, ISDN 128 / Internet. Internet , , .
, , .
, DSL (Digital Subscriber Line ).
xDSL:
;
;
Internet;
( Internet) ISDN ;
DSL 32 / 50 /, ;
xDSL 1 1. DSL ;
, ;
, , . DSL , Internet.
xDSL .
13.1 xDSL .
13.1. xDSL - | |||
IDSL Digital Subscriber Line ISDN | 128 /c | ISDN -, | |
ADSL Asymmetric Digital Subscriber Line | 1,5 /c 8 /c 64-1544 /c | - - | Internet, (LAN) , . . |
ADSL G. lite ADSL | 1,536 / 384 / 384 / | - - | Internet, (LAN) , . |
HDSL High data rate Digital Subscriber Line | 1,544 /c 2048 /c | E1 (T1) (LAN) (WAN) | |
VDSL Very High Digital Subscriber | 13-52 /c 1,5 2,3 /c | - - | , ADSL, . |
SDSL Symmetric Line Digital Subscriber Line | 1,544 /c 2048 /c |
ADSL (Asymmetric Digital Subscriber Line ): DSL, 8,192 /, 768 /.
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ADSL G. lite ADSL, 1,536 / 384 / , 384 / .
IDSL ( ISDN) , BRI ISDN 128 /.
HDSL (High Speed Digital Subscriber Line) ): DSL , 1,5 / ( 1) 2 / ( 1) .
SDSL (Simple Digital Subscriber Line , ); : MSDSL ( SDSL) HDSL2, .
VDSL (Very High Speed Digital Subscriber Line ) DSL, 52 /.
" ", , . " ":
- ;
- - ;
- ;
- ( "-Ethernet");
, DSL. DSL Digital Subscriber Line ( ).
, DSL .
ISDN-BA (DSL)
4- PAM (- , , ), 2B1Q.
ISDN-BA -, . ISDN-BA, , 10 100 , DSL, 2B1Q, 40 .
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ISDN-BA , , . , .
ISDN-BA ISDN U ( ) , S/T( ).
DSL » ( ) 64 / , D ( ), 16 / . 128 / 16 / .
1. ISDN-BA (DSL).
ADSL (Asymmetric Digital Subscriber Line )
ADSL ( ) 1990- . , , , , , . , () (.). , ADSL.
, , . , ( ), ADSL , () .. , .
ADSL 0,5 .:
- 1,5 / 8 /;
- 640 / 1,5 /.;
- 1,5 / 5,5 ;
- 6-8 / 3,5
ADSL ADSL ADSL2, ADSL2+.
ADSL2 , . . ADSL2+ 1,5 .
, ADSL , ISDN-BA , . () ().
(ADSL).
ADSL (Frequency Division Multiplexing FDM) (.). FDM , ( ) . . . (Echo Cancellation), .
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. ADSL, ANSI :
- (Quadrature Amplitude Modulation - QAM)
- - (Cariereless Amplitude/Phase Modulation CAP)
- (Discrete MultiTone Modulation DMT)
, DMT, ADSL.
DMT . (symbol period), DMT , . . , , DMT . , . , . , DMT AM , , DMT ( ). , DMT , DMT.
ADSL.
/ (Fast Fourier Transform FFT). DMT . , - , AM- .
(N). N=256, , .
. R /. , DMT . DMT , , , b=R.T. (.. 1/). b , bi (i=1, , N=256) I , :
N , bi , DMT Xi, . Xi, AM fi. 2bi . bi AM, i DMT . N AM . N (Inverse Fast Fourier Transform IFFT). Xi , AM . N AM N=256 . IFFT . N IFFT , . , (DAC). DMT- , ( , (). .
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, , . , . , , .
DMT , . , . , . , AM . , , AM . , , .
ADSL
ADSL (Asymmetric Digital Subscriber Line) , (" ") . (ADSL) DSL.
ADSL , ( Internet, , ), . "" " - " (downstream) " - " (upstream).
ADSL . Internet, , . ADSL Internet, , , , , , . 1,5 / 8 /. 64 / 1,5 / (. 13.1). , .
