atm交換技術(shù)與bisdn原理-文庫(kù)吧
2025-04-21 22:55 本頁(yè)面
【正文】 (CPCS)AALPDU PrimitivesAAL Service Access Point (AALSAP)SARPDU PrimitivesSSCSPDUPrimitivesCPCSPDUPrimitivesAAL Common Part(CP)AALCPCSSSCSCSSAR7 Mapping of AAL、 ATM SDU/PDU AALSDUATMSDUCell infarmation Field(cell Payload)CellHeaderAALSAPATMSAPCSPDUHeaderCSPDUtrailerCSPDUPayloadCSPDUSegmentationadnreassenbly(SAR)Sablayerno SAP defined between CS and SARSARPDUHeaderSARPDUPayloadSARPDUtrailerSARPDUATMPDU(=Cell)ATMLayer物理媒體（PHY）CSAALSARATM Layer8 Summary of Adaptation Layer Process User DataConvergence SublayerCS PDU CS PDU CS PDU SAR PDU SAR PDU48 bytesSegmentation and Reassembly SublayerATM Adaptaion LayerTo ATMLayer9 ATM適配層協(xié)議 AAL1 ? 面向的業(yè)務(wù) (class A) －信源與信宿之間有嚴(yán)格的定時(shí)要求 －恒定比特率編碼 －面向連接方式 ?業(yè)務(wù)舉例：話(huà)音業(yè)務(wù)、電路仿真 (如 E1仿真 )、恒定比特率的圖象編 碼業(yè)務(wù)。 ? AAL1向 AAL層用戶(hù)提供四種層服務(wù) －以恒定比特率傳送業(yè)務(wù)源的 SDU，并在目的地以同樣的比特率 遞交這些 SDU －在源和目的地之間信送數(shù)據(jù)結(jié)構(gòu)信息 －根據(jù)需要，指示出 AAL1本身無(wú)法恢復(fù)的丟失或錯(cuò)誤信息 10 ATM適配層協(xié)議 AAL1 A / Dp r o c e s sA / Dp r o c e s sBit rateCBRTimetime slotntime slot1CBR signals(n@sec)Analog signal Analog signal11 AAL1的一般結(jié)構(gòu) User data bit stream47 bytes 47 bytesPayload(47 bytes)Information Field(48 bytes)Header(5 bytes)SN(4bits)SN(4bits)Higher LayersConvergence SublayerSegmentation and ReassemblyATM LayerFigure AAL praess for AAL Type 112 AAL1 SAR sublayer SARPDU payloadSNPSNSCCSIP4 bits 4 bits 47 octetsCRCSARPDU headerSARPDUCSI Convergenco sublayerindicationCRC Cycttc redundancy checkP Even panity bitPDU Protocol data unitSAR Segmentation and reassemblySC Sequence countSN Sequence numberSNP Sequence number protection13 AAL1 SAR Layer: Concepts － SARPDU: 48 octets。PCI=first octet,remaining 47 octets available for SARPDU Payload － PCI: 4bit SN and 4bit SC － SN = CSI bit and 3bit SC － SNP: 3bit CRC for SN field and an even parity bit calculated over resulting 7bit code word － SN sequence count to detect loss or misinsertion of cells － SNP provides correction of all single errors and detection of multiplebit errors: (1) SN protected by G(x)=x3+x+1 (2) Resulting 7bit code protected by even parity check 14 AAL1 CS子層 CS子層與特殊的業(yè)務(wù)有關(guān)，它完成下面一些功能： （ 1）對(duì)用戶(hù)信息進(jìn)行拆和裝 （ 2）處理信元時(shí)延變化（ CDV） （ 3）處理信元凈荷組裝時(shí)延 （ 4）處理丟失的各誤插的信元 （ 5）在接收器中完成源時(shí)鐘恢復(fù) （ 6）在接收器恢復(fù)源數(shù)據(jù)結(jié)構(gòu) （ 7）監(jiān)視 AALPCI比特錯(cuò)誤 （ 8）處理 AALPCI比特錯(cuò)誤 （ 9）監(jiān)視用戶(hù)住處域的比特錯(cuò)誤并在可能的情況下予以糾正 15 AAL2 ? 面向的業(yè)務(wù) (class B) －信源與信宿之間有 (較 )嚴(yán)格的定時(shí)要求 －可變比特率編碼 (VBR) －面向連接方式 ? 業(yè)務(wù)舉例：可變比物率實(shí)時(shí)視頻編碼 ? 正在標(biāo)準(zhǔn)化之中 ? 新的研究用于傳送話(huà)音 16 Variable bit rate(VBR) applications A/Dprocess amp。presionDepressionamp。 D/AprocessBit rateCBRTimetime slotntime slot1Compressedsignals(variable rate)Analog signal Analog signal17 AAL 2 PDU PayloadSN IT CRCLISN Sequence numberIT Information typeLI Length indicatorCRC Cyclic redundancy check48 Octets18 ATM 適配層 AAL3/4： (1)基本說(shuō)明 AAL3 AAL
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