ATM has its own reference model. It consists of 3 layers physical, ATM, ATM adaptation layer
physical layer:-
- Physical layer deals with the physical medium like voltages, bit timing etc.
- ATM has been designed to be independent of transmission medium.
ATM layer:-
- ATM layer deals with cells and cell transport and defines the layout of the cell.
- It deals with establishment and release of virtual circuits.
- congestion control is done here.
ATM Adaptation Layer:-
It is defined to allow users to send packets larger than cell. It segments the packets into cells and reassembles them at the other end.
ATM model is 3D so it has planes.
user plane:- It deals with data transport, flow control error correction and for other issues.
control plane:- It is for connection management.
layer management:- It relates to resource management.
plane management:- It is for inter layer co-ordination.
The Physical layer has been divided into two sublayers.
Physical Medium Dependent:- It interfaces with actual cable. It moves bits and handles bit timing.
Transmission Convergence:- It converts from ATM layer into bit streams and at the other side , it has difficult job converting streams into cells.
ATM Adaptation layer has been further subdivided into two layers
Convergence layer:- It breaks coming from upper layers into cells and given ATM layer.
Segmentation And Reassembly:- at the other end the cells reassembled into segments.
Upper layer:- ATM offers different kinds of services to different Applications through this upper layers.
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