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Data Link Layer protocols HDLC

Data Link Layer protocols HDLC. HDLC Frame Format. Opening Flag , 8 bits [01111110], [7E hex] Address , 8 bits [ could be more] Control , 8 bits, or 16 bits Information , Variable CRC , 16 bits, or 32 bits Closing Flag , 8 bits [01111110], [7E hex].

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Data Link Layer protocols HDLC

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  1. Data Link Layer protocolsHDLC Instructor: Sam Nanavaty

  2. HDLC Frame Format Opening Flag, 8 bits [01111110], [7E hex]Address, 8 bits [ could be more]Control, 8 bits, or 16 bitsInformation, VariableCRC, 16 bits, or 32 bitsClosing Flag, 8 bits [01111110], [7E hex] Instructor: Sam Nanavaty Source: Warren HiokiTelecommunications,Fourth Edition

  3. Address field LSB = “1” signifies the last octet of address field Address field is extended by setting the LSB of address byte to “0” Instructor: Sam Nanavaty Source: Warren HiokiTelecommunications,Fourth Edition

  4. Control Field Function Info Xfer D2 D1 Frame Type X 0 Information 0 1 Supervisory 1 1 Unnumbered Polling, Data Ack Connection management Instructor: Sam Nanavaty Source: Warren HiokiTelecommunications,Fourth Edition

  5. Information frame (I frame) # of frames that can be received without ack = window size. For 3 bit NS and NR, the max window size = 7 P/F bit when set by primary, it mandates response from Secondary (who also sets the P/F bit to 1 when responding NR = The send sequence number (NS) of next received frame NS = Send sequence Number of current frame Besides carrying information, the “I frames” also carry Piggyback acknowledgements to the “I frames” flowing in opposite direction Instructor: Sam Nanavaty Source: Warren HiokiTelecommunications,Fourth Edition

  6. Supervisory frame RR and RNR used for flow control and ack REJ – NAK, Go back N frames Instructor: Sam Nanavaty Source: Warren HiokiTelecommunications,Fourth Edition

  7. Unnumbered frame SABM – Set Asynchronous balanced mode UA - Unnumbered ack DISC - Disconnect DM - Disconnect mode FRMR – Frame Reject Unnumbered Frame types Instructor: Sam Nanavaty Source: Warren HiokiTelecommunications,Fourth Edition

  8. SABM UA Session Established at this point Information transfer may begin now I(0,0) I(1,0) I(2,0) RR(3) I(3,0) Instructor: Sam Nanavaty

  9. SABM UA Link est. Information xfer DISC UA Link terminated Instructor: Sam Nanavaty

  10. SABM UA I(0,0) I(1,0) I(2,0) I(0,3) I(3,1) Instructor: Sam Nanavaty

  11. SABM UA I(0,0) I(1,0) I(0,2) I (7,1) Send seq # (NS) wraps around to 0 after reaching 7 RR(0) Instructor: Sam Nanavaty

  12. SABM UA Link est. I(0,0) I(1,0) I(0,2) I(2,1) Idle Timer Expiry RR(1) RR(3) Idle Timer Expiry RR(1) Instructor: Sam Nanavaty RR(3)

  13. SABM UA I(0,0) I(1,0) I(2,0) I(3,0) Reject(2) I(2,0) I frames starting with NS =2 are re-transmitted I(3,0) Instructor: Sam Nanavaty

  14. SABM UA I(0,0) I(1,0) I(2,0) I(0,3) RNR(3) RR(1) RNR(3) RR(1) Instructor: Sam Nanavaty

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