Data Link Control Protocols
Data Link ControlProtocolsRaj JainWashington UniversitySaint Louis, MO 63131Jain@cse.wustl.eduThese slides are available on-line at:http://www.cse.wustl.edu/ jain/cse473-05/Washington University in St. LouisCSE473s7-1 2005 Raj Jain
OverviewqFlow ControlqEffect of propagation delay, speed, frame sizeqError RecoveryqHDLCWashington University in St. LouisCSE473s7-2 2005 Raj Jain
Flow ControlqqFlow Control Goals:1. Sender does not flood the receiver,2. Maximize throughputSender throttled until receiver grants permissionWashington University in St. LouisCSE473s7-3 2005 Raj Jain
Space-Time DiagramsTimeSpaceWashington University in St. LouisCSE473s7-4 2005 Raj Jain
Stop and Wait Flow ControlU tframeData tpropDataα tproptframetframe2tprop tframe12α 1AckLight in vacuumAck 300 m/μsLight in fiberDistance/Speed of Signal 200 m/μs Bits Transmitted /Bit rateElectricityDistance Bit rate 250 m/μs Bits Transmitted Speed of SignalWashington University in St. LouisCSE473s7-5 2005 Raj Jain
Utilization: ExamplesqqSatellite Link: Propagation Delay tprop 270 msFrame Size 500 Bytes 4 kbData rate 56 kbps tframe 4/56 71 msα tprop/tframe 270/71 3.8U 1/(2α 1) 0.12Short Link: 1 km 5 μs,Rate 10 Mbps,Frame 500 bytes tframe 4k/10M 400 μsα tprop/tframe 5/400 0.012 U 1/(2α 1) 0.98Note: The textbook uses B for tprop and L for tframeWashington University in St. LouisCSE473s7-6 2005 Raj Jain
Efficiency PrincipleqFor all protocols, the maximum utilization (efficiency)is a non-increasing function of α.Not PossibleBestpossibleMaxUtilizationα tproptframeProtocol 1Protocol 2αDistance Bit rate Bits Transmitted Speed of SignalWashington University in St. LouisCSE473s7-7 2005 Raj Jain
Sliding Window ProtocolsqqWindow Set of sequence numbers to send/receiveSender windowq Sender window increases when ack receivedq Packets in sender window must be buffered atsourceWashington University in St. LouisCSE473s7-8 2005 Raj Jain
Sliding Window DiagramWashington University in St. LouisCSE473s7-9 2005 Raj Jain
Sliding Window ExampleWashington University in St. LouisCSE473s7-10 2005 Raj Jain
Sliding Window Protocol EfficiencyU tframeDataW tframe2tprop tframeWtprop 1 if W 2α 1AckWashington University in St. Louis2α 1CSE473s7-11 2005 Raj Jain
Effect of Window SizeUqαLarger window is better for larger αWashington University in St. LouisCSE473s7-12 2005 Raj Jain
PiggybackingtframeDatatpropHeaderDataHeader Ack DataData AckWashington University in St. LouisCSE473s7-13 2005 Raj Jain
Error ControlqqError Control Deliver frames without error, in the properorder to network layerError control Mechanisms:q Ack/Nack: Provide sender some feedback about other endq Time-out: for the case when entire packet or ack is lostq Sequence numbers: to distinguish retransmissions fromoriginalsTimeoutWashington University in St. LouisCSE473s7-14 2005 Raj Jain
Stop-and-Wait ARQAutomaticRepeatreQuest(ARQ)Washington University in St. LouisCSE473s7-15 2005 Raj Jain
Go-Back-N ARQSenderRcvr01123Nack 123qq1Receiver does not cache out-of-order framesSender has to go back and retransmit all frames afterthe lost frameWashington University in St. LouisCSE473s7-16 2005 Raj Jain
Go-back-N (Cont)All possible scenarios are handled:1.Damaged Frame:qFrame received with errorqFrame lostqLast frame lost2.Damaged Ack:qOne ack lost, next one makes itqAll acks lost3.Damaged Nack:qMaximum Window 2n -1with n-bit sequence numbersWashington University in St. LouisCSE473s7-17 2005 Raj Jain
