ATM Layer Model Layer Name Functions Higher LayersHigher Layer Functions AALAAL Convergence Sublayer (CS) SAR Sublayer Common Part (CP) Service Specific (SS) ATM Generic Flow Control Cell Header Generation/Extraction Cell VCI/VPI Translation Cell Multiplexing/Demultiplexing Segmentation And Reassembly PhyPhy Transmission Convergence (TC) PMDBit Timing, Phy. Medium Cell Rate Decoupling Cell Delineation Transmission Frame Adaption

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

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

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

v HEC check  CRC-8: x 8 +x 2 +x+1  Remainder XOR to avoid too many zeros in the header  Single bit error detection rate: 99.64% v Cell Reception based on HEC  SONET uses SPE pointer (no framing)  Use HEC to detect cell boundary u 40-bit registers, shift one bit each time until matched correct HEC incorrect HEC Presyn Syn Hunt connective corrected HEC connective in- corrected HEC