[工學]07-datalinkcontrol-資料下載頁
2025-01-19 10:31本頁面
【正文】 isticsz2. 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) ARQ when piggyback not usedzUnnumbered (U frame) supplementary（附助的） link control信息幀 無編號幀 監(jiān)控幀 control field format 50Poll/Final BitzPoll/Final Bit:yCommand frame:1 to solicit (poll) （請求） response yResponse frame:1 indicates responseyUse depends on contextzInformation Field:yMust contain integral number of octets, Variable lengthzFrame Check Sequence Field: FCSyError detection,16 bit (or 32) CRC513. HDLC Operation : Examples523. HDLC Operation : Examples53Exercise。 011111011110111111011111110Transmitter 011111001111011111010111110110Receiver 011111 01111011111 1011111 11054Homework zP231 X等待式 ARQ: 發(fā)送窗口 WS=1,接收窗口 WR=1X連續(xù) ARQ協(xié)議：回退 N幀 ARQ:X發(fā)送窗口 WS1,接收窗口 WR=1XMaximum window size is limited to 2k1選擇重發(fā) ARQ:X發(fā)送窗口 WS1,接收窗口 WR1,且 WR≤WSXMaximum window size is limited to 2k155HomeworkP231
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