V.42 , LAPM (Link Access Procedure for Modems), HDLC (High-level Data Link Control). LAPM MNP2. , LAPM .
LAPM , . : .
, : , (01111110, 7Eh). , (). . . , ; ; , , .
LAPM :
(7Eh);
;
;
;
;
(7Eh).
() . :
DLCI (Data Link Connection Identifier) , . / , .
. . V.42 DLCI:
- 0 ;
- 131 ;
- 3262 ;
- 63 .
MNP
, . V.42 MNP.
X16 + X12 + X5 + 1. X32+X26+X23+X22+X16+X12+X11+X10+X8+X7+X5+X4+X2+X+1. CRC-16 CRC-32 XID.
. MNP, .
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. (I-) . (S-) , . , , (U-) , : / , , break, . LAPM 13 :
1 I-;
4 S-: RR, RNR, REJ SREJ;
8 U-: SABME, DM, UI, DISC, UA, FRMR, XID TEST.
LAPM S:
RR ( S): 00.
, , . ,
RNR ( S): 01.
( , ). . , .
REJ ( S): 10.
. , , , .
SREJ ( S): 11. ( MNP)
, ( ).
.
U (Unnumbered) :
, ; (1,1) . . .
.
- ;
- ;
- ;
- .
SABME ( U):
DM " " ( U):
UI ( U):
DISC ( U):
UA ( U):
FRMR ( U):
XID ( U):
TEST ( U):
V.42 . .
V.42 ( )
, , , , .
. ? . : , .
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. . - :
0 1000 1000 1 11...11 0 1000 1 11...11 .
8 16 . -, 750 .
. :
0 1010 0010 1 11...11 0 1100 0010 1 11...11
0 1010 0010 1 11...11 0 0000 0000 1 11...11.
, V.42 , . V.42, .
()
. 01111110 , .. . ( ) 011111 , 0 . . 0 . - 15 15 . 7 .