Selective Reject ARQSenderRcvr01123Nack 145qq1Receiver caches out-of-order framesSender retransmits only the lost frameWashington University in St. LouisCSE473s7-18 2005 Raj Jain
Selective Reject: Window Size01234567TimeoutAck0Sequence number space 2 window sizeWindow size 2n-1Washington University in St. LouisCSE473s7-19 2005 Raj Jain
Performance: Maximum UtilizationqqqqStop and Wait Flow Control: U 1/(1 2α)Window Flow Control:1W 2α 1U W/(2α 1)W 2α 1{Stop and Wait ARQ: U (1-P)/(1 2α)Go-back-N ARQ:U q{{(1-P)/(1 2αP)W 2α 1W(1-P)/[(2α 1)(1-P wP)] W 2α 1Selective Reject ARQ:(1-P)W 2α 1U W(1-P)/(2α 1)W 2α 1Washington University in St. LouisCSE473s7-20 2005 Raj Jain
Performance Comparison1.00.8W 127 Go-back-NUtilizationW 127 Selective-reject0.6W 7 Go-back-N &Stop-and-wait0.4W 7 Selective-reject0.20.00.1Washington University in St. Louis1α101001000More bps or longer distanceCSE473s7-21 2005 Raj Jain
HDLC FamilyqqqqqqqqqqSynchronous Data Link Control (SDLC): IBMHigh-Level Data Link Control (HDLC): ISOLink Access Procedure-Balanced (LAPB): X.25Link Access Procedure for the D channel (LAPD): ISDNLink Access Procedure for modems (LAPM): V.42Link Access Procedure for half-duplex links (LAPX): TeletexPoint-to-Point Protocol (PPP): InternetLogical Link Control (LLC): IEEEAdvanced Data Communications Control Procedures (ADCCP): ANSIV.120 and Frame relay also use HDLCWashington University in St. LouisCSE473s7-22 2005 Raj Jain
HDLCqqqqqqqqPrimary station: Issue commandsSecondary Station:Issue responsesCombined Station: Both primary and secondaryUnbalanced Configuration: One or more secondaryBalanced Configuration: Two combined stationNormal Response Mode (NRM): Response from secondaryAsynchronous Balanced Mode (ABM): Combined StationAsynchronous Response Mode (ARM): Secondary may respond beforecommandWashington University in St. LouisCSE473s7-23 2005 Raj Jain
FrameFormatHDLC Frame StructureFlagAddress ControlINFORMATIONFCSFLAG888n16 or 3288ExtendableExtendablebits12345678Control Field Format0N(S)P/FN(R)I: Information10SP/FN(R)S: Supervisory11MP/FMU: UnnumberedN(S) Send sequence number N(R) Receive sequence numberS Supervisory function bitsM Unnumbered bits P/F Poll/final bitExtended Address Field1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 1600.8n1Extended Control FieldInformationSupervisory1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 160N(S)P/FN(R)1 0 S 0 0 0 0 P/FN(R)Washington University in St. LouisCSE473s7-24 2005 Raj Jain
Bit StuffingqqHDLC Flag 01111110Every where else in the frame:Replace 11111 with 111110Original Pattern111111111111011111101111110After ton University in St. LouisCSE473s7-25 2005 Raj Jain
Bit Stuffing (Cont)FlagFlag TransmittedBit invertedFlagFlagFlag Received(b) An inverted bit splits a frame in twoFlagFlagFlag TransmittedBit invertedFlagFlag Received(c) An inverted bit merges two framesWashington University in St. LouisCSE473s7-26 2005 Raj Jain
HDLC FramesqqqInformation Frames: User dataq Piggybacked Acks: Next frame expectedq Poll/Final Command/ResponseSupervisory Frames: Flow and error controlq Go back N and Selective Rejectq Final No more data to sendUnnumbered Frames: Controlq Mode setting commands and responsesq Information transfer commands and responsesq Recovery commands and responsesq Miscellaneous commands and responsesWashington University in St. LouisCSE473s7-27 2005 Raj Jain
