The ATM architecture uses a logical model to describe the functionality that it supports. ATM functionality corresponds to the physical layer and part of the data link layer of the OSI reference model.
The ATM reference model is composed of the following planes, which span all layers:
•Control—This plane is responsible for generating and managing signaling requests.
•User—This plane is responsible for managing the transfer of data.
•Management—This plane contains two components:
–Layer management manages layer-specific functions, such as the detection of failures and protocol problems.
–Plane management manages and coordinates functions related to the complete system.
The ATM reference model is composed of the following ATM layers:
•Physical layer—Analogous to the physical layer of the OSI reference model, the ATM physical layer manages the medium-dependent transmission.
•ATM layer—Combined with the ATM adaptation layer, the ATM layer is roughly analogous to the data link layer of the OSI reference model. The ATM layer is responsible for the simultaneous sharing of virtual circuits over a physical link (cell multiplexing) and passing cells through the ATM network (cell relay). To do this, it uses the VPI and VCI information in the header of each ATM cell.
•ATM adaptation layer (AAL)—Combined with the ATM layer, the AAL is roughly analogous to the data link layer of the OSI model. The AAL is responsible for isolating higher-layer protocols from the details of the ATM processes. The adaptation layer prepares user data for conversion into cells and segments the data into 48-byte cell payloads.
Finally, the higher layers residing above the AAL accept user data, arrange it into packets, and hand it to the AAL. Figure illustrates the ATM reference model.
The ATM reference model is composed of the following planes, which span all layers:
•Control—This plane is responsible for generating and managing signaling requests.
•User—This plane is responsible for managing the transfer of data.
•Management—This plane contains two components:
–Layer management manages layer-specific functions, such as the detection of failures and protocol problems.
–Plane management manages and coordinates functions related to the complete system.
The ATM reference model is composed of the following ATM layers:
•Physical layer—Analogous to the physical layer of the OSI reference model, the ATM physical layer manages the medium-dependent transmission.
•ATM layer—Combined with the ATM adaptation layer, the ATM layer is roughly analogous to the data link layer of the OSI reference model. The ATM layer is responsible for the simultaneous sharing of virtual circuits over a physical link (cell multiplexing) and passing cells through the ATM network (cell relay). To do this, it uses the VPI and VCI information in the header of each ATM cell.
•ATM adaptation layer (AAL)—Combined with the ATM layer, the AAL is roughly analogous to the data link layer of the OSI model. The AAL is responsible for isolating higher-layer protocols from the details of the ATM processes. The adaptation layer prepares user data for conversion into cells and segments the data into 48-byte cell payloads.
Finally, the higher layers residing above the AAL accept user data, arrange it into packets, and hand it to the AAL. Figure illustrates the ATM reference model.