<Li> At the receiving device the data is passed from the lowest to the highest layer as a series of SDUs while being successively stripped from each layer's header or footer, until reaching the topmost layer, where the last of the data is consumed . </Li> <P> Some orthogonal aspects, such as management and security, involve all of the layers (See ITU - T X. 800 Recommendation). These services are aimed at improving the CIA triad - confidentiality, integrity, and availability - of the transmitted data . In practice, the availability of a communication service is determined by the interaction between network design and network management protocols . Appropriate choices for both of these are needed to protect against denial of service . </P> <P> The physical layer is responsible for the transmission and reception of unstructured raw data between a device and a physical transmission medium . It converts the digital bits into electrical, radio, or optical signals . Layer specifications define characteristics such as voltage levels, the timing of voltage changes, physical data rates, maximum transmission distances, and physical connectors . This includes the layout of pins, voltages, line impedance, cable specifications, signal timing and frequency for wireless devices . Bit rate control is done at the physical layer and may define transmission mode as simplex, half duplex, and full duplex . The components of a physical layer can be described in terms of a network topology . Bluetooth, Ethernet, and USB all have specifications for a physical layer . </P> <P> The data link layer provides node - to - node data transfer--a link between two directly connected nodes . It detects and possibly corrects errors that may occur in the physical layer . It defines the protocol to establish and terminate a connection between two physically connected devices . It also defines the protocol for flow control between them . </P>

Which layer of the osi model defines the signal rates and voltages that are used