[工學(xué)]07-datalinkcontrol(參考版)
2025-01-22 10:31本頁面
【正文】 Frame Frame RR4. Damaged RejectionGo Back N ARQ Diagram第 4幀丟失第 4幀的否定確認(rèn)丟棄后續(xù)收到的幀收到否定確認(rèn)后，第 4幀及后續(xù)幀重發(fā)RR7確認(rèn)幀丟失計時器超時詢問 響應(yīng)393. Selective Reject ARQ P220zAlso called selective retransmission( SREJ)zOnly rejected frames are retransmittedzSubsequent frames are accepted by the receiver and bufferedzThe maximum window size is 2k1zAppear to be more efficientzReceiver must maintain large enough bufferzMore plexSelective Reject Diagram第 4幀丟失第 4幀的否定確認(rèn)緩存后續(xù)收到的幀收到否定確認(rèn)，只重發(fā)第 4幀確認(rèn)幀RR1丟失計時器超時詢問 響應(yīng)41APPENDIX 7A ARQ 鏈路利用率 P236zIf errors occurNr: 平均傳輸次數(shù) p: 任何一幀有差錯的概率42?StopandwaitSelective rejectGobackNAPPENDIX 7A PERFORMANCE ISSUESARQ P23643 High Level Data Link Control (HDLC) P221z1. Basic characteristicsz2. Frame StructureyI frameyS frameyU frame1. Basic characteristics 基本特性zPrimary station 主站yFrames issued are called mandszSecondary station 從站yFrames issued called responseszCombined station 混合站yMay issue mands and responseszUnbalanced 不平衡模式y(tǒng)primary and secondary stationszBalanced 平衡模式y(tǒng)Two bined stationsLink Configurations鏈路配置Station Types站的類型zNormal Response Mode (NRM) 正常響應(yīng)方式y(tǒng)Unbalanced configurationzAsynchronous Balanced Mode (ABM) 異步平衡方式y(tǒng)Balanced configurationyMost widely usedzAsynchronous Response Mode (ARM) 異步響應(yīng)方式y(tǒng)Unbalanced configurationySecondary may initiate transmission without permissionyrarely usedTransfer Modes傳輸方式1. Basic characteristics462. Frame Structure 幀格式zFlag : Delimit (定界限） frame at both ends, 01111110yBit stuffing（ 位填充 ） is used to avoid confusion yInserts an extra 0 bit after each occurrence of five 1szAddress Field: Identifies the secondary station yAll ones (11111111) is broadcast 廣播zControl Filed: First one or two bits identify frame type 控制域Three types of frameszInformation (I frame) data to be transmitted to user yFlow and error control piggybacked on information frameszSupervisory (S frame)
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