The Physical Device Symbian OS has no control over hardware That is API design. We will treat as an abstract. Can handle wide variety of devices now and also future.
The Device Driver Layer Logical Device Driver( LDD): Layer interfaces with the protocol implementation layer and Symbian OS policies. Physical Device Driver( PDD): Layer interfaces directly with the physical device through a specific hardware port.
The protocol Implementation Layer Four types of modules: CSY Modules: Communicate directly with the hardware through PDD portion of device driver. Implementing the various low-level aspects of protocol. TSY Modules: Implement the telephony fuctionality. PRT Modules: Central modules used for protocol implementation. MTMs: Handle all type of messaging.