ATM is connection-oriented network (vs connection-less IP network).
Protocol reference model:
- Physic layer
- Physical Medium Dependent: responsible for the transmission and reception of individual bits on a physical medium. These responsibilities encompass bit timing, signal encoding, interacting with the physical medium, and the cable or wire itself.
- Transmission Convergence: functions as a converter between the bit stream of ATM cells and the PMD sublayer. When transmitting, the TC sublayer maps ATM cells onto the format of the PDM sublayer
- ATM layer
- ATM layer multiplexing blends all the different input types so that the connection parameters of each input are preserved. This process is known as traffic shaping.
- ATM layer demultiplexing takes each cell from the ATM cell stream and, based on the VPI/VCI, either routes it (for an ATM switch) or passes the cell to the ATM Adaptation Layer (AAL) process that corresponds to the cell (for an ATM endpoint).
- Supervises the cell flow to ensure that all connections remain within their negotiated cell throughput limits.
- ATM Adaptation Layer (AAL):
- Convergence sublayer - specifies type of services for higher layers (transmission timing synchronization, connection-oriented or connection-less, constant/variable bit rate)
- Segmentation and Reassembly sublayer - segment to or reassemble ATM cells
AAL only presents in end systems, not in ATM switches
AAL laer segment is analogous to TCP segment in many IP packets