Ø  Representation of bits. The physical layer data consists of a stream of bits (sequence of 0s and 1s ) with no interpretation. To be transmitted bits must be encoded into signals (electrical or optical). The physical layer defines the type of encoding (how 0s and 1s are changed to signals).

Ø  Data rate.            The transmission rate – the number of bits sent each second –is also defined by the physical layer. In other words, the physical layer defines the duration of a bit, which is how long it lasts.

Ø  Synchronization                                The sender and receiver must not only use the same bit rate but must also be synchronized at the bit level. In other words, the sender and the receiver clocks must be synchronized.

Ø  Line configuration.          The physical layer is concerned with the connection of devices to the media. In a point-to-point configuration, two devices are connected together through a dedicated link. In a multipoint configuration a link is shared between several devices .

Ø  Physical topology.            The physical topology define how devices are connected to make a network. Devices can be connected using a mesh topology (every device connected to every other device), a star topology (devices are connected through a central device), a ring topology (each device is connected to the next. Forming a ring), or a bus topology (every device ion a common link)

Ø  Transmission mode         The physical layer also defines the direction of transmission between two devices: simplex, half duplex. In the simplex mode, only one device can send; the other can only receive. The simplex mode is a one way communication. In the half duplex mode, two devices can send and receive, but not at the same time, in a full-duplex (or simple duplex) mode, two devices can send and receive at the same time.