Cell Switching
In TDM, each time-slot is assigned to a certain connection
If a time-slot is not used it is wasted
In ATM, each cell carries in it the identification of the virtual circuit it belongs to
This makes it possible to assign fixed capacity with a constant delay to a virtual connection and have non-real-time traffic use the cells that were not used by the connection
ATM is first and foremost a technique for service differentiation:
- Real-time voice and video can use Circuit Emulation Services (CES) with a constant bit-rate (CBR) and delay
- There are also real-time and non-real-time variable bit-rate (VBR) services for non-constant data streams
- IP traffic can use unspecified bit-rate (UBR) services
All of these are implemented by switching standard ATM cells