ATM Layer Model Layer Name Higher Layers A

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

Physical Medium Dependent (PMD) Sublayer v PMD provides actual clocking of bit transmission over the physical medium v ANSI T 1. 624 standards - SONET-based interfaces u STS-1 at 51. 84 Mbps u STS-3 c at 155. 52 Mbps u STS-12 c at 622. 08 Mbps - PLCP of DQDB u DS 3 at 44. 736

v ITU-T I. 432 - STM-1 at 155. 520 Mbps - STM-4 at 622. 08 Mbps - DS 1, E 1, DS 2, E 3, DS 3, E 4 v ATM Forum - DS 3, STS-3 c - FDDI at 100 Mbps - Fiber Channel at 155. 52 Mbps - STP at 155. 52 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 0101 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 Hunt connective incorrected HEC incorrect HEC Syn Presyn connective corrected HEC