HDLC Commands and ResponsesNameFunctionInformation (I)Supervisory (S)Receive Ready (RR)DescriptionC/RExchange user dataC/RPositive Acknowledgement; readyto receive I-framePositive acknowledgement; notready to receiveNegative acknowledgement; goback NNegative acknowledgement;selective rejectSet mode;extended two-octet controlfieldSet mode;extended two-octet controlfieldSet mode;extended two-octet controlfieldInitialize link control functions inaddressed stationReceive Not Ready (RNR)C/RReject (REJ)C/RSelective Reject (SREJ)Unnumbered (U)Set Normal Response /Extended Mode (SNRM / SNRME)Set Asynchronous Response /Extended Mode (SARM / SARME)Set Asynchronous Balanced /Extended Mode (SABM / SABME)Set Initialization Mode (SIM)C/RWashington University in St. LouisCSE473sCCCC7-28 2005 Raj Jain
HDLC Commands and Responses (cont)NameFunctionDisconnect (DISC)Unnumbered Acknowledgement (UA)CRDisconnect Mode (DM)Request Disconnect (RD)Request Initialization Mode (RIM)RRRUnnumbered Information (UI)Unnumbered Poll (UP)Reset (RSET)Exchange Identification (XID)C/RCCC/RTest (TEST)C/RFrame Reject (FRMR)RWashington University in St. LouisCSE473s7-29DescriptionTerminate logical link connectionAcknowledges acceptance of one of theabove set-mode commandsSecondary is logically disconnectedRequest for DISC commandInitialization needed; request for SIMcommandUsed to exchange control informationUsed to solicit control informationUsed for recovery; resets N(R), N(S)Used to request/report identity andstatusExchange identical information fieldsfor testingReports receipt of unacceptable frame 2005 Raj Jain
Examples of HDLC tDISCUAI,3,4RR,4(a) Link setup anddisconnectWashington University in St. Louis(b) Two-way dataexchangeCSE473s7-30(c) Busy condition 2005 Raj Jain
Examples of Operation (Cont)I,3,0I,2,0I,4,0RR,3I,5,0*I,3,0TimeoutRej, 4I,4,0RR,3,FI,5,0I,3,0I,6,0RR,4(d) Reject RecoveryWashington University in St. LouisRR,0,PCSE473s7-31*(e) Timeout Recovery 2005 Raj Jain
SummaryqqqqqqFlow Control: Stop and Wait, Sliding windowEffect of propagation delay, speed, frame sizePiggybackingError Control: Stop and wait ARQ, Go-back-N, SelectiveRejectHDLC: Primary and secondary stations, NRM, ABM, ARMHDLC Frames: Flag, Bit stuffing, I-Frame, RR, RNRWashington University in St. LouisCSE473s7-32 2005 Raj Jain
Reading AssignmentqqqRead Chapter 7 and Appendix 7A of 7th edition ofStallings.Do the following Exercise from the textbook:7.8 (maximum link utilizations)There is no need to submit the answers.Next Monday is the first mid-term.Washington University in St. LouisCSE473s7-33 2005 Raj Jain
7-8 Washington University in St. Louis CSE473s '2005 Raj Jain Sliding Window Protocols Window Set of sequence numbers to send/receive Sender window Sender window increases when ack received Packets in sender window must be buffered at source
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Data and Computer Communications Chapter 7 - Data Link Control Protocols. High Level Data Link Control (HDLC) an important data link control protocol specified as ISO 33009, ISO 4335 station types: Primary - controls operation of link- frames sent by primary are called commands
Chapter 3: The Data Link Layer Computer Networks Maccabe Computer Science Department The University of New Mexico August 2002. . Sliding Window Protocols Protocol Verification Example Data Link Protocols Chapter 3 – p.31/69. Elementary Protocols Utopia Simplex Stop-and-Wait
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