Frame relay (. , FR) OSI. Frame Relay . , FR 34,368 / ( E3). : -. Frame relay (Virtual Circuits, VC) , FR- (Data Link Connection Identifier, DLCI). . (CIR) .
, , (VoIP, . .).
[ (1 Byte) (2-4 Byte) ( ) FCS (2 Byte) (1 Byte)
01111110. , 1, 0. (bit stuffing) FR, 0 .
FCS (Frame Check Sequence) HDLC.
1 , Frame Relay Forum 1600 , FR- ( 4096 ).
Frame Relay, , :DLCI (6 Bit) C/R (1 Bit) EA (1 Bit) DLCI (4 Bit) FECN (1 Bit) BECN (1 Bit) DE (1 Bit) EA (1 Bit)
:
DLCI Data Link Connection Identifier (PVC), . DLCI .
C/R Command / Response "-", HDLC.
EA Address Field Extension Bit . DLCI 10 , , , 10 . EA ; 1, , .
FECN Forward Explicit Congestion Notification .
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BECN Backward Explicit Congestion Notification .
DE Discard Eligibility Indicator . 1 , (EIR) , .
CIR EIR[ | ]
CIR (. Committed Information Rate) PVC Frame Relay (FR).
(ANSI T1S1) CIR , B(c) (bits committed, Committed Burst Size), B(e) (bits excess) T(c) (Committed Rate Measurement Interval). B(c) , T(c) , B(e) , T(c) , : , B(c) DE (discard eligible, CLP ATM) .
, :
CIR=B(c)/T(c)
EIR=(B(c) + B(e))/T(c) ( )
FR- CIR, .
ANSI T1S1 T(c) , T(c), B(c) B(e) , , , FR-
29 .25 қ
2. .25 . .25, . 1974 ().
.25 :
1. .25 .
2. .25 , .
.25
* 2
- ,
Host- ,
* 1
8, 16, 24 32, 64 128 .
-> -> RS-232C
3, (), .25
, .3
1. .25 .
2. , .
|
|
3. , , .
,
.25 () ( ) DTE, ; DCE
.25 :
-> ( .25, RS-232C) -> -> ( ) -> -> ( .25) ->
.25
.25 3 , .. .25 3 OSI , , .
, .
2 , .. .
3 .
.25
LAP-B, balanced Link access protocol
LAP-B .
X.25/3
.25/3:
1.
2. , ( )