ADSL
. 13.1 ADSL .
. 13.1. ADSL
ADSL . ADSL , ADSL. """. , : , . . . . 300 3400, ADSL , 30 . ISDN ISDN 80 , ADSL , 138 . , (Frequency Division Multiplexing, FDM) . FDM : , . , , . , " . , ", , . ADSL . 1993 (ANSI) " " (Discrete MultiTone, DMT) ADSL. . , DMT .
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DMT, , .. :
, , ;
( ).
ANSI ADSL 256 (downstream) 32 (upstream) . , 4,3125 . , , , . , ADSL 4 , .
DMT - (Carrierless Amplitude / Phase, CAP). .
ADSL - , , splitter , .
, ( ) ADSL. , , . ADSL , . , : ADSL, , ADSL. , . , DSL, , (.. ). . , DSLAM.
:
;
;
;
, Internet;
( , , );
(, , ).
0,4 . 13.2 [13.17].
13.2. ADSL | ||
- (downstream) | - (upstream) | |
8,160 / | 1,216 / | 1,8 |
7,872 / | 1,088 / | 2,7 |
3,648 / | 864 / | 3,7 |
1,984 / | 640 / | 4,3 |
1,408 / | 544 / | 4,6 |
960 / | 416 / | 4,9 |
576 / | 320 / | 5,2 |
320 / | 224 / | 5,5 |
128 / | 128 / | 5,8 |
, ADSL:
1. ADSL , , ;
2. ADSL , Internet , online-
o 100 , 56 /.
o 70 , ISDN - 128 /c.
3. ADSL , , , , ;
4. ADSL , ( , . , , . , , ;
5. ADSL " " , . ; ADSL .
DMT
ADSL . , , ANSI - (Reed-Solomon RS) ADSL.
- .
RS . . RS 256 . .
(n,k) RS , k n (n£255).
RS n k, .. dmin=n-k+1 (dmin ).
RS , 32 , 255 .
RS (255,239). 16 8
dmin=255-239+1=17=2q+1.
R-ADSL (Rate-Adaptive Digital Subscriber Line )
R-ADSL , ADSL, . R-ADSL . , , .
G. Lite (ADSL.Lite) ADSL, 1,5 / 512 / 256 / .
HDSL (High Bit-Rate Digital Subscriber Line )
HDSL ( ) ISDN-BA. HDSL , DSL ISDN, , . , DSP ( ). . , 4- PAM (- ) 800 / ( Carrier Serving Area ). -, 784 / , , .
(HDSL).
HDSL , . (1,544 / 2,048 / ) HDSL T1/E1. ( 1 1,544 /, 1 2,048 /.) , HDSL ( 3,5 4,5 ), , ADSL, , , HDSL . HDSL , .. HDSL2 HDSL. , HDSL, .
HDSL , . , .
HDSL, , . , , . , , . , , 150 ; , 3 10 . .
, (bridged taps). , , , . .
, xDSL, ANSI ETSI.
:
- ;
- ;
- ;
- , 500 .
HDSL . ETSI ETR-152 HDSL 107. .
/ HDSL. HDSL . HDSL, . HDSL , , , .
HDSL , , . , HDSL ETSI.
SDSL (Single Line Digital Subscriber Line )
DSL (SDSL) HDSL, , . , 3 . SDSL , , , . SDSL , , .
, . SDSL , 2 . IP ATM. , SDSL HDSL, ADSL VDSL.
VDSL (Very High Bit-Rate Digital Subscriber Line )
VDSL ( ) ADSL . - .
(VDSL).
VDSL xDSL. 13 52 /, 1,5 2,3 /, . 26 /. VDSL - . , 300 1300 . , , - (, , ). VDSL , ADSL; , (HDTV), ..
.
ISDN-BA (DSL) | 128 Kbps | ~ 12 |
ADSL | 1 Mbps u/s, 8 Mbps d/s | ~ 5,5 |
HDSL | 2 Mbps | ~ 6,5 |
SDSL | 2 bps - 144 Kbps | ~ 6 |
VDSL | 6,4 Mbps u/s, 52 Mbps d/s | ~ 1,5 |