17
(TEI)
Control , (Information, Supervisory, or Unnumbered), N(r) N(s).
Information 3- .
CRC .
2- :
1. (Terminal Endpoint) RR (Receive-Ready ).
2. SAPI=63 (: ) TEI127 ( ).
3. TEI ( 64-126).
4. SABME (Set Asynchronous Balanced Mode ) SAPI=0 ( ) TEI.
5. , TEI SAPI=0 (setup) 3- .
(3-) ISDN ITU Q.930-Q.939. , .
, , ISDN, SPID (Service Profile ID). SPID 10- ISDN, . , . SPID, , 2- , 3- , , . 3- . 33.
Q.931:
Protocol Discriminator 3- , Q.931 08h.
CRV Length CRV.
CRV (Call Reference Value ) 1-2- , , . e .
Message Type (SETUP, CONNECT,...).
, .
. 33. 3-
3- : (Caller), R (Receiver) S (Switch). , , , ISDN .
1. SETUP.
2. SETUP , CALL PROC SETUP R.
3. R SETUP, , R ALERTING .
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4. ALERTING .
5. R , CONNECT.
6. CONNECT .
7. CONNECT .
8. CONNECT R .
.25
.25 , 70- . .25 OSI. . 34, :
DTE (data terminal equipment) (, . . ).
DCE (data circuit-terminating equipment) (), .
PSE (packet switching exchange) , .
, .25 , PAD (packet assembler/disassembler) - . , , , , .25. PAD, ( ) . .
CCITT (ITU) .25 DTE ( ) DCE () , . .21, X.21bis, V.24, RS-232C, V.35, RS-449, G.7Q3. , DTR, DSR, RTS, CTS , . .
.25 , , . LAP-B. (.25 Session) DTE . . DTE, . , DTE, (virtual circuit). PSE. . : .
SVC (Switched Virtual Circuit) , .
PVC (Permanent Virtual Circuit) - , DTE , .
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(DTE) , DCE, . DCE PSE, . , PSE, DCE, DTE , .
.25 PLP (Packet-Layer Protocol). PLP . PLP LAPB. PLP LLC2 , ISDN (LAPD). PLP 5 :
(Call setup) DTE, .121. , , . .
(Data-transfer mode) . , (padding), . (PV SV).
(Idle mode) , , . SVC, V .
(Call-clearing mode) SVC.
(Restarting mode) DTE DCE. , DTE, DCE, .
4096 ( 128). DTE X.1 21, . :
: 0, (250 /), (1 ) ( 10 ).
: 9, , ( 11 ).
: , ( 10 ).
.25 , , (, , , . .), . . .25 ISDN, D- -. .25 ( ).
.25 OSI, . .25 , . ( ).
, - , , .
Frame Relay
Frame Relay , 2 /. Frame Relay OSI. UNI (User-to-Network Interface) 9,6-64 / ( ). NNI (Network-to-Net-work Interface) .
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, . . , . PVC (Permanent Virtual Circuit) SVC (Switched Virtual Circuit).
Frame Relay , . .
HDLC 4 CRC. - , - .
CRC, . .
(Virtual Circuits), DLCI (Data Link Connection Identifier): 10- DLCI, , 1-2 . (Extended Address). DLCI . ( ) . DLCI .
. 35. Frame Relay:
a 1-2, 3 4 ( )
C/R (Command/Responce /) .
, (56 / 1) CIR (Committed Information Rate) DLCI. . , DE (Discard Eligibility ) . Frame Relay CIR=0, DE cex . FN (Forward Explicit Congestion Notification ) BECN (Backward Explicit Congestion Notification ). , - .
Frame Relay CIR, - CIR . CIR , .
Frame Relay, (Customer Premises Equipment), DLCI. 10 , . , . FS (Full Status ), , DLCI . FS DLCI . (status polling) . LMI (Link Management Interface), . ANSI T1.617 Annex D, . Q.933 . .
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Frame Relay (IPX TCP/IP) j (public) . , SNA . . ( .25 ). Frame Relay , . . .
AT
ATM (Asynchronous Transfer Mode ) (, ) . ITU BISDN (Broadband ISDN) . ATM, ( BISDN), . ATM . - ATM, .
ATM (cell) 53 , 48 . , . : . , . , , (, 8 ) 6 . . , .
UNI NNI
ATM . : UNI NNI. UNI (User-to-Network Interface) . NNI (Network-to-Network Interface) . , UNI NNI (public) (private). UNI , NNI . UNI , . NNI . B-ICI (Broadband Interexchange Carrier Interconnect) , ( ). . 36.
. 36. ATM
ATM 5- , UNI NNI (. 37). :
GFC (Generic Flow Control) , ( , ATM). , UNI .
VPI (Virtual Path Identifier) , VCI . NNI .
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VCI (Virtual Channel Identifier) , VPI .
PT (Payload Type) . , (0) (1). , , AAL 5. , (Operations Administration and Maintenance), . , , . .
CLP (Congestion Loss Priority) . CLP=1 , CLP=0.
EG (Header Error Control) , . .
ATM:
PVC (Permanent Virtual Circuits) ( ). , .
SVC (Switched Virtual Circuits) , . , .
(connectionless service).
ATM , V-(Virtual Channel). : VP (Virtual Path), VPI, , VPI VCI. , VPI. VPI VCI .
ATM . VCI VPI (), . VPI VCI . .
ATM
ATM . 38. (, plane), :
(Control) .
(User) .
(Management) , ( , ), .
ATM:
(Physical layer) OSI .
ATM (ATM layer) ATM, . OSI.
ATM, AAL (ATM Adaptation Layer) -.
AAL, , AAL .
ypo , , , . :
PMD (Physical Medium-Dependent), , , . PMD SONET/SDH, DS-3/E3, - 155 / 8B/10B.
(Transmission-Convergence) , (), . , , . . , . (SONET/ SDH) (PDH) .