? broadcast radio Knh truy?n du?c c?p pht ngay c? khi khng c d? li?u (c?p pht tinh)

    137. FDM

    138. FDM

    139. FDM

    140. FDM

    141. FDM

    142. Wavelength Division Multiplexing Nhi?u chm nh sng v?i t?n s? khc nhau Truy?n trong cp quang M?t d?ng c?a FDM M?i mu nh sng (chi?u di sng khc nhau) du?c truy?n trn knh d? li?u ring bi?t 1997 t?i Bell Labs 100 chm nh snh M?i chm t?c d? 10 Gbps 1 terabit per second (Tbps) H? th?ng thuong m?i hi?n t?i c 160 knh, m?i knh 10 Gbps Phng th nghi?m (Alcatel) c th? c 256 knh v?i t?c d? 39.8 Gbps m?i knh 10.1 Tbps Trn 100km

    143. Ho?t d?ng WDM Cng ki?n trc t?ng qut nhu cc FDM khc Ngu?n sng t?o ra cc chm laser v?i t?n s? khc nhau Nhi?u chm sng k?t h?p v?i nhau d? lan truy?n trn cng m?t cp quang B? khu?ch d?i quang h?c Khu?ch d?i t?t c? chi?u di sng khc nhau Thng thu?ng kho?ng cch ~10km Phn knh t?i dch d?n Thng thu?ng t?m chi?u di sng 1550nm 200MHz per channel Hi?n t?i ln d?n 50GHz

    144. Dense Wavelength Division Multiplexing DWDM Chua c d?nh nghia chnh th?c (chua chu?n ha) Cc knh st nhau hon WDM 200GHz

    145. Time Division Multiplexing (TDM) Synchronous TDM Phuong php ny ch? hi?n th?c du?c khi t?c d? d? li?u (bang thng,) mi tru?ng truy?n l?n hon t?c d? d? li?u m tn hi?u du?c truy?n yu c?u Nhi?u tn hi?u (c? analog v digital) c th? du?c truy?n d?ng th?i trn cng m?t du?ng truy?n b?ng cch dan xen cc ph?n c?a m?i tn hi?u theo th?i gian (time slot) Time slot du?c gn tru?c v tinh (time slot du?c c?p pht ngay c? khi khng c d? li?u d? truy?n) Time slot c th? du?c gn khng d?ng d?u gi?a cc ngu?n d? li?u

    146. TDM

    147. TDM

    148. TDM

    149. TDM i?u khi?n lin k?t Khng c?n header v tailer Khng c?n cc nghi th?c di?u khi?n lin k?t d? li?u (cho ton b? du?ng truy?n phn/h?p) i?u khi?n dng T?c d? d? li?u c?a du?ng truy?n phn/h?p c? d?nh N?u c m?t knh khng th? nh?n d? li?u, cc knh khc v?n ti?p t?c Ngu?n pht tuong ?ng ph?i ngung ? b? knh tr?ng (empty slot) i?u khi?n l?i L?i du?c pht hi?n v x? l b?i t?ng knh ring bi?t

    150. TDM i?u khi?n lin k?t

    151. TDM Framing Khng c c? (flag) ho?c cc k t? SYNC d? dng khung cc b TDM Ph?i c co ch? d?ng b? Co ch? dng khung s? M?t bit di?u khi?n du?c thm vo m?i b TDM Cc bit di?u khi?n ny t?o thnh m?t knh khc knh di?u khi?n Dng m?u bit d?nh d?ng trn knh di?u khi?n V d? m?u 01010101, khc v?i knh d? li?u So snh m?u bit d?n trn t?ng knh v?i m?u bit m?u bit d?ng b?

    152. TDM pulse stuffing V?n d?: d?ng b? cc ngu?n d? li?u khc nhau Tn hi?u clock trn cc ngu?n d? li?u khc nhau b? tri (drift) T?c d? d? li?u c?a cc ngu?n d? li?u khc nhau khng quan h? theo m?t t? l? don gi?n Gi?i php Pulse Stuffing T?c d? d? li?u d?u ra (khng tnh cc bit khung) cao hon t?ng cc t?c d? d?u vo Chn thm cc bit/xung khng c nghia vo m?i tn hi?u d?u vo cho d?n khi n b?ng v?i clock c?c b? Cc bit/xung du?c thm vo t?i nh?ng v? tr c? d?nh (bi?t tru?c) trong khung v n s? b? lo?i b? khi d?n b? phn knh

