The ATM physical layer has four functions:
1.Cells are converted into a bitstream
2.The transmission and receipt of bits on the physical medium are controlled
3.ATM cell boundaries are tracked
4.cells are packaged into the appropriate types of frames for the physical medium.
The ATM physical layer is divided into two parts:
1.The physical medium-dependent (PMD) sublayer
2.the transmission convergence (TC) sublayer.
The PMD sublayer provides two key functions.
First, it synchronizes transmission and reception by sending and receiving a continuous flow of bits with associated timing information.
Second, it specifies the physical media for the physical medium used, including connector types and cable.
The TC sublayer has four functions:
1.cell delineation
2.header error control (HEC) sequence generation and verification,
3.cell-rate decoupling
4.transmission frame adaptation.
The cell delineation function maintains ATM cell boundaries, allowing devices to locate cells within a stream of bits. HEC sequence generation and verification generates and checks the header error control code to ensure valid data. Cell-rate decoupling maintains synchronization and inserts or suppresses idle (unassigned) ATM cells to adapt the rate of valid ATM cells to the payload capacity of the transmission system. Transmission frame adaptation packages ATM cells into frames acceptable to the particular physical layer implementation.
1.Cells are converted into a bitstream
2.The transmission and receipt of bits on the physical medium are controlled
3.ATM cell boundaries are tracked
4.cells are packaged into the appropriate types of frames for the physical medium.
The ATM physical layer is divided into two parts:
1.The physical medium-dependent (PMD) sublayer
2.the transmission convergence (TC) sublayer.
The PMD sublayer provides two key functions.
First, it synchronizes transmission and reception by sending and receiving a continuous flow of bits with associated timing information.
Second, it specifies the physical media for the physical medium used, including connector types and cable.
The TC sublayer has four functions:
1.cell delineation
2.header error control (HEC) sequence generation and verification,
3.cell-rate decoupling
4.transmission frame adaptation.
The cell delineation function maintains ATM cell boundaries, allowing devices to locate cells within a stream of bits. HEC sequence generation and verification generates and checks the header error control code to ensure valid data. Cell-rate decoupling maintains synchronization and inserts or suppresses idle (unassigned) ATM cells to adapt the rate of valid ATM cells to the payload capacity of the transmission system. Transmission frame adaptation packages ATM cells into frames acceptable to the particular physical layer implementation.