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ATM Layer Model

ATM Layer Model. Layer Name. Functions. Higher Layers. Higher Layer Functions. Service Specific (SS). A A L. Convergence Sublayer (CS). Common Part (CP). SAR Sublayer. Segmentation And Reassembly. Generic Flow Control Cell Header Generation/Extraction Cell VCI/VPI Translation

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ATM Layer Model

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  1. ATM Layer Model Layer Name Functions Higher Layers Higher Layer Functions Service Specific (SS) A A L Convergence Sublayer (CS) Common Part (CP) SAR Sublayer Segmentation And Reassembly Generic Flow Control Cell Header Generation/Extraction Cell VCI/VPI Translation Cell Multiplexing/Demultiplexing ATM Cell Rate Decoupling Cell Delineation Transmission Frame Adaption Transmission Convergence (TC) P h y PMD Bit Timing, Phy. Medium

  2. Physical Medium Dependent (PMD) Sublayer • PMD provides actual clocking of bit transmission over the physical medium • ANSI T1.624 standards • SONET-based interfaces • STS-1 at 51.84 Mbps • STS-3c at 155.52 Mbps • STS-12c at 622.08 Mbps • PLCP of DQDB • DS3 at 44.736

  3. ITU-T I.432 • STM-1 at 155.520 Mbps • STM-4 at 622.08 Mbps • DS1, E1, DS2, E3, DS3, E4 • ATM Forum • DS3, STS-3c • FDDI at 100Mbps • Fiber Channel at 155.52 Mbps • STP at 155.52 Mbps • ......

  4. Transmission Convergence (TC) Sublayer • Functions • map ATM cells to/from TDM frame format • HEC check • Cell rate decoupling • TC mapping • SONET

  5. HEC check • CRC-8: x8+x2+x+1 • Remainder XOR 01010101 to avoid too many zeros in the header • Single bit error detection rate: 99.64% • Cell Reception based on HEC • SONET uses SPE pointer (no framing) • Use HEC to detect cell boundary • 40-bit registers, shift one bit each time until matched correct HEC Presyn Hunt incorrect HEC connective in- corrected HEC Syn connective corrected HEC

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