6. DSS-1
ITU-T 1 (DSS-1 - Digital Subscriber Signaling 1) ISDN D- . (ITU-T) D :
) 16 /, -;
) 64 /, ( 30) -.
DSS-1 -7 , ITU-T, . , DSS-1 -7 . . 1 ISDN, -7, ISDN D- -. D- -7. D-, , (SU) -7.
. 1. DSS-1 ISUP: () - DSS-1 () -7
DSS-1 ( OSI) . , , , , -7 :
, ;
, . ;
, . , , , .
1 ( ) DSS-1 D, , , , 2 3 D. 1 :
S- D;
;
.
2 , LAPD (link access protocol for D-channels), D- NT. 2 , 2 D. , 2 , .
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2 . . (SAPI) (TEI).
SAPI , 3, 0 63. SAPI =0, , , .
TEI , . TEI 0 126, 127 . 8 , . 1=127 ( ).
: . 3 , 2 .
2 . () . , . , , . .
3 ( ) :
, 1.451 Q.931 ( ). SAPI=0, , ;
, .25 9 . SAPI= 16;
, . SAPI .
Q.931 ( 3) , , . 3 , 2 . D- ( ) D-.
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DSS-1
1 ( ) 1.430. 2.2 (. 2.4), 1 192 / - 64 / D- 16 /. 48 / , , NT. 48 , 250 . , , , S . , , , INFO. INFO.
, INFO 0, - , S-, , . , S- INFO 1 NT. INFO 1 NT INFO 2. INFO 2 , (. 2.4), - D-, 0. INFO 2 , INFO 2. , , 0, , , 1. INFO 2 , D- F , , L (. .2).
, NT INFO 3. NT INFO 4, - D- . INFO 3 NT INFO 4 NT .
, , .. NT , , : NT , INFO 0, INFO 2. INFO 1 .
. 2. S-: () ;
() NT
LAPD
2 (LAPD Link Access Procedure on the D-channel) , ITU-T 1.440 ( ) 1.441 ( ). Q Q.920 Q.921. LAPD , - 7.
3 , 2. 2 . 2 HDLC (High-level Data-Link Control procedures), ISO : LAPB, LAPV5 . LAPD, HDLC, , D-, , .
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. 3.
, , , / C/R. LAPD . 3.
. (0111 1110) , -7. , . , - (bit-stuffing), , . , , .
( 2 3) . 3. SAPI (Service Access Point Identifier) TEI (Terminal Equipment Identifier) . , , .
SAPI 6 , . , SAPI , . Q.921 SAPI, . 1.
1. SAPI
SAPI | |
ISDN ( ) | |
Q.931 | |
.25 | |
2 |
TEI , . TEI=127 (1111111) () , . (0126) . TEI (..2) , TEI ( TEI), , TEI ( TEI).
2. TEI
TEI | |
0-63 | TEI |
64-126 | TEI |
( NT2) ISDN PR1 ETSI, , 1==0. TEI .
/ C/R (Command/Response bit) DSS-1 .25. LAPD . C/R (..3) . , , , . , .
3. C/R
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, | , | |
C/R=1 | C/R=0 | |
C/R=0 | C/R=1 |
(Extended address bit) . , 0, , . , 1, , . , 0, . 1, , . , , .
. 3. 16- PCS (Frame check sequence) , . , ( ) -7 LAPD . FSC 16- , ( 2), : ) ( 2) k (x15+x14++x+l) (16+12+5+1), k - , , ;
) ( 2) 16 , , , , . , , , , FCS. LAPD , ( 2) 16 , FCS, 0001110100001111 ( 7439), . , . , , .
. , : (I-), , (S-), (U-). . 4 DSS-1.
.
(I) MSU -7). 1- . , . 1- , 1 ( 128) , . 1- .
(S) . S- LSSU -7., 1-, S- (RNR). 1-, S- (RR). S- , .
4. LAPD
(I) | - | , 3 | |
(PR-receive ready) | (RR-receive ready) | I- 1- | |
(S) | (RNR) | (RNR) | I- |
/ (REJ-reject) | / (REJ-reject) | 1- | |
(UI-unnumbered information) | |||
(DM-disconnected mode) | |||
(U) | (SABME-set asynchronous balanced mode extended) | ||
(FRMR-frame reject) | |||
(DISC-disconnect) | |||
(UA-unnumbered ask) | , , SABME, DISC |
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, .
(U) -7. (UI), . U- . , S-, UI 1==127. U- .
, 3, , , , , , . , (, , S-). 2 3 , .
P/F (poll/final) ( .4), .25. 1 LAPD LAPD . F== 1 , = 1. 4 .
2 DSS-1, : .
. , -, . . MSU -7.
[N(S)] [N(R)]. FSN, BSN MSU -7 LAPD N(S) , : N(S)=0, 1, 2,... 127, , 1,... .. .