, , , .
, ().
.
, , , , :
- 
;
- 
;
- ;
.
, .
, () :
- ( );
- ( );
- () .
:
- ;
- ;
- .
. .
, (.. ).
, .
33. () ADSL ? ?
ADSL ( ) , . , .
(SRA)
SRA . SRA ADSL2 .
Bit Swapping (BS)
, .
|
|
|
BS .
ADSL2
L0 ( ).
L2 ( , ).
L3 (, ADSL).
34. () ADSL .
DSLAM :
( - handshake);
(training);
;
.
handshake
ADSL :
1, CLR: ATUR , ;
2, CL: ATUC , DSLAM;
3, ASK: ;
4, MS: ATUR ;
5, ACK: ATUC ;
6, MS: ATUR ;
7, REQ-MR: ATUC MR;
8, MR: ATUR MR, MS;
9, MS: ATUC ;
10, ACK: ATUR .
training
DSLAM. , .
:
1, (Upstream) (Downstream).
2, AGC (Automatic Gain Control).
3, .
4, .
-DSLAM:
1, ;
2, / (SNR) ;
3, ;
4, .
5, ( DSLAM) , SNR .
DSLAM (Upstream/Downstream).
35. ADSL ? ?
|
|
|
DMT , . , RFI ( ).
, , , , .
, (addition - ). , (multiplication - ).
, (jitter - ), - (wander - , ).
- ( ) , . - .
, .
36. () VDSL ? ?
VDSL2 , . VDSL2 (seamless rate adaptation, SRA) (SNR). .
SRA , , , DSL .
Rapid Rate Adaptation (RRA). DSL retrain .
