ATM Layer ModelLayer Name Functions

Higher Layers Higher Layer Functions

AAL

ConvergenceSublayer (CS)

SAR SublayerCommon Part (CP)

Service Specific (SS)

ATMGeneric Flow ControlCell Header Generation/ExtractionCell VCI/VPI TranslationCell Multiplexing/Demultiplexing

Segmentation And Reassembly

Phy

TransmissionConvergence (TC)

PMD Bit Timing, Phy. Medium

Cell Rate DecouplingCell DelineationTransmission Frame Adaption

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

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 ......

Transmission Convergence (TC) Sublayer

Functions map ATM cells to/from TDM frame format HEC check Cell rate decoupling

TC mapping SONET

HEC check CRC-8: x8+x2+x+1 Remainder XOR 01010101 to avoid too many zeros in the he

ader 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

incorrect HEC Presyn

Syn

Hunt

connective corrected HECconnective in-corrected HEC