    153. TDM ngu?n tuong t? v ngu?n s?

    154. TDM h? th?ng truy?n mang Phn c?p TDM USA/Canada/Japan dng m?t h? th?ng ITU-T (chu Au) dng m?t h? th?ng khc (nhung tuong t?) H? th?ng M? xy d?ng d?a trn d?nh d?ng DS-1 24 knh du?c phn h?p M?i khung c 8 bit/knh v 1 bit khung ? 193 bit/khung ?i v?i truy?n tho?i, m?i knh ch?a m?t t? c?a d? li?u du?c s? ha (PCM, 8000 m?u/giy) T?c d? d? li?u 8000 x 193 = 1.544Mbps 5 trong s? 6 khung c cc m?u PCM 8 bit Khung th? 6 ch?a m?t t? PCM 7 bit v m?t bit tn hi?u Cc bit tn hi?u t?o thnh m?t dng (stream) cho m?i knh d? di?u khi?n v ch?a thng tin tm du?ng ?nh d?ng tuong t? cho d? li?u s? 23 knh d? li?u (7 bit/khung v 1 bit ch? th? cho d? li?u ho?c di?u khi?n h? th?ng) Knh th? 24 dng d? d?ng b? DS-1 c th? dng h?n h?p d? li?u s? v tuong t? Dng c? 24 knh Khng c k t? d?ng b?

    155. TDM T1 vs. E1

    156. TDM T1 D?ch v? s? m?c 0 (DS0) = 64 kbps T1 = 24 knh tho?i = d?ch v? s? m?c 1 (DS1) TDM ng khung don gi?n: thm 101010 (1 bit/khung) B?t k? chu?i khc ? ti d?ng b?

    157. TDM du?ng truy?n E1 E1 Dng ? chu u, tuong t? nhu T1 (dng ? M?) C 32 bytes trong m?t khung di 125s = 2048 Mbps 30 knh du?c dng cho d? li?u 1 knh dng d? d?ng b? 1 knh dng d? bo hi?u (di?u khi?n)

    159. TDM phn c?p

    160. TDM b?t d?ng b? TDM th?ng k/thng minh Trong TDM d?ng b?, nhi?u slot c th? b? b? tr?ng TDM b?t d?ng b? c?p pht time slot d?ng ty theo nhu c?u B? h?p knh qut cc du?ng nh?p v t?p h?p d? li?u cho d?n khi d?y khung T?c d? d? li?u ra th?p hon t?c d? cc du?ng nh?p g?p l?i C th? gy v?n d? trong th?i gian cao di?m ?m cc du?ng nh?p Gi? kch thu?c b? d?m t?i thi?u d? gi?m th?i gian tr?

    161. TDM b?t d?ng b? mc t?c d? d? li?u t?i da c?a du?ng truy?n trung k? mi t?c d? d? li?u t?i da c?a ngu?n th? i pi xc xu?t d? li?u c?a ngu?n th? i mc c th? nh? hon t?ng cc mi ?pimi < mc Nguyn t?c 80% Bao nhiu terminal t?c d? 9600bps c th? dng chung du?ng truy?n 56Kbps khi dng k? thu?t TDM ho?c STDM (pi l 75%)

    162. Kch thu?c b? d?m v th?i gian tr?

    163. TDM b?t d?ng b? - d?nh d?ng khung

    164. Asymmetrical Digital Subscriber Line ADSL xDSL High data rate DSL Single line DSL Very high data rate DSL Lin k?t gi?a thu bao v m?ng u?ng thu bao Hi?n t?i dng cp twisted pair C th? c bang thng l?n hon 1 MHz ho?c l?n hon B?t d?i x?ng T?c d? dng d? li?u xu?ng (downstream) l?n hon t?c d? dng d? li?u ln (upstream) FDM 25kHz th?p nh?t cho tho?i Plain old telephone service (POTS) Dng k? thu?t lo?i b? echo (echo cancellation) ho?c FDM d? cho 2 bang t?n Dng FDM trong cc bang t?n Ph?m vi 5.5km

    165. C?u hnh knh truy?n ADSL

    166. Discrete Multitone DMT Nhi?u tn hi?u sng mang ? cc t?n s? khc nhau Vi bit trn m?i knh Knh ph? 4kHz G?i t/h test v dng knh ph? v?i t? s? SNR t?t hon 256 knh ph? downstream m?i knh 4kHz (60kbps) 15.36MHz Impairments bring this down to 1.5Mbps to 9Mbps

    167. DMT Transmitter

    168. ?c thm W. Stallings, Data and Computer Communications (7th edition), Prentice Hall 2004, chapters 3, 5, 6, 8 Web pages from ITU-T on V. specification Cc website v? ADSL v SONET

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