Physical Layer

The physical layer in ATM directly relates to the layer 1 on the OSI model. However, in ATM there are two sub-layers to the physical layer. They are the Transmission Convergence and the Physical Medium.

The Physical Medium sub-layer interfaces with the actual wires or fiber and passes recovered bitstreams to the Transmission Convergence sub-layer. The Transmission Convergence sub-layer extracts and inserts ATM cells within the plesiochronous or synchronous TDM frame and passes them to the ATM layer.

All that talk sounds complicated, right? It is. All it says however is how ATM is interfaced to existing physical mediums. This saves companies the cost of having to run new networks just to work with ATM.