atm交換技術(shù)與b－isdn原理(編輯修改稿)
2024-10-22 16:31 本頁面
【文章內(nèi)容簡介】 y e rA A L 1 A A L 2 A A L 3 / 4 , A A L 5A T M L a y e rP h y s i c a l L a y e r26 ATM適配層的一般結(jié)構(gòu) (1) QoS分類 －－ QoS Parameters ? Cell Loss Ratio (CLR):The ratio of lost cells to the total number of transmitted cells. ? Cell Error Ratio (CER):The ratio of errored cells to the total cells transmitted. ? Cell Transfer Delay (CTD): The average time for a cell to be transferred from its source to its destination over a virtual connection. ? Cell Delay Variation (CDV): The difference between the expected transfer delay of that cell. The CDV is induced by buffering and cell scheduling at the different switches. ? Cell Misinsertion Rate (CMR): The ratio of the misinserted cells (i. e. those arrive from the wrong source) to the total number of properly received cells per virtual connection. 27 ATM適配層的一般結(jié)構(gòu) －－ QoS Classes: ? QoS Cell 0:Refers to the best effort service, no objective is specified for the performance parameters. ? QoS Cell 1:Specifies the parameters for circuit emulation and VBR. It is a connectionoriented class that is supported by AAL1 and should yield performance parable to that of current digital private Line. It supports a QoS that will meet class A performance requirements. ? QoS Cell 2: Specifies parameters for VBR video and audio. It is also a connectionoriented, delaydependent class that is supported by AAL2. It is interoperation of packetized video and audio teleconferencing and multimedia applications. It supports a QoS that will meet class B performance requirements. 28 ATM適配層的一般結(jié)構(gòu) ? QoS Cell13: Specifies the parameters for connectionoriented, delay independent data transfer. It’s supported by AAL3/4 and AAL5. It is intended for interoperation of conionoriented protocols, such as frame relay. It supports a QoS that will meet class C performance requirements. ? QoS Cell4: Specifies the parameters for connection less data transfer. It’s supported for connection less data transfer. It’s supported by either AAL3/4 or AAL5. It is intended for interoperation of connectionless protocols, such as IP. It supports a QoS that will meet class D performance requirements 29 ATM適配層的一般結(jié)構(gòu) CS PDU CS PDU CS PDU SAR PDUSAR PDUATM Adaption LayerConvergence Sablayer Segmentation and Reassembly Sublayer48 Bytes 48 BytesUser Data To ATM Layer圖示 Summary of Adaptation Layer Process30 ATM適配層的一般結(jié)構(gòu) User InformationUser InformationHeader TrailerHeader CSSDU Trailer Header CSSDU Trailer Header CSSDU TrailerH SARSDU T H SARSDU T H SARSDU T H SARSDU TH SARPDU H SARPDU H SARPDU H SARPDU(may be absent)(may be absent)(may be absent)CS processSAR processATM LayerCSPDUSARPDUsATM cells(5 bytes H amp。 48 Bytes SARPDU)圖示 Generic AAL Process31 BISDN 用戶 網(wǎng)絡(luò)接口 (UNI) UNI： UserNetwork Interface BISDN UNI參考配置 ITUT UNI的參考配置。 ATM NetworkBTE1orBTE2BTABLT/ETBNT2BNT1ATMendpointATMendpointPublic ATMSwitchPrivate ATMSwitchTAR S B T B U BCPE NetworkPrivate UNI Public UNI32 基本概念 參考點(diǎn) Reference Point: R, SB, TB, UB 功能群 Function Group BTE2 BNT2 BTE1 BNT1 B:表示寬帶 PrivateBISDNPublicBISDNT B用戶基地設(shè)備CPECustomer Premises Equipment用戶網(wǎng)絡(luò)CNCustomer Network公用BISDN網(wǎng)絡(luò)33 BISDN功能部件 －－ BNT1：完成 OSI參考模型第一層的功能，包括： ?線路傳輸設(shè)備 ?傳輸接口處理 ? OAM －－ BNT2：完成 OSI參考模型第 1層＋第 1層以上的功能，包括： ?對各種接口媒體和網(wǎng)絡(luò)拓?fù)涞倪m配功能 ?復(fù)用 /分路和業(yè)務(wù)集中 ? ATM信元緩沖功能 ?資源分配及用法參數(shù)控制
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