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End Application Process Distributed Information Services Application Services: FTAM, MHS, EDI SyntaxIndependent Message Interchange Data Representation, Transfer Syntax, Data Transformation Dialog Synchronization and Control Network Independent Message Interchange EndtoEnd Message Transfer Network Routing and Addressing Data Link Control, Error Checking, Framing Mechanical and Electrical Interface Physical Connection Data Communications Network OSI Layer Application Presentation Session Transport Network Link Physical Application Process (AP) to AP Messages Source AP L_DATA.request Source Link Link Layer PDU s Layer Physical Transmission Medium Desintation AP L_DATA.indication Desintation Link Layer Page 2 2
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Connect Send (File) Call Setup Connect Receive V(S) = 0 I[0,S,Init] V(R) = 0 V(S) = 1 ACK[0,Y,Init] V(R) = 1 I[1,F,Filename] V(S) = 2 ACK[1,Y] I[2,D,data] V(R) = 2 V(S) = 3 ACK[2,Y] V(R) = 3 Time V(S) = 2 V(S) = 3 V(S) = 4 I[2,D,data] ACK[2,Y] I[3,D,data] NACK[3,N] I[3,D,data] ACK[3,Y] V(R) = 2 V(R) = 3 V(R) = 3 V(R) = 4 Time V(S) = 2 V(S) = 3 V(S) = 4 I[2,D,data] ACK[2,Y] I[3,D,data] V(R) = 2 V(R) = 3 Timeout I[3,D,data] ACK[3,Y] V(R) = 4 Time Page 5 5
V(S) = 2 V(S) = 3 V(S) = 4 Timeout I[2,D,data] V(R) = 2 ACK[2,Y] I[3,D,data] V(R) = 3 ACK[3,Y] V(R) = 4 I[3,D,data] ACK[3,Y] V(R) = 4 Time Data Block [n*] V(S) = n* I[n*,D,data] ACK[n*,Y] I[(n+1)*,Z] V(R) = n* Data Block [n*] EOF Exit ACK[(n+1)*,Y] I[(n+2)*,B] ACK[(n+2)*,Y] EOF EOT Destination Computer Exit Time Page 6 6
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² 8VHGÃIRUÃHUURUÃDQGÃIORZÃFRQWURO ² &RQWDLQÃVHTXHQFHÃQXPEHUV Frame Format 8 8/16 8/16 0 to N 16/32 8 Flag Address Control Information FCS Flag Control Field for Normal Information Frame 0 N(S) P/F N(R) Control Field for Normal Supervisory Frame 0 1 S P/F N(R) Control Field for Normal Information Frame 1 0 M P/F M P/F = Poll/Final Bit N(S) = Send Sequence Number N(R) = Receive Sequence Number S: RR RNR REJ SREJ M: Defines 9 Commands and 4 Unnumbered Responses ² 5HFHLYHGÃIUDPHÃFRXQWHUÃ95 ² 6HQWÃIUDPHÃFRXQWHUÃ96 ² &RQWHQWVÃRIÃIUDPH ª 95Ã65 ª )UDPHÃW\SH ª 'DWD ² 8QDFNQRZOHGJHGÃOLVW Page 8 8
Sender Receiver (N(S), N(R)) UnACK ed V(S) V(R) V(S) UnACK ed List 0 0 I(0,0) 0 V(R) 0 List 0 1 0 N(S) = V(R) => Frame OK RR(1) 0 1 I(1,0) 1 2 0 N(S) = V(R) => Frame OK 1,2 3 0 I(2,0) 0 2 N(S) = V(R) => Frame OK RR(2) 2 0 3 RR(3) Sender Receiver (N(S), N(R)) UnACK ed V(S) V(R) V(S) V(R) UnACK ed 3 0 I(3,0) 0 3 List 3 4 0 3,4 5 0 I(4,0) N(S) = 4 V(R) = 3 ERROR! 3,4 REJ(3) I(3,0) I(4,0) RR(5) N(S) = V(R) => Frame OK 0 4 N(S) = V(R) => Frame OK 0 5 Sender Receiver (N(S), N(R)) UnACK ed V(S) V(R) V(S) V(R) UnACK ed List 0 0 I(0,0) 0 0 List 0 1 0 0 1 1 1 I(0,1) 1 1 0 1 2 1 I(1,1) 1 2 I(2,1) 1,2 3 1 1 3 3 2 I(1,3) 2 3 1 RR(2) 2 3 Page 9 9
DTE Interface Part (UIP) Error Correcting Part (ECP) Modem (DCE) Public Telephone Network Error Correcting Part (ECP) Interface Part (UIP) Modem (DCE) DTE Page 